dual air density explorers (explorers 54-55) press kit

8/7/2019 Dual Air Density Explorers (Explorers 54-55) Press Kit

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NUASA\ News tQ?National Aeronautics andSpace AdministrationWashington. D.C. 20546AC 202 755-8370

For Release IrM4EDIATE

Press Kit Project Dual Air DensityExplorersRELEASE NO: 75-300

ContentsGENERAL RELEASE..............**** ***...... 1-5MISSION DESCRIPTION .....* * **.....***** ** ** *** 67SATELLITE DESCRIPTION. ............... ....... 7-9LAUNCH VEHICLE .................................... 10FLIGHT SEQUENCE ................................... 11

DUAL AIR DENSITY EXPLORER/SCOUT TEAM ....... ...... 12-14

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National Aeronautics andSpace AdministrationWashington, D.C. 20546AC 202 755-8370

For Release:Nicholas Panagakos IMMEDIATEHeadquarters, Washington, D.C.(Phone: 202/755-3680)Maurice ParkerLangley Research Center, Hampton, Va.(Phone: 804/827-3966)

RELEASE NO: 75-300

DUAL SATELLITES SET FOR LAUNCH

NASA is preparing to launch two satellites with a singlerocket to measurethe vertical structure of Earth's upperatmosphere around the globe.

Called Dual Air Density (DAD) Explorers, thesatellites will be boosted into a polar orbit by a Scoutrocket from the Western Test Range near Lompoc, Calif.,about Dec. 3. A 23-minute launch window begins at 10:40 p.m.Eastern Standard Time.

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Measurements from the satellites should lead to a betterunderstanding of the upper atmosphere's density, composi-tion and temperature; reveal how these features areaffected by changes in solar heat input; and show howrapidly the atmosphere is escaping from Earth. The mea-surements may also provide insight into the relationshipsbetween Earth's upper and lower atmosphere.

The vertical atmospheric measurements will be madeby mass spectrometers and atmospheric drag instrumentsaboard each satellite. The spectrometers will measureatmospheric particles that are separated according totheir respective molecular weights. Both vertical andlateral distribution of atmospheric gases such as helium,atomic oxygen and molecule- nitrogen will be measured.

The two satellites were designed and built at NASA'sLangley Research Center, Hampton, Va. Scientists formu-lated a unique design that permits mass spectromnrter andatmospheric drag measurements to be completely insensitiveto orientation of the two satellites, yet highly sensitiveto the atmospheric environment. The design also allowsthe instruments to be recalibrated in flight.

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The first satellite, a hollow sphere measuring0.76 meter (30 inches), will be placed into an orbit of350 by 1,500 kilometers (217 by 932 miles) above Earth.The second satellite, a 3.6-rn (12-ft.) diameter sphere,

IA will then be inflated and kicked into an orbit with ahigher perigee (closest d4-tance to Earth) of 700 km

435 mi.) and the same 1,500-km apogee (farthest dis-j

The system of dual satellites is being used becausea single satellite cannot directly measure %vertical dis-tribution of the atmosphere; whenever a satellite changesposition vertically, it also changes position laterally.

The atmosphere's vertical structure will be obtainedjby comparing measurements from the two satellites as theypass over one of several ground tracking stations at theirseparate altitudes. The ground stations, spread aroundthe Earth, include a special DAD station at the South Pole.j

The DAD satellites will be the fifth and sixth space-craft launched in Langley's continuing Air Density Explorerprogram. Two earlier satellites, Explorers 19 and 39, arestill in orbit, measuring atmospheric densities and helpinginfer atmospheric composition at satellite altitudes.

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These earlier measurements, which began with Explorer 9in 1961, helped Langley scientists discover the winterhelium bulge, a phenomenon in which peak helium concentra-tions in the atmosphere, at satellite altitudes, were un-expectedly found to shift between Earth's northern hemispherein December to the southern hemisphere in June. This shiftis apparently caused by a previously undetected global at-mospheric circulation system, which also redistributesother atmospheric constituents.

The most recent results in Langley's aeronomy researchinclude the first evidence that the seasonal variations inthe northern and southern hemispheres are substantiallydifferent at satellite altitudes; discovery that atomichydrogen concentrations 2,000 km (1,240 mi.) above Earthare about three cimes greater than previously assumed;and measurement of mean east-west winds of 322 km an hour(200 mph) at record altitudes of 550 km (340 mi.)

The DAD project is directed by NASA's Office ofSpace Science in Washington, D.C. The Langley ResearchCenter designed and built the two spacecraft, and alsomanages the Scout launch vehicle.

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The University of Minnesota, Minneapolis, builtthe two mass spectrometers for NASA and the Scoutlaunch vehicle was built by the Vought Systems Divisionof the LTV Aerospace Corp., Dallas, Tex.

Launch services will be provided by LTV, undertechnical direction of the U.S. Air Force 6595th SpecialTask Group at the Western Test Range and supportedby NASA's Unmanned Launch Operations Division, Lompoc,and Langley's Scout Project Office.

After the DAD satellites achieve orbit, they willbe designated Explorers 56 and 57.

(END OF GENERAL RELEASE. BACKGROUND INFORMATION FOLLOWS.)


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MISSION DESCRIPTION

The Dual Air Density Explorer (DAD) satellites arescheduled for launch from Spacecraft Launch Complex 5 (SLC-5)at the Western Test Range, located at Vandenberq Air ForceBase near Lompoc, Calif.

The four-stage, solid-fueled Scout-D launch vehicle,numbered S-196, will place the dual satellites into a polarorbit with an inclination of go degrees. Inside a protectiveshroud atop the vehicle are the small satellite and a packagehousing the large satellite, folded inside a canister, anorbital transfer rocket motors a pressure vessel for inflat-ing the satellite, and a despin device to stabilize the satel-lite before inflation.

When the fourth stage of the Scout vehicle has achievedorbit, the small satellite will be separated. The spin-stabilized package containing the large satellite will thenbe separated from the vehicle and retrorockets will be firedto displace the Scout's fourth stage.

When the large satellite package reaches its 1,500-km apogee, the orbital transfer rockets will be ignited,kicking the package into an orbit with a perigee of 700 km(435 mi.).The package will then be despun and the satellite un-folded, inflated by its erection system and separated fromthe package. By inflating the satellite to a pressure betweenthe yield and failure points of the skin material, a permanentset in the skin is obtained that maintains the satellite'sspherical shape throughout the two-year lifetime of the mission.The satellites in their polar orbits will be in thesame orbital plane. Polar (90-degree) orbits have the specialcharacteristic of remaining inertially fixed in space. Thetwo satellite orbits will remain essentially in a common planethroughout the mission, thereby periodically intersecting oneanother.The altitudes at which the orbits of the satellitesintersect will change each day because the perigee of thesmall (lower) satellite precesses more rapidly than that ofthe large satellite. During 85 per cent of the mission, how-ever, the intersection altitude will be less than 1,000 km(62 mi,).

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Measurements of the upper atmosphere's vertical struc-ture will be made as each satellite passes over ground track-ing stations. When the large satellite, in the generallyhigher orbit, comes within range of a station, ground commandswill turn on the satellite's mass spectrometer. As the satellitecrosses certain latitudes, data on the number densityof atmospheric constituents will be telemetered to the station.When the small satellite comes within range of thesame station, its mass analyzer will be activated. As thesatellite passes the same latitudes, data on atmos-pheric constituents at the lower altitude will be sent to thestation. Measurements will be obtained, therefore, at two

different altitudes, but at the same latitudes and at the samelocal hour angle of the Sun. Because of the Earth's rotationabout the Sun, measurements will be gradually obtained at dif-ferent times of day.Measurements will cover a vertical range from the upperthermosphere about 350 km (210 mi.) into the lower exosphere,about 1,500 km (900 mi.).Reduction of data from the mass spectrometers and thedrag measurements will be performed by scientists at LangleyResearch Center and at the University of Minnesota. Dataanalysis is expected to provide a fairly comprehensive pic-ture of the neutral atmosphere above 350 km (217 mi.), lead-ing to major improvements in our understanding of Earth'satmosphere and, possibly, a better insight into the generalnature of planetary atmospheres.

SATELLITE DESCRIPTION

Both Dual Air Density Explorer satellites are similarin design. Both are spherical and uniformly perforated withholes over one per cent of their surfaces to make certain thatthe same amount of atmospheric constituents (gases) enters thesatellites, regardless of satellite orientation in orbit.Major difference between the satellites is that theupper one is a large inflatable structure similar to previousAir Density Explorers, while the lower one is a rigid sphere.Because of the differences in size, each satellite is sensi-tive to its own drag environment.

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Small SatelliteThe small satellite, 0.76 meter (30 inches) in dia-meter, is hollow, made of aluminum and weighs about 35 kilo-grams (78 pounds).Within the hollow sphere is an instrument packagecontaining a mass spectrometer and associated electronics, atelemetry transmitter and beacon, a command receiver and de-coder and a PCM encoder and batteries. The package is about31 centimeters (14 in.) in diameter and length, and weighsabout 25 kg (54 lb.).Solar cells, symmetrically located around the satellite'souter surface, replenish the instrument package batteries,which can continuously power the mass spectrometer's ioniza-tion source, the command receiver and the tracking beacon, andintermittently power the mass spectrometer, PCM encoder andassociated electronic systems. The satellite has four antennasprotruding aft.The mass spectrometer which requires approximately sixwatts of power, will be operated one or two hours a day. Aver-age power requirement for the satellite is about four watts,including 2.5 watts of continuous power.The small satellite's aluminum internal surface has alow outgassing rate. To further reduce this rate, the sphere'sexternal surface is partially covered with a thermal controlcoating to reduce the average temperature of the satellite.Wall temperature distribution will be determined by thermo-couples located on the instrument package and by thermistorson the walls of the sphere.

Large SatelliteThe large satellite, 3.6 m (12 ft.) in diameter, ishollow and weighs about 36 kg (79 lb.). It is made of a five-ply aluminum/mylar laminate with an anodyzed outer surfacefor thermal control.The satellite contains an instrument package of thesame size, weight and power requirements as that of the smallsatellite, including a mass spectrometer. Average power andsolar cell requirements are essentially the same as for thesmall sphere.After being placed in its planned orbit, the foldedsatellite will Le inflated by a gas system and separated fthe storage package in which it is housed during launch andorbital placement.

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Mass SpectrometersThe two DAD mass spectrometers are double-focusing

magnetic mass analysis systems with a special design thatallows a compact, light instrument with a low power consump-tion. Their sensitivities are so great that useful data canbe obtained through the entire altitude range between thetwo satellites.Electrons emitted from a heated filament are focusedby a magnet into a small beam. Neutral particles are ionizedand accelerated through an object slit before passing into anelectrostatic analyzer.From there the beam of ions goes into a magneticanalyzer, where it is split into high and low mass streams.Two high-gain electron multipliers, one for each ion mass,will be used as ion collectors. Counting technigaes will beused to measure the low ion currents.The mass spectrometers measure atmospheric concentra-tions within each sphere, so the measurements are independentof either satellite's orientation. The most important con-stituent to be measured is helium, but measurements are alsoplanned for atomic oxygen, molecular nitrogen and, perhaps,hydrogen.The average velocity of a particle entering the spheresthrough their uniform perforations is much greater than thevelocity of particles leaving the spheres. The density ofparticles is much higher inside the spheres than outside,* therefore allowing the measurement of very low densities.The mass spectrometers have been calibrated on Earth beforethe mission in special facilities at the University of Minne-sota. Once in orbit, the spectrometers will be periodicallyrecalibrated by an inflight calibration system. The systemwill provide the first opportunity to insure that a 'lightinstrument's response does not degrade during the life of themission. Data obtained at the end of the mission tierefore

should be as accurate as that obtained in the first few weeksof operation.The calibration system consists of two gas bottles-- one arqon, one helium. When the pressurized bottles areopened in space, the gas escapes through a valve into thesatellite. Calibration is done from the known pressure-timehistory. The calibration can be cross-checked when the two7satellite orbits intersect.

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LAUNCH VEHICLEThe Scout-D launch vehicle is a four-stage, solid-fueled rocket system. Scout S-196 and the Dual Air DensityExplorer spacecraft will be placed in initial azimuth of180 degrees to obtain a retrograde orbit.The four Scout-D motors -- Algol III, Castor IIB,

Antares IIIB and Altair III -- are interlocked with tran-sition sections that contain guidance, control, ignition,instrumentation system, separation mechanics and the spinmotors required to stabilize the fourth stage.Guidance for Scout-D is provided by an autopilot andcontrol is achieved by a combination of aerodynamic surfaces,jet vanes and hydrogen peroxide jets. The vehicle is approx-imately 22.25 m (73 ft.) long and weiqhs about 17,000kg (38,000 lb.) at liftoff. 1

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FLIGHT SEQUENCETimeEvent (Min-Sec)

Liftoff 00:00First Stage Burnout 01:22.6Second Stage Ignition 01:28.3Second Stage Burnout 02:07Payload Heat Shield Separation 02:30.3Third Stage Ignition 02:32Third Stage Burnout 03:00.9Spin Motor Ignition 07:55Third Stage Separation 07:56.2Fourth Stage Ignition 08:01.1Fourth Stage Burnout and Orbital Injection 08:35.3Payload Separation 11:06.1Small Satellite and Large SatellitePackage Separation 11:36.2Large Satellite Package Separation 62:16.8Despin (Yo-Yo) 63:16.9Large Satellite Ejection 63:19.9Begin Satellite Inflation 63:23.9Close Inflation Valve 63:32.9Satellite and Package Separation 63:33

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DUAL AIR DENSITY EXPLORER/SCOUT TEAMNASA HeadquartersDr. Noel W. Hinners Associate Administratorfor Space ScienceDr. Alois W. Schardt Director, AstrophysicsProgramsDr. E. R. Schmerling Chief, MagnetosphericPhysics ProgramsJohn R. Holtz Director, Explorers, SoundingRockets and BalloonsJoseph B. Mahon Director, Expendable LaunchVehicles and PropulsionProgramI. T. Gilliam IV Manager, Small LaunchVehicles and InternationalProgramsPaul E. Goozh Manager, Scout ProgramLangley Research CenterDonald P. Hearth DirectorPaul F. Holloway Director for SpaceJohn E. Canady, Jr. Project ManagerWilliam F. Hinson Assistant Project ManagerJGames W. Mayo Project Chief EngineerJames W. Cheely Spacecraft System ManagerTheodore M. Squires Reliability, Quality Assuranceand Safety EngineeringWilliam L. Gaster Project Schedules and Analysis

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Langley Research Center(cont'd.)Alfred G. Beswick Mass Spectrometer andCalibration ManagerLouis H. Hunt, Jr. Electronics and Instru-

mentation ManagerDavid H. Butler Technical Project EngineerDonald E. Forney Head, Langley Mission SuppoztOffice, Western Test Range

Roland D. English Heady Scout Project OfficeA A Samuel J. Ailor Assistant Head, Scout ProjectOffice and Launch Vehicle

ManagerDavid E. Morris Scout Payload IntegratorLee R. Foster, Jr. Scout Project Operations

HeadJohn L. Van Cleave Scout Reliability and Quality

Assurance HeadClyde W. Winters Scout Launch Operations Head

DAD Science TeamGerald M. Keating Principal Investigator,

Langley Research CenterDr. Alfred O.C. Nier Investigator, University

of MinnesotaDr. Konrad Mauersberger Co-Investigator, University

of MinnesotaEdwin J. Prior Co-Investigator, Langley

Research Center

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Kennedy Space CenterLee R. Scherer DirectorJohn J. Neilon Director, Unmanned Launch-OperationsHenry R. Van Goey Manager, Western LaunchOperations DivisionC. R. Fuentes DAD Coordinator, WesternLaunch Operations Division

Goddard Space Flight CenterDr. John F. Clark DirectorTecwyn Roberts Director, NetworksDirectorateKenneth D. McDonald Tracking and Data Acquisi-tion Manager

November 25, 1975

dual air density explorers (explorers 54-55) press kit

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