Gravity Recovery and Interior Laboratory (GRAIL) Launch Press Kit

8/4/2019 Gravity Recovery and Interior Laboratory (GRAIL) Launch Press Kit

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Gravity Recovery and InteriorLaboratory (GRAIL) Launch

Press Kit/AUGUst 2011


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http://www.nasa.gov/grail

http://grail.nasa.gov

For more information

Media Contacts

Dwayne Brown Policy/Program 202-358-1726

NASA Headquarters, Management [email protected]

Washington, DC

DC Agle GRAIL Mission 818-393-9011

Jet Propulsion Laboratory, [email protected]

Pasadena, Calif.

Caroline McCall Science Investigation 617-253-1682

Massachusetts Institute of [email protected]

Technology,

Cambridge, Ma.

Gary Napier Spacecraft 303-971-4012

Lockheed Martin Space Systems, [email protected]

Denver, Colo.

George Diller Launch Operations 321-867-2468

Kennedy Space Center, [email protected]

Cape Canaveral, Fla.


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Contents

Media Services Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Quick Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Why GRAIL? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Mission Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Mission Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Why Study Gravity? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Science Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Science Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Missions to the Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

NASAs Discovery Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Program/Project Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

GRAIL Launch 3 Press Kit


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Media Services Information

NASA Television Transmission

In continental North America, Alaska and Hawaii,NASA Televisions Public, Education, Media and HD

channels are MPEG-2 digital C-band signals carriedby QPSK/DVB-S modulation on satellite AMC-3,transponder 15C, at 87 degrees west longitude.Downlink requency is 4000 MHz, horizontalpolarization, with a data rate o 38.86 MHz, symbolrate o 28.1115 Ms/s, and 3/4 FEC. A Digital VideoBroadcast (DVB) compliant Integrated ReceiverDecoder (IRD) is needed or reception. Note: EectiveWednesday, Sept. 1, 2010, at 2 p.m. Eastern, NASA

TV is changing the primary audio conguration oreach o its our channels to AC-3, making eachchannels secondary audio MPEG 1 Layer II.

For digital downlink inormation or NASA TVs MediaChannel, access to NASA TVs Public Channel onthe web and a schedule o programming or GRAILactivities, visit http://www.nasa.gov/ntv.

Media Credentialing

News media representatives who wish to cover theGRAIL launch must contact NASA/Kennedy SpaceCenter Public Aairs in advance at 321-867-2468.

News Conerences

Two GRAIL pre-launch news conerences will be heldat the Kennedy Space Center Press Site. The GRAILmission news conerence will be held on Sept. 6,2011, at 1 p.m. EDT. The second, the GRAILscience news conerence, will be held on Sept. 7,2011 at 10 a.m. EDT. The news conerences will betelevised on NASA TV.

Launch Status

Recorded status reports will be available beginningtwo days beore launch at 321-867-2525 and 301-286-NEWS.

Internet Inormation

More inormation on the GRAIL mission, includingan electronic copy o this press kit, news releases,status reports and images, can be ound at http://grail.nasa.gov and http://www.nasa.gov/grail .



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Quick Facts

Mission Name

GRAIL is an acronym or Gravity Recovery AndInterior Laboratory.

Spacecrat

The two spacecrat (GRAIL-A and GRAIL-B) aremirror twins.

Structure

Main structure: 3.58 eet (1.09 meters) high, 3.12 eet(0.95 meters) wide, 2.49 eet (0.76 meters) deep

Power

Total solar array power at 1 AU: 763 watts

Power: Four panels o silicon solar cells mounted onsatellites top and side exterior suraces

Batteries: 10 nickel-hydrogen cells providing up to16 amp-hours o 28-volt power

Instruments

Microwave ranging instrument, accelerometer, starcamera

Mass

Launch: 677 pounds (307 kilograms)Dry: 443 pounds (201 kilograms)Fuel/He: 234 pounds (106 kilograms)

Launch Vehicle

Type: Delta II 7920H-10C (also known as a Delta IIHeavy)Height with payload: 124 eet tall (37.8 meters) and8 eet (2.4 meters) in diameterMass ully ueled: 622,662 pounds (282,435kilograms)

First Stage:

Main engine (RS-27A) and nine (46-inch, or1.2 meter) strap-on solid rocket motors LOX and RP-1 (kerosene), lito thrust o207,000 pounds Each solid rocket motor produces136,400 pounds o thrust

Second Stage:

Aerojet AJ10-118K second stage engine Burns Aerozine-50 and nitrogen tetroxide oxidizer

Vacuum-rated thrust: 9,645 pounds

Launch Site: Space Launch Complex 17B, CapeCanaveral Air Force Station, Fla.

GRAIL Mission Milestones and Distances

Traveled

Launch period: Sept. 8 Oct. 19, 2011 (42 days).Launch location: Pad SLC-17B, Cape Canaveral AirForce Station, Fla.Moon Arrival Date:

GRAIL-A: Dec. 31, 2011GRAIL-B: Jan. 1, 2012

Science Orbit Altitude: 34 miles (55 kilometers)

The distances travelled by GRAIL-A and GRAIL-Bto the moon are similar but not the same. Also, thedistance travelled to the moon changes (decreases)as a unction o launch date. The distance thespacecrat will have travelled or a Sept. 8 launchis much larger than the distance travelled on an

Oct. 19 launch.

Distance travelled to the moon (launch to lunar orbitinsertion) or a launch on Sept. 8:GRAIL-A = 2,594,378 miles (4,175,246 kilometers)GRAIL-B = 2,663,793 miles (4,286,959 kilometers)

Distance travelled to the moon or a launch onOctober 19:GRAIL-A = 2,243,336 miles (3,610,300 kilometers)GRAIL-B = 2,305,784 miles (3,710,800 kilometers)

Distance spacecrat travel in lunar orbit (rom lunarorbit insertion to end-o-mission):GRAIL-A = 13,193,550 miles (21,232,961kilometers)GRAIL-B = 12,800,869 miles (20,601,001kilometers)


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Program

The GRAIL mission totals about $496.2 million,which includes spacecrat development and scienceinstruments, launch services, mission operations,science processing and relay support.

Moon Facts

The actual Earthmoon distance ranges rom about223,700 to 251,700 miles (360,000 to 405,000kilometers), depending on the moons position in itsorbit.

The mean radius o the moon is 1,080 miles(1,737.4 kilometers); the diameter is 2,159.1 miles(3,474.8 kilometers).

Total mass o the moon is 81 quintillion tons (74sextillion kilograms). The surace temperature at the

equator during the day is as high as 273 degreesFahrenheit (134 degrees Celsius) and at night is ascold as minus 244 degrees Fahrenheit (minus 153degrees Celsius).

Gravity at the surace o the moon is 1/6 that o Earth.The moons magnetic eld is less than 0.01 that oEarths.

The orbital speed o the moon is 2,287 mph (3,680kilometers per hour).

At the closest distance, it would take 135 days todrive by car at 70 mph (113 kilometers per hour) tothe moon.

The moon is actually moving away rom Earth at arate o 1.5 inches (3.8 centimeters) per year.

The moons widest craters are 1,553 miles (2,500kilometers) in diameter.

From Earth, we always see the same side o the

moon.

I Earth did not have its moon, Earth would spin threetimes as ast, making a day last only 8 hours insteado 24.

The age o the oldest moon rock collected byastronauts is 4.5 billion years old. The rocks collectedduring NASAs Apollo program weigh in at 842pounds (382 kilograms).

The moons highest mountains are 5.6 miles high (9kilometers).

The lunar day (or the time rom sunrise to sunrise) onthe moon is approximately 708 hours (29.5 days).

The surace area o the moon is 23,559,000 squaremiles (37,914,000 square kilometers). It has almostthe same surace area as the continent o Arica.

I you weighed 120 pounds, you would weigh only 20pounds on the moon.

The moon has no signicant atmosphere or clouds,and no known active volcanoes.

There are two high tides and two low tides everyday on every beach on Earth because o the moonsgravitational pull.


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Why GRAIL?

The Gravity Recovery And Interior Laboratory(GRAIL) will unlock the mysteries o the moon hiddenbelow its surace. It will do so by creating the mostaccurate gravitational map o the moon to date,

improving our knowledge o near-side gravity by 100times and o ar-side gravity by 1,000 times.

The high-resolution map o the moons gravitationaleld, especially when combined with a comparable-resolution topographical eld map, will enablescientists to deduce the moons interior structure

and composition and to gain insights into its thermalevolution that is, the history o the moons heatingand cooling, which opens the door to understandingits origin and development. Accurate knowledge

o the moons gravity will also be an invaluablenavigational aid or uture lunar spacecrat. Finally,GRAIL will also help us understand the broaderevolutionary histories o the other rocky planets in theinner solar system: Mercury, Venus, Earth and Mars.Indeed, the moon is a linchpin or understanding howthe terrestrial planets evolved.


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Mission Overview

This fgure shows a timeline o the GRAIL mission phases rom launch through the various mission phases.

Since the relative position o Earth and the moon change over this entire period, it is simplest to illustrate the

events relative to the sun, or heliocentric view.

The twin GRAIL spacecrat (called GRAIL-A andGRAIL-B) will be launched side-by-side on a singleDelta II vehicle during a 42-day launch period thatopens on September 8, 2011.

The GRAIL mission is divided into seven missionphases: Launch, Trans-Lunar Cruise, Lunar OrbitInsertion, Orbit Period Reduction,Transition toScience Formation, Science and Decommissioning.

Once launched, GRAIL will enter a three-and-a-hal-

month Trans-Lunar Cruise phase, which allows thetwo spacecrat to eciently venture rom Earth to themoon via the Sun-Earth Lagrange point 1. Lagrangepoint 1 is named or the Italian-French mathematicianJoseph-Louis Lagrange. In 1764, he authored anessay or the Paris Academy o Sciences, deningpoints between bodies in space where the gravitybetween them balances the centriugal orceexperienced at those points while orbiting withthe bodies. This low-energy transer was chosen

Heliocentric View View rom Ecliptic Z-axis


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to reduce the size o the rocket required to placeGRAIL on its correct trajectory, allow more time orspacecrat check-out and increase the number odays available in the launch period.

Arrival at the moon occurs on a xed date or bothorbiters and is independent o the launch date. The

year ends with the arrival o the GRAIL-A orbiter atthe moon on Dec. 31, 2011, and the new year isushered in with the GRAIL-B orbiter arriving at themoon on Jan. 1, 2012. Both spacecrat approachthe moon under its south pole, where they executea 38-minute Lunar Orbit Insertion maneuver to putthem in an elliptical orbit with an orbital period o justover 11.5 hours.

A series o maneuvers is then perormed to reducethe orbits to become nearly circular with a 34-mile(55-kilometer) altitude.

The 82-day Science Phase is divided into three27.3-day mapping cycles. During the SciencePhase, the moon will rotate three times underneath

the GRAIL orbit. The collection o gravity data overone complete rotation (27.3 days) is reerred to as aMapping Cycle.

Following the Science Phase, a ve-daydecommissioning period is planned, ater whichthe spacecrat will impact the lunar surace inapproximately 40 days.


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Mission Phases

Launch Phase

The Launch Phase begins when the orbiters transerto internal power at six minutes beore lito and

extends through the initial 24 hours ater lito.During this phase, the orbiters will undergo launch,separation rom the launch vehicle, initial Deep SpaceNetwork acquisition and solar array deployment.

Launch Strategy

To ensure a high probability o launching, GRAIL hasdeveloped a launch period strategy that has a 42-daylaunch period. On each day, there are two separateinstantaneous launch opportunities separated in timeby approximately 39 minutes. On Sept. 8, the rstlaunch opportunity is at 8:37 a.m. EDT (5:37 a.m.PDT). The second launch opportunity is 9:16 a.m.EDT (6:16 a.m. PDT).

Solid Rocket Motors

Oxidizer Tank (LO2)

Centerbody

Miniskirt

RS-27A Engine

GRAIL Spacecraft10-ft dia.Composite

Payload Fairing

Interstage

First Stage

AJ10-118K Engine

Fuel Tank (RP-1)

Second Stage

Guidance Section


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GRAILs Ride Into Space

The launch vehicle selected or the GRAIL missionis the United Launch Alliance Delta II 7920H-10C.

This is a two-stage (liquid propellant) launchvehicle with nine strap-on solid rocket motors anda 9.8-oot-diameter (three-meter) payload airing.

The H designation identies the vehicle as a

Heavy lit Delta II launch vehicle. This vehicleprovides more perormance than the standardDelta II vehicle by using larger strap-on solidsdeveloped or the Delta III launch vehicle. Thelaunch vehicle is slightly more than 125 eet (38meters) tall.

Stage I

The rst stage o the Delta II uses a RocketdyneRS-27A engine. This main engine is a single start,liquid bipropellant RS-27A engine. The Delta II

propellant load consists o RP-1 uel (thermallystable kerosene) and liquid oxygen or the oxidizer.The RP-1 uel tank and the liquid oxygen tankon the rst stage are separated by a centerbody section that houses control electronics,ordnance sequencing equipment, a telemetrysystem and a rate gyro. The main engine will burnor approximately 263 seconds, and will then be

jettisoned into the Atlantic Ocean.

Graphite-Epoxy Strap-on Solid Rocket Motors

For the Delta II Heavy, nine strap-on graphite-epoxy motors are used to augment the main-engine thrust during the initial part o the ascent.

The strap-ons or the Delta II Heavy launch vehicleare 46 inches (1,168 millimeters) in diameter andare ueled with approximately 37,500 pounds(17,000 kilograms) o hydroxyl-terminatedpolybutadiene propellant. Six o the nine solidrocket motors are ignited at the time o lito. Theremaining three, with extended nozzles, are ignitedshortly ater the initial six strap-on motors burn out.Each solid rocket motor will burn or approximately

80 seconds.

Second Stage

The second stage o the Delta II is powered by anAerojet AJ10-118K engine, burning a combinationo Aerozine 50 (a 50/50 mix o hydrazine andunsymmetric dimethyl-hydrazine) and nitrogentetroxide as the oxidizer. The second stage is arestartable stage. The rst burn o the secondstage occurs during the nal portion o the boost

phase and is used to insert the vehicle into low Earthorbit. Ater a coast phase, the second stage is usedonce again to precisely provide the velocity changeneeded to inject the spacecrat onto the desired low-energy fight path toward the moon.

Payload Interace and Fairing

The two GRAIL orbiters are housed side-by-sidewithin a payload airing that is 9.8 eet (3 meters) indiameter and 30 eet (8.88 meters) tall. The airing isused to protect the orbiters during the early portiono the boost phase when the aerodynamic orces aregreat. The airing will be jettisoned shortly ater theignition o Stage II, at about 281 seconds into fightand an altitude o approximately 94.4 miles (152kilometers).

Launch Profle

The rst stage or main engine and six o the ninestrap-on solid rocket motors are ignited at lito.

The remaining three solids are ignited ollowing theburnout o the rst six solids.

Following the main engine burn, the second stage willperorm the rst o its two burns, placingthe orbiters into a 90-nautical mile (167 kilometer)near-circular parking orbit. Following a coast periodo just under an hour, the second stage will berestarted, delivering the orbiters on their trajectory tothe moon.

Orbiter-Launch Vehicle Separation

Beginning approximately three minutes ater theupper-stage has completed its nal burn, the stagewill perorm an attitude maneuver that will reorientthe stage to the required separation attitude. Atthe completion o this maneuver, nine minutes and30 seconds ater the upper stage engine cuto,the second stage will send a signal that will causethe separation o GRAIL-A to occur. A little morethan seven minutes later, the upper stage will begin

the maneuver to the desired attitude or GRAIL-Bseparation. This maneuver will reorient the secondstage 45 degrees away rom the GRAIL-A separationattitude. Once the proper attitude is achieved or theGRAIL-B spacecrat, a second signal will trigger theseparation o GRAIL-B at 8 minutes and 15 secondsater the GRAIL-A separation.

Separation o a GRAIL spacecrat rom the launchvehicle is detected using three separation breakwires


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on the spacecrat. Once a majority o these breakwiresindicate that separation has occurred, the spacecratwill autonomously begin to execute commandsthat were loaded prior to lito. Conrmation o theseparation events will be provided by the launchvehicle telemetry. In addition, visual conrmation oeach orbiters separation is expected via video roma RocketCam mounted on the second stage o thelaunch vehicle.

The deployment o the solar arrays occurs in sunlight,shortly ater exit rom solar eclipse, and is visiblerom NASAs Deep Space Network tracking stations

at Goldstone, Cali. This will allow the telemetryassociated with the deployment to be downlinked toEarth in real time.

Both solar arrays will be commanded to deploy atnearly the same time. It will take, at most,127 secondsor the arrays to reach their ully deployed positions.

Separation and initial acquisition graphic or a Sept. 8 launch date.

Trans-Lunar Cruise Phase

The Trans-Lunar Cruise Phase is the period o timewhen both orbiters will be en route to the moon viaa low-energy trajectory. This phase will include aseries o checkouts and calibrations to characterizethe perormance o the spacecrat and payloadsubsystems, as well as navigation activities requiredor determining and correcting the vehicles fightpath, and activities to prepare or lunar orbit insertion.

During the Trans-Lunar Cruise Phase, up to vetrajectory correction maneuvers will be perormed.

The second and third maneuver will separate the

GRAIL-A and GRAIL-B arrival times at the moon byapproximately one day.

Lunar Orbit Insertion Phase

The primary ocus or this phase is the critical lunarorbit insertion maneuver. This phase begins threedays prior to GRAIL-A arrival at the moon, and ends


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one day past the Lunar Orbit Insertion burn orGRAIL-B.

Both orbiters approach the moon rom the south,fying nearly directly over the lunar south pole. Thelunar orbit insertion burn or each spacecrat lastsapproximately 38 minutes and changes the orbitervelocity by about 427 mph (191 meters per second).Separated by about 25 hours, the lunar orbit insertion

maneuvers will place each orbiter into a near-polar,elliptical orbit with a period o 11.5 hours. Thesemaneuvers will be simultaneously visible rom DeepSpace Network tracking stations in Madrid, Spain andGoldstone, Cali.

Orbit Period Reduction Phase

The Orbit Period Reduction Phase starts one dayater the lunar orbit insertion maneuver or GRAIL-Band continues or ve weeks. It includes a series o

The fgure shows GRAIL-A and GRAIL-B trajectories or a launch at the open and close o the launch period.

The low-energy trajectories leave Earth ollowing a path towards the sun, passing near the interior Sun-Earth

Lagrange Point 1 (Earth Libration Point 1) beore heading back towards the Earth-moon system.

maneuvers, grouped into two dierent clusters oreach orbiter, perormed to reduce the orbit periodrom 11.5 hours down to just under two hours.

Transition to Science Formation Phase

From launch through the end o the previousphase, the two orbiters will be operated essentiallyindependently. Activities on GRAIL-A and GRAIL-Bare separated in time to reduce operations conficts

and competition or ground resources. No attemptis made to fy the two orbiters in a coordinatedmanner. That all changes in the Transition to ScienceFormation Phase, when or the rst time, the positiono one orbiter relative to the other becomes relevant.

The conguration o the two GRAIL orbiters is slightlydierent, making the order in which they orbit themoon extremely important. At the beginning o the

Transition to Science Formation Phase, the orbit

View o GRAILs trajectory looking down atEarth-moon system


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period or GRAIL-B is targeted to be approximatelythree minutes larger than the period o GRAIL-A. Thisdierence in period means that the GRAIL-A orbiter,fying below the GRAIL-B orbiter, will lap the GRAIL-Borbiter once every three days. This creates a situationwhere subsequent maneuvers can be timed sothat the distance between the two orbiters can bemanaged and reduced in a controlled manner.

A series o rendezvous-like maneuvers will be

perormed in this phase to achieve the desired initialseparation distance and ensure that GRAIL-B isahead o the GRAIL-A in the ormation.

Science Phase

The Science Phase activities consist o the collectiono gravity science data and the execution oEducation and Public Outreach activities using theMoonKAM system.

The incoming trajectory and Lunar Orbit Insertion (LOI) burn o GRAIL-A.Blue line depicts the burn arch or

the spacecrat. Yellow line marks the moons terminator at time o insertion.

At the start o the Science Phase, the GRAIL spacecratwill be in a near-polar, near-circular orbit with an altitudeo about 34 miles (55 kilometers). The initial conditionshave been designed so that the natural perturbationso the lunar gravity eld allow the orbit to evolve withoutrequiring any orbit maintenance maneuvers.

The science orbit is designed to satisy the basicscience requirements o the GRAIL mission, which

are or a low-altitude, near-circular, near-polar orbitthat does not require any maneuvers to maintain theorbit. The primary design parameter rom a scienceperspective is the orbit altitude, since sensitivity tothe lunar gravity eld is driven by orbit altitude (i.e.the lower the altitude, the more sensitive the sciencemeasurements). Limits on the minimum orbit altitudeare driven primarily by orbit lietime considerations.

End o LOI Burn

Start o LOI Burn

Moon North Pole


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During the 82-day Science Phase, the moon will

rotate three times underneath the GRAIL orbit. Thecollection o gravity data over one complete rotation(27.3 days) is reerred to as a Mapping Cycle.

During Mapping Cycle 1, the mean separationdistance between the two spacecrat is designed toincrease rom approximately 62 to 140 miles (100kilometers to 225 kilometers). A very small Orbit

Trim Maneuver executed near the end o MappingCycle 1 will then be used to change the separationdrit rate. Following this orbital trim maneuver, themean separation distance will decrease rom 140

miles (225 kilometers) to approximately 40 miles (65kilometers) at the end o Mapping Cycle 3 (the endo the Science Phase). The change in separationdistance is required to meet the GRAIL scienceobjectives. The data collected when the orbiters arecloser together helps to determine the local gravityeld, while data collected when the separationdistances are larger will be more useul in satisyingthe science objectives related to detection andcharacterization o the lunar core.

Decommissioning Phase

The nal phase o the GRAIL mission is theDecommissioning Phase. During this seven-dayphase, the orbiters will perorm a nal Ka-bandcalibration and will continue to acquire science data,as power and thermal resources allow. The missionphase ends at the time o a partial lunar eclipse onJune 4, 2012.

The design o the GRAIL science orbit is such that,at the end o the Science Phase, the orbits o thetwo spacecrat carry them to within approximately9.3 to 12.4 miles (15 to 20 kilometers) above thelunar surace at their lowest point. I no maneuversare executed ater this point, both orbiters willimpact the lunar surace during, or shortly ater, thismission phase. The GRAIL mission is expected toend within a ew days o the partial lunar eclipse inJune 2012. There are no plans to target the impactpoints on the lunar surace.

The two GRAIL spacecrat.


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Spacecraft

Two orbiters are part o the GRAIL mission; one isdesignated GRAIL-A and the other GRAIL-B.

The two Lockheed-Martin built spacecrat arenearly identical, but there are a ew importantdierences between them due to the need to pointthe spacecrat at one another during the SciencePhase o the mission. These include the angles atwhich their star trackers are pointing, the LunarGravity Ranging System antenna cant angle, and theMoonKAM mounting. In addition, during the SciencePhase, the orientation o the orbiters is dierent.

They will fy acing each other one orward and theother backward so they can point their Ka-bandantennas at each other.

Technicians prepare to hoist one o the two GRAIL spacecrat upon completion o a thermal vacuum test at the

Lockheed Martin Space Systems acility in Denver. Image Credit: NASA/JPL-Caltech/LMSS

Structure

GRAIL comprises twin spacecrat built on theLockheed Martin Experimental Small Satellite (XSS-11) bus, with a science payload derived rom theGRACE terrestrial gravity mission. The GRAIL bus isa rectangular composite structure with a dry mass oabout 443 pounds (201 kilograms), and ully ueledmass o about 677 pounds (307 kilograms).

Attitude Control Subsystem

The Attitude Control subsystem is used to providethree-axis stabilized control throughout the mission.


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This subsystem consists o a sun sensor, a startracker, reaction wheels, and an inertial measurementunit.

Propulsion System

The propulsion subsystem provides propulsiveimpulse or all large maneuvers including trajectory

correction maneuvers, lunar orbit insertion andcircularization maneuvers. The propulsion systemconsists o a propellant storage tank, a high-pressurehelium recharge tank, a eed system or propellantloading and distribution, a hydrazine catalytic thrusteror change-in-velocity impulse delivery, a warm gasattitude control system, and eight warm gas attitudecontrol system thruster valves.

The main engine is an MR-106L 22 Newton liquidhydrazine thruster. The main engine provides the

majority o the thrust or spacecrat trajectorycorrection maneuvers. The warm gas attitude controlsystem thrusters will be used or the small maneuversplanned or the Science Phase o the mission.

The warm gas attitude control system utilizes eight0.9 Newton thrusters. The attitude control thrustersare canted to provide coupled thrust during mainengine maneuvers. The warm gas thruster locationshave been designed to minimize plume impingementon the main body and solar arrays.

Command & Data HandlingThe Command and Data Handling subsystem isused or telemetry and command processing or theorbiter. The single-string command and data handlingsubsystem also eatures an enhanced RAD-750spacecrat computer with 128 megabytes o StaticDynamic random access memory. In addition, thereare 512 megabytes o storage within the Memory andPayload Interace Card or recorded data.

Power

The electrical power subsystem is responsible orgenerating and storing energy or each orbiter and itssystems. This power subsystem includes two solararrays and a lithium-ion battery.

There are two solar arrays, which generate the energyto operate the orbiter systems. Each solar array hasan area o 6.2 square eet (1.88 square meters) andis capable o producing 700 watts o power at theend o the mission. There are 20 cells per string and

26 strings per panel. The solar arrays are deployedshortly ater separation rom the launch vehicle andremain xed throughout the mission.

The lithium-ion battery has a capacity o 30 amp-hours, and is used to provide energy to the orbiterduring periods when the solar arrays are not able to

generate enough power or the orbiter systems.

Telecommunications

The telecom subsystem is responsible or sendingtelemetry and radiometric data rom the orbiter andreceiving commands rom the ground during themission. The telecom subsystem or GRAIL consistso an S-band transponder, two low gain antennas,and a single-pole, double-throw coaxial switch usedto alternate between the two antennas. The low gainantennas are the mission controllers primary means

o communicating with the spacecrat and enableeach spacecrat to communicate with each other.

Science Instruments

The payload on each orbiter consists o a LunarGravity Ranging System and an education and publicoutreach MoonKAM System.

Lunar Gravity Ranging System

The primary payload o the GRAIL spacecrat isthe Lunar Gravity Ranging System. The system is

responsible or sending and receiving the signalsneeded to accurately and precisely measure thechanges in range between the two orbiters as theyfy over lunar terrain o varying density. To accomplishthis, the Lunar Gravity Ranging System consists oan ultra-stable oscillator, microwave assembly, a timetranser assembly, and the gravity recovery processorassembly.

The ultra-stable oscillator provides a steady reerencesignal that is used by all the instrument subsystems.

The microwave assembly converts the oscillators

reerence signal to the Ka-band requency, whichis transmitted to the other orbiter. The unction othe time transer assembly is to provide a two-waytime transer link between the spacecrat to bothsynchronize and measure the clock oset betweenthe clocks aboard the two spacecrat.

The time transer assembly generates an S-bandsignal rom the ultra-stable oscillator reerencerequency and sends a GPS-like ranging code to


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the other spacecrat. The gravity recovery processorassembly combines all the inputs received to producethe radiometric data that is downlinked to the ground.

Outreach Instrument MoonKAM

MoonKAM is a digital video imaging system that isused as part o the education and public

outreach activities or GRAIL. Each MoonKAMsystem (one per spacecrat) consists o a digital videocontroller and our camera heads one pointedslightly orward o the spacecrat, two pointed directlybelow it, and one pointed slightly backward. Thedigital video controller serves as the main interaceto the spacecrat and provides storage or imagesacquired by the camera heads. This system can beused to take images or video o the lunar surace witha rame rate up to 30 rames per second.

The MoonKAM system is provided by EclipticEnterprises Corporation, Pasadena, Cali., and isoperated by undergraduate students at the Universityo Caliornia at San Diego under supervision o acultyand in coordination with Sally Ride Science. Middleschool students rom around the country will havean opportunity to become involved with MoonKAMimaging. During the Science Phase, operations will beconducted in a non-time-critical, ground-interactivemode.

GRAIL Bloodline

GRAIL will build on the heritage o a predecessormission called the Challenging Minisatellite Payload,or Champ. Built by Germanys Earth ResearchCenter (GeoForschungsZentrum) and launched inJuly 2000, Champs instruments and its orbit haveallowed it to generate simultaneous, highly precise

measurements o Earths gravity and magnetic eld.

While Champ has signicantly advanced the eld ogeodesy, scientists desired an even more advancedmission based upon dual satellites fying in ormation.

The unique design o NASAs GRACE Earth-observingmission led to a hundred-old improvement in existinggravity maps and allow much improved resolutiono the broad- to ner-scale eatures o Earthsgravitational eld over both land and sea, while alsoshowing how much Earths gravitational eld varies

with time.

The design o the GRAIL spacecrat is based on theExperimental Small Satellite-11 (XSS-11) technologydemonstration mission or the United States AirForce, the Mars Reconnaissance Orbiter (MRO)and the Gravity Recovery and Climate Experiment(GRACE) missions or NASA.


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Why Study Gravity?

Gravity is Newtons apple and the stu o Einsteinstheory o relativity, but it is also the law that we alllearn to obey rom our rst breath o lie. Gravity is the

mutual attraction that pulls two masses together andkeeps us rmly planted on Earth.

Sir Isaac Newton rst revealed the law o gravitymore than 300 years ago. During the 20th century,geophysicists developed techniques to locate mineraldeposits and underground ormations using spatialchanges in Earths gravity eld. Their work laid themodern oundation or the science o geodesy. Today,scientists use measurements rom several dozensatellites to develop models o Earths geoid animaginary surace upon which the pull o gravity is

equal everywhere.

Planetary scientists have taken the study o gravityelds to new heights and other worlds. The GRAILmission will orward this scientic endeavor, creatingthe most accurate gravitational map o the moon todate.

I the moon were a smooth sphere o uniorm density,there would be no need or a missionlike GRAIL it would measure no changes in the

gravity eld. However, the moon isnt smooth andhomogeneous its surace includes mountains that

are many miles high, lava fows several hundredmiles long and enormous lava tubes and craters oevery size. Below the surace, things are even more

complex and variable. In act, the moon has thelumpiest gravitational eld known in our solarsystem. Studying its gravity allows us to betterunderstand the orces that have shaped our naturalsatellite.

For example, the material that makes up the moonshighlands has a dierent density than that makingup its seas, or maria. Since the highland materialis less dense than maria material, the gravity in themaria region is usually subtly stronger. Such unevendistribution o mass on the moons surace and in

its interior maniests itsel as lumps in the planetsgravity eld.

Previous space missions have mapped thegravity elds o asteroids, Venus, Mars, Jupiter,Saturn and Earth. Even Earths moon, the objecto GRAILs attention, has had its gravity eldmeasured on numerous occasions with varyingdegrees o success. But the accuracy o the GRAILdata will surpass by orders o magnitude thatpreviously obtained, which will allow a new level ounderstanding about Earths nearest neighbor.


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Science Overview

GRAIL Science Overview

The primary science objectives are to determine thestructure o the lunar interior, rom crust to core, and

to advance understanding o the thermal evolutiono the moon. The secondary science objective is toextend knowledge gained rom the moon to otherterrestrial planets. These objectives will be achievedby obtaining a global, high-accuracy, high-resolutionlunar map during a 90-day Science Phase.

The GRAIL mission will create the most accurategravitational map o the moon to date, improvingour knowledge o gravity on the side acing Earth by100 times and o gravity on the side not acing Earthby 1,000 times. The high-resolution gravitational

eld, especially when combined with a comparable-resolution topographical eld, will enable scientiststo deduce the moons interior structure andcomposition, and to gain insights into its thermalevolution that is, the history o the moons heatingand cooling, which opens the door to understandingits origin and development. Accurate knowledgeo the moons gravity will also be an invaluablenavigational aid or uture lunar spacecrat. Ultimately,the inormation contributed by the GRAIL mission willincrease our knowledge o how Earth and its rockyneighbors in the inner solar system developed into thediverse worlds we see today.

Science Objectives

The moon is the most accessible and best studiedo the rocky (aka terrestrial) bodies beyond Earth.Unlike Earth, however, the moons surace geologypreserves the record o nearly the entirety o 4.5billion years o solar system history. In act, orbitalobservations combined with samples o suracerocks returned to Earth indicate that no other bodypreserves the record o geological history as clearly

as the moon.

The need to understand the lunar internal structurein order to reconstruct planetary evolution motivatesGRAILs primary science objectives, which are todetermine the structure o the lunar interior romcrust to core and to urther the understanding o thethermal evolution o the moon.

Why thermal evolution? A planetary body suchas the moon, Earth, and the other terrestrialplanets,orms by accretion o primordial dust androck. Eventually, this protoplanet is heated to themelting point by meteoroids smashing into it andby breakdown o radioactive elements within it.

Then, over the eons, it cools o by radiating its heatinto space. While its still molten, heavy materialssink down toward the core and lighter materialsfoat on top, ultimately orming a crust. The storyo how a particular planetary body processes itsheat and how, when and where heat is replenishedby meteorite impacts and radioactive elementsbreak down is the story o how its structure cameto be. So understanding the moons thermal

evolution is essential to understanding its origin anddevelopment.

The missions secondary objective is to extend theknowledge it will gain about the moon to inormour understanding o the development o the otherplanetary bodies in the inner solar system: Mercury,

Venus, Earth and Mars. As the most accessibleplanetary body besides Earth, and as one thatis thought to have changed little since its initialdevelopment (unlike Earth, Mars, and Venus), themoon oers a unique look into the distant past o

planetary evolution.

The GRAIL missions six science investigations:

1. Map the structure of the lithosphere.

The lithosphere is the portion o the crust and uppermantle with signicant strength over a geologicaltime scale. Since the strength o rock is highlydependent on temperature, the thickness o thelithosphere is directly related to thermal evolution.

GRAIL will provide evidence o how rigid thelithosphere was and thereore what the thermalconditions were at various locations wheneatures were ormed.

2. Understand the moons asymmetric thermal

evolution.

The thickness o the crust suggests the extent towhich the surace was melted in its early history. The


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moons crust has a variable structure, thinner on thenear side than on the ar side, except or the southpole Aitken basin region, and thinned beneath themajor impact basins. Scientists would like to knowwhy.

3. Determine the subsurface structure of impact

basins and the origin of mascons.

A surprising discovery was made in the 1960s,when it was ound that the moons gravity wasunexpectedly strong over certain impact basins, andthat this is what had been pulling lunar spacecrato course. It was deduced that these impact basinshave large mass concentrations (or mascons orshort) underneath them. GRAIL will provide moreinormation about the nature o these mascons.

4. Ascertain the temporal evolution of crustal

brecciation and magmatism.

Analyses o a set o lunar craters indicate that thosethat ormed less than 3.2 billion years ago showless gravity than the surrounding plain, while thoseormed earlier show about the same gravity as thesurrounding plain. GRAIL will help to explain thereasons, including the roles played by brecciation(the ormation o new rocks by cementing togetherragments o older rocks, oten ound beneath

impact craters on Earth), magmatism (the movemento molten rock inside the moon), and isostaticcompensation (a process by which a planetary bodyevens out the distribution o its mass or example,by distorting the boundary between the crust andmantle beneath a large impact basin).

5. Constrain deep interior structure from tides.

Earths gravity creates tides in the solid moon, just asthe moon creates tides in Earths ocean. O course,the moons rocky surace doesnt bulge as much aswater would it only deorms about 3.5 inches (9centimeters) in response to Earths gravity rom onepart o the lunar orbit to another. But whats signicantto GRAIL is that the moon responds to Earths gravityall the way down to the core, and dierent internalstructures would produce dierences in the waythe moons gravitational eld deorms. By analyzing

how the eld deorms at various parts o the moonsorbit around Earth, scientists will be able to deduceinormation about the core and other deep eatures.

6. Place limits on the size of a possible solid inner

core.

GRAIL scientists will search or evidence o a solidcore within the liquid core the moon is believed tohave, and the data they receive will place limits onhow big that solid core could be.


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Science Team

GRAIL Science Team

Maria Zuber,

principal investigator,Massachusetts Institute o Technology,Cambridge

David E. Smith,deputy principal investigator,Goddard Space Flight Center,Greenbelt, Md.

Michael Watkins,project scientist,Jet Propulsion Laboratory,Pasadena

Sami Asmar,deputy project scientist,Jet Propulsion Laboratory, Pasadena

Co-Investigators

Alexander S. Konopliv,NASAs Jet Propulsion Laboratory,Pasadena, Cali

Frank G. Lemoine,Goddard Space Flight Center,Greenbelt, Md.

Jay Melosh,University o Arizona, Tucson

Gregory A. Neumann,Goddard Space Flight Center,

Greenbelt, Md.

Roger J. Phillips,Southwest Research Institute,San Antonio

Sean C. Solomon,Carnegie Institution or Science,Washington, DC

Mark Wieczorek,University o Paris

James G. Williams,Jet Propulsion Laboratory,Pasadena, Cali.


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Missions to the Moon

Historical Exploration o the Moon

1609Hans Lippershey invented the telescope.

1610Italian astronomer Galileo Galilei made the rsttelescopic observation o the moon.

1610Thomas Harriot and Galileo Galilei drew the rsttelescopic representation o the moon.

1645Michael Florent van Langren made the rst map othe moon.

1647Johannes Hevelius published the rst treatise

devoted to the moon.1651Giovanni Battista Riccioli named craters aterphilosophers and astronomers.

1753Roger Joseph Boscovich proved the moon has noatmosphere.

1824Franz von Gruithuisen thought craters wereormed by meteor strikes.

1920Robert Goddard suggested sending rockets to themoon.

1959Soviet spacecrat Luna 2 reached the moon,impacting near the crater Autolycus.

1961President John F. Kennedy proposed a mannedlunar program.

1964NASAs Ranger 7 produced the rst close-up TV

pictures o the lunar surace.

1966Soviet spacecrat Luna 9 made the rst sotlanding on the moon.

1967NASAs Lunar Orbiter missions completedphotographic mapping o the moon.

1968NASAs Apollo 8 made the rst manned fight to themoon, circling it 10 times beore returning to Earth.

1969

Apollo 11 mission made the rst landing on the moonand returned samples.

1969(Nov.) Apollo 12 made rst precision landing on thethe moon.

1972Apollo 17 made the last manned landing o the ApolloProgram.

1976Soviet Luna 24 returned the last sample to bereturned rom the moon (to date).

1990NASAs Galileo spacecrat obtained multispectralimages o the western limb and part o the ar side othe moon.

1994NASAs Clementine mission conducted multispectralmapping o the moon.

1998NASAs Lunar Prospector launched.

2007

Japanese SELENE (Kaguya) launched.

2007Chinese Change 1 launched.

2008Indian Chandrayaan 1 launched.

2009NASAs Lunar Reconnaissance Orbiter launched

Future NASA Lunar Missions

2012 LADEE (orbiter) Lunar Atmosphere and DustEnvironment Explorer is a NASA mission that will orbitthe moon. Its main objective is to characterize theatmosphere and lunar dust environment. In additionto the science objectives, the mission will be testinga new spacecrat architecture called the ModularCommon Bus, which is being developed by NASAas a fexible, low-cost, rapid-turnaround spacecrator both orbiting and landing on the moon and otherdeep space targets.



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NASAs Discovery Program


GRAIL will be the eleventh Discovery Program missionto enter space.

As a complement to NASAs larger fagship

planetary science explorations, the DiscoveryProgram goal is to achieve outstanding resultsby launching many smaller missions using ewerresources and shorter development times. The mainobjective is to enhance our understanding o thesolar system by exploring the planets, their moons,and small bodies such as comets and asteroids. Theprogram also seeks to improve perormance throughthe use o new technology and broaden universityand industry participation in NASA missions.

Further inormation on NASAs Discovery program can

be ound at: http://discovery.nasa.gov/.

Previous NASA Discovery program missions:

Near Earth Asteroid Rendezvous was launchedFeb. 17, 1996. It became the rst spacecrat toorbit an asteroid when it reached Eros in February2000. Ater a year in orbit, it achieved the rstlanding on an asteroid in February 2001, aterreturning more than 160,000 detailed images.Shoemaker was later added to the spacecratsname in honor o the late planetary scientist

Eugene Shoemaker.

Mars Pathnder was launched Dec. 4, 1996,and landed on Mars on July 4, 1997. It was therst ree-ranging rover to explore the Martiansurace, conducting science and technologyexperiments. Pathnders lander operated nearlythree times longer than its design lietime o 30days, and the Sojourner rover operated 12 timesits design lietime o seven days. Ater sendingback thousands o images and measurements,the mission ended Sept. 27, 1997.

Lunar Prospector was launched Jan. 6, 1998. Itorbited Earths moon or 18 months, looking orwater and other natural resources and returningextensive mapping data to provide insights intolunar origin and evolution. At the missions endon July 31, 1999, the spacecrat was intentionallycrashed into a crater near the moons south polein an attempt to detect the presence o water.

Launched Feb. 7, 1999, Stardust captured andreturned to Earth interstellar dust particles andcomet dust using an unusual substance calledaerogel. On Jan. 2, 2004, it few within 149 miles

(240 kilometers) o the nucleus o Comet Wild 2,collecting samples o comet dust and snappingdetailed pictures o the comets surace. OnJan. 15, 2006, Stardusts sample return capsulereturned to Earth, providing scientists worldwidewith the opportunity to analyze the earliestmaterials that created the solar system. NASAextended Stardusts mission to fy by comet

Tempel 1, which occurred on Feb. 14, 2011.That mission was reerred to as Stardust-NExT.The spacecrat obtained images o the scar onTempel 1s surace produced by NASAs Deep

Impact in 2005 and revealed changes to thecomets surace since a recent close approachto the sun. It also imaged new terrain not seenduring the Deep Impact mission and took newdust measurements.

Launched Aug. 8, 2001, Genesis collected atomso solar wind beyond the orbit o Earths moon toaccurately measure the composition o our sunand improve our understanding o solar systemormation. Its sample return capsule made ahard landing at the time o Earth return on Sept.8,2004. The missions samples o solar windwere recovered and are currently being analyzedby scientists at laboratories around the world.

The Comet Nucleus Tour launched rom CapeCanaveral on July 3, 2002. Six weeks later,contact with the spacecrat was lost ater aplanned maneuver that was intended to propelit out o Earth orbit and into a comet-chasingsolar orbit. The probable proximate cause wasstructural ailure o the spacecrat due to plume

heating during the embedded solid-rocket motorburn.

The Mercury Surace, Space Environment,Geochemistry and Ranging (MESSENGER)spacecrat was launched Aug. 3, 2004. Itentered orbit around the planet closest to thesun in March 2011. The spacecrat is mappingnearly the entire planet in color and measuringthe composition o the surace, atmosphere andmagnetosphere.


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Launched Jan. 12, 2005, Deep Impact was therst experiment to send a large projectile intothe path o a comet to reveal the hidden interioror extensive study. On July 4, 2005, travelingat 23,000 mph (39,000 kilometers per hour) alarger fyby spacecrat released a smaller impactorspacecrat into the path o comet Tempel 1 as

both recorded observations. The Spitzer, Hubbleand Chandra space telescopes also observedrom space, while an unprecedented globalnetwork o proessional and amateur astronomerscaptured views o the impact, which took place83 million miles (138 million kilometers) romEarth. NASA extended the Deep Impact missionas EPOXI, a combination o the names or themissions two components: the Extrasolar PlanetObservations and Characterization (EPOCh),andthe fyby o comet Hartley 2, called the DeepImpact Extended Investigation (DIXI). The EPOXI

mission successully few by comet Hartley 2 onNov. 4, 2011, obtaining the rst images clearenough or scientists to link jets o dust and gaswith specic surace eatures.

Launched on Sept. 27, 2007, NASAs Dawnspacecrat will be the rst to orbit two bodies inthe main asteroid belt, Vesta and Ceres. Dawnarrived at Vesta on Friday, July 15. The spacecratwill spend a year orbiting the giant asteroid,beore traveling to its second destination, arriving

at Ceres in February 2015. Studying Vesta andCeres, the two most massive objects in theasteroid belt, allows scientists to do historicalresearch in space, opening a window intothe earliest chapter in the history o our solarsystem. At each target, Dawn will acquire colorphotographs, compile topographic maps, map

the elemental composition, map the mineralogicalcomposition, measure the gravity eld and searchor moons. The data gathered by Dawn willenable scientists to understand the conditionsunder which these objects ormed, determinethe nature o the building blocks rom whichthe terrestrial planets ormed and contrast theormation and evolution o Vesta and Ceres.

Launched on March 6, 2009, Kepler is in themiddle o its prime mission to monitor more than100,000 stars similar to our sun. The mission

was designed to nd Earth-sized planets in orbitaround stars outside our solar system. Withits vast eld o view, Kepler detects transits othousands o planets. So ar, it has identied morethan 1,200 planet candidates, some o whichlie in the habitable zones o their stars, wheretemperatures permit water to be in a liquid state.Kepler has also discovered the smallest knownrocky planet, called Kepler-10b, measuring at 1.4times the size o Earth.


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Program/Policy Management

GRAILs principal investigator is Maria Zuber o theMassachusetts Institute o technology, Cambridge.

Michael Watkins and Sami Asmar, o NASAsJet Propulsion Laboratory, Pasadena, Cali., areGRAILs project scientist and deputy-project scientist,respectively.

The GRAIL project is managed by the Jet PropulsionLaboratory, Pasadena, Cali., or NASAs ScienceMission Directorate, Washington. The GRAIL missionis part o the Discovery Program managed atNASAs Marshall Space Flight Center in Huntsville,

Ala. Launch management or the mission is theresponsibility o NASAs Launch Services Program at

the Kennedy Space Center in Florida.

At NASA Headquarters, Ed Weiler is associateadministrator or the Science Mission Directorate.

James Green is director o the Planetary Division.

William Knopf is GRAIL program executive, andRobert Fogel is GRAIL program scientist.

Dennon Clardy o NASAs Marshall Space FlightCenter is the Discovery program manager.

At JPL, David Lehman is GRAIL project manager.Tom Homan is deputy project manager. JPL isa division o the Caliornia Institute o Technology,Pasadena, Cali.

Lockheed Martin Space Systems Company,Denver built the GRAIL spacecrat and will handleits day-to-day operations. John Henkis is thecompanys GRAIL program manager and leads the

fight team.

The United Launch Alliance is responsible orthe Delta II rocket which will carry GRAIL into space.

More information about NASAs GRAIL

mission can be found online at http://www.

nasa.gov/grail and http://grail.nasa.gov.

Documents

Gravity Recovery and Interior Laboratory (GRAIL) Launch Press Kit