sage press kit

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Washington. DC. 20546AC 202 755-8370

For Release IMMEDIATE

Press Kit Project Stratospheric Aerosoland Gas Experiment(SAGE)RELEASE NO: 79-6

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RELEASE NO: 79-6

CONTENTS

GENERAL RELEASE .............................. 1-6BACKGROUND ................................... 7ROLE OF NIMBUS-7 EXPERIMENT .................. 8GROUND TRUTH MEASUREHENTS.....................DATA COLLECTION AND PROCESSING ............... 9MISSION DESCRIPTION .......................... 9-10SAGE INSTRUMENTATION ......................... 11-14THE SPACECRAFT ............................... 15-17LAUNCH SEQUENCE .............................. 18SAGE EXPERIMENT TEAM MEMBERSHIP .............. 19

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

Fo~r Releasseick McCormackHeadquarters, Washington, D.C. IMMEDIATE(Phone: 202/755-2070)

John KleyGoddard Space Flight Center, Greenbelt,, Md.(Phone: 301/344-8955)

Keith KoehlerLangley Research Center, Hampton, Va.(Phone: 804/827-2934)

RELEASE NO: 79-6

SAGE TO EXAMINE EARTH'S STRATOSPHERE

A 14 7-kilogram (324-pound) spacecrz.ft will be launchedby NASA Thursday, Jan. 25 to obtain data on the aerosols andozone in the stratosphere. Called SAGE, for StratosphericAerosol and Gas Experiment, the applications satellite willbe lifted into orbit from Wallops Flight Center, WallopsIsland, Va., by a four-stage Scout launch vehicle.

The SAGE mission is international in scope, as its findingswill be checked against extensive "ground truth" measurementsconducted by special teams in the U.S., Japan and Europe.

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2 ;Worldwide concern has developed in recent years overthe environmental quality Of the stratosphere, that regionof the Earth's atmosphere beginning above cloud tops at about12 kilometers (8 miles) and extending to approximately 50 km(30 mi.). The stratosphere is a very fragile and importantportion of the Earth's environment; its ozone, for example,is known to protect the Earth and its inhabitants from muchof the Sun's ultraviolet (UV) radiation.

The stratosphere also contains a layer of dust-likeparticles, or aerosols, that are concentrated below the ozonepeak. Aerosols, small solid particles or liquid droplets sus-pended in the surrounding air, are typically less than onemillionth of a meter in diameter.

The aerosol layer acts somewhat like a filter by reducingthe amount of sunlight that reaches the Earth's surface andthe amount of reflected sunlight that eventually escapes tospace. Small changes in aerosol concentration may causechanges in climate with important implications for agriculture.

Concerns have developed that man's industrial andtechnological activities on and above the Earth may lead toaerosol and gas buildup in the stratosphere, causing unknownand possibly adverse affects to life on the Earth's surface.-more-


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Pesides man-made injections directly into the ptra-tosphere, aerosols and gases are generated in the tro-posphere (starting at the Earth's surface and extendingto the stratosphere) by processes that are on.y partlyunderstood,

The main objective of SAGE is to obtain and useglobal data on stratospheric aerosols and qzone invarious studies concerning the Earth's climate and en-vironmental quality. The mission is designed to obtainthis data from tropical to high latitudes for a period ofat least one year.

Comparable aerosol data for the polar regioni is beingE obtained by a Stratospheric Aerosol Measurement (SAM-II)experiment on the Nimbus-7 satellite, launched Oct. 24, 1978

The information will complement the SAGE data base.The SAGE experiment aboard the Applications Explorer

Mission-B (AEM-B) spapecraft will obtain its informationby means of a photometric device. Flying at a 600-km(370-mi.) altitude in a circular Earth orbit,t'he SAGE photometer "looks" at the Sun through thestratosphere's gases and aerosols each time the satel-lite enters and leaves the Earth's shadow.

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I The device will "see" approximately 15 sunrisesand 15 .sunsets each 24-hour day. The photometer records,in four color bands, the light as it fades in a sunsetand brightens in a sunrise. This information is con-verted to define concentrations of the atmospheric con-stituents, namely ozone and aerosols. The four differentSAGE color bands are centered at 1.0, 0.60, 0.45, and0.38 micrometers from the near infrared (IR) .o bluebands of the electromagnetic spectrum.

According to the SAGE experiment scientist, Dr.M. Patrick McCormick of NASA's Langley Research 'enter,Hampton, Va., the satellite's ozone measurements, whencombined with other measurements, will help confirmor negate the predicted chlorofluormethane (CF1M1) effecton ozone depletion. Current models or theories predictthat, if the CFM releases into the atmosphere were tocontinue at the 1975 rate, 8 to 30 per cent of the glo-bal ozone would eventually be destroyed with the greatestrelative reduction occurring between 35 to 45 km(22 to 28 mi.). This region will be measured with1 km (0.6 Mi.) vertical resolution and high accuracy bySAGE.

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The aerosol populatioan in the stratosphere, on theother~hand, is changed.abruptly by large.volcanic erup-tions which spew particlew,.apd gases into.this.regioncreating optical e~fecj.s (e.g.., -prolonge i and olorfulsunsets) - ;n4dpossible cooling at the Earzth's *surface.Since trends in environmental quality or 'climat:areusually masked by daily and seasonal variations, ittakes a very long period Ef time to delineate them,says McCormick. Thus, a vo.canic eruption duringSAGE's meastrement lifetime, would provide a' niqueopportunity for sqjentipts to study the long-termdistribution throughout the stratosphere of high-vqlumeaerosols and other gases from a single point source.

The NASA Headquarters Environmental ObservationsProgram has overall responsibility for the AEM/SAGEprogram. The NASA Goddard Space Flight Center, Greenbelt,M~i., is responsible for project management of the spage-raFt, scientific planning and coordination, and thetracking And data acquisition system, NASA Langley isresponsible for the instrument module systems and theScout launch vehicle. The NASA Wallops Flight Centerat WalJops Island is responpiblp for the launching and

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Boeing Aerospace Co., Seattle, a division of theBoeing Co., built the spacecraft. Ball Aerospace Division,Ball Corp., Boulder, Colo., built the SAGE radiometerunder contracts administered by GSFC and LARC. VoughtCorp., Dallas, a subsidiary of LTV Corp., built theScout launch vehicle.

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(ENID OF GENERAL RELEASE. BACKGROUND INFORMATION FOLLOWS.)

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BACKGROUND

Aerosols and ozone play an important role in the radia-tion balance of the Earth's environment on a global scale.There is serious concern that industrial and aviation activi-ties may lead to aerosol and gas entrapment and buildup inthe stratosphere where constituents have residence times ofthree to five years.In addition to natural or anthropogenic injections, aero-sols and gases are generated by the atmosphere's chemistrythrough processes that are only partly understood. These, aswell as unknown factors, determine not only the stratosphere'saerosol and gaseous content but also its changeable character.How much radiation the pollutants absorb, for example, is un-known because of ignorance about the optical properties of theaerosols themselves and their global distribution.The concentration and distribution of ozone and, there-fore, the ultraviolet radiation that reaches the Earth's sur-face must be better understood. Scientists know that: aerosolsand lower stratospheric ozone act as tracers for circulationand transport phenomena; certain gases act as precursors formany of the aerosols; and the presence of aerosols may changethe radiation fluxes in the ozone layer significantly. Verylittle is known, however, about the stratospheric aerosol orits optical properties. If one is going to determine the im-pact of new additions to the stratosphere, one must determineon a global basis: (1) the natural background or ambient con-stituents; (2) the aerosol and gaseous sinks; and (3) theaerosol and gaseous sources, both natural and anthropogenic(related to the activities of mankind).Concern over the environmental quality of the stratos-phere has been displayed recently by a sizable portion of thescientific community. New multi-million dollar internationalprograms to study the stratosphere (e.g., the Department ofTransportation's Climatic Impact Assessment Prvgram) haveemerged.An evolution of new measurements is taking place concern-ing stratospheric gases, photo-chemical and chemical rate co-

efficients, ozone and submicron particulates. Many of thesenew measurements are being accomplished through the use ofcumbersome laboratory equipment with stratospheric platformsprovided by balloons and high-flying aircraft. Such measure-ments are not done quickly enough for many purposes not on aglobal basis. Both aspects are considered necessary foraccurate monitoring. As a result, it is expected that moni-toring will need to be done from space through remote-sensingtechniques.-more-


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IA DATA COLLECTION AND PROCESSINGThe SAGE sensor will measure the attentuation of theolar intensity by the limb of Earth's atmosphere in foureparate wavelength bands during each spacecraft sunrisend sunset. With proper correction for atmospheric refrac-ion effects, using measured or standard atmospheric tem-erature profiles, and solar limb darkening effects, datarom each spacecraft sunrise and sunset will be bonvertedo an intensity versus atmosphere tangent altitude profile.Data from the SAGE instrument will'bed stored on-boardhe satellite and transmitted to a ground station once peray or more frequently, depending upon stdrage capacity anduration of events. Data will be gathered for'a period oft least 12 months. Data collection will be the responsi-ility of the Goddard Space Flight Center Networks Direc-orate. SAGE raw data, along with orbital parameters syn-hronized to a common' time base, will be provided to thexperiment scientist at Langley Research Center.

The Goddard processed data will'be reduced and analyzedt Langley utilizing computer programs developed at Langleynd operational on Langley computers. The raw data will beonverted first to measures of physical quantities and sub-equently presented in a manner to permit the most rapidnderstanding of the physical processes being studied.A SAGE Experiment Team (SET) has been created and wille involved in developing the data analysis techniques sohat the resulting data products and software will representstep toward truly operational methods.Data from the SAGE instrument will be forwarded to theASA National Space Science Data Center (NSSDC) at Goddardor archiving and distribution to other agencies and thecientific community on request.

MISSION DESCRIPTIONThe Earth-orbital SAGE mission is to map vertical pro-iles in the stratosphere of ozone, aerosol, nitrogen dioxidend molecular extinction in a wide band around the globe.he ozone data will extend from about 9 to 46 kilometers6 to 29 miles); aerosol data from the cloud tops to 35 km22 mi.); nitrogen dioxide data from about 25 to 40 km (16o 25 mi.); and molecular extinction from about 15 to 40 km9 to 25 mi.).

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SAGE will lock on to the Sun as the spacecraft exper-ience3 a sunrise or sunset and measure the Sun's brightnessat four wavelengths. This information is interpreted interms of vertical profiles of the atmospheric constituentthat attenuated or dimmed the sunlight. Thirty profiles perday will be obtained in this manner spread over latitude andlongitude. Over a year, 10,000 profiles will be measuredfrom 78 degrees south to 78 degrees north latitude.The main objective of SAGE is to obtain measurements ofglobal, spatial and temporal distributions of stratosphericaerosols and ozone, and to use these to study their effectson the Earth's radiation budget and environmental quality.From SAGE data and ground truth information, researchersexpect to conduct the following investigations:* Map vertical extinction profiles of stratosphericaerosols and ozone globally from 78 degrees southto 78 degrees north latitude.* Determine global concentrations of aerosols andozone and their spatial distribution.o Determine the optical properties of stratosphericaerosols.* Investigate transient phenomena.* Determine hemispherical differences.* Investigate transport phenomena.* Investigate the tropospheric-stratospheric exchange.* Determine the radiation effects of stratosphericaerosol and ozone on the global climate and avail-able solar energy.

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SAGE INSTRUMENTATIONThe SAGE sensor is a four-spectral channel radiometerwhich measures the extinction of solar radiation during solar occultation. As the spacecraft emerges from the Earth'shadow during each orbit, the sensor will acquire the Sunand measure solar intensity in four wavelength bands centeredat 0.385 micrometers (um), 0.45 um, 0.6 um and 1.0 um.As the spacecraft continues in orbit, the line of sightrom the spacecraft to the rising Sun will scan the Earth's atmosphere, resulting in a measurement of the attenuatedsolar intensity at different atmospheric layers. Theprocedure will then be repeated in a reverse sense duringpacecraft sunset.Each sunrise and sunset will be monitered from the top ofhe clouds to approximately 60 km (37 mi.) above the Earth'surface. The sensor has an instantaneous field of view ofpproximately 0.5-arc minutes, which corresponds to approximately.5 km (0.3 mi.) measured at the horizon for a GOO km (372 mi.)rbit.The dynamic range of each radiometric measurement at theorizon is approximately 3,000 and the uncertainty in anyadiometric measurement is specified to be less than 0.1 perent of the unattenuated solar intensity. The sensor isartly self-calibrating in that a measurement of theunattenuated solar intensity is made before each spacecraftsunset or after each spacecraft sunrise.

The instrument module consists of optical and electronicubassemblies mounted side by side. The optical assemblyconsists of a flat scanning mirror, Cassegrain optics anddetector package.The solar input is reflected from the scan mirror throughhe Cassegrain telescope, which produce a solar image upon# the science detector aperture. The radiation through theperture is dispersed by a holographic to four silicon photoiode detectors. The outputs of the detectors are fed tosignal conditioning amplifiers. Their outputs go to thePCM encoder, which multiplexes and digitizes the signalsand then transfers data to the AEM-B data system.

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Instrument module characteristics follow:Detector wavelength 0.385, 0.45, 0.6, 1.0 micronsField of view 0.15 milliradians (0.5 km)Altitude range 10 to 100 km aboveEarth horizonAltitude resolution 1 kmDetector operatingtemperature 19 deqrees to 30 degrees CScan rate 15 km/secSampling rate 64 samples/secInformation bandwidth 1 Hz/km/channelRadiometer resolution 3000 : 1S:N Ratio (1.0 micronchannel) 1.5 X 105 at peak

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THE SPACECRAFTThe SAGE AEM-B is a small, vest lowcottyepacecraft which uses three low-cost viewing instruments The structure primarily consists of tWoajor components: a base module which contains the necessaryttitude control, data handling, communications, command and

Boasemodule.(5 n.

subsystems for the instrument and an instrumentodule containing the spectrometer and its supporting equip-ent. T solar paddles for converting sunlight to electricityxtend from the structure.

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tum into increased momentum of the Yo-yo:weights and cables.eight release will be 'initiated by the spacecraft timer'soonfter the Scout's fourth-stage burnout.Spacecraft characteristics follow:Shape: Six-sided prismHeight:

Base module: 64.0 cm (25 in.)Overall heightincluding antenna: 161.85 cm (63.7 in.)

Weight:

lb.).Base module and adptr 10,.2 kg 23 l.)

Spacecraft total: 147.0 kg (324 lb.)

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:SAGE ORBIT

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D -18-LAUNCH SEQUENCE

The Scout vehicle is equipped with a preprogrammedguidance system where each expended stage separates from thevehicle on a timed sequence. The payload is protected from- the high aerodynamic pressures and temperatures duringascent by a two-piece heatshield which is ejected just prioreo third stage ignition.Event Time (Seconds)Lift-off 0.00Stage 1 burnout 82.93Stage 2 ignition andStage 1 separation 87.87stage 2 burnout 127.211Heatshield ejection 155.39Stage 3 ignition andStage 2 separation 3,7.39Stage 3 burnout 190.97Stage 3 separation 605.86Stage 4 ignition 610.71Stage 4 burnout 644.02

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-19-SAGE EXPERIMENT TEAM MEMBERSHIP

Institute of Atmospheric PhysicsUniversity of Arizona, TucsonDr. David G. MurcrayUniversity of DenverDept. of Physics & AstronomyDr. Theordore J. PepinDept. of Physics & Astronomy

tUniversity of Wyoming, LaramieDr. Derek M. ConnoldMassachusetts Institute of TechnologyDept. of Meteorology, CambridgeDr. Philip B. RusselltAtmospheric Sciences LaboratoryStanford Research Institute, Menlo Park, Calif.Dr. Walter G. PlanetNational Oceanic and Atmospheric AdministrationNational Environmental Satellite ServiceSatellite Experiment Laboratory, Suitland, Md.Dr. Gerald W. GramsSchool of Geophysical SciencesGeorgia Institute of Technology, AtlantaDr. D. E. MillerHigh Atmospheric BranchMeteorological Office, Bracknell, United KingdomTeam Leader & Experiment ScientistDr. M. P. McCormickInstrument Research DivisionNASA/Langley Research Center,. Hampton, Va.

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