Chapter 3 SPACE INFRASTRUCTURE - Princeton University

Chapter 3

SPACE INFRASTRUCTURE

Contents

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Considerations For Any Space Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . .Orbits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Low-Earth-Orbit Environment . . . . . . . . . . . . . . . .Technical Considerations . . . . . . . . . . . . . . . . . . .Space Transportation . . . . . . . . . . . . . . . . . . . . . . .

NASA’s Approach to Space Infrastructure . . . . . . .“Mission Analysis Studies” Summary . . . . . . . . .Infrastructure Functions. . . . . . . . . . . . . . . . . . . . .

Reactions of National Research Council Boards . .

Alternative Infrastructure . . . . . . . . . .Uninhabitable Platforms . . . . . . . . .Habitable Infrastructure . . . . . . . . .Extended Duration Orbiter (EDO) .Spacelab . . . . . . . . . . . . . . . . . . . . . .ShuttleShuttle

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as PermanentExternal Tank

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A Possible Configuration for NASA’s Initial Operational Capability . . . ‘ . .Space Station Involving a Solar Power Array, Habitat Module,Logistics Module, Two Laboratory Modules, and SatelliteServicing Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .An Artist’s Conception of a LEASECRAFT Enroute to Orbital AltitudeWith Payload Attached . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A Free-Flying Permanent Industrial Space Facility. . . . . . . . .Major Spacelab Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . .Shuttle-Spacelab Flight Profile. . . . . . . . . . . . . . . . . . . . . . . . .An Artist’s Conception of a Free-Flying Pressurized Modulean Attached Resource Module (second phase of ColumbusExternal Tank Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Possible Uses of External Tank ., . . . . . . . . . . . . . . . . . . . . . .Concept of Infrastructure Utilizing Four External Tanks . . . .

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Chapter 3

SPACE INFRASTRUCTURE

SUMMARY

Since 1957 various spacefaring nations havelaunched hundreds of spacecraft, many of whichremain today in Earth orbit or on itineraries withinthe solar system or beyond. Many of these space-craft, and some of those to be launched in thefuture including any “space station” elementsand associated launch and transportation sys-tems, are elements of space infrastructure, enabl-ing humans at the surface and in space to carryout activities outside of Earth’s atmosphere. Thischapter begins with a discussion of the spaceenvironment, orbits, and the technical aspects ofspace infrastructure. NASA’s specific aspirationsfor a “space station” and the functions that NASAexpects it to provide are listed in detail. The pro-jected uses of such a facility are summarized,taken from the response of a number of majoraerospace contractors to NASA’s Mission Anal-ysis Studies. The reaction of the National Re-search Council’s Space Science Board and the

Space Applications Board to NASA’s “space sta-tion” aspirations are then discussed. The re-mainder of chapter 3 lists and describes alterna-tives to NASA’s aspirations for space infrastructure,including a number of currently existing platformsand other infrastructure elements, and some thatare under development or in the planning stage. 1

A “USA Salyut” concept is presented as an op-tion that could provide in-space infrastructurethat is roughly comparable to the Soviet Union’scurrent Salyut 7.

‘Among the sources for the material presented in this chapterare background repcrts prepared for OTA by Dr. Jerry Grey,aerospace consultant (on space systems and transportation) andby Teledyne-Brown Engineering on alternatives to wholly new tech-nology in-space infrastructure. Additional material on existing orproposed space platforms and spacecraft was furnished by indi-vidual aerospace companies. Also available were results of an OTAworkshop on lower cost alternatives to a space station; workshopparticipants included aerospace industry and international repre-sentatives.

INTRODUCTION

The United States is currently pursuing a widevariety of civilian space activities. The argumentis being forcefully advanced that additional in-space infrastructure would permit scientific, tech-nology-development and commercial activitiesto be performed more easily or economicallythan at present, and might allow new types ofactivities in space. Plans for a civilian “space sta-tion, ” i.e., space infrastructure, were includedin the ambitious U.S. publicly supported spaceeffort which commenced immediately after thelaunch of the first Sputnik over a quarter centuryago. NASA undertook preliminary designs for

such “space stations” in the early sixties.2 In theearly seventies, astronauts were successfully sup-ported for long durations aboard Skylab, the firstU.S. space laboratory. Now, at the beginning ofthe second-quarter century of the space age, U.S.space infrastructure that would support long-du-ration human activities in space is again underconsideration.

‘The first realistic design initiative for a space station appears tohave been taken prior to the NASA efforts by the Lockheed Corp.Missiles and Space Division in the late 1950s (S. B. Kramer and R.A. Byers, “Assembly of a Multi-Manned Satellite, ” LMSD ReportNo. 48347, December 1958).

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50 . Civilian Space Stations and the U.S. Future in Space

CONSIDERATIONS FOR ANY SPACE INFRASTRUCTURE

The space environment is quite different fromthat on and near the Earth’s surface. There area number of orbital, environmental, and techni-cal factors that must be considered to ensure safeand successful operations in space.

Orbits

Infrastructure elements could be located inone, or several, of a wide range of orbits. Mostcommunications satellites and some meteorologi-cal and Earth observation satellites utilize loca-tions in geostationary orbits, 35,800 km abovethe Equator, as fixed vantage points from whichto transmit and receive signals or to observe theEarth’s surface and its atmosphere. It has beenfrequently suggested that on-orbit servicing ofgeostationary satellites, their orbital transfer pro-pulsion systems, and inter-orbit transportationvehicles, could be done more efficiently from in-frastructure located in low-Earth-orbit (LEO) witha low inclination relative to the Equator. An or-bital inclination of 28.5° (see fig. 1) would be rea-sonable for this infrastructure, because launchesover the Atlantic Ocean from Cape Canaveralinto orbits of this inclination consume the leastenergy.

These two functions–servicing geostationarysatellites and launching into the lowest energyorbit from Cape Canaveral—are reasonably com-patible, because the additional energy neededper unit mass at great altitudes to transfer apayload into geostationary orbit from 28.5° isrelatively small.

However, full repetitive coverage of the Earthfor low-altitude meteorological and other Earth-viewing satellites requires near-polar orbits (suchas the near-900 inclination illustrated in fig. 1).Such satellites are therefore launched from theVandenberg Air Force Base in California, whichoffers a safe launch trajectory to the south, overthe Pacific Ocean. A Sun-synchronous near-polarorbit that follows the dawn-dusk line is possible;it avoids Earth shadowing of solar-powered orsolar-viewing instruments, but does not accom-modate Earth-viewing instruments that require il-lumination of the Earth’s surface by the Sun.

b

Figure 1Representative Uses

● Earth observation

Near-polar(land, ocean, atmosphere)

orbit

IMaterialsprocessingLife sciencesAstrophysics/solar

When repetitive but not full coverage of theEarth is essential, a lower inclination can be used;an orbit inclination of 57o is favored because itis the maximum practical inclination obtainablewith a Cape Canaveral launch. It may be desir-able to use infrastructure elements in several or-bital planes, or perhaps to develop and employa reusable orbital transfer vehicle (ROTV) fortransportation between orbits having various in-clinations, although this would be expensive.

Orbital altitudes are also related to several phys-ical characteristics of space. One of these is the“solar wind,” a radiation flux of high-energy par-ticles from the Sun, that can present a threat tohuman beings and equipment. However, the re-gion from 200 to 600 km in altitude (LEO) isshielded by the Earth’s magnetosphere and theradiation there is almost negligible compared withthe radiation in and beyond the Van Allen belts,which extend to 50,000 km in altitude. The mag-netic field is less effective in shielding against ra-

Ch. 3—Space /infrastructure . 51

Photo credit: Nat/ona/ Aeronautics and Space Administration

Diagram showing Earth’s magnetosphere and other near-Earth phenomena.

diation approaching the Earth near its magneticpoles, including that associated with solar flares.Thus, high-altitude orbits and near-polar orbitsare much less hospitable than low-Earth-orbits oflow inclination.

Orbit altitude also affects the amount of globalEarth coverage available to viewing instruments.If a sensor is required to provide daily global cov-erage, for example, the physical limitations onthe angular swath width impose a minimum sat-ellite altitude much higher than 500 km.

Aerodynamic drag becomes an important con-sideration for lower altitude orbits. Aerodynamicdrag decreases for higher orbits; at 400 km, thedrag is two orders of magnitude less than at 200km. The minimum economical, long-term alti-tude for large semipermanent infrastructure ele-ments that would be serviced using the Shuttleordinarily would be above 300 km, and it willlikely be below 600 km because of the rapid de-crease in Shuttle payload capacity with greateraltitude.

Since locations in LEO are above most of theatmosphere, astronomical observations of all sortsare favored there. As well, one revolution aroundthe Earth in a typical circular LEO takes 90 min-utes, allowing vast areas of Earth’s surface to beobserved in continuous succession and on a fre-quently repeated basis. However, higher orbitsprovide a broader field of view for remote sens-ing of Earth.

Another consideration is the energy that mustbe expended to take material to a sufficient alti-tude to obtain a relatively low drag, long-life or-bit. To reach LEO requires more than half of theenergy required either to reach geostationary or-bit or to escape the Earth’s gravitational fieldaltogether. This is the physical basis for some ofthe projected cost savings of a permanently orbit-ing infrastructure base: large launch costs wouldbe paid only once when infrastructure compo-nents are carried into orbit and left there, avoid-ing additional, repetitive, launch costs for heavyequipment that would be frequently used inspace. Of course, resupply launches would stillbe needed and would offset some of this cost sav-ing.3

Low-Earth-Orbit Environment

Four characteristics of the LEO physical envi-ronment are of particular interest: microgravity,high vacuum, periodic high-intensity sunlight,and the combination of solar exposure and shad-owing that makes thermal control possible. Forany infrastructure elements located beyond theVan Allen belts, a fifth environmental parameteris high-energy radiation,

3The number of resupply launches required would depend onthe types and levels of activities carried out, the presence or absenseof people, etc.

52 Ž Civilian Space Stations and the U.S. Future in Space

Above the minimum practical orbital altitudeof a permanent space facility, the presence ofmicrogravity and vacuum are essentially inde-pendent of orbital inclination and altitude. In par-ticular, the exploitation of microgravity or near“weightIessness, ” which occurs when gravita-tional and orbital acceleration counteract oneanother, shows promise for the processing of ma-terials under such unique conditions. Energy gen-eration depends on radiation from the Sun, andthermal control depends on radiating waste heatout into deep space. For most orbits, the Sun iseclipsed nearly half of the time by the Earth, butthis effect can be tolerated if energy storage sys-tems are used; batteries charged from solar pho-tovoltaic arrays can be used to supply electricpower during times that sunlight is blocked bythe Earth.

Of course, for many human beings, simply be-ing in orbit, and being able to view the Earth andheavens from this perspective, are the outstand-ing characteristics of space.

Technical Considerations

The design of infrastructure components andsystems will depend heavily on a number oftechnical considerations. While a considerableamount of workable “space station” technologyexists, as demonstrated by the success of Skylab,SPAS, MESA, and the Shuttle itself, the develop-ment of new technology may be desirable to ob-tain a long, and particularly useful and efficientlifetime for space infrastructure.

Data Management.– Space infrastructure ele-ments would use an extensive data handling net-work both on-board and on the ground. The net-work would serve orbiting elements including theShuttle, communication, navigation and remotesensing satellites, orbital transfer vehicles, crewmembers on spacewalks, tended free flyers, andsupport staff and scientific researchers on Earth.Cost, program control, and reliability prompt con-sideration of a wide variety of hardware and soft-ware technologies just now coming into being.For example, faster processors, laser disk storage,and flat display terminals will provide large in-creases in capacity at lower unit cost and weight.

Communications.—A number of communica-tion links would be desirable using frequenciesthroughout the electromagnetic spectrum and en-compassing a wide variety of distances, informa-tion content, and line-of-sight propagation direc-tions. Space communications must be designedto avoid interference with established ground-based systems and to take privacy, cost, capac-ity, and reliability into account. Another consid-eration is the location of communications anddata processing nodes. The various space infra-structure elements could require a large numberof antennas and lenses (the Shuttle has 23) that,altogether, would cover a wide field of view.Phased-array antennas, whose radiation patternscan be “pointed” electronically rather than me-chanically, could be widely used.

Systems for locating and tracking natural andmanmade debris, loose tools, and approachingspacecraft is also necessary. System concepts forthis purpose include radar with beacons or pas-sive reflectors, radio transponders, interferometry,the Global Positioning System, ground-based ra-dar, or Iidar (laser radar),

Although space communications can rely ini-tially on current technology, millimeter and op-tical wavelengths may be desirable for use inspace. The development of systems in these partsof the spectrum would offer significant techno-logical challenge.

Electromagnetic Interference (EMl).–This isa significant problem that can occur in space, par-ticularly when high-power microwave sourcesand sensitive detectors are involved. It is difficultto protect some electronic circuits from this “pick-up” problem. In some cases EM I could force theuse of a constellation of individual platforms sep-arated rather widely from each other rather thana single large structure.

Attitude Control and Stabilization .–Althoughspace infrastructure elements do not have to con-tend with gravity, wind, earthquakes, precipita-tion, and other problems encountered on Earth,they must deal with quite different problems suchas the absence of both a “firm footing” and the‘‘stiffening” influence of gravity. Of particularconcern is the control and stabilization of large,

Ch. 3—Space Infrastructure • 53

flexible, evolving, structural assemblies and mod-ules. Elaborate control systems for each module(sensors, actuators, computers, , . .) that are co-ordinated by a single “supervisory” controllermay have to be employed.

Power.–Solar photovoltaic power generatorswith nickel-cadmium battery storage are com-monly used in space. Systems employing themtoday cost at least several thousands of dollarsper watt and have useful lifetimes of 10 years orless in orbit. One alternative is a nuclear powerreactor, perhaps of the type now being exploredin the Space Power Advanced Reactor program,but development time and hazards to human be-ings (and perhaps cost) may well preclude theuse of nuclear reactors for inhabited infrastruc-ture in the near future.

Significant cost reduction in photovoltaic arrayshas been achieved using optical focusing devicesthat concentrate sunlight on the photocells, butconsiderable effort would be needed to developand demonstrate practical arrays of this type foruse in space. Coupled with this technique couldbe the use of more efficient solar cells, such asgallium-arsenide, in place of silicon cells. Effortsto increase the lifetime and reduce the mass ofbatteries could also lead to cost reduction. Onepromising replacement for present nickel-cad-mium devices is the nickel-hydrogen battery.Another, at an earlier stage of development, isthe regenerative fuel cell/electrolysis method, inwhich a fuel cell produces electricity and waterwhen in the Earth’s shadow and splits water intohydrogen and oxygen when in sunlight.

Thermal Energy Management.–For infrastruc-ture composed of connected modules, it may notbe practical to use individual thermal control sys-tems for each module. Although individual sys-tems would offer maximum flexibility, such anapproach would prevent heat thrown off fromone module from being used by another, andeach module’s radiator, which is by far the big-gest and most exposed component of the ther-mal system, would impose its own orientationand location constraints on the overall structure.Hence, a centralized, automated system may beneeded both to minimize total mass and to op-timize radiator orientation (i.e., edge to Sun).

38-798 0 - 84 - 5 : QL 3

However, such a system would require both alarge, massive single radiator and considerabletransfer of energy among the various modules viaa heat-transport medium. Therefore, the trade-offs between centralized and modular thermal re-jection systems need to be examined in detail.The centralized system might utilize a gimbaledradiator maintained in an edge-to-Sun orienta-tion, not only maximizing heat dissipation andthereby requiring perhaps a 60-percent smallerarea than a fixed radiator, but also minimizingsolar-wind degradation of its thermal coating.

A conventional separate-tube radiator, similarto that used in the Shuttle, would be extremelycomplex and massive because of the need forredundant piping, valving, and other plumbingcomponents. For a typical 100-kW heat rejectionsystem, a Shuttle-type radiator would requirealmost 6,000 meters (almost 4 miles) of tubingin over 1,500 individual pumped fluid tubes,more than 50 fluid manifolds, and more than 75isolation valves, fluid swivels or flexible linesegments. Hence, a heat pipe radiator may bea better choice. Heat pipes transfer heat by boil-ing a fluid such as ammonia at one end of asealed tube and condensing it at the other. Theliquid is then returned to the hot end by capillary(surface-tension) forces in a specially designedwick which forms part of the tube. The heat pipehas no moving parts, and each pipe is self-con-tained. Single pipes have demonstrated heat re-jection rates up to 2 kW; hence, as few as 50could handle 100 kW of power in space, Whilethe technology is relatively well known, consid-erable development is called for to evolve a prac-tical, reliable, long-life, heat pipe radiator at thispower level.

Another technological challenge would be aninter-module system that transfers thermal energyto a radiator. Shuttle-type pumped-loop systemsusing Freon 21 would consume large amountsof power (up to 5 kW for a 100-kW system), andwould also require the development of large,costly, space-rated pumps and their attendant re-pair and maintenance. A two-phase heat trans-port system using the same principle as the heatpipe would consume only about one-tenth asmuch power. Hence, it may be worth the costof its development.

54 ● Civilian Space Stations and the U.S. Future in Space

The use of passive cryogenic coolers for electro-optical detectors will present a difficult techni-cal challenge. Active cryogenic systems are prob-ably not satisfactory for long-term operation. Pas-sive coolers require exposure to dark space andan environment that is free from effluents thatwould condense on the cooler’s cold patch.

Propulsion.— Infrastructure elements requirepropulsion systems for attitude control, orbitchange, station-keeping, and acceleration con-trol. Propulsion systems currently use storable liq-uid mono- and bi-propellant pressure-fed thrust-ers. Near-future plans include cryogenic oxygen/hydrogen propulsion systems. Longer term pros-pects are electromagnetic thrusters including ionrocket (ions can be accelerated to much higherexhaust velocities than those provided by chem-ical rockets) and mass drivers (“buckets” of heavymaterials can be accelerated, very rapidly by elec-trical motors rather than by conventional chem-ical combustion).

A principal challenge will be the creation of astorage and transfer system for handling liquidfuels in space. Specific needs are leak-proof fluidcouplings and leak-detection techniques, fluid-quantity gauges that operate with acceptable ac-curacy in microgravity where conventional liquid-Ievel sensors are not suitable, reusable, low-mass,nontoxic, long-life insulation for cryogenic stor-age and transport, and the liquefaction and refrig-eration systems needed for long-term cryogenicstorage. Improvements in cryogenic refuelingprocedures now used on the surface for Shuttleoperations would be necessary—preferably pro-cedures that would use automation—to obviatethe need for a large technical staff that would bevery expensive to accommodate in space.

Life Support Systems.–Some of the materialsnecessary for the support of humans in spacewould be supplied from Earth, others would berecovered in orbit from metabolic byproducts.With the exception of food, recovery technologydemonstrated since 1967 can provide for oxygen,carbon dioxide scrubbing, and water for bothdrinking and washing. Such a “partially closed”system accommodating an eight-person crew,each drinking about 3.5 kg of water and usingabout a liter of wash water per day, would have

to be resupplied every 90 days and would havea 30-day contingency supply. Compared with theShuttle system, which does not use recovery,almost 7,OOO kg per resupply launch could besaved. If reclaimed water were also used forshowers, and for washing utensils and clothes,thereby replacing “wet wipes,” disposable clothes,and disposable food service utensils, another5,000 kg could be saved for each launch. There-fore, the development cost of such a systemcould be offset by associated transportation sav-ings of over $100 million per year.

Food supply technology will also require somedevelopment, including improvements in packag-ing, preservation, bulk storage, reconstitution,and on-board preparation. Proper sanitation toreduce the incidence of debilitating illness in thecompletely closed environment of a “space sta-tion” will require waste disposal, contaminationcontainment, disease-prevention measures, andheakh-maintenance facilities unique to micro-gravity environments to be developed and used.Some of this technology has already been devel-oped for the long-duration Skylab project, but im-provements are needed. Particular attentionshould be given to the proper design of residen-tial, exercise, and recreational facilities if peopleare to remain in orbit for periods of much longerthan several weeks.

Space Transportation

Vehicles will be needed for transportation be-tween Earth and LEO, between various LEO or-bits, between LEO and higher, including geosta-tionary, orbits, and beyond to the Moon andperhaps to other planets and some asteroids. Inthe near future, supply for a “space station” fromEarth would rely primarily on the present Shut-tle and possibly its derivatives. Local checkoutand maintenance services requiring people work-ing directly in space could be conducted bytethered or free-flying spacesuited astronauts,sometimes augmented by the existing mannedmaneuvering units (MMUs). Servicing of moredistant spacecraft could be accomplished with aplanned orbital maneuvering vehicle (OMV), pos-sibly in combination with either the Shuttle or aplanned space-based ROTV, or by an ROTV (or


the Shuttle) carrying an astronaut equipped withan MMU.

Launching spacecraft into higher orbits or onEarth-escape trajectories requires the use of anupper stage rocket, which could be automatic,teleoperated, or used with a crew, plus kickstages or planetary landing stages, depending onthe project. ROTVS, either teleoperated or em-ploying crews, could be used to service satellitesin orbits of significantly different altitude andsomewhat different inclination.

Shuttle.-The Shuttle (fig. 2) meets most of thecurrent needs for transportation between the

Figure 2.—Diagram of

Earth’s surface and LEO at any Inclination. TheShuttle can deliver 30,000 kg to a 200-km (120-mile) orbit inclined at 28.5° to the Equator. Anyincrease in orbit altitude or change from this or-bit inclination reduces the payload capacity.However, most payloads are volume-limited bythe cargo bay’s 18-meter length and 4.6-meterdiameter rather than weight-limited. By the early1990s, the earliest date considered practical forobtaining a “space station,” NASA projects a totalof some 24 to 30 Shuttle flights per year, andsome 50 per year by the year 2000. The Shut-tle’s cargo bay could be used to carry infra-structure- elements

Shuttle Mission Profile

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SOLID ROCKETBOOSTER RECOVERED

A

APPROACH ANDLANDING

56l Civilian Space Statlons and the U.S. Future in Space

its crew of up to seven persons could be usedto assist with any assembly and checkout. TheShuttle could also resupply expendable, ferrypersonnel, and serve for emergency rescue.

Manned Maneuvering Unit (MMU).–TheMMU is a backpack equipped with a computer-operated propulsion system that permits an astro-naut to “free fly, ” thereby projecting his senses,his strength and dexterity, and his judgment be-yond the confines of the Shuttle or other habit-able infrastructure out to a few hundred meters.It is a general-purpose device that can be usedfor inspection, servicing and deployment or re-trieval of equipment, for construction and assem-bly operations, for crew rescue, for emergencyrepairs, etc. A Shuttle-based MMU was success-fully demonstrated on two flights in early 1984.

Orbital Maneuvering Vehicle (OMV).-Localtransportation in LEO would be provided by theOMV. It would be operated remotely from theShuttle, other space infrastructure, or possiblyfrom Earth. It would be designed to have a six-degree of freedom propulsion system that wouldallow satellite or platform servicing operations atdistances well beyond the MMU’S few-hundred-meter limit. One version of the OMV would beable to make altitude changes of 1,000 km ormore above its initial LEO and orbit plane changesof up to 8°, depending on payload weight.

Basic OMV equipment includes propulsionunits and propellent tanks; television cameras andlights for inspection and operator guidance; com-munications; control systems for remote opera-tions; electric power; thermal control; and variousmanipulators and docking attachments. CurrentNASA plans are to have such a new-technologyvehicle developed and operating in time to beuseful in the deployment and assembly of a“space station.”

Expendable Launch Vehicle (ELV)-Up to No-vember 1982, all payloads launched into spacewere carried there by ELVS. There are now threebasic U.S. families of ELVS: the Delta, Atlas-Cen-taur, and Titan III. The European Space Agencyhas its Ariane family of boosters, Japan has itsN-2 (derived from the U.S. Delta) and is devel-oping others, the People’s Republic of China haslaunched a geostationary satellite using its FB-3

“Long March” rocket, and the Soviet Union isoffering to make its Proton launcher commercial-ly available. In addition, several private corpora-tions in the United States and Germany have an-nounced plans to develop ELVS. Many of thesevehicles and possibly others may be availablecommercially throughout the next decade. How-ever, it is not likely that they will be suitable forlaunching spacecraft that carry people, althoughthey could launch supply spacecraft as the Sovi-et Proton boosts the Progress into orbit.

Expendable launch vehicles that can launch tohigh orbits, or to Earth-escape trajectories, useeither their own upper stages or uniquely com-patible orbital transfer vehicles (OTVS). The pay-load itself carries the “kick stage” or other pro-pulsion needed to move from high, inclined,elliptical orbits to geostationary orbits.

Reusable Orbital Transfer Vehicle (ROTV).-Areusable, high-performance, liquid propellant“space tug” could provide transportation be-tween LEO and geostationary and lunar orbits,or between Earth orbits of various inclination andaltitude. Reusability and space-basing give prom-ise of economic benefit for the use of an ROTVin launching and servicing communications andother satellites that utilize the geostationary or-bit. An ROTV could be piloted by a crew or re-motely operated.

Development of an “Advanced Space Engine”suitable to power an ROTV has yet to be started.Space-basing implies reusability, of course, aswell as flexibility of thrust and duration of rocketburn, and the ability to refuel and perform main-tenance in space. Thus, space-basing requiressome form of orbital logistics system, includingtanks, pumps, controls, and other equipment forrefueling, people or teleoperator devices to checkout the ROTV, refurbish it as needed, and resetits operating systems for each new trip, and per-haps crew quarters.

Space-basing also requires docking, servicing,and storage facilities in space to make ROTV op-eration possible. Moreover, as fuel for the ROTVmust always be brought from the surface to LEO,alternative ways of transporting it are under con-sideration. More efficient delivery systems thanthe Shuttle, such as a Shuttle-derived tanker vehi-



cle, are being looked at. Scavenging left-over fuelfrom the Shuttle external tank is being given con-sideration. Considerable development time andexpense would be involved in any of these efforts.

A prospect which offers an opportunity for con-siderable propellant savings is to dissipate theROTV’S excess kinetic energy, on return fromhigh altitudes to LEO, by allowing it to dip intothe upper reaches of the Earth’s atmosphere, amaneuver called “aerobraking.” The return flightwould consist of a brief de-orbit burn that wouldplace the ROTV into an elliptical transfer orbit

that intersects the top of the atmosphere. If theROTV could dissipate enough energy to decreaseits velocity by 2,400 meters per second, it wouldhave just enough energy left to raise it to a “spacestation’s” (typical) 300-km orbit. There, it coulddeliver its return payload (if any) and refuel forits next trip. This aerobraking concept promisesa saving of over half of the propellant needed(compared to an all-propulsive ROTV) for a re-turn trip with payload from geostationary Earthorbit.

NASA’S APPROACH TO SPACE INFRASTRUCTURE

“Mission Analysis Studies” Summary

In 1982, as part of NASA’s planning to acquirelong-term inhabited infrastructure, i.e., a civilian“space station, ” the agency authorized “missionanalysis studies” in the United States, and reachedan agreement with foreign countries for parallelstudies, of the desires or needs for, and charac-teristics of, such infrastructure. The results ofthese studies appear in appendix A.

The “mission analysis studies” started with thesupposition that the United States would builda civilian “space station, ” and did not require thepotential user to address either justification of thebasic “space station” concept or its funding. Thestudies were simply to identify uses that eitherwould require or would materially benefit fromthe availability of a “space station” and to sug-gest some of its fundamental characteristics.

Of the several hundred potential activities inscience, commercialization, and technology de-velopment identified by the U.S. companies (pri-marily aerospace) conducting the studies, theselection was narrowed by NASA to a set of about100 time-phased missions for the first 10 yearsof “station” operation, 70 percent of which couldbe accomplished from a central base facility lo-cated in a 28,5° inclination in LEO. Free-flyingplatforms, either co-orbiting or in polar orbit,could accommodate most of the others.

The contractors viewed activities such as equip-ment servicing, research (especially in the lifesciences and materials processing), and assemblyand modification of large space systems as areasin which presence of a human crew would beparticularly beneficial. They recommended archi-tectural concepts involving several types of mod-ules for the initial central complex: a command/habitability module with accommodations for acrew of four; an electrical power system provid-ing about 25 kW to the users; logistics modulesfor periodic resupply; airlocks, docking ports, andpallets to enable mounting of equipment and lab-oratory modules. Subsequent development andgrowth of the facility over a 10-year period andincorporation of an ROTV and several free-flyingplatforms were anticipated.

Estimation of acquisition costs ranged from ap-proximately $4 billion to $5 billion (1984$) forthe initial facility, to about $12 billion for anevolved complex envisioned as being completed6 to 8 years after the system first became opera-tional. Other than the performance and socialbenefits of such a “space station,” they estimatedthat economic benefits from servicing satellitesin orbit, transfer of satellites to higher orbits byan ROTV, and human-tended long-term researchactivities would be considerable. The increasedability to launch planetary probes, establish alunar settlement, and undertake human explora-

Ch. 3—Space /infrastructure • 59

tion of Mars was considered of great significancein terms of long-range goals.

The foreign mission analysis studies paralleledthose of the U.S. contractors and defined a simi-lar set of space activities appropriate for infrastruc-ture use. All participating agencies from Europe,Canada, and Japan expressed great interest in tak-ing part both in providing elements of space in-frastructure and in actively participating as part-ners in its use. Many of them look upon it asfundamental to their future role in space andtherefore want long-term understandings andagreements with the United States on partici-pation.

NASA assembled the United States and foreignmission analysis reports and held a workshop inMay 1983 to synthesize the results. The workshopestablished a minimum time-phased “missionset” (for the initial decade of use) of 107 specificspace activities, plus four generic commercial-

industrial service activities (e. g., satellite servic-ing). Of the total set, 48 were categorized underscience and applications, 28 under commercial,and 31 under technology-development.

In parallel with the contractor studies, NASAhired two consulting firms to communicate witha variety of non-aerospace companies to iden-tify and encourage interest in the use of in-spacefacilities for commercial purposes. The consult-ants discussed prospects with approximately sOcompanies, and more than 30 expressed activeinterest in using a “space station” if it were avail-able. Most of the companies moving towardagreements with NASA to become active in spaceare well-known U.S. industrial firms (one with anannounced agreement is the 3M Co.), but sev-eral are from the small business sector or Europe.Interest is concentrated on the possible produc-tion of particular chemicals, metals, glass, com-munications, and crystals. Among the half dozencompanies now actively investigating the possi-

80X D.-NASA's Current Aspirations

$ 8 ., , . .


bility of sponsoring space experiments, most aremore interested in crew-tended operations ratherthan automated procedures. Further details of theconsulting firms’ studies are discussed in the finalsection of appendix A.

Infrastructure Functions

The NASA planning process has dependedheavily on the “Mission Analysis Studies” of U.S.and foreign aerospace contractors and foreignspace agencies. From the views assembled there-in, functions were identified for any space in-frastructure (“space station”) that could provideefficient and effective assets and services to sup-port the projected space activities.

NASA’s aspirations for a “space station” weremost recently presented to the Senate Commit-tee on Appropriations in March 1984. The in-frastructure envisioned in their plans would pro-vide the following:

1.

2.

3.

4.

5.

an on-orbit laboratory supporting researchon a wide range of life, materials, and otherscience topics, and the development of newtechnology (e.g., studies of biology, cosmicrays, processing methods for pharmaceuti-cals and semiconductors, testing of spacematerials, and advanced communicationstechnology);permanent observatories for astronomy andEarth remote sensing (e.g., a solar optical tel-escope to examine the surface of the Sun,a starlab to study the structure of galaxies,and Iidar equipment to probe the at-mosphere);a facility for microgravity materials process-ing and manufacture of products (e.g., phar-maceuticals, semiconductors, glasses, andmetals);servicing of satellites and platforms (e.g., themaintenance or replacement of compo-nents, replenishment of consumables, andexchange of equipment);a transportation hub to assemble, check out,

6.

7.

8.

and launch vehicles (e.g., those carryingcommunications satellites) to geostationaryor other high orbits, and as automated in-terplanetary probes (e.g., a Mars orbiter oran asteroid rendezvous vehicle;an assembly facility for large space structures(e.g., antennas for advanced satellite com-munications systems);a storage depot for spare parts, fuel, and sup-plies for use as needed by satellites, plat-forms, vehicles, and people; anda staging base for more ambitious futureprojects-and travel (e.g., a lunar settlementor a human voyage to Mars).

Questions such as the following must be askedrelative to the corresponding functions listedabove:

1.

2.

3.

4.

5.

6.

7.

8.

How much of an investment do these (andother) capabilities warrant?Is use of a “space station” the optimum wayto accomplish these missions?When will the need for a microgravity pro-duction facility be demonstrated, and howmuch of its cost should its users pay for?What kinds of satellites will be repaired,why, and who will bear the cost?When will the transportation hub be readyand why is it needed then?What is the purpose of the assembly facilityfor the large space structures–and of thelarge space structures themselves?What is the justification for a storage depotin space?When will a staging base be required for alunar settlement or a manned Mars expe-dition?

And, underlying all of these specific questionsis the hazard that too great a commitment to theacquisition of in-space infrastructure, and the re-sulting long-term operations and management ex-penditures, might preempt the adequate supportof other important civilian space activities.

Ch. 3—Space Infrastructure ● 67

REACTIONS OF NATIONAL RESEARCH COUNCIL BOARDS

Other science and engineering organizationshave participated in the study of space infrastruc-ture acquisition. NASA invited the National Re-search Council (NRC) to review its possible utili-zation for space science and applications. (TheNRC is a private organization of distinguishedscientists and engineers operating within the char-ter of the National Academy of Sciences to actas an advisor to the U.S. Government (and others)on science and technology issues. It worksthrough its committees, boards, and institutes,two of which, the Space Science Board (SSB) andthe Space Applications Board (SAB), studied theseissues in workshops during the summer of 1982.)

The Space Science Board concluded that al-most all of the space science research projectsforecast for the next 20 years (a forecast madewithout giving great attention to the possible useof sophisticated in-space infrastructure) could becarried out without the use of a “space station”as then characterized by NASA. These projectscould be carried out by using Shuttle/Spacelab,satellites, interplanetary probes launched with ex-pendable launch vehicles, or contemplated up-per stages compatible with the Shuttle. The SSBstated it was not opposed to a “space station, ”that a decision on it should be made for reasonsbeyond science uses, and that some science in-terests would make use of it if it were available.But the SSB expressed concern that any delaysin launching science payloads that might be im-posed as a consequence of waiting for comple-tion of any “space station” could harm scienceprograms unnecessarily, as the SSB believes hap-pened during the development of the Shuttle(when several programs used up funds for em-ployee salaries and other program costs duringsuch delays),

The Space Applications Board expressed guardedsupport for use of a “space station .“ It indicatedinterest in applications made possible, or mademore efficient, through use of appropriate infra-structure, such as servicing of free-flying plat-forms, launching of geostationary satellites, repair-ing LEO satellites, and serving as a materialsprocessing laboratory. Communications experi-

mentation, especially for large antennas, wasanother likely use in their estimation. The pres-ence of a human crew was deemed desirable,particularly for materials science experiments andfor modification and repair of instruments. TheSAB also concluded that a platform in near-polarorbit would be an important infrastructure com-ponent, to be used for Earth remote sensing ofresources, Earth environmental studies, andocean observations. The capability of the plat-form to merge and process a variety of data priorto transmission to the ground would be an advan-tage compared to independent, unprocessedtransmissions from individual satellites. The SABcautioned that sufficient resources must be madeavailable to develop instruments and payloads foruse on any “space station. ”

Another body examining the role of expandedspace infrastructure was the NASA Solar SystemExploration Committee (SSEC). The SSEC is agroup of the Nation’s outstanding planetary scien-tists directly advising NASA on planetary research.The SSEC, which spent 2 years defining a newU.S. planetary space strategy, looked at theusefulness of any new infrastructure for planetaryexploration. It concluded that, in the near term,the facility could be used beneficially as anassembly and launch base for deep space probeswith potentially important advantages for plane-tary spacecraft requiring large internal propulsionsystems. In the longer term, this could greatly fa-cilitate the return of samples from Mars by pro-viding a fully loaded booster such as a Centaurrocket. A “space station” could also serve as aholding facility for returned samples to alleviateconcerns of their possible contamination of theEarth.

In January 1984, NASA created a 15-memberadvisory panel of academic space scientists that,over a 2-year interval, is expected to give NASAadvice on suitable research projects for long-term,habitable, space infrastructure.

Of related interest to NASA programs, the NRC’sAeronautics and Space Engineering Board (ASEB)conducted a workshop during 1983 on NASA’s

62 • Civilian Space Stations and the U.S. Future in Space

Space Research and Technology Program. Whilenot directly addressing “space station” issues,their report noted the high payoff uses of spacein the communications and meteorology fields,the present speculative nature of manufacturingin space, the high cost of space transportationand systems as an inhibiting factor in the com-mercial use of space, and that, in the face offoreign competition, the United States shouldcontinue to explore and stimulate potential usesof space.

The ASEB urged NASA to provide access tospace for experimental purposes as a natural ex-tension of national aerospace facilities on theEarth’s surface. Overall, the report recommendedthat NASA devote a significant portion of its ef-forts to develop technology that would reducethe cost of spacecraft subsystems, payloads, trans-portation, and operations.

ALTERNATIVE INFRASTRUCTURE

Because of the large public costs associatedwith the NASA plans for acquiring in-space in-frastructure, and considering the view of theSpace Science Board (and others) regarding theNASA plans, it is important to explore alterna-tive approaches for providing the desired capa-bilities of such infrastructure. OTA has identifiedseveral alternatives that could provide various ca-pabilities, at various times, and at various initialcosts to the Government. These alternatives in-clude system components that currently exist orare currently under development. OTA has alsoconsidered a gradual approach to infrastructureacquisition with various average annual fundingrates; lower cost alternatives could be used asearly steps in an evolutionary development lead-ing to increasingly sophisticated and capable ar-rays of infrastructure. Each of these approacheshas different implications for initial Governmentcost, life-cycle costs, pace of commercial devel-opment, and the pace for carrying out humanactivities in space.

Uninhabitable Platforms

Regardless of the outcome of the debate overthe need for infrastructure that includes and/orsupports a long-term human presence in space,there is a significant community of users whowould benefit from having uninhabited space fa-cilities and services available to them. A numberof so-called free-flying automated platform alter-natives now exist, are in development, or havebeen conceived, that could take advantage of the

Shuttle or expendable vehicles for launch andservice.

The Shuttle can be used to launch to, and re-turn equipment or other materials from, LEO. Thisability allows for the use of space platforms of-fering electric power, heat rejection, communi-cations, attitude control, and other services to anumber of users. Some time after insertion intoorbit (typically several months to a year), the Shut-tle or an ROTV would rendezvous with such aplatform, and servicing intervals for platform-mounted instruments would be coordinated withthe rendezvous schedule, keeping costs in mind.Payloads could be exchanged, attitude control,fuel and other expendable replenished, batteriescharged, or the platforms could be returned toan LEO base or to Earth. Platforms could avoidcontamination and stability problems associatedwith inhabited infrastructure. The cost of thecommon platform facilities could be amortizedover a long lifetime and a large number of ac-tivities.

Fairchild LEASECRAFT.-The Fairchild LEASE-CRAFT (fig. 4) is designed to support equipmentthat can be exchanged on orbit. This design ap-proach anticipates that the costs (special equip-ment, crew training, etc.) and risks associatedwith performing maintenance and payload modi-fications and substitutions on orbit are outweighedby the saving in transportation cost and improve-ment in spacecraft utilization, which avoids fre-quent launch and return of the platform.


Figure 4.—An Artist’s Conception of a LEASECRAFT Enroute to Orbital Altitude With Payload Attached

LEASECRAFT was inspired by the MultimissionModular Spacecraft (MMS) system on which theLandsat D and Solar Maximum Mission spacecraftare based. It can provide up to 6 kW of powerand other services to user payloads, and is in-tended to serve LEO space projects that includedata acquisition/transmission and materials proc-essing.

Data acquisition activities generally require finepointing and high data rates but relatively mod-est power levels. Materials processing projects,on the other hand, require high power but lowdata rates and relatively coarse pointing. TheLEASECRAFT could be converted from one con-figuration to the other on orbit from the Shuttleor from other inhabited infrastructure.

The LEASECRAFT design includes a centrallymounted propulsion module that contains 2,700kg of hydrazine for transfer from the standardShuttle orbit of about 300 km to an operating

altitude of 480 km. Later it can be returned tothe Shuttle orbit for rendezvous. The total weightof the LEASECRAFT bus is expected to be 6,400kg (including the initial charge of propellant).

The power and other services provided by theLEASECRAFT are dependent on the number andtype of its modules. Details of how module andpayload changes will be handled will depend onlessons learned from the Solar Max repair. Pos-sibilities include the manipulation of tools by theRemote Manipulator System (RMS), spacewalk-ing outside the Shuttle cargo bay by payloadspecialists, and retrieval of the LEASECRAFT bythe RMS to a position in the cargo bay wherepayload specialists would perform the workneeded.

An automated electrophoresis payload beingdeveloped by McDonnell Douglas is frequentlymentioned in conjunction with the LEASECRAFT.It will consist of an electrophoretic processing fa-

. —


cility and a separate supply module having a com-bined weight of some 10,000 kg. The process-ing unit will use 3.5 kW of power and will requirean acceleration environment of less than 0.1 per-cent of gravity on Earth.

Another prospective payload for the LEASE-CRAFT system is NASA’s Advanced X-Ray Astron-omy Facility (AXAF). AXAF is a 9,000-kg telescopethat will operate in a 500-km orbit, require 1.2kW of power, and periodic change of imagingand spectrographic instruments.

The LEASECRAFT’s ability to accommodatespecific payloads is very similar to that of the highpower version of EURECA (see below), with oneimportant exception: the higher data handlingability of LEASECRAFT would allow it to accom-modate most science and applications instru-ments. It would not accommodate some instru-ment projects that are very large, or those thatrequire human involvement.

The initial LEASECRAFT reportedly will cost atleast $150 million (1984$) apiece to purchase.Users may also purchase partial services ofLEASECRAFT or lease an entire platform fromFairchild for $20 million to $40 million (1984$)per year. Transportation costs will include initiallaunch of the LEASECRAFT and its payload andother payloads that, subsequently, are taken toit for exchange.

Boeing MESA.–The Modular ExperimentalPlatform for Science and Applications (MESA) isa low-cost satellite system designed by Boeing forlaunch on the Ariane. The MESA design followsfrom Boeing small spacecraft designs and produc-tion of the last decade. This includes three space-craft known as S-3 for the Department of De-fense, two Applications Explorer Modules (AEMs)for NASA, and the Viking Spacecraft being pro-duced today for the Swedish Space Corp.

The MESA program utilizes existing hardwareand previous experience to achieve a low-costplatform for modest payloads that do not requirerecovery, and for special cases that do requirerecovery.

An interesting feature of the MESA system inits Viking configuration is that it duplicates the

Ariane structural interface on its top side, whichenables it to share a launch by fitting betweenthe Ariane and the primary payload. This use ofresidual launch capacity can reduce the cost oftransportation to orbit.

The total mass of the MESA/Viking platform issome 500 kg. The design of the platform providesfor attitude control and propulsion. Once the Vik-ing separates from the main satellite after launch,the propulsion unit can boost the Viking into itsoperational orbit. The spacecraft is spin stabilizedat 3 rpm, and Earth/Sun sensors and magnetictorquers are elements of the attitude control sys-tem. A combination of solar arrays and a batteryprovide 60 W of average power with a peak pow-er of 120 W.

Limited changes can be made in solar array sizeand power output. The overall diameter of theMESA with payload cannot exceed the 2.95-me-ter internal diameter of the Ariane’s payload com-partment. The central core of the platform is de-signed to accommodate both platform (420 kg)and payload weights (0o kg for the design refer-ence) and up to nearly 2,OOO kg of host satelliteweight during Ariane launch. The available vol-ume for the payload is 1.6 cubic meters (m J).Should the solid-propellant rocket motor not berequired, an additional internal volume of ap-proximately 0.6 m3 would be available for pay-load use.

MESA is limited in its applicability because ofits small size, limited resources, the use of spinstabilization, and the intention to have the pay-load integrated within the structure. This makesit best suited to small, scanning or nonviewing,dedicated activities. While suited for some spaceplasma physics or cosmic ray investigations, thespin stabilization is not appropriate for micrograv-ity activities. MESA will accommodate only asmall fraction of the science and applicationsprojects identified in NASA’s Mission AnalysisStudies.

MESA is reported to cost $10 million (1984$).Transportation charges on the Ariane are uncer-tain since it can share a launch with another pay-load. If it is carried in the Shuttle, it should qualifyfor the minimum charge of $12.5 million (1984$).

Ch. 3—Space Infrastructure ● 6 5

Photo ” Boeing Aerospace

The Boeing MESA spacecraft undergoing ground processing.


Shuttle Payload Support Structure (SPSS).–An example of a structure supporting payloadsthat remain attached within the Shuttle cargo bayis the SPSS that has been developed for NASA.Teledyne Brown expects to commercialize SPSSduring 1985. It will provide a mount, electricalpower, data handling, and environmental con-trol for payloads weighing up to 1,400 kg.

Long Duration Exposure Facility (LDEF).–Aplatform housing 57 experiments, many of themseeking to record how manmade materials holdup in the LEO environment, was released fromthe Shuttle in April 1984. The 10,000 kg-satellite,called the Long Duration Exposure Facility (LDEF),will be retrieved by the Shuttle in 1985. The LDEF,basically a free-flying support structure for scien-tific experiments, cost $14 million (1 984$), notincluding launch and retrieval.

Pleiades Concept.–A concept to expand theuse of platforms for space science research hasbeen proposed by students in a 1983 systems en-gineering course at Stanford University. In thisconcept (called “pleiades”), a platform locatedin the Shuttle cargo bay would provide data proc-essing and other support for several co-orbitingfree flyers equipped for long-term astrophysicsresearch. Periodic servicing would be feasiblefrom the Shuttle. If developed, it might becomea permanent space infrastructure element.

Space Industries’ Platform.-A free-flying per-manent industrial space facility (lSF), designed pri-marily for materials processing, has been pro-posed by a new commercial space company,Space Industries, Inc. (fig. 5). An automated plat-form suited for production purposes, it could beplaced in LEO by the Shuttle and serviced sev-eral times a year by it and/or any eventual long-term space infrastructure. The ISF would includea pressurized volume where equipment could beserviced by a crew during resupply periods; thefacility, however, would provide no life supportfunctions when occupied other than a suitableatmosphere compatible with the Shuttle or ROTV,to which it is expected to be attached duringthese periods.

Assuming successful financing, the facility couldbe placed in operation in the late 1980s. No costfigures have been made public, but some indus-

try sources estimate that it would cost some hun-dreds of millions of dollars to develop and con-struct.

MBB SPAS.–The concept of a Shuttle-tendedplatform was tested, to a limited degree, with theSpace Pallet Satellite (SPAS) payloads during twoShuttle flights. SPAS was developed at the initia-tive of the German company Messerschmitt-Bol-kow-Blohm (MBB). Its structure is constructed outof graphite epoxy tubes to form a modular trussbridge that spans the Shuttle cargo bay in widthand fits that length dimension for which a mini-mum launch charge is made by NASA. The struc-ture provides mounting points for subsystem andexperiment hardware and includes a grapple fix-ture for handling by the Remote Manipulator Sys-tem, i.e., the Shuttle arm. The SPAS is designedto operate in either a Shuttle-attached mode oras a free-flying platform, and it was released dur-ing the seventh Shuttle flight to operate in the lat-ter mode for about 10 hours before retrieval. Inthat operation it provided the first opportunityto demonstrate the Shuttle’s ability both to de-ploy and retrieve a satellite. The SPAS payloadremained in the cargo bay during the 10th Shut-tle flight, where it successfully handled equip-ment for several commercial users.

Having only battery power and compressed gasthrusters, the initial SPAS is designed for short-Iifetime projects (7 to 15 days), but subsequentversions could undoubtedly extend the lifetimeby incorporating solar photovoltaic arrays andpropellant-type thrusters, and maybe even a kickmotor to achieve a wider range of orbits and/orto be able to return to a Shuttle-compatible or-bit for rendezvous. In its present form, SPAS willonly accommodate relatively small, low-powerinstruments used for short periods of time.

The basic SPAS platforms costs less than $1 mil-lion (1984$); subsystem equipment required byspecific payloads is not included. SPAS is de-signed to qualify for the minimum Shuttle launchcharge of $12.5 million (1984$) but, with a largepayload, it may exceed this qualification.

EURECA.–The European Space Agency (ESA)is developing a small unmanned platform carrierthat would be released from the Shuttle and re-trieved after free flights in space of 6 to 9 months.

.— — —


Figure 5.—A Free-Flying Permanent Industrial Space Facility

Initial Operating Configuration

‘ - - -

Four ISF Module Configuration

. .

---

Two ISF Module Configuration

ISF Docked to NASA’’ Space Station’

Ch. 3—Space /infrastructure Ž 69

Shuttle. The ability to fly from the Shuttle to auseful orbit and back for rendezvous with theShuttle is typical of most space platform concepts.

The EURECA will have a payload capacity ofabout 1,100 kg with the combined carrier andpayload weighing approximately 3,500 kg. Thetotal length of the carrier/platform, plus itspayloads, in the Shuttle’s cargo bay will be 2.3meters, with an option for a shorter length of 1.6meters if desired.

Energy for EURECA will be provided by deploy-able and retractable solar arrays that will initiallydeliver 5.4 kW of power at 28 volts. Of this out-put, 1 kW will be available to the payload on acontinuous basis, while much of the balance willbe required to charge the batteries that supplypower when sunlight is not available.4 The powersupply for EURECA and its payload will be cooledusing a fluid loop connected to a radiator.

EURECA payload and housekeeping data willbe relayed to Europe via circuits employing theL-Sat communications satellite as a test. Thetelemetry system will normally use ground sta-tions in Europe, but it will also be compatible withthe Shuttle. The maximum data rate that can beprocessed on the ground by the proposed sys-tem is 2.5 kbps, although the on board system willbe capable of transmitting up to 1 Mbps.

Size, mass, capacity, and data handling abilityare the most stringent EURECA design constraints.If the data rate is restricted to 2.5 kbps, only filmcameras can be accommodated. But if the full1 Mbps data rate can be utilized, many scienceand applications instruments can be accommo-dated. However, large, high power, or high datarate payloads, such as telescopes, radars, Iidars,multispectral scanners, or a combination of theseor other instrument payloads cannot be accom-modated. Increasing the available power levelalone does not significantly improve the abilityto accommodate such payloads, since scienceand applications instruments that require highpower (e.g., remote sensing radars) also tend tohave high data rate requirements (tens to hun-dreds of Mbps).

4More power would be available for payload use if it proves pos-sible to operate the platform in a Sun-synchronous dawn-dusk or-bit where it does not enter the Earth’s shadow.

The cost of EURECA has not been clearly stated,although ESA has referred to a program cost of$170 million (1984$) that appears to include somepayload costs.

Plans are also being developed for EURECA 11,an advanced version having increased power andpayload capacity. The new design will allowspace-basing and equipment exchange on-orbit,using the Shuttle or a yet-to-be-developed Arianeautomatic docking system.

SOLARIS.-This French concept includes pre-liminary designs for an automated platform. Itwould be unmanned, located in LEO, and woulduse furnaces, a robot manipulator arm, solarpower, and other subsystems. Ariane 4 wouldlaunch a transfer and supply stage, and a ballisticreentry capsule will bring processed materialsback to Earth.

The first generation facility would have the fol-lowing major elements:

● The Orbital Service Module (OSM), whichis a user-shared platform with docking portsfor payloads and transport vehicles.

● An in-orbit Transport Modular Vehicle (TMV)for resupply, transport, and servicing ofspace payloads.

● A Data Relay Satellite CommunicationsSystem for control and high data rate trans-missions.

. The Ariane 4 launcher.

The intent is to fly the OSM in a circular “Sun-synchronous” orbit following a path over the twi-light line, thus avoiding the Earth’s shadow andthereby achieving a relatively high 10 kW of con-tinuous power output for its users. Activities suchas materials processing, microwave Earth obser-vation, and assembly and check-out of large ve-hicles in orbit are envisioned. The orbit altitudecould be adjusted from 600 to 1,000 km. Twodocking ports would be available for TMV berth-ing, with five ports for payloads. Data transmis-sion rates would not exceed 400 Mbps. The en-tire OSM weight would be 4,500 kg (excludingpropellant).

The function of the TMV is to provide transpor-tation service between the Ariane delivery orbitand the OSM, and to permit the return of a lim-

38-798 0 - 84 - 6 : QL 3


ited amount of equipment and products to Earth.The TMV will consist of an expendable modulewith propulsion, attitude and trajectory control,and the ability to rendezvous and dock.

The TMV can be used in either one-way orround-trip service. For one-way service the pay-load would be attached directly to the TMV mod-ule, and both would be placed inside the fairingof the Ariane 4 for launch. A 5,000-kg payloadcould be accommodated in this manner.

Round-trip service requires the use of a reen-try vehicle similar to the Apollo reentry module.The TMV module is attached to the reentry bodyfor launch in a manner similar to the arrangementfor a one-way payload, and the two are separatedduring reentry. About 2,500 kg and 15 m3 of pay-load could be accommodated within the reen-try vehicle; it could touch down on either landor water and is designed for reuse.

The first generation SOLARIS concept is func-tionally similar to the science and applicationsspace platform studied by NASA, except thatSOLARIS specifies a dawn-dusk Sun-synchronousorbit. This orbit restricts its usefulness for manyEarth-viewing projects that require lighting fromthe Sun. However, radars, Iidars, and some mi-crowave instruments can “see” in the dark andwould not be affected, while solar-viewing in-struments wouId gain the advantage of continu-ous visibility of the Sun. The ability of SOLARISto support large, multiple instrument facilitiesshould allow for accommodation of most of thesolar physics payloads. However, a continuousfull Sun orbit would be a problem for many celes-tial-viewing instruments that depend on Earthshadow to eliminate scattered light from the Sun.All automated life science activities and allmaterials processing, except for those requiringhuman presence, could be accommodated.

The orbit of SOLARIS is not suited to launch,retrieval, or servicing of low inclination satellites(including geostationary satellites), since a largeorbit plane change is required. And, since mostSun-synchronous satellites are not in dawn-duskorbits, a “latitude drift” would be required toservice them. Some studies consider satelliteassembly and service to be a major role for a

“space station”; SOLARIS would be able to ac-commodate only a small fraction of this market.

Costs of the evolutionary SOLARIS programhave not been defined, but they likely would beseveral billions of dollars (1984$) if the entire con-cept is developed.

Habitable Infrastructure

Although uninhabited platforms can be usedto support many experiments and commercialprocesses that do not require human presence,and some activities require a stability that wouldbe difficult to achieve if humans were present,other activities require or can be greatly aidedby human presence. These include life sciencestudies of humans in space, which are necessaryto prepare for long duration human travel inspace, and interactive experimentation in mate-rials processing (e.g., pharmaceuticals, semicon-ductors, crystals), which is required in order toexplore the commercial potential of materialsprocessing.

A number of infrastructure elements other thanthe proposed NASA “space station” are availablethat can support humans in space.

Extended Duration Orbiter (EDO).–A majorconstraint on the duration of the on-orbit timefor the Shuttle is the availability of electricalpower. The current Shuttle power system usesthree fuel cell powerplants fed by cryogenicallystored hydrogen and oxygen, and delivers 21 kWon a continuous basis, of which 14 kW is allo-cated to the Shuttle itself and 7 kW is availablefor payloads. The fuel cells are fed from tank sets(one hydrogen and one oxygen tank in each set)located under the floor lining in the Shuttle cargobay. Three tank sets are considered standardequipment. Two additional sets (for a total of five)can be installed with no volume penalty to pay-loads, but with a combined weight penalty (fullyfueled) of 1,500 kg. The full complement of fivetanks will provide a stay time of 8 days if the full7-kW payload allocation is drawn upon continu-ously. Where little payload power is drawn, asmight be the case for satellite repair or remote


sensing activities, the stay time could be as muchas 12 days.

One obvious approach to extending the staytime is to add more tank sets. One such conceptresults in a stay time of 15 to 22 days, againdepending on power consumption, by loadinga four-tank-set carrier into the cargo bay. Sucha carrier would shorten the usable length of thecargo bay by some 2 meters out of 18, and re-sult in a 3,700-kg decrease in payload capacity.Extension of this approach to even longer dura-tions has a practical limit because of the volumeand weight capacity lost, and the limited storagelifetime of cryogens.

A 20-day stay time with 7 kW of power con-sumed by the payload, or up to 26 days if lesspower is consumed, can be achieved by usinga solar array in conjunction with the five stand-ard cryogenic tank sets. In one concept, the solararray would deliver 18 kW in sunlight, and thefuel cells would deliver 3 kW makeup power fora total 21 kW. During orbital eclipse of the solararray, the fuel cells would supply the full 21 kw.The RMS could deploy the array underneath theShuttle, to avoid interference with the power sys-tem heat radiator and the field of view from thecargo bay. A previously proposed Power Exten-sion Package (PEP) was identical in concept butwas sized to provide 15 kw, instead of the nor-mal 7 kw to payloads. The payload weight pen-alty for these concepts, including tank sets, is esti-mated at 2,300 to 2,700 kg. The cost to modifyone Shuttle was estimated to be $100 million to$200 million (1984$). Spacelab would have beenthe principal beneficiary of the PEP, but theplanned flights of Spacelab were judged to be notfrequent enough to justify the expenditure.

To achieve stay times well beyond 20 days re-quires some radical changes in the power system,but the Shuttle could be designed for essentiallylimitless duration as far as power is concerned.Batteries would be used for power during Shut-tle eclipse, and operation of the existing fuel cellswould be limited to launch, reentry, or emergen-cies. The fuel cell reactants would be stored atambient temperature and high pressure, therebyeliminating the storage lifetime constraint asso-ciated with cryogens. A 48-kW solar array would

be required to provide power to recharge the bat-teries in sunlight; this power would be in additionto the basic 21 kW needed for Shuttle and pay-load power. The weight penalty for such a powersubsystem is estimated to be about 3,200 kg.

Modifications are required in other areas aswell. Flash evaporators that are currently usedto supplement radiator heat rejection requirelarge amounts of water in some attitudes, and tominimize reliance on them it would be neces-sary to increase the capacity of the radiators. Withregard to habitability, water tanks must be addedto compensate for water that is no longer gener-ated by fuel cells and a regenerative CO2 systemwould be required. Furthermore, for 15- to 30-day durations, the Shuttle habitable volume isonly adequate to marginal for a crew of four. Areconfiguration of the mid-deck, recommendedfor 30- to 60-day durations on orbit, includesmoving the airlock to the cargo bay. A Spacelabmodule would also be added to provide suchcrew amenities as a shower and an exercise andoff-duty area as well as increased work area.

Among the activities which an EDO would beexpected to support is satellite servicing. TheShuttle can reach a wide range of orbit inclina-tions and LEO altitudes, and the cargo bay, withits RMS and space for supplies and other supportequipment, seems well suited for this type of ac-tivity. The technical feasibility of repairing satel-lites from the Shuttle was demonstrated on theSolar Maximum Mission Satellite in April 1984.With the Shuttle launch charges alone projectedto be as much as $100 million for a dedicatedflight before the end of the decade, the prospectof sharing a launch for this purpose along withother payloads and/or activities is a significant fac-tor in the economic viability of such an operation.

In theory, with on-orbit infrastructure servingas an operations and distribution center, a Shut-tle destined for it could carry not only suppliesand equipment for the operation at hand butcould be loaded with payloads and supplies tobe left in space. Subsequent transfers to free-flyers, for instance, could then be accomplishedwith a lighter, more energy-efficient proximity-operations vehicle in contrast to the relativelymassive Shuttle. The premise is that the saving

72 . Civilian Space Stations and the U.S. Future in Space

to be realized by utilizing the launch capacity ofthe Shuttle more effectively would, over time,more than offset the cost of the on-orbit infra-structure specifically designed to handle equip-ment and supplies. It is not clear to what extentthe on-orbit infrastructure operations costs (bothon-orbit and ground-support) are included inanalyses of such operations. It is also not clearhow total costs (facilities and operations) wouldbe allocated among all users of a shared “spacestation” to establish the economic viability of anyparticular activity such as satellite repair andservicing.

Finally, an EDO could function as an observa-tory and a laboratory. There are adequate accom-modations in the aft flight deck to control andmonitor an observing payload such as one con-taining a large telescope. The Shuttle has no pro-vision for laboratory operations beyond the ac-commodations available in the mid-deck lockersand, on some early flights, the main galley area.However, a Spacelab module, discussed in thefollowing section, could be added to provide ashirt-sleeve working environment in the cargobay. One drawback is that Spacelab consumesnearly half of the available 7 kW of payload pow-er. Thus, electrical power for experiments wouldrequire careful management, and a more capa-ble power system would be desirable for an EDO.

An EDO is estimated to cost about $2 billion(1984$) for the basic Shuttle, $300 million (1984$)for an upgraded habitation module similar toSpacelab, and $200 million (1984$) for the PEP.The full Shuttle launch cost would be incurredfor each flight.

Spacelab.–The Shuttle carried Spacelab intoorbit for its maiden flight in November 1983.Spacelab is a set of hardware that converts thecargo bay into a general-purpose laboratory forconducting science, applications, and technol-ogy investigations. It was financed and builtjointly by ESA in close cooperation with NASA,providing a convenient means for working witha collection of experiments in a shirt-sleeve LEOlaboratory environment. It augments the Shuttleservices for powering, pointing, cooling, and con-

trolling experiment hardware and for data handl-ing and transmission to Earth.

Spaceiab is composed of two primary buildingblocks: modules and pallets. The module is a can-Iike pressure vessel approximately 4 meters indiameter that provides a shirt-sleeve workingenvironment for the crew and rack accommoda-tions for experiment hardware. The module con-sists of two end cones and one or two center sec-tions (each 2.7 meters long). It may be used ineither its long form (7.0 meters) or short form (4.3meters) and may be flown alone or in combina-tion with one or more pallets. The pallets are U-shaped structures 3 meters long that span the car-go bay and provide mounting for instruments thatare to be exposed to the space environment. pal-lets may be flown individually or tied togetherin trains. For pallet-only projects, the computersand other subsystem elements normally carriedin the module are housed in an “igloo” that canbe attached to the forward pallet, The Spacelabhardware set also includes an Instrument Point-ing Subsystem (IPS) capable of high-accuracypointing for clusters of small instruments or alarge telescope.

While both pallets and modules can be consid-ered for use as independent space infrastructure,in its present form Spacelab is totally dependenton the Shuttle for its resources. Specifically, theShuttle provides 7 to 12 kW of electrical power,8 to 12 kW of cooling, data handling and datacommunication at rates of up to 50 megabits persecond. Further, the Shuttle provides oxygen re-plenishment, and serves as both a crew residenceand a safe haven under emergency conditions.Spacelab depends on these resources to providea safe, stable laboratory environment.

Several stages in the evolution of the Space-Iab module beyond the current generation havebeen studied, moving from complete depend-ence on, and attachment to, outside support ele-ments, to relatively independent operation as afree-flyer that is resupplied every 6 months or soby the Shuttle or an OMV.

Spacelab With an EDO.–One version of theSpacelab that would be carried by an EDO uti-lizing a PEP, was studied by ESA in collaborationwith NASA, The electrical and heat rejection sys-


Figure 6.— Major Spacelab Elements

MODULE

terns would be modified to handle increasedpower, and the command and data managementsystem wouId be modernized. Since two Space-Iab modules are now owned by NASA, additionalcosts would involve only the modifications andlaunch costs.

Spacelab as an Attached Module.–Anotherversion would see the Spacelab used as a labora-tory component of a “space station.” The modulewould be lengthened to provide a greater shirt-sleeve volume for more experiments and people,but in this case other connected infrastructureelements would replace the Shuttle as a supportsystem. Either an existing NASA Spacelab modulecould be used for this purpose, or an additionalmodule could be provided at a cost of $300 mil-lion (1984$).

Spacelab as a Free-Flyer.–A third version isthat of Spacelab as an inhabited free-flyer. Thiswould require the development of a dedicatedservice module that would provide the types ofresources currently provided by the Shuttle.

For attitude control, there are a number of pos-sible candidate systems which could be adopted.In Europe, for example, there is the ESA ModularAttitude Control (MAC) system, which is designedfor general satellite application. This subsystemis in prototype form, and hardware tests are u riderway at present. Electrical power and cooling pro-visions would be required, as part of the dedi-cated services module, in the form of solar ar-rays, batteries, and a heat radiator with a coolingfluid loop. It is possible that the increased-capac-ity (12 kW) solar arrays under development byESA, together with the ESA radiator, would besuitable. Command and data handling could besatisfied by commercial computer technology.Oxygen supply for the free-flying Spacelab couldbe handled by using the nitrogen tanks that arealready available in Spacelab. However, for longdurations on orbit, additional provision for ox-ygen supply would be necessary, which mightpossibly take the form of a water electrolysis sys-tem (as yet undeveloped). For crew habitation,the developed Spacelab free-flying module would


Figure 7.–Shuttle-Spacelab Flight Profile

I L A N D I N G /7 ~

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Y<.! L-, ,,, V,L, . , L, , ;“ SPACELABSPACE FLIGHTnnel-n, kl A -?-, nh , m EXPERIMENT

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USER COMMUNITY

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need to be based on a two-segment-long moduleas a minimum (7.0 meters), or preferably a three-segment-long module (1 O meters), in order toprovide the necessary volume for sleeping, foodpreparation and consumption, waste disposal, ex-ercise and recreational equipment, and commod-ity stowage. Crew-supported experiment and lab-oratory activities could be accommodated in aSpacelab-derived two-segment module, con-nected to the habitation moduIe by an airlock;it would contain the necessary laboratory equip-ment and Spacelab-derived racks. The use of twomodules connected via an airlock would providethe basis for a necessary safe haven in the eventof a major failure in, or of, either module.

The use of two Spacelab-derived modules,combined with the associated dedicated service

module, could provide long-duration infrastruc-ture for human and automatic operations inspace. An intermediate step in this directionwould be the development of a two-segmentSpacelab-derived module, coupled with a dedi-cated service module. The cost of such a devel-opment (designed for Shuttle resupply every 90days) could be some $400 million (1984$). Thetwo-module development costs would be consid-erably greater than for a one-moduIe configura-tion, perhaps approaching $800 million (1984$).

To put the size of a Spacelab-derived free-flyerinto perspective, it is interesting to compare thefacilities described above to the Skylab facilitywhich was orbited 10 years ago. A three-segmentSpacelab module has roughly the same externaldimensions as the Apollo Command and Serv-


ice Module’s propulsion/resource system plusreentry vehicle, that part of the Apollo transpor-tation system that rendezvoused with Skylab. TheSkylab Orbital Workshop (OWS) provided pri-mary habitation and work space 6.7 meters in di-ameter by 8.2 meters long or about 280 m3 ofvolume. Thus, the volumes enclosed by the two-and three-segment-long modules contain 25 and40 percent, respectively, of the habitable volumeof the OWS, and together would total just 70 per-cent of the OWS volume. In addition to the OWS,some Skylab control and utility functions werehoused in the airlock module and the MultipleDocking Adapter. Because of the dimensions ofthe Shuttle cargo bay, a number of ShuttleLaunches would be required to build up a Space-Iab-based infrastructure on a scale equal toSkylab.

The free-flying Spacelab could accommodateany payload currently envisaged for the Space labmodule on the Shuttle. Some life science facilityconcepts now being studied use a dedicatedSpacelab module as their basic structure. All lifesciences studies could probably be performed;high-temperature furnaces for material process-ing may require higher power and cooling thatcould, if necessary, be provided by additionalpower modules. Commercial production facilitiesare not yet clearly defined, but if such produc-tion proves to be desirable, additional power andSpacelab modules could be added, if necessary,to accommodate it. A small fraction of the Earthor celestial-viewing instruments could utilize thescientific airlock or window of Spacelab, but thisis a cumbersome way to handle such instruments.The only advantage of the Spacelab window orscientific airlock over a permanent external mount-ing position is easier access to the instrument,while the disadvantages include limited space,restricted field of view, and the necessity to han-dle the instrument whenever it is installed. How-ever, viewing instruments could be installed andoperated on one or more co-orbiting platforms.

Spacelab could serve as an operations controlcenter for other space activities. Properly equipped,it could accommodate 100 percent of this func-tion, although, depending on the number ofactivities conducted, more than one Spacelabmodule might be needed. The characteristics of,

and the problems associated with, exchangingequipment in the Spacelab module indicate thatits best use might be as a dedicated life and/ormaterials science laboratory, or as an in-spacecontrol center.

The idea of developing and using. existingSpacelab hardware for long duration humanactivities in space remains attractive in view ofthe maturity of the system building blocks. Limita-tions of the free-flying Spacelab concept, how-ever, may be significant. As an example, it wouldbe difficult to develop an efficient closed-loop lifesupport system.

Spacelab as free-flyer, including a utilitiesmodule based on EURECA, has been estimatedto cost $1 billion (1984$). Transportation costswould include an initial full Shuttle launch andsubsequent supply and transport services via theShuttle. An automatic docking service could bedeveloped for resupply by expendable launchvehicles, but the cost of such a development isuncertain.

Columbus.–The Germans and Italians haveproposed to ESA that the Columbus project, usingSpacelab modules as components of a more ex-tensive infrastructure, should become the ESAcontribution to the U.S. “space station” program.

The plan, including three steps or phases, be-gins with a Spacelab module attached to a U.S.“space station, ” providing laboratory workspaceand deriving life support, power, attitude con-trol, and other services from the parent “station. ”A second step (fig. 8) is an independent free-flyingSpacelab with power, attitude control, and mod-est life support supplied by a service module fash-ioned after the EURECA platform. It would re-quire direct resupply by the Shuttle or an OMV,provide laboratory workspace, and allow tendingby a crew for up to 8 hours at a time. A third stepwould add another Spacelab one-segment mod-uIe, with propulsion, to be used as a crew trans-port and servicing vehicle which might also beable to accommodate a small crew for short peri-ods at the laboratory. By servicing the free-flyer,it would enable the Columbus module to oper-ate autonomously for a few months at a time. Thislast phase is projected in Columbus program liter-ature for possible implementation near the end


Figure 8.—An Artist’s Conception of a Free-Flying Pressurized Module Withan Attached Resource Module (second phase of Columbus concept)


of this century. Cost estimates for a Columbusproject are not yet available.

NASA Minimum Cost “Space Station. ”-Astudy regarding a “space station” that would min-imize costs by using Spacelab modules was per-formed at the NASA Marshall Space Center andwas reported in 1982. It would provide soundand useful infrastructure, but would be of rela-tively modest dimensions in comparison withNASA’s present aspirations. It would include ahabitat module, a separate safe haven for emer-gencies, and a support systems module. It wouldbe launched by the Shuttle and would have 1 kwof power and a scientific workspace. Later,another support system module and a dockingadaptor would be attached, providing for thelong-term support of three persons, an experi-ment module, pressurized and unpressurized ex-periment ports, gyroscopic attitude control, com-munications and data handling, and 6 kw ofnominal user power. According to the NASAstudy, the cost of this facility would be $2 billionto $2.5 billion (1984$), assuming the use of anexisting Spacelab module already in the in-ventory.

Shuttle as permanent Infrastructure. -In thediscussion of the EDO, it was shown how rela-tively modest changes to the existing Shuttle vehi-cle could result in 20- to 25-day on-orbit staytimes while more extensive modifications couldmake 30- to 60-day stay times attainable. A con-cept has been proposed by one Mission Analy-sis Study contractor group that would have ma-jor Shuttle and its external tank assemblies carriedinto orbit together to form permanent infrastruc-ture. The basic Shuttle would be stretched to add30 feet to the cargo bay and would be utilizedwithout the wings, tail, and thermal protectionsubsystem. The main engines and the OMS engineswould remain in place. The crew compartmentwould be stripped to make room for a controlmodule. A command module would be locatedin the cargo bay. Major external tank modifica-tions would include a power module with solararrays which would mount on the nose, and awraparound radiator for thermal control.

The Shuttle and its external tank also would usethe Shuttle solid rocket boosters for launching asis the case for the conventional Shuttle. Upon itsreaching orbit, the solar arrays would be de-ployed, the cargo bay doors would be opened,and the command module would be rotated intoan upright position, thereby freeing the cargo bayfor use in servicing and staging operations. Asubsequent Shuttle launch could deliver a habit-ability module, logistics module, and crew.

The use of a basic Shuttle in this fashion wouldallow the very rapid acquisition of infrastructureable to serve as a habitable “space station” fora relatively low development cost.

Shuttle External Tank (ET) .-Application of theET as an infrastructure element is intriguing be-cause of its large size, because it achieves a near-orbital velocity during normal Shuttle launchoperations, and because it “comes free of extracost” to orbit. As a result, several aerospace com-panies have studied the ET for possible use onorbit.

The ET has an interior pressurized volume ofsome 2,OOO m 3 in the form of two separatetanks—one for hydrogen, the other for oxygen.

In present Shuttle launch operations, the ETseparates from the Shuttle and reenters the atmos-phere after main engine cutoff. On average, atseparation from the Shuttle, the ET still containsabout 4,500 kg of liquid O2 and H2. The chal-lenge is to identify practical methods of salvag-ing the tank and scavenging these residual pro-pellants.

The ET in orbit, initially viewed as a construc-tion shed and distribution center, might serve asa mounting structure for telescopes, large anten-nas, large solar power collectors, and experimentpallets, or it could be used as a component ofinhabited infrastructure, in which case it wouldneed windows and entry hatches. The most ob-vious use for the ET is for on-orbit fuel storage.This requires the least on-orbit modification,but assumes that the techniques and equipmentneeded to scavenge leftover fuel from the Shut-tle and to store it for long periods in space are

.


The addition of a free-flyi~g’SPAS platform, at a ctwt of $(h~ b@i~n {1,~$) would increase the

science/applications uses by three. Other platforms suc!h a~ k4ESAj lXA3ECRAFf or EURECA could alsobe added. For example, the use of three EURECAS, wh[dhcould be purchased at a cost of $0.6 billion(1984$) or leased annually at a fraction of this cost, would increase science/applications uses by lo.(In addition, while the system as described here would rtot serve as an assembly/launch platform, 9out of 10 projected solar system probes could be designed ~ be launched with upper stages from theShuttle.) “,,., , ,

in summav, a “USA Salyut” that approximates the, S@i~ SaIyut 7 could be assembled using e=n-

tially existing or currently underdevelopment technol~g Iie;;,Spacelab modths and a service modulecomposed of EURECA or LEASECRAFT-type power ad at!t\t@&”ccmttol% With the added cost of sever-al free-flying platforms, it could support most of the ‘Wiend@~~d applications experiments and aboutone-third of the commercial and technology developwnt-adities’ now described by NASA as requir-ing long-term space infrastructure. Anwhg the sciene~ a@@@ it cdt)ld not support are what NASAdescribes as the Latge Deployable Reflector, Mars %~@h:@!tum, I!atth Wiences Research Platform,and Experimental Geosynchronous Communications l%t@i!ti. Operationally, the size, power, and portcapabilities of the infrastructure would mean the pace@ rg#@%h And ckwelopment work would neces-sarily be less than half as rapid as with the NASA”pro#m@~@ swce infr=tructure. [f sta~ed in 1985,it could be operational by about 1990 # a -t of rw~ly, $2 biilion (1984$).

. .Of course, any design aimed speclft~liy t@yard CjJr#@-~&@I e@ivalence with the Salyut 7 may

miss the mark by the time it becomes op@fitiondlfi wati~ %wiet space infrastr~cture could be quitedifferent by 1990. However, the general”-c~mparkon of Capability and cost is illuminating.

.4 .. . ,.,

‘Described in detail in the OTA Technical Mernorarrdum Sa/yut-Sot4tH StepS 7%ard Awrwnmt Human Presence in Space, December 1993.

developed. Use as an uninhabited warehouse orunpressurized, sheltered workshop in space onlyrequires that the tank be purged of residual fuel,since several access openings (larger than 1 me-ter diameter) already exist.

A concept to use ETs as components of habita-ble infrastructure has been developed by theHughes Aircraft Co. In this concept, four ETswould be taken separately into orbit and thenjoined to form the spokes of a large wheel-likestructure. Solar panels would be mounted on arim connected to the outer ends of the ET spokes,providing 150 kW of power. The wheel wouldrotate, and a “despun“ module at the hub of thewheel would provide zero gravity workspace.The basic feasibility of this “dual-spin” system hasbeen demonstrated on a much smaller scale inover 100 successful communications satellitesbuilt by Hughes. Modules attached to the outerends of the ETs, carried into space as aft cargo

carriers, would be available for habitation andpressurized workspace. Rotation of the wheelwould provide artificial gravity in the spinningpart of the facility and gyroscopic action for at-titude control.

This innovative concept has several obvious ad-vantages. There is no doubt that many humanactivities, such as eating, drinking, food prepara-tion, showering, and dealing with human waste,would be much easier to carry on in the artifi-cial gravity environment provided by this system.And possible health problems associated withlong-term living in microgravity, such as decalci-fication of bones and atrophy of muscle and con-nective tissue, could be avoided. In general, thepresence of spin and a choice of gravity regimes,ranging from microgravity to artificial gravitysimulating what we are used to on Earth, shouIdprove to be useful in solving a number of human,scientific, and engineering problems.


Figure 9.— External Tank Structure

INTE

L H2


Figure IO.— Possible Uses of External Tank

PROPELLANT SCAVENGING ET AS A HANGAR

\ ’’

ET AS A STRONG BACK

.

ET WITH ACC HABITAT


Figure 11 .—Concept of Infrastructure Utilizing Four External Tanks

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Chapter 3 SPACE INFRASTRUCTURE - Princeton University