Atmospheric Structure Satellite S-6 Press Kit

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C3- 10OOON 63 14101N EWS R E LEAS E

NATIONAL AERONAUTICS AND SPACE ADAINISTRATION40 0 MARYLAND AVENUE, SW, WASHINGTON 25, D.C.TELEPHONES, WORTH 2-4155-WORTH.3-6925

e n FOR RELEASE: P,M. TUESDAYMarch 26~ 1963

RELEASE No: 63-59

NASA TO LAUNCH ATMOSPHERIC STRUCTURE SATELIITE (S-6)

Within the next few days, no earlier than March 28,the National Aeronautics and Space Administration will attemptto launch an Atmospheric Structure Satellite (S-6) from CapeCanaveral, Florida, aboard the Delta launch vehicle.

The satellite will carry experiments to measure thedensity, composition, pressure and temperature of the atmos-phere at altitudes between 155 and 580 miles.

Primary mission of the satellite is atmosphericresearch. However, the direct temperature and pressuremeasurements to be made will also be useful in predicting theorbital characteristics of unmanned and manned spacecraftoperating in these altitudes.


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When atmospheric temperature increases, the atmospheregenerally tends to expand upward, thus increasing gas densitiesat higher altitudes. This thickening of the atmosphere increasesthe "drag" on spacecraft, markedly reducing their velocities ataltitudes below 600 miles, thus decreasing lifetimes in robit.The same effects would be experienced by manned spacecraftand winged or unwinged vehicles during re-entry operationsenroute to the surface of the earth.

T he Satellite Project, a part of the space explorationprogram of NASA's Office of Space Sciences, is managed by theNASA's Goddard Space Flight Center, Greenbelt, Md.

The launch can only be made during a three-hourperiod each day. On March 28, this will be between 9 p. m.and midnight EST. Each day thereafter, the "window" willslip about four minutes per day. The satellite is to belaunched during this nighttime period so that an earth sensorused for satellite attitude control will not accidentallyacquire the sun and be damaged by the intense solar radiation.A second sensor is provided to initially "lock on" the moon,and later switch onto the sun to provide earth-sun or earth-moon two-point references for correlation of scientific data.

The spacecraft is a spherically-shaped 35-inch-diametersatellite weighing 405 pounds. Its stainless steel shell isonly 25/lOths of an inch thick. It is to be placed into anorbit inclined 58 degrees to the earth's equator, and isexpected to have a useful lifetime of two to three months.-more-


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-3-If S-6 is successfully ori ed, at ;wt, ',. the six-

teenth straight success for the Delta \'ehic&e which ismanaged by the Goddard Space Flight Center.

The spacecraft will carry eight primiary detectors:two neutral mass spectrometers, -our vacizuin (pressure) gauges,and two electrostatic probes.

A neutral mass spectromet-:" counts electricallyneutral particles in space. It doe. this by breaking such par-ticles into positive ions and negative e ectrons. The X.P.'il-I'ngparticles are electrically charged and they are nmade to movethrough electric and magnetic fields of known strength. Theextent to which these particles are deflected by the fieldsdepends largely on the mass of the particles, and particleswith the same mass will be deflected along the same path.By placing a sensing device so that it intercepts this streamof particles, the number of particles can be counted. Sincethe field strength and location of the sensor is specific forcertain masses of particles, and since the mass of the ionis specific for each component that is ionized, selectedcomponents of the atmosphere can be identified.

Pressure gauges determine the atmospheric pressureby collecting, ionizing, and measuring the neutral particlesalong the satellite's orbit.


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The electrostatic probes measure the temperaturesof electrons and the density of positive ions along the orbit.The individual probe has in it two points of different electri-cal potential, that is,,a voltage difference is maintainedacross the spaces separating the two points. Since electronsand ions are charged partIcles, their passage across thepotential gap constitute a flow of electricity, a current thatcan be measured. The amount of the current is an indicationof the number of particles or density. Other characteristicsof this current depend upon the kinetic energy of theparticles, and this is an indication of their temperature.

Direct sampling of atmospheric constituents has beenaccomplished in the last four years through use of a few rocketsand satellites. Sputnik III, the first Russian satellite foratmospheric experiments, provided the first ion composition,gas density, and ion density data. Explorer VIII provided,through ion energy measurements, the first direct indicationof the presence of helium, making possible a correlation withsimilar indications from satellite drag measurements. TheP-21 probe to measure ionospheric electron density conductedby NASA-Goddard scientists in October 1961, for the firsttime, made direct measurements - - and thus positive identification -of helium and hydrogen ions were obtained.

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Measurements of the diurnal variations of neutralparticle density have been made with an instrument carriedby a Discoverer satellite. Measurements showed a factor offour variation in density on the daytime side of the earth

as compared to the nighttime side. This confirmed the fact,first obtained from satellite drag studies, that the earth's/atmosphere bulges on the sunlit side as a result of atmosphericheating.

But while such measurements have added to scientificknowledge of the high altitude regions, new and more preciseinformation is desired through use of the atmospheric struc-ture satellite.

The satellite is designed to be near "leak-proof,"thus minimizing contamination of the atmosphere of space asit orbits at a speed of more than five miles a second between155 to 580 statute miles. For example, at apogee internalsatellite pressure will be 1013 (1 followed by 13 zeros)times greater than the hard vacuum of space on the outside. Anygas leakage from the spacecraft would interfere with measure-ments of the tenuous space enviornment.

In addition to making sure that the gas sample is notcontaminated, the concentration of each constituent -- whether itbe helium, atomic nitrogen, atomic oxygen, molecular nitrogenor molecular oxygen -- must be measured throughout the satellitersorbit. These measurements may be interpreted in terms of ambientdensities and temperatures.

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-6-Complicating such measurements are the large dynamic

range of particle concentrations the instruments must acceptthroughout the orbit, and the possible alteration of a sampleby the presence of a hot cathode -- or other metallic orcatalytic surfaces of the spacecraft.

Electrical energy to the spacearaft will be suppliedsolely by approximately 150 pounds of silver-zinc chemical batteries,With all instrumentation on, the satellite will consume 110watts of power and can operate properly at this load for about70 hours. Since there is no data storage aboard the spacecraft,and since satellite "turn ons" will last about five minutes,several hundred data passes should be obtained. The scarcityof directly measured neutral particle values is such that onlyone or two days of data from this new spacecraft would more thandouble existing data.

A reasonable useful lifetime of the satellite will bebetween two and three months. When injected into orbit, thesatellite will be spin stabilized at 1.5 cycles per second.A planned inclination of 58 degrees from the equator will giveit a latitude extension to within several degrees of the ar6ticand antarctic regions. Orbit period will be 90 minutes.

The spacecraft carries an aspect system to determine theorientation of its spin axis against some reference plane. Thisinformation is needed to allow the experimenters to correctlyinterpret their data. The satellite's aspect system is designedto use either the sun or the moon, and the earth as references.

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-7-S-6 is the first scientific earth satellite containing

a new pulse code modulation telemetry system. This solidstate system provides an output pow;er of 500 milliwatts, and iscapable of supplying 40 separate channels of information indigital form.

Scientists will be able to make experiment selectionwhile the satellite is in orbit. Two independent commandreceivers will be used. Each one is capable of two independentcommands. Command A of each receiver will "turn on" thesatellite, while Command B of either receiver will cause theexperiment selector switch to move one position. Thus, fo rexample, each pair of primary detectors can operate aloneor in different combinations with other primary sensors. Suchexperiment selection, however, necessitates rapid data reduction.For this purpose, a microwave link has been installed betweenthe Blossom Point, Maryland, tracking station and the AtmosphericStructure Satellite Technical Control Center, located atGoddard.

PROJECT PARTICIPANTS

The Atmospheric Structure Satellite project is managedand directed by NASA's Goddard Space Flight Center, Greenbelt,Maryland for the Office of Space Science, NASA Headquarters.Most of the work on the spacecraft was done by Goddard'sSpacecraft Technology Division and the Aeronomy and MeteorologyDivision.

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-8-Prime contractor for the Delta vehicle is Douglas

Aircraft Company, Inc., Santa Monica, California, which isalso responsible for pre-launch and launch operations. Logisticsupport is provided by the Air Force Missile Test Center whichoperates the Atlantic Missile Range.Key personnel on the project are:NASA Headquarters

Dr. Homer E. Newell, Director, Office of Space SciencesDr. John Naugle, Director of Geophysics and Astronomy ProgramsDr. Robert F. Fellows, Chief, Chemistry ProgramsMaurice Dubin, Program Scientist, Office of Space SciencesEugene Ehrlich, Atmospheric Structure Satellite Project OfficerRichard Horowitz, Pressure Gauge ExperimenterT. B. Norris, Delta Program Manager

Goddard Space Flight CenterDr. Harry J. Goett, DirectorDr. John W. Townsend, Jr., Astistant Director, SS&AN. Whitney Matthews, Chief, Spacecraft Technology DivisionRobert Baumann, Chief, Spacecraft Integration & SoundingRocket DivisionWilliam Stround, Chief, Aeronomy and Meteorology DivisionNelson W. Spencer, Head, Physics Branch, Aeronoray andMeteorology Division, Project Managerand Electrostatic Probe ExperimenterJ. E. Cooley, Project CoordinatorCarl.A. Reber, Mass Spectrometer Experimenter

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George P. Newton, Pressure Gauge ExperimenterLarry Ho, Brace, Electrostatic Probe ExperimenterDonald F. Fitzpatrick, Shell and Mechanical AssemblyRobert Kidwell, Thermal ControlPaul C. Donnelly, Power SupplyJames Albus, Aspect SystemRonald M. Muller, TelemetryJoseph P. Corrigan, Ground Support SystemsJohn N. Libby, Control and Electronics SystemsChris C. Stephanides, Payload IntegrationWilliam D. Hoggard, Environmental Test and EvaluationAnthony G. Brozena, Delta LiaisonWilliam Schindler, Delta Project Manager

Principal commercial contractors involved in the S-6 Projectincludes:The Budd CompanyPhiladelphia, Penna. Satellite ShellConsolidated Systems Corp.Monrovia, Calif. Mass SpectrometerN. R. C. Equipment Corp.Newton, Mass. Redhead Vacuum GaugeWestinghouse Electron Tube Div.Elmira, New York Bayard-Alpert Vacuum GaugeYardney Electric CompanyNew York, New York Batteries

University Participant: Space Physics Research Laboratory,University of Michigan -- Electronics Atmospheric Structure

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Spacecraft and Supporting Flight EqidipmentThe size and shape of the spacecraft were selected to

fit the launch vehicle capability, to satisfy the missionobjectives by reducing possible detector interference fromthe spacecraft itself, and to permit that data analyses tofollow techniques successfully used on rockets, The mainjoint uses a copper shear gasket to preserve the satellite'spressure integrity. Stainless steel was used because ofits excellent vacuum properties. The mass spectrometers aremounted along the spin axis to insure that the spectra arenot disturbed by signal modulations due to the satellitetranslating and spinning. The two Langmiur probes, theaspect sensors, and two of the four vacuum gauges are moun-ted along the satellite equator. Since the ratio of in-ternal satellite pressure to outside pressure at apogeewill be iol3, and since significant gas leakage from thespacecraft can distort the measurements, extreme care wastaken in leak testing the satellite to insure pressureintegrity.Batteries

Electrical energy is supplied solely by approximately150 pounds of silver-zinc chemical batteries. With allinstrumentation on,-the satellite will consume 110 wattsof power and can operate properly at this load for about70 hours. Since there is no data storage aboard the satellite,

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-11-and since satellite "turn-ons" will last about five minutes,it is expected that several hundred data passes will beobtained. A reasonable useful lifetime will be between twoand three months.

Using batteries has posed several problems for thespacecraft. For example, because the satellite is herme-tically sealed some catalyst had to be included to reducethe buildup of internal satellite pressure resulting fromthe batteries outgassing. Another concern was that thesecells could not be tested fox capacity and recharged forflight. Not only Is the battery capacity reduced after asiecond charging, but its discharge characteristics changeenough to disturb some of the flight equipment.Aspect System

The function of the aspect system is to determine theorientation of the spin axis of the satellite against somereference frame. This information is needed to permit theexperimenters to correctly interpret their data. A fourcomponent aspect system is used, comprised of a digitalfan sensor, a slit fan sensor, a sun-moon switch, and twoinfrared earth sensors. The system is designed to useeither the sun or the moon, and the earth as referencesagainst which to locate the satellite spin axis.

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The digital fan sensor uses an optical masking tech-nique and six photodiodes to measure the angle of a lightsource viewed by the sensor. The slit fan, physicallylocated in the same housing as the digital fan, ie usedto accurately measure azimuth angles. The sun-moon switchreduces the gain of the amplifier when sunlight is viewedand restores full gain when the moon is the reference object.

The two earth sensors have a pencil beam of approx-1mately 20 solid angle and are mounted in the same housing.One sensor has. an elevation of 220 north of the equator,the other points 220 south of the equator. These earthsensors operate in the seven to fifteen micron region anddetect the discontinuity at the earth's horizon. Prior tolaunch, steps will be taken to insure that the satelliteis stable about its predetermined axis of rotation. Thebattery and electronics packages are distributed to insuremaximum moment of inertia about this axis. The measuredratio of the polar moment of inertia to that about a trans-verse axis is approximately 1.2. The spin rate will be setnominally for 1.5 rotations per second. A mutation damperis included in the spacecraft to eliminate any mutationmotion which may appear. If the satellite should becomeunstable and tumble- many 'light objectives will still bemet but the data analysis job will be"more difficult.

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The Atmospheric Structure Satellite is the firstscientific earth satellite containing a pulse code mod-ulation (PcM/PM) telemetry system. Previous satellitesused the PFM-AM system. This solid-state PCM system willprovide an output power of 500 milliwatts, and is capableof supplying 40 separate channels of information in digitalform. Each channel consists of 20 words per second, eachword consists of nine bits. Three channels are devoted tosixteen channel subcommutation, and two channels are devotedto a zero and five volt reference level. The turnstileantennas provide an approximate omnidirectional pattern withKowsxpected to be less than about four db. They will beused with the command receiver, tracking transmitter, andthe telemetry system.

TrackingThe satellite will be tracked by NASA's world-wide

Scientific Satellite Network (SSN). Preliminary calcula-tions indicate that for the planned orbit, the spacecraftwill initially average daily more than 30 proper passesover the ground stations. A proper pass means that thesatellite will be above an elevation of 100 for more thanfour minutes.

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-1 .-Provisions have been made to permit experiment vej.oc-

t,.Ion while the satellite is in orbit. Two independentci;aand receivers are used, each capable of two independentc lemands*. Command A of each receiver will effect "turn-on"vt t.e satellite, while comnand B of either receiver willCause the experiment selector switch to move one position.Thus, for example, each pair of primary detectors canoperate alone, in different combinations with other primarysensors, etc. The different allovwable I-ombinatc.ons pemlitresolution of possible interference between the variousdetectors. While equipment "turn-on" is controlled fromthe ground, "turn-off" of all equipment is automatic, andprodtced from on-board instFrumentation to insure that poweris not wasted because the satellite passes out of the rangeof' the command receiver. The advantage of experiment selec-tion .ecessiitates rapid data reduction. 1"or this purpose,a microwave link has been installed between the BlossomPoint, Marylands SSN station and the Atmospheric StructulreSatellite Technical Control Center at Goddard.

TM DELTA BOOSTERThe 90-foot, 57-ton, three-stage Delta booster, devel-

oped by NASA, will be used to launch the S-6 spacecraft.Considered the nation's most reliable space booster, Deltawill be reaching for its 16th consecutive successful launchoperation. This will be its 17th launch attempt.

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Delta's first stage is the Douglas Aircraft Company'sDM-21 Thor, a 57-foot, liquid-fuel rocket which generates170,000 pounds thrust during its burning time of two minutesand 25 seconds.

The liquid fuel second stage, produced by AerojetGeneral, has a 7,500 pound-thrust engine which burns forabout 160 seconds. Guidance system for the second stageis the Bell Telephone Laboratories Series "600" system.The S-6 mission calls for the Delta to coast for 57 secondsafter second stage burn out.

The third stage is an M1PP-X-248 solid >`Iel, 3,000-pound thrust engine with a Zrningtime of about 4) seconds.It is producqd by the Neval Propellant Plant.

The Delta flight sequence is as followz. After burnout,the spent first stage falls away. T"he second stage ignitesimmediately. Thirty seconds after necond Stage ignition,the nose fairing covering the taird stage and the payloadis Jettisoned. After virnouts the vehiole begins its 57-second coast period. Thn, the thir'u stage is spin stabi-lized, the empty second stile falls away, and third stageignition occurs. At this poialt the rocket achieves orbitalvelocity of about 17,000 miles and hour, third stage separa-tion then takes place, and the payload is pushed into itsorbit.

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Delta program management is by the Office of SpaceSciences, NASA Headquarters.

Project management of the Delta program is charged tothe Goddard Space Flight Center, Greenbelt, Md. William R.Schindler is the Goddard Delta Project Manager. Primecontractor for the Delta is the Douglas Aircraft Company,Santa Monica, Calif.

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Atmospheric Structure Satellite S-6 Press Kit

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