Download pdf - Orbital stations and studies of the earth from space

Automatica, Vol. 7, pp. 181-190. Pergamon Press, 1971. Printed in Great Britain.

Orbital Stations and Studies of the Earth from Space Les stations orbitales et les 6tudes de la Terre h partir de l'espace

Orbitalstationen und Studien der Erde vom Raum aus

O p 6 r t T a . r I b H b l e CTaHIII, II4 rt r I 3 y q e H r I e 3eM,rII, I I43 KOCMOCa

B. N. PETROV~"

Long lived, manned orbiting space stations, operating in unison with unmanned satellites to benefit greatly science and humanity, shouM be realized in the near future.

Summary--The uses and benefits of long lived, or long standing manned orbiting space stations are reviewed along with the history and progress of their development. Finally the special problems associated with the design of the control system structures and equipment are discussed, some of the promising mathematical solutions are presented, and it is concluded that after appropriate experimental verifications are made, the long lived space stations will be developed in the near future.

INTRODUCTION

THE ADVANCES in space exploration have opened a new era in the progress of science and they are a powerful impetus to technological developments. New discoveries have been made in physics and cosmology, geophysics and biology. Quite new branches of science have emerged such as space meteorology and aeronomy, space astronomy, space biology and medicine.

Now the Earth resources, the World ocean, the upper atmosphere, weather and hydrological processes can be studied from space; astrophysical and radioastronomical phenomena can be observed without the interference of the atmosphere.

During the 12 years of the Space Age the automatic devices such as artificial satellites, automatic interplanetary stations and probes and relatively short manned flights have given us tremendous experimental evidence that expands our knowledge of the Earth, the Moon, the nearest planets, and space.

Long-standing orbital stations with periodically relieved crew are still more promising.

OBJECTIVES

Long-standing manned orbital stations in team- work with automatic space laboratories and ob- servatories will enhance space research and provide

* Received 11 May 1970; revised 28 August 1970. The original version of this paper was presented at the IFAC Symposium on Automatic Control in Space which was held in Toulouse, France during March 1970. It was recom- mended for publication by the Editorial Board.

t Academy of Sciences, Moscow, U.S.S.R.

us with a continuous flow of scientific and experimental data, permit the staging of complex scientific and technological and medical-and-biological experiments, and facilitate the selection of the hardware for protracted space voyages.

Let us take up the main problems that can be solved with longstanding manned orbital stations (LOSMOS).

I. PHYSICAL AND GEOPHYSICAL RESEARCH

A LOSMOS is envisioned as a large space-borne physical laboratory where most challenging experiments on elementary particles and cosmic rays can be staged in high vacuum. In particular, cosmic rays can be studied and their high-energy content used to discover new nuclear reactions and new elementary particles with an energy three orders of magnitude higher than that which is currently achieved. Also, attempts may be made to detect quarks, the hypothetical particles with fractional charge; to discover these would be very important for the modern theory of the matter.

Very interesting experiments to verify the rela- tivity theory can be staged on LOSMOS which are equipped with nuclear clocks, and studies of the nature of gravitation and the detection of gravity waves would be of no lesser interest. In addition, studies of plasma and experiments in magnetic hydrodynamics, of magnetic and electric fields in space by artificial sodium and barium clouds, of the magnetosphere and the Earth 's radiation belt would be very promising.

2. ATMOSPHERIC STUDIES, HYDROLOGICAL AND METEOROLOGICAL OBSERVATIONS

Satellite observations of atmospheric conditions, clouds and snow cover, acquisition of data on ice fields, boundaries in oceans and seas and their changes, changes in ice caps in mountainous regions, floods and other natural phenomena are

181

182 B.N. PETROV

exceedingly important. Studies of the upper atmosphere and the weather situation from an orbital station and satellites have a great scientific interest in that they will augment the knowledge on the processes in the Earth's atmosphere and find wide applications. Significant data may be derived by direct observation from an orbital station and study of the still photographs of the Earth's twilight glow. Analysis of photographs made by cosmonaut K. P. Feoktistov from "Vostok- l" has revealed stable aerosol layers at the altitudes of 10 and 19 km which were responsible tbr the bands of higher brightness against the background of the dawn glow.

Measurements of the Earth-reflected solar" radiation made on board enable one to judge the state of the atmosphere. Valuable information is obtained by measuring the radiation of the Earth as a heated body in the i.r. range; data are thus obtained not only on the temperature of the Earth's surface but also on the composition and the state of the atmosphere. Studies of the Earth and its atmospheric thermal balance are very important. The space detection of cyclone, typhoon, and hurricane origination, their development and movement cannot be overestimated. An early warning service will help save lives, reduce the damage; and divert ships to safe routes.

The progress of space meteorology will substan- tially improve weather forecasts, predict the movements of icefields in the ocean, floods, the exact time of rains and snowfalls. Studies from orbital stations at altitudes of thousands or even tens of thousands of kilometers will be more corn prehensive if they are integrated with the operation of weather and geophysical satellites and rocket probes.

Space meteorology and aeronomy using space technology will undoubtedly play a decisive role in weather control, a most involved problem of the future.

3. STUDIES OF THE EARTH'S RESOURCES

Space exploration opens up new possibilities for the study of our own planet. Many new interesting and useful things can be learned by observing the Earth from space.

Air photography is already widely used in geo- detics, mapping and study of natural resources. Analysis of colored and black-and-white pictures taken from a satellite or an orbital station is still more rewarding, especially if photographs of the Earth's surface and objects are made simultaneously at various wavelengths, from the visual spectrum through the radio frequencies, with the normal photography, i.r., lasers, and other hardware. A combined study of areas in the u.v., visual, i.r. and microwave ranges of electromagnetic radiation

yields much information about the nature of the Earth's surface and the rocks near the surface Analysis of images of the areas and of the spectr~ yields valuable scientific and practical data including the geomorphological characteristics of the area, conditions of the terrain, the minerals, soils, vegetation, crops, woods, and pest-stricken zones. Knowledge of the area characteristics and types of the terrain, including shifts and ruptures o1' the crust, provides information for detecting ores.

Observations from space would identify salinated areas, help spot lbrest fires, estimate the degree or" erosion, the stores of fresh water and the degree of its contamination.

Explorations of oceans, ira particular the temperature distribution, currents, water pollution, sea roughness, the detection of plankton and fish con- centrations, icefields and icebergs, tsunami waves will also give tangible results.

4. SPACE ASTRONOMY AND RADIOASTRONOMY

The age-old dream of astronomers, space ob- servatories, now comes true. The Earth atmosphere absorbs practically all of the short wave electromagnetic radiations at wavelengths below 2900 A, including X-rays and most of the ultra-violet, while the ionosphere reflects a wide range of radio frequencies from the cosmos and the Sun. Much noise is introduced by the atmospheric fluctuations. Astronomical, astrophysical, and radioastronomical research and observations from manned and special crewless orbital stations will thus be very fruitful. Studies of the Sun's X-, u.v.- and corpuscular radiations and its corona will help to better assess the effects of its activity on the processes on the Earth and to improve the forecast of Sun bursls which is very important for the security of long- distance flights and prolonged stay of cosmonauts in orbital stations.

Science will gain very much from the study oJ supernew stars, radiogalaxies, quasars, pulsars, and sources of X-radiation in the entire spectrum of radiomagnetic waves. With the advent of orbital stations, new branches of astronomy, u.v.-, X-ray, and gamma-ray astronomy will appear.

5. MEDICAl_ AND BIOLOGICAL EXPERIMENTS

One important contribution of LOSMOS's to science will be medical and biological research to solve the problems of protracted manned flights and the fundamental problems of biology, to understand the role of gravity and the 24-hr cycle in the development of life and life processes in various organisms from protozoa to humans, to learn the effect of the penetrating radiation and other kinds of cosmic radiation, to study various extremal conditions of existence, etc.

Orbital stations and studies of the earth from space 183

Far-reaching protracted space flights are un- thinkable without the preceding tests of the effect of various space flight conditions on the man. Orbital stations will serve this purpose. It is first of all required to study the effect of complete or partial weightlessness on human organism and the transition to overloads. The behaviour and working capacity of a man in a long flight should be esti- mated, life support systems completely tested, food rations, preventive and curing drugs selected, the requirements to a comfortable flight established, the optimal division of labor between men and automatic devices found, the activity of humans in emergency situations determined, the maintenance and repair of the station systems evaluated.

6. SCIENTIFIC AND TECHNOLOGICAL EXPERIMENTS

Orbital stations will be the test stands for many assemblies, devices, and systems such as engines, power plants, control and orientation, life support, space suits, EVA gadgets, assembly, and docking.

On orbital stations, large antennas for radioastronomy and space communication, optical and laser reflectors will be tested and assembled.

The high vacuum and weightlessness in space will permit the development of many sophisticated processes to be used in microelectronics, electron beam technology, crystal growing, obtaining super- pure materials, and other processes that are hard to contemplate now.

7. BASES FOR INTERPLANETARY SPACECRAFT

Orbital stations will evidently be used as launch pads for interplanetary spacecraft, for their assembly, fueling and testing before the long journey. They will also be used for the training and "con- ditioning" of cosmonauts.

The question is often asked whether man's participation in space flights is justified and could not the same results be obtained by automatic equipment.

Orbital stations should incorporate first class laboratories. This implies highly automated research which presumes, however, the creative activity of an experimenter who would decide on the strategy and tactics of the experiment depending on its course and outcome. Experiments can not be effective unless they are monitored and controlled by highly-skilled personnel.

The human capability of analysing the information, collating possible outcomes, and making decisions in complex situations, including un- expected emergencies, cannot be matched by any equipment.

Human participation is no less important in the control of all systems of the orbital station, its

assembly, communication with the outside world, with supply spacecraft and other spacecraft, in maintenance and repair, in the adjustment and calibration of instrumentation.

If all systems are to operate in the most effective possible way and the mission completed, the crew and the automatic systems should cooperate in an optimal way, data processing and computer systems must be installed to help man in making the decisions on how to control the station, its systems and scientific equipment; the crew should perform the functions requiring reason and creativity.

ADVANCES OF SPACE TECHNOLOGY DIRECTLY RELATED TO ORBITAL STATION ASSEMBLY

The idea of manned orbital stations has been long since expounded by the founder of space research K. E. Tsiolkovsky, the Russian scientist. In his works "Dreams about the Earth and the Skies", "Beyond the Earth", "The Objectives of Astro- nautics", "Space Exploration by Jet Equipment" he proved the feasibility of orbital stations, life support systems, and foresaw relief crews delivery by rockets. As indicated in Fig. l, he described possible configurations of stations, possible ways of creating artificial gravity; he formulated the idea of station assembly of ready-made parts to be put into orbit by special rockets, the idea of using solar energy to raise plants and vegetables in greenhouses inside the station, and he discussed other problems regarding the assembly and use of orbital stations and what he termed "ether settlements" of humans.

K. E. Tsiolkovsky wrote, "We can conquer the solar system by very simple tactics. Let us first solve the easiest problem, an ether settlement in the vicinity of the Earth as a satellite at the distance of 1000-2000 km from the surface, outside the atmosphere. . . After settling down there and obtaining a reliable and safe base, feeling at home in the ether (outer space), we will change our speed more easily, move from the Earth and the Sun and generally go wherever we please". "We will need good homes, safe, illuminated, with the desired temperature, with restorable oxygen, with a continuous food supply, with all amenities for life and work. These homes and all accessories should be supplied from the Earth in a collapsed (compact) form, unfolded and assembled in space upon delivery. All homes should rotate slowly to obtain gravity".

Sketching the long-term plan for space exploration, he wrote, "Large settlements will be established around the Earth. Solar energy will be used for flights within the entire solar system as well as for nutrition and amenities. Colonies will be founded in the asteroid belt and elsewhere in the solar system's small celestial bodies. Industry will advance as the number of colonies increases".

184 B.N. PETROV

Many of Tsiolkovsky's predictions are now coming true.

The outstanding successes of Soviet and U.S. space technology within the first 12 years of the Space Age have made long-standing manned orbital stations a near reality. Many fundamental problems of assembly have been settled already.

Let us say a few words on those space experiments which have already determined the processes and systems which are directly involved in the operation of orbital stations, although it should be noted that, naturally, every single manned flight and test of each system ranging from spacecraft to the spacesuits has also been an important step along that road.

Maneuvering. As early as 1963 and 1964 the Soviet Union put into orbit pilotless maneuvering spacecraft, "Polyot - l " and "Polyot-2", which change their altitudes in the apogee and perigee and the inclination of the orbit plane. Since then numerous Soviet and U.S. manned and unmanned vehicles have tested various techniques of space maneuver.

EVA (Extravehicular Activity). Many operations of space missions require that man leave the craft. These include the assembly of large orbital stations, different assembly operations outside the spaceship or station, examination of the outside surfaces and instruments, technological and scientific instruments in the open space, and, finally, changing the vehicles.

The first man to step out into open space was Alexei Leonov, who on 18 March 1965 travelled about five meters from the spaceship piloted by Pavel Beliaev and returned into the vehicle in about 20 min after performing a number of operations in the open space.

Special spacesuits and life support hardware had been constructed for the EVA, while the vehicle had an air lock chamber which made it possible to leave the vehicle without its depressurization.

Many U.S. and Soviet cosmonauts have performed the EVA since then.

Docking in orbit. Space stations and heavy spacecraft are extremely hard to launch into orbit and would require gigantic boosters with a tremendous initial weight: to launch 1 kg of payload into an orbit around the Earth, 30-50 kg of the booster initial weight are required. To launch a vehicle with one or two cosmonauts requires rockets with an initial weight of hundreds of tons. Therefore, assembly in orbit is a major problem faced by space rocketry. Each building block of such a station may be put into orbit by a separate booster. Methods and systems for mutual search of two vehicles put into close orbits should be developed

and so should those used in maneuvering, rendez- vous, docking, link-up, undocking elc. All these operations should be made feasible both automatically and manually.

These methods and systems have been developed and tested. In the U.S.S.R. this has been done by stages. The problem of putting spacecraft into the rendezvous regions has already been solved in the grouped flights of "Vostok-3" and "Vostok-4"'~ "Vostok-5" and "Vostok-6", and later in the flights of the "Soyus" series.

Manual docking of a manned vehicle with a pilotless object was first performed by U.S. astro- nauts J. Young and M. Collins on 18 June 1966. Their "Gemini-10" was docked with the "Agena- 10", rocket launched earlier. Then the rocket engines were fired and the tandem performed a number of maneuvers, in particular, approached the "Agena-8" and was about 15 m from it. M. Collins stepped out into space, approached that rocket, removed meteor traps from its body and returned to his vehicle.

Automatic docking of pilotless spacecraft was first performed on 30 October 1967 when "Cosmos- 186" and "Cosmos-188" were docked automatically and then undocked during the orbital flight. One vehicle was "active" and the other "passive". The active spaceship searches for the passive spaceship in space, detects, approaches it and docks with it. The functions of the passive vehicle are simpler; it has to be oriented in space and be the lighthouse for the other. An orientation and automatic control system fires the jets that correct the orbit and per- forms the rendez-vous. The orientation, stabilization, and precise control of the actual docking are performed by low-thrust engines. The docking assemblies ensure the approach and reliable link-up.

The docking qf two manned vehicles and the first experimental orbital station. On 16 January 1969 Soviet "Soyuz-4", piloted by V. Shatalov, and "Soyuz-5" flown by B. Volynov, A. Yeliseev, and E. Khrunov shown in Fig. 2 were docked. The search and approach to a distance of 100 m were automatic, the cosmonauts monitoring the operation of the system. Then Vladimir Shatalov performed the rendez-vous and docking. The first orbital experimental station with the crew of four was assembled of four compartments, two cabins for the crew and two orbital compartments for rest and work that also served as air lock chambers for the crew to step out into space as shown in Fig. 3.

The first group EVA was performed also during that flight. Yevgenii Khrunov and then Alexei Yeliseev left the orbital compartment, performed experiments in space and entered another orbital compartment to join Vladimir Shatalov. After

FIG. 1. Schematics of an orbital station with artificial gravity according to notes of Tsiolkovsky.

Facing page 184

FIG. 2. Spacecraft "Soyuz-4" and "Soyuz-5" before the docking.

FIG. 3. The first experimental orbital station with the crew of four.

FIG. 4. The Orbital Workshop.

FIG. 5. Long-standing orbital station for the crew of 12; an artist's impression of North American Rockwell design.

FIG. 6. Station similar to Fig. 5 designed by McDonnell Douglas.

FIG. 7, A version of a large orbital station.

F~6. 8. An orbital base for the crew of 50 as designed by McDonnell Douglas.

Fie. 9. Some modules of an orbital station for the crew of 12 as designed by McDonnell Douglas.

FIG. 10. An orbital base for the crew of 50-100 as designed by G r u m m a n Aerospace.

FiG. 1 I. Schemat ics of a large orbital s tat ion to be assembled o f modules as a hub of a wheel.

Orbital stations and studies of the earth from space ! 85

experiments in control of the orbital station the vehicles undocked and then flew together to complete the program. The cosmonauts, who changed vehicles in space for the first time, landed with Vladimir Shatalov, while "Soyuz-5" was landed by Boris Volynov.

The orbital station assembly and the program of operations performed by its crew is a landmark on the way to large, longstanding orbital stations.

Restructuring and docking the compartments, or modules, of a space vehicle. The U.S. Apollo program scheduled tests of a number of operations and systems for a lunar vehicle and these will also be involved in the assembly, maintenance, and relief of an orbital station and spacecraft crew. In particular, we should note in this connection the restructuring of modules in orbit, the docking of the command module with the lunar module, the test and development of spaceborn computers, etc. These operations were performed by "Apollo-7" and "Apollo-9" on the circum-earth orbit and "Apollo-8" and "Apollo-10" that flew around the Moon in 1968 and 1969. That the technical solutions were correct was proved by the success of "Apollo-11" and "Apollo-12" that delivered men to the Moon and returned them safely to the Earth.

Interaction and control of several spacecraft. The orbital assembly is not the sole problem involved in the construction of orbital stations; the service systems, their cooperation with supply vehicles that deliver goods and new crews, data communication and ground control complexes should also be developed and tested.

A tangible contribution to the solution of this problem was made by the grouped flight of three spacecraft "Soyuz-6", "Soyuz-7", and "Soyuz-8" in October 1969. For the first time seven cosmonauts performed scientific and scientific-technological experiments, sweeping maneuvers, rendez- vous, mutual orientation, the test of manned control, interaction with the ground control and instrumentation stations.

In performing the latter task, a large system was established which included three manned spacecraft, the ground stations, research ships in numerous points of the World Oceans and the communication satellite "Molniya-l". The pilots co- operated with the ground control, complex systems of automatic control, and data communication and processing systems. During the grouped flight, the manual control and orientation processes were especially significant. Semi-automatic control was also performed. Over 30 maneuvers to change the orbit were completed by instructions from the Earth or autonomously. In the course of changing

the relative positions, the parameters of the orbits were determined very accurately; the magnitudes and direction of correcting pulses to ensure the optimal rendez-vous were calculated.

The stability and reliability of communication between the flight control center and the spacecraft, when these were outside the direct radio communication range of ground stations in the U.S.S.R., through the "Molniya-l" was tested as was the use of one vehicle to relay signals to other vehicles when these were outside the direct communication range.

A number of scientific-and-technological experiments were also performed. The welding equipment was tested in space for the first time and data required for further perfection of these operations in high vacuum and weightlessness gathered. Space welding is very promising for orbital station assembly and repair and in preparation of space vehicles for flights to other planets.

POSSIBLE TYPES OF ORBITAL STATIONS

Long standing orbital stations will beyond an doubt be general-purpose spacecraft that will solve a wide range of scientific and technological problems. This does not mean, however, that no orbital stations can be specialized. Those whose mission is to study the Earth's resources will be put into relatively low orbits to make the studies as effective as possible.

On the contrary, astronomic and radioastro- nomic stations would be more effective at orbits of tens and hundreds of thousands kilometers. Lunar orbital stations would be very useful in exploring the Moon, the circumlunar space and performing astrophysical observations and landing special- purpose modules periodically on the Moon.

Presumably, small stations will be put into orbit. Their crew will be three to twelve and they will stay in orbit from a month to a year or more. They will incorporate the experience already gained in the construction and testing of spacecraft and their systems in orbital and lunar flights.

The debugged modules of spacecraft and stages of boosters will be the building blocks of such stations. This does not preclude the development of structures specifically intended for orbital stations. These may be launched already assembled by one booster or in parts to de docked in space. The crew may be delivered by a transportation vehicle that would later also bring relief crews. The station and the vehicles should, of course, have the docking facilities. Medical and biological experiments should be conducted in such stations to develop further design requirements and to learn the basic characteristics of large long standing orbital stations.

186 B.N. PETROV

The next stage will evidently be large long standing orbital stations of modular design, with a crew of 12-20, to be assembled in a circum-earth orbit and intended to stay in orbit up to 10 years at a stretch. In the future, we can also contemplate super stations with a crew of 50-70 and later of 100-120.

At the same time, it is feasible to have special- purpose unmanned scientific orbital stations which would be periodically visited by personnel who would adjust and check the state of the hardware, replace the magnetic and photographic films containing records of scientific data.

An example of such a station is the Orbital Work- shop developed by the NASA Langly Research Center and McDonnell Douglas for the Apollo applications program. As indicated in Fig. 4, the station consists of the used-up stage of the Saturn- IB and an Apollo spacecraft. First a "Saturn-4B" stage would be launched into a circular orbit at the altitude of 350 km; then, within an interval of 24 hr an "Apollo" vehicle with the crew of three would be injected into the same orbit. After docking, the crew would transfer to the Saturn through an air lock compartment to overhaul it into a laboratory. The crew would be scheduled to stay in the Work- shop for 28 days and then return to the Earth with the "Apollo". Then another crew would be delivered to stay for 56 days. The third shift would stay for 10 months. The final phase would be to dock the Orbital Workshop to an improved Apollo craft containing a telescope.

The designs of North American Rockwell and McDonnell Douglas on contract with NASA are examples of multi-purpose orbital stations. These would carry a crew of 12 and serve for 10 or more years. Provisions should be made for the assembly of a large base made of two or more stations at the altitude of about 500 km to carry 50 and later 100 men. The preliminary design of North American Rockwell in Fig. 5 envisages a station weighing 54 tons with a useful capacity of 700 m 3. The station is to consist of five modules. Supply vehicles will dock at five air lock compartments. The power plant will generate 25 kW using solar panels with a total area of about 900 m 2 as power sources.

The design of McDonnell Douglas in Fig. 6 envisages a station with the useful volume of over 300 m a made of three basic modules and a compartment for gas and liquid storage.

Super stations for a crew of 50-100 men are under consideration by McDonnell Douglas and also Grumman Aerospace as indicated in Fig. 7. The former has made a preliminary design of a base for 50 men with the weight of 450 tons and useful volume of 2700 m a and the length of the central unit equal to 114 m as shown in Figs. 8 and 9. To

obtain artificial gravity, the station is to rotate at the rate of 3.5 rev/min along the longitudinal axes of the central unit. The power is to be supplied from a nuclear reactor.

Grumman Aerospace has worked out a design for a base housing 50-100 men as depicted in Fig. 10. This will have a central module and three peripheral modules 10 m in diameter each. The station is to rotate along the longitudinal axis; artificial gravity is to be created in the peripheral modules.

Many other schemes such as that shown in Fig. 11, have been described in the literature. A major problem is to select the optimal shape and the assembly technique. The assembly of a station of several standard units requires a progressive approach. The shape of a station with artificial gravity may be either toroidal, or beamed, or a hub with blades, or starlike, etc. Another major problem is to ensure the atmospheric pressurization of compartments for maximal reliability and security, and to make the service and supply as convenient as possible.

One important thing is to create supply craft to bring relief for the crew and all kinds of supplies, to ensure transportation between stations and also rescue in case of emergency. Some designs envisage special workshop compartments for maintenance personnel to examine the surface of the station and its external equipment to detect parts requiring repair or replacement. Such a workshop should be highly automated and have automatic controllers and instruments, welding equipment, manipulators and other facilities for a cosmonaut to work in open space.

Future supply spacecraft must be reusable and ensure landing through the atmosphere with small overloads. A possible shape is a delta-winged vehicle. For large orbital stations, it is important to have facilities for docking several supply ships simultaneously. Provisions must be made to rescue the crew in emergency situations. Special on-board shelters might be made for the crew to await supply ships if the vehicles docked to the stations cannot ensure a safe return. Another possibility is to have special emergency vehicles docked to the station.

ORBITAL STATION CONTROL

The assembly of large long-standing orbital station introduces new requirements to the control systems and space-borne automatic units which must be used.

We will not discuss the launch of separate modules into orbit. This process does not differ much from the launches of artificial satellites. We will note only that the succeeding units should be launched very accurately into a rendez-vous point


in the same orbital plane to save fuel needed in the maneuvers. The docking technique should also be optimal. Apart from the usual methods already tested in the docking of both Soviet and U.S. vehicles, there is a possibility of using a tow vehicle for the rendezvous and assembly. The docking equipment on all vehicles could thus be simplified and the costs reduced. A tow vehicle with special automatic systems can look for a module, capture it, and tow it to the assembly point. On completion of the docking operation with one module, the tow vehicle is ready to deal with another module. A tow vehicle can be either completely at~tomated, or remotely controlled from the ground, or piloted by a cosmonaut with the tow gear and space-borne systems being sufficiently automated.

Development of automated control systems for the station assembly and for testing the quality of the assembly is very important. There must be proper division of labor between the cosmonauts, manipulators, and automated control systems.

When a station is to stay in orbit for a long time, severe requirements will be made on the control hardware, to the orientation and stabilization and other automated space-borne systems, and quite naturally, to the safety margin and reliability of all the assembled equipment. Indeed, integrated microelectronic circuits are the only possible solution. Multi-level computer systems should envisage both fully automated control and control combined with the participation of ground centers that may set up various fright programs, operating conditions, and corrections. The programs must be flexible; adaptive control must be widely used; the computer system, its elements and the station equipment should incorporate features of high repaira- bility and self-diagnosis. The long term of the station's stay in orbit explains the especially severe requirements on the use of propellants necessary to control the attitude and correct the orbit. These processes should be made optimal. Use of electro- jet engines with high unit thrust to control the attitude and stabilization is very advisable in large stations. An adaptive system to control the angular movements of an orbital station would ensure high precision of control where the station characteristics change in time and under the action of changes in the inertia and the perturbations due to the docking or undocking of supply ships. Such a system would also be effective when elements and units of the equipment and computer fail or in emergency situations.

It is also important to automate the experiments and the data processing. Modern technology makes it possible to automate the onboard experimental studies on board to a high degree; this is also true for the processing of data to be communicated to

the Earth. In this case there also must be a rational division of labor.

Classical autonomous control and orientation systems contain a gyro-stabilized platform or systems of platforms. The need for long-standing stations to have a large safety margin makes the development of such a system difficult. Therefore platformless systems with lase~ angular rate sensors, accelerometers and computers with correction by stars are highly promising. The chief problems here are accuracy and noise immunity.

Control of orbital stations, their docking and assembly raise a number of new theoretical problems and require higher efficiency of the computa- tion and control system synthesis techniques than those previously required.

The theory of terminal control, which came into existence to solve the problems of moving body control, is especially important and must be used extensively. Terminal control systems ensure a high accuracy of control in a certain, finite interval for the given process, or for a certain point in space. Such systems include those that control the rendez- vous and docking, soft-landing, etc. Discrete systems of terminal control are especially effective since the optimization can be achieved by the methods of statistical decision theory with the use of dynamic programming procedures.

The terminal control problem in discrete systems with on-line digital computers can be formulated as follows. The plant is described by the finite difference equation

Xi = Fi(v, u i - 1, Vi) (i= 1, 2 . . . . . I + 1),

where ~i is the value of the control coordinated vector at the time where the monotonically changing quantity V reaches the value V:; the quantity V can be represented by the time t, altitude h or the landing control, etc.; u s is the value of the control vector at the time

is the disturbance vector, a vector of changing coordinates

Yi = ~b(2i, f~)

f is the measurement error vector. It is required to find the optimal control function

Ui~---Ui(Yi, fl--l) (i= 1, 2 . . . . I)

from a certain feasible area co, the vector

V=(Vl, v2 . . . . . Vi+1)

and the quantity I which ensure the minimal values for the risk-functionals of finite states of the plant at the time when Vreaches the required value Vx+ 1 :

RK-----M[WK(f~, fir, V, I)] (K= l, 2, . . . , K).

188 B.N. PETROV

The risks R K can estimate the accuracy of control, relative cost of control, cost of the control system hardware, etc.

Since generally there is no control at which all risk functions have the minimal values simultaneously, it is advisable to find controls which ensure conditional minima for some risks provided that others do not exceed specified values; for instance, find the most economical docking control provided that the required accuracy is maintained.

Space-borne control systems should meet strin- gent requirements in reliability, dimensions, and weight. These are easier to achieve if the optimal control recognizes the constraints on the structure of the control system such as the capacity of the control unit u, when the control function is determined from the class

l l i = ~ i ( Y j i , f i j ( i - 1)),

L~-- (?J, Yj+i . . . . Y,),

Hji= (Ul, H2 . . . . . Hi) . ~ = i - n ,

and the constraint on the kind of operations realizable by the control unit, e.g. when the control functions are determined in the class

A i = A i Y i - F B i u i - t •

where A~B~ are matrices of coefficients, the constraint on the number of units that reproduce the coefficients of the control algorithm, etc.

As mentioned, the problem stated can be solved by using statistical decision theory and special dynamic programming procedures. Invariant control procedures are useful in certain cases.

Long-standing stations and laboratories make quite specific requirements on the accuracy, reliability and cost of control systems. For such vehicles, the details of the control systems structures should be investigated and the factors which were earlier neglected should now be recognized. During the flight random disturbances come into the picture. The operation of an actual control system is better described by stochastic non-linear differential equations. The synthesis of flight control is essentially reduced to finding the control actions and the way they are formed. The synthesis of optimal control can be divided into three stages:

(1) Synthesis of the control program ; (2) Synthesis of the control law; (3) Synthesis of the control system.

The most comprehensive figure of merit for a control system is determined by the criterion of the "maximal probability" that the flight program or the control system parameters will lie within a specified area [1, 4] or region. The control system is optimized by achieving the maximal value of that probability.

Tile chief criterion for an orbital station or laboratory is the minimal power, or propellant, consumption while the specified flight parameters are lnaintained, e.g. ;ingles and angular velocities. Control systems should be optimized by the maximal probability that the power, or propellant, consumption will not exceed the admissible value W,J:

J=maxP~(W~ W~I)

provided that the specified probability of finding the angles (?, ~, v) and angular velocities (9, ~), i') within the specified limits

e=(Io~l<&, t,;)l < Rz)> C, where

co is a vector with the coordinates 7, ~, v. & is a vector with the coordinates 9, ~/), ~".

The synthesis of a statistically optimal control system can be represented as the problem of finding the extremum for a function of many variables. It is required to find the construction parameters of a control system at which the probability will be at its highest while the stability is preserved.

A complete solution of this problem by the Monte Carlo technique even on most sophisticated computers would require years of computer time. By using the algorithmic methods of statistic nodes combined with the method of direct statistical optimization, the problem can be solved within acceptable time, measured by tens of hours for the most complicated systems. These methods developed by V. T. Kochetkov and others do not require any conversion of the initial set of differential equations that describe the dynamics of a vehicle with a control system, and this is very important in engineering calculations. We can roughly say that the external disturbances affecting a vehicle, the aerodynamic drag moments, the moment of gravitational forces, the moment of the live conductors interacting with the Earth's magnetic field, etc. are random quantities with specified mathematical expectation and dispersion.

Each channel is affected by the disturbance nloments.

i i i M d - - Mex t + Minter + Mehannel

where

Me×t

Minter

Mchannel

external moment;

interaction moment;

moment from the elements of each channel.

Figure 12 shows a possible scheme for the angular stabilization of one channel [I, 3]. To simplify the system, to increase the reliability and to reduce the cost, the angular velocity sensor,


Logic and control A c c e l e r o m e t e r circui t

" ~ - - ~ ~ . Jet englhe

(

...... ' Mavs M vshical Dis turbance

FIG. 12. One channel angular stabilization schematics.

which is a source of noise, can be disconnected while a signal from the "pseudo-velocity" system is formed by connecting the non-linear element to an aperiodic feedback loop. The optimization of such a system is hard to achieve. I f all the three channels are considered simultaneously, the system is described by a set of stochastic differential equations of order greater than the twentieth with the number of disturbances about 20, and also including quite a few non-linearities. Meanwhile, the techniques of statistic nodes and direct statistic optimization ensure an elegant solution. The criterion is the maximal probability that phase coordinates, the angles and angular velocities, of the vehicle and power consumption, W, will stay within the specified boundaries

max PEIo l <R,, <R=, Iwl< Wgom]"

An example from these calculations has shown that this probability is P = 0.1 at usual synthesis and P = 0.99 after optimization. The output coordinates remained within the specified limits for a certain time'(Fig. 13).

y, deg

" ~ - ~ ~ ' : f s .;Y/l/x,; hY/ / / / / / / / / / / / / / / /~

' ' ' ~ t , s e e

I i :4 ~Y///X~ ,'/"" ;/X :f;':':" ;

Fw,. 13. Transition process curves.

The synthesis of nonlinear vehicle systems with an on-line digital computer in the presence of random control and disturbing actions is an in-

volved problem. For the example considered, the optimization methods can yield a control system that would ensure the maximal probability that power consumption will not be in excess of the specified value with the constraints on the angles and angular velocities of the vehicles observed. Figure 14 shows the structure of a digital control system resulting from this synthesis technique.

t Md3 r

: .-6 H i

:l ~ F T - - I

' i v I ,

J ~ Lk_ ~ L._ •- __J

Dynamical p~--~r~-~ equations equations I , I [

Fic,. 14. Schematics of the digital control system.

CONCLUSIONS

The assembly of effective orbital stations is largely a problem of developing high-quality scientific and operating equipment, computers and automatic control systems.

The 1960's saw man's first steps into space, orbital flights of satellites, the first manned journey to the Moon; we can expect that in the seventies long-standing orbital stations will fly and large orbital bases will be assembled to serve science and economy.

REFERENCES [1] K. ~). l_[no.nrOBCrn~: Tpy~bi no pareTno~ TexrmKe.

M., O6opoHrn3 (1947). [2] A. A. JIe6e~ea , B. B. Coronos: BcTpe~a Ha

op6aTe. M., Mamm~mocTpoerme (1969). [3] Ox rOCMmiecrnx ropa6ne~ r op6nxan1,.I, lM CTaHUnfiM.

M., MamnnocTpoeHue (1969). [4] Astronaut. Aeronaut. 6, No. 1 l, 1968. [5] Space Aeronaut. 52, No. 4, September (1969). [6] Aviation Week, 22/IX, 91, No. 12 (1969). [7] Flight, 9/X, 96, No. 3161 (1969). [8] Air et Cosmos, I/XI, 7, No. 313 (1969). [9] Aerospace Daily, 26/XI, 40, No. 17 (1969).

[10] Aerospace Daily, 28/XI, 40, No. 18 (1969). [11] B. H. HeTpOa, A. ~. Auapnem¢o nIO. H. Hopr.oB-

Col<oaoa: "Oue.Ka TO'mOCTH CrlCTeMbi aBTOMaTI~eC- Koro ynpaB~enn~ roc~m~ecrr~x o6beKTOa", 1I CHM- noa~yM HOAK "AaTOMaTn~ecroe ynpaBaem~e a

r r'npOCTpa,cTae", Bena (1967). [12] A. YA. ANDRIYENKO: In Automn remote Control 29,

No. 7 (1968). [13] E. D. SCOTT: Pseudorate sawtooth-pulse-reset control

system analysis and design. J. Spacecraft Rockets 4, NO. 6, June 1967.

[14] V. T. KOCHETKOV: Theory of remote control and homing guidance systems of rockets. Eng. Trans. Wright-Patterson Air Base, Ohio, 1966.

190 B . N . PETROV

[15] B. T. KO'mTKOB a A. B. Flotteayem O CrtHTe3e onrHMa.rll~HO~ HeJ'IHHe.~HOI~ ClelCTeMbl ynpaB.qeHrla rio Kprlrepn~o "MaKcrIMyMa BepO~THOCTI, I". ]/~3BeCTH~I AH CCCP. TexrlmiecKa~ Ka6epHeTm(a, 1966, .NO 4.

[16] B. T. Ko'teIKOB H A. B. 1-1otmsxyem CTaxucTr~necsrfft CI, IHTe3 ~I'ICKpeTHblX He~Hneitnb~x cllcreM yripaBsteHrt~. H3BeCTUS AH CCCP. Texrm,tecsa~ irt6epHeTr~sa, .No 4 (I 968).

anhand ihrer Geschichte und dem Fortschritt ihrer Ent- wicklung eingeschiitzt. SchlieBlich werden die speziellen mit dem Entwurf der Strukturen und der Ausri.istung der Regelungssysteme verkniipften Problemc diskutiert. Einigc der aussichtsreichsten mathematischen LSsungen werdet~ angefiihrt. Es wird daraus geschlossen, dal?, nach Vornahme geeigneter experimenteller Verifizierungen langlebigc Raum- stationen in naher Zukunft emwikkelt werden.

R~um6----L'article passe en revue l'emploi et les avantages des stations longuement habit6es sur orbite, ensemble avec l'histoire et les succ6s de leur deveioppement. II discute finalement les probl6mes sp&:iaux li6s ~ l'6tude des structures et du materiel des systSmes de commande, il presente cer- taines des solutions math6matiques prometteuses et il conclut qu'apr6s les verifications experimentales appropri6es, les stations spatiales longuement habit6es se developperont dans un proche avenir.

Zusammenfassung--Die Anwendung und der Nutzen von langebigen und sffindig bemannten Orbitelstationen werden

Pe3mMe--B craTbe paccMa rpHBatoTCa Nep¢iteKr HBbt nocTpoeHua B, OJIFOBpeMeHtlO ,ael~iCTByrOUlH× O6141aeMblX KOCMI, IqeCKI, IX op6HTa.rlbHblX CFaHIlH~, a TaKa<e Hc'rop,- qecKne npe~mocb~Jm~ ~t ycilexrt B 9KcnepHMeHtax, HO~.FO- TaBJIHBalOIUl.lX HX pa3pa6oxKy. B He'Tt o6cy>KllalOTC~ npo6~eMbl, CB~13aHnble C 3alta,~aMrl HccnelloaaHHfi, pacqeToM H nbl6OpOM crpyKayp r~ o6opyaoBaHH~ cucle~ ynpanaearIa, HeKOTOpble MaTeMaTHqecKHe ,~e'roLtbi rt I3 3aK~roqeHr~e BblCKa3blBaeTc,q Haae~(~a, tlTO llOC~le aeo6xo- 2111MOi:i 9KCllepl,lMeHTaJqbHON oTpa6oTK~, ~IOYtFOBpeMeHHO )~eficTBy~omne o6HtaeM~,m KOCMnaeCKHe cxammn 6y.qyr co3JIam, i B 6aa3KOM 6y~yttteM.