nasa facts how we get pictures from space

8/6/2019 NASA Facts How We Get Pictures From Space

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#NASA-NF-1S1/8-86)PICTURES FROM SP CENTI S II C A 21M F 1

NASA FACTS: HOW WE GEINAS A) 12 p Av a ~ l : cseL 22N87-29903

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combined through computerenhancement The 'mill mage Shawsthat the brightest or epsilon ring at thetop IS nelJtral mcolor, with the (amtereight other rm9s shoWing colordifferences between them. SCientistswill use this color information to try tounderstand the nature and origin of the"ng material.

On Miranda, two types of te"am canbe seen: cratered and grooved. Thedark area was visible several daysbefore the Voyager's closest approach.Scarps, or cliffs, along the limbs have arugged relief several kilometers high.

The surface of Uranus IS almost voidof contrastmg features. Here, however, adistinct cloud (lower left) is shown as abright streak near the planets 11mb Togam thiS resolution, however, the Imagehad to be so highly enhanced that faintblemishes on the camera lens appearedas donut-shaped features (as seen onthe top and to the right of the Image).

OR1GlNAl NIl.COLOR PHOTOOfMPH

ince the first cavedweller ventured out togaze up at the night sky,mankind has sought toknow more about themysterious images hesaw there. Being limited by what hecould see with his naked eye, this earlystar gazer relied on his intellect andimagination to depict the universe. Heetched images in stone by hand,measured and charted the path of thewanderers he watched, and becameas familiar with them as his limitedtechnology would allow.Although traveling down somewrong turns over the centuries,mankind began to overcome his limitsone by one. The images he could seeexpanded dramatically when Galileopeered through the first telescope andsaw the "cup handles" of Saturn.Bigger and more powerful telescopeswere built , sharpening images stillfurther and answering some of thecontinuing mysteries as well asunfolding new ones.In the 1950s, mankind's view of theheavens reached beyond theobscuring atmosphere of Earth asunmanned spacecraft carried camerasand data sensors to probe moons andplanets of the Solar System. Imagesthese vehicles sent back to Earthmade most previous visual planetaryobservations from the Earth 's surfaceobsolete. Spacecraft s flew close toplanets, orbited them, and somelanded. They provided scientists withexceptionally clear and close views ofplanets and moons as far away asSaturn. In January 1986, the Voyager 2spacecraft flew close to the planetUran us and re turned the first close-upimages of this distant wanderer toscientists on Earth. Voyager is now onits way to Neptune for close-up viewsin 1989 of an object we can barely seefrom Earth.The knowledge humans have todayof ou ter space would astound Galileo.Spacecrafts have sent back pictures to

Earth-bound scientists of a crateredand moon-like surface on the planetMercury and revealed circulationpatterns in the atmosphere of Venus.From Mars, they have sent backimages of craters, giant canyons, andvolcanoes on the planet's surface.Jupiter's atmospheric circulation hasbeen revealed, active volcanoes on theJovian moon 10 have been seenerupting, and previously unknownmoons and a ring circling the planetdiscovered. New moons were foundorbiting Saturn and the Saturnian ringswere resolved in such detail that over1 000 concentric ring features becameapparent. At Uranus, Voyager sentback details of a multi-colored ringsystem with sheparding moons, and

Planetary radio astronomyand plasma wave antenna (2)

Radioisotope thermoelectr icgenerator (3)


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measured a magnetic field that is tilted55 from the planet 's axis of rotation ,These discoveries and thousands ofothers like them were made possiblethrough the technology of telemetry,which is the technique of transmittingmeasurements to distant locations,Measurements made on board aspacecraft may be telemetered to adistant receiving station , such as ahuge dish antenna on Earth, Telemetryincludes th e spacecraft technology forscanning objects in space andtransmitting images to Earth,Low- fie ld magne tome ter

High -ga in ant enna(3,7 meter diameter)

A canning system on board thespacecraft measures reflectedlight from a planet or moon asit enters the spacecraft's opticalsystem, A computer converts themeasurements into numerical data,which are transmitted to a receiver onEarth by radio waves, On Earth,computers reassemble the numbersinto a picture,Because the measurements aretaken point by point , the images fromspace are not considered "true"photographs, or what photographerscall a "continuous tone ," but rather afacsimile image composed of a patternof dots assigned various shades fromwhite to black, The facsimile image ismuch like the halftones newspapers,and even the printers of this booklet,use to re create photographs, (If youexamine one of th e pictures in thisbooklet with a magnifying glass, youwill see that it is composed of manysmall , various shaded dots,)Even more closely related to the wayimages are rece ived from space is theway a tel evision set works, For apicture to appear on a television set , amodulated beam of light rapidly

Infraredspec trometerand radiometer

Pla sma

Ultraviole tspecectrome ter

illuminates long ro ws of tiny dots, fillingin one line then the next until a pictureforms, These dots are called pictureelements, or pixels for short, and thescreen surface where they are locatedis called a raster. Raster scanningrefers to the way the beam of light hitsthe individual pixels at variousintensities to re create the originalpicture, Of course, scanning happensvery fast , so it is hardly perceptible tothe human eye, Images from spaceare drawn in much the same manneron a television-like screen (a cathoderay tube ),Although cameras on a spacecraftprobing the Solar System have muchin common with those in motion picturestudios, they also have their share ofdifferences, For one, the space-boundcameras take much longer to form andtransmit an image, While this mayseem like a disadvantage, it is not. Theimages produced by the slowscanning cameras are of a muchhigher quality and contain more thantwice the amount of informationpresent in a television picture,The most enduring image gathererin space has been the Voyager 2spacecraft. Voyager carries a dualtelevision camera system, which canbe commanded to view an object witheither a wide-angle or telephoto lens,The Voya ger spacecraft weighs 795kilograms, Of th is, 113 kilograms arescientific instruments, Th e large dishantenna measures 3,66 meters in diameter.A gold-p la ted copper record of Earthgreetings, sights, and sounds is attached tothe cra ft inside a gold-plated aluminumcanister, which has instruction symbols onits face, On the boom at the left are thenuclear power generators and above thisboom is the 13-meter magnetometer boom.Th e boom to the right con tains the opticalequipmen t, including the camera and othersensors, Two 1O -meter whip antennas,which study planetary radio astronomy andplasma waves, extend from thespacecraft's body below the magnetometerboom.

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The system is mounted on a scienceplatform that can be tilted in anydirection for precise aiming. Reflectedlight from the object enters the lensesand falls on the surface of a seleniumsulfur vidicon television tube, 11millimeters square. A shutter in thecame ra controls the amount of lightreaching the tube and can varyexposure times from 0.005 second forvery bright objects to 15 seconds orlonger when searching for faint objectssuch as unknown moons.

The vidicon tube temporarily holdsthe image on its surface until it can bescanned for brightness levels. Th esurface of the tube is divided into 800parallel lines, each co ntaining 800pixels, giving a total of 640 ,000. Aseach pixel is scanned for brightness, itis assigned a number from 0 to 255.This range (0 to 255) was chosenbeca use it coincides with the basicway a computer operates. In acompu ter, information is read in unitscalled "bits" and "bytes." A bit containsone of two possible values , and canbest be thought of as a tiny on-offswitch on an electrical circuit. A byte,on the other hand, contains the totalvalue represented by 8 bits. This valuecan be interpreted in many ways, suchas a numerical value, an alphabetcharacter or symbol, or a pixel shadedbetween black and white. As each bitis set either "on" (a value of 1) or "o ff"(a value of 0) , the value of the byteincreases or decreases in multiples of2 (2x2x2x2x2x2x2x2, or 28 or 256).Keep in mind, 8 binary digits, insequence, represent a doubling ofnum erical value. The Binary Table onthe right shows how bits are arrangedaccording to their value.Each byte, therefore, can contain a"binary" va lue from 0 to 255, with 0being one of its possible 256 values. Ifo epresents pure white, and 255 pure

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Jupiter5 Mar 79

The Voyager missions began August 20, 1977, from Cape Canaveral, Florida. Two probeslaunched 16 days apart were to explore the outer planets, returning images and data.Both explored Jupiter and Saturn and their moons, but Voyager 1 veered up out of theecliptic plane to return data on fields and particles it encounters, while Voyager 2 flew onto encounter Uranus. It sent back striking images of this planetary system which is barelyvisible from Earth. Voyager 2 i s now on its way to Neptune and should arrive in late 1989.

Binary TableBit of Data 8 7 6 5 4 3 2Sequence Value 128 64 32 16 8 4 2 1Binary Value 0 0 1 0 1 1 0 1Byte Value 0 + 0 + 32 + 0 + 8 + 4 + 0 + 1 45

Seguence Value 128 64 32 16 8 4 2Brightness Values Binar:t Values

0 (white) 0 0 0 0 0 0 0 09 (pale gray) 0 0 0 0 1 0 0 162 (g ray) 0 0 1 1 1 1 1 0183 (dark gray) 1 0 1 1 0 1 1 1255 (black) 1 1 1 1 1 1 1 1


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~ S u n - Earth

Ariel

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Flight path ofVoyager 2

occultation zonesClosest approachto Uranus (0 hrs)

Previous planetary encounters for the Voyager spacecrafts were almost leisurelyexcursions. At Saturn, for example, the spaceship encountered one planetary feature at atime, exploring it before focusing on the next, until it had photographed all it could.Howeve r, at Uranus the planetary system is tilted almost 90 0 to the planetary plane. Forthis reason Voyager has been compared to a dart tossed at a bull's-eye, passing thecenter, the outer rings, and virtually everything at the same time. This meant cameras hadto scan many areas very quickly to catch even scant glimpses of features, because thespacecraft wouldn't have a second chance.

black, then th e values between willrepresent subtle shades of gray.When th e va lues for all the pixelshave be en assigned, th ey are eithersent directly to a receiver on Earth orstored on magnetic ta pe to be sentlater. Data is stored when radiocommunications between the Earthand the spacecraft are temporarilyblocked , such as when Voyagerpasses behind a planet or moon. Foreach image, and its total of 640,000pixels , 5,120,000 bits of data must betransmitted (640,000 x 8). WhenVoyager flew close to Jupiter, data wastransmitted back to Earth at a rate of

more than 100,000 bits per second .This meant that once data beganreaching the antennas on Earth'ssurface, information for completeimages was rece ived in about 1 minutefor each transmission.As the distance of the spacecraftfrom Earth increases, the quality of theradioed data stream decreases.However, by lowering the rate at whichVoyager transmits its data, controllersreduce to an acceptable level theamount of noise that will arrive mixedwith the signal.For the Uranus encounter, scientistsand engineers devised a techniquethat allowed Voyager to transmit morethan 200 images each day. To do this ,they reprogrammed the spacecraft enroute. Instead of having Voyager

transmit the full 8 bits for each pixel, itscomputers were instructed to sendback only the differences betweenbrightness levels of successive pixels.Th is reduced the number of data bitsneeded for an image by about 60percent. By slowing the transmissionrate , noise did not interfere with theimage reception, and by compressingthe data, a full array of striking imageswere received. The computers atNASA's Jet Propulsion Laboratoryrestored the correct brightness to eachpixel, producing both black-and-whiteand full-color images.

T he radio signals that aspacecraft such as Voyagersends to Earth are received bya system of large dish antennas calledthe Deep Space Network (DSN). TheDSN is designed to provide command,control, tracking, and data acquisitionfor deep space missions. Configuredaround the globe at locationsapproximately 120 0 apart, DSNprovides 24-hour line-of-sightcoverage.Stations are located at Goldstone,California; Madrid, Spain; andCanaberra, Australia. The total DSN ,managed by NASA's Jet PropulsionLaboratory in Pasadena , California,consists of three 64-meter (2 10-ft)diameter dish-shaped antennas, five34-meter (111-ft) diameter antennas,and three 26 -meter (85-ft ) antennas.As antennas at one station losecontact, due to Earth's rotation ,antennas at th e next station rotate intoview and take over the job of receivingspacecraft data. While one station istracking a deep space mission, suchas Voyager, the other two are busytracking spacecraft elsewhere inthe sky.During Voyager's contact withSaturn , the DSN recovered more than99 percent of the 17,000 imagestransmitted. Th is accomplishment5


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ORIGINAL PAGECOLOR PHOTOGRA


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ORIG !NAL PAGECOLOR PHOTOGRA PH

NASA's Deep Space Network consists of huge dish antennas like these positioned at three receiving stations around the globe. Thestations in Goldstone, AZ; Madrid, Spain; and Canaberra, Australia, track the spacecraft as it speeds through deep space. The farther thespacecraft travels away from Earth, the weaker its s(gnal becomes. To compensate for th is weaker signal, the antennas are electronically"arrayed" so that two or more antennas focus on receiving the same signal. Arraying not only increases the apparent strength of thesignal, but also gives valuable information about the spacecraft's speed and distance.

required the use of a technique knownas "antenna arraying." Arraying for theSaturn encounter was accomplishedby electronically adding signalsreceived by two antennas at each site.Because of the great distance Uranusis from the Earth, the signal receivedfrom Voyager 2 was only one-fourth asstrong as the signal received from

Saturn. A new arraying technique,which combined signals from fourantennas, was used during the Uranusencounter to allow up to 21 ,600 bits ofdata to be received each second.T he DSN was able to trackVoyager's position at Saturnwith an accuracy of nearly 300kilometers (about 200 miles) during itsclosest approach. This accuracy wasachieved by using the network 's

radiometric system, the spacecraft'scameras, and a technique called VeryLong Baseline Interferometry, or VLBI.VLBI determines the direction of thespacecraft by precisely measuring theslight difference between the time ofarrival of the signal at two or moreground antennas. The same techniquewas used at Uranus to aim the

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spacecraft so accurately that thedeflection of its trajectory caused bythe planet's gravity would send it onto Neptune.When the DSN antennas receive theinformation from the spacecraft,computers at the Jet PropulsionLaboratory store it for future use andreassemble it into images. To recreatea picture whose image has been sentacross the vacuum of space,computers read the data bit by bit,calculating the values for each pixeland converting the value into a smallsquare of light. The squares aredisplayed on a television screen thatduplicates the vidicon screen on thespacecraft: a grid 800 lines by 800pixels, or 640,000 pixels for the fullimage. The pixels are lighted up one ata time until the screen is full. Theresulting image is a black-and-whitefacsimile of the object being measured.

C olor images are composedusing the same telemetrictechnology as for black-andwhite images. However, instead oftransmitt ing just one image, threeimages are sent in rapid successionfor each picture Measurements aretaken through colored filters: onethrough blue, one through green , andone through orange. Filters havevarying effects on the amount of lightbeing measured. For example, light thatpasses through a blue filter will favorthe blue values in the image makingthem appear brighter or transparent ,whereas red or orange values willappear much darker than normal. OnEarth the three images are given theappropriate colors of the filters throughwhich they were measured and thenblended together to give a "true" colorimage.

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ORIG!NAL PAGECOLOR PHOTOGRAPH

This image of the coma of Comet Halley was sent to Earth from the Pioneer Venusspacecraft and was compiled from more than 20,000 separate vertical ultraviolet scans.The coma, or cloud of gases surrounding the nucleus, is 20 million kilometers in diameter.Concentric areas show decreasing brightness from the comet's center outward. Data wascollected and beamed to Earth on February 2-5, 1986.


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An important feat the interplanetaryspacecraft must accomplish isfocusing on its target while traveling atextremely high speeds. Voyager hurtledpast Uranus at more than 40,000 milesan hour. To get an unblurred image, thecameras on board had to steadily tracktheir target while the camera shutterswere open. The technique to do this ,called image-motion compensation,involves rotating the entire spacecraftunder the control of the stabilizingcomputers. The strategy was usedsuccessfully both at Saturn's moonRhea and at Uranus. Both times ,cameras tracked their targets withoutinterruption.Once the image is reconstructed bycomputers on Earth, it sometimeshappens that objects appearnondescript or that subtle shades inplanetary details such as cloudtopscannot be discerned by visualexamination alone. This can beovercome, however, by adding a fina l"enhancement" to the production. Theprocess of computer enhancement islike adjusting the contrast andbrightness controls on a television set.Because the shades of the image are

ORIGINAL PAGEcc: '-''-' .' t '"\T"""''- ' ' r-,'-fIn January 1986, Voyager 2 made itsclosest encounter with the planetUranus. It returned never-before-seenclose-up views of a planet barely visiblefrom the Earth 's surface.

broken down into picture elements, thecomputer can increase or decreasebrightness values of individual pixels,thereby exaggerating their differencesand sharpening even the tiniest details.For example, suppose a portion ofan image returned from space revealsan area of subtle gray tones. Data fromthe computer indicates the range inbrightness values is between 98 and120, and are all fairly evenly distributed.To the unaided eye, the portionappears as a blurred gray patchbecause the shades are too nearlysimilar to be discerned. To eliminatethis visual handicap, the brightnessvalues can be assigned new numbers.The shades can be spread furtherapart, say five shades apart rather thanthe one currently being looked at.Because the data is already stored oncomputers, it is a fairly easy task toisolate the twenty-three values andassign them new ones: 98 could be

assigned 20, 99 assigned 25, and soon . The resulting image is "enhanced"to the naked eye, while the informationis the same accurate data transmittedfrom the vicinity of the object in space.

T he past 25 years of spacetravel and exploration hasgenerated an unprecedentedquantity of data from planetarysystems. Images taken in space andtelemetered back to Earth have greatlyaided scientists in formulating betterand more accurate theories about thenature and origin of our Solar System.Data gathered at close range, and fromabove the distorting effects of Earth'satmosphere , produce images far moredetailed than pictures taken by eventhe largest Earth-bound telescopes.In mankind 's search to understandthe world as well as the universe inwhich he lives, he has in onegeneration reached farther than in anyother generation before. He hasovercome the limitations of lookingfrom the surface of his own planet andtraveled to others. Whatever yearningdrew that first star gazer from thesecurity of his cave to look up at thenight sky and wonder still draws menand women to the stars.

ORIG INA[ PAGF::COLOR PHOTOGRAPH

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Br ief History of Pictures By Unmanned SpacecraftName Year Mission

1959 Moon: measured particles and fields in a flyby, entered heliocentric orbit~ = - = - " : : - - : - - = = =

Ranger 7 1964 Moon: 4,316 high-resolution TV pictures of Sea of Clouds; impacted= = = = . - ~ = = ~ ~ ~ = = = = = =Ranger 8 1965 Moon: 7,137 pictures of Sea of Tranquility; impacted

Ranger 9 1965 Moon: 5,814 pictures of Crater Alphonsus; impactedSurveyor 1 1966 Moon: 11 ,237 pictures, soft landing in Ocean of StormsSurveyor 3 1967 Moon: 6,315 pictures, first soil scoop; soft landed in Sea of CloudsSurveyor 5 1967 Moon: more than 19 ,000 pictures; first alpha scatter analyzed chemical structure;soft landed in Sea of TranquilitySurveyor 6 1967 ==Moon: 30,065 pictures; first lift off from lunar surface, moved ship 10 feet , softlanded in Central Bay region

~ - - - - - - ~ ~ ~ = - - - - - - - - - ~ - -Surveyor 7Lunar Orbiter 1

Lunar Orbiter 2Lunar Orbiter 3Lunar Orbiter 4Lunar Orbiter 5

Mariner 2

Mariner 4

1968

1966

1966196719671967

1962

1964

Moon: re turned television pictures, performed alpha scatter, and took surfacesample; first soft landing on ejecta blanket beside Crater TychoMoon: medium and high-resolution pictures of 9 possible landing sites; first orbitof another planetary body; impactedMoon: 211 frames (422 medium and high-resolution pictures) ; impactedMoon: 211 frames including picture of Surveyor 1 on lunar surface; impactedMoon: 167 frames; impacted

====Moon: 212 frames, including 5 possible landing sites and micrometeoroid data;impactedVenus: first succesful planetary probe; determined planet mass and measuredhigh temperatures; close fly by

........Mars: pictures of cratered moon-like surface, measured planet's thin mostlycarbon dioxide atmosphere; fly by~ ~ = = = = = = = = = = = = = = = = = = = = ~ ~ = = = = = = = = = = Mariner 5

Mariners 6 and 7

Mariner 9Mariner 10

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19671969

19711973

Venus: found dense magnetic field and dense atmosphere; fly byMars: verified atmospheric findings: no nitrogen present , dry ice near polar caps;both fly bys

=======Mars: 7,400 pictures of both moons and planet's surface ; fly byVenus: ultraviolet images of atmosphere, revealing circulation patterns;atmosphere rotates more slowly than planetary body; fly byMercury: pictures of moon-like surface with long , narrow valleys and cliffs; fly by


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Name YearPioneer 10 1972

Mission

ORIGINAL PAGE'COLOR G ~ ~ P H

Jupiter: first close-up pictures of Great Red Spot and planetary atmosphere; firstspacecraft to leave Solar System (5 am PDT, June 13 , 1983) carries plaque withintergalactic greetings from Earth~ = = = = ~ = = = = = = = = ~ ~ ~ Pioneer 11(Pioneer Saturn)

Pioneer Venus 2

Viking 1Viking 2

Voyager 1

Voyager 2

1973 Jupiter: pictures of planet from 42 ,760 km (26,725 mil above cloudtops; onlypictures of polar regions; used Jupiter 's gravity to swing it back across the SolarSystem to SaturnSaturn: pictures of planet as it passed through ring plane, w ith in 21,400 km(13 ,300 mil of cloudtops new discoveries were made; spacecraft renamedPioneer Saturn after leaving Jupiter

1978 Venus: first full-disc pictures of planet; studied cloud cover and planetarytopography ; orbited1978

19751975

1977

1977

Venus: multi probe, measuring atmosphere top to bottom; probes designed toimpact on surface but continued to return data for 67 minutes= = = = = = = = = = = = = = = = = = = ~ Mars: first surface pictures of Mars; landed July 20, 1976

Mars first color pictures; showed a red surface of oxidized iron ; landedSeptember 3, 1976, and some equipment remained operating until November1982Jupiter: launched after Voyager 2 but on a faster trajectory; took pictures ofJupiter's rapidly changing cloudtops; discovered ring circling planet, plasmacloud covering 10 , and first moons with color: 10 , orange; Europa, amber; andGanymede, brown; fly bySaturn: pictures showed atmosphere similar to Jupiter's, but with many morebands and a dense haze that obscured the surface ; found new rings within rings ;increased known moon count to 15 ; fly byJupiter: color and black-and-white pictures to complement Voyager 1; time-lapsemovie of volcanic action on 10 ; fly bySaturn: better cameras resolved ring count to more than 1 000; time-lapse moviesstudied ring spokes; distinctive features seen on several moons; 7 new satelliteswere discovered; fly byUranus first encounter with this distant planet; revealed detailed surfaces ofmoons, resolved rings into multicolored bands showing anticipated shepardingmoons; discovered planetary magnetic field ; fly byNeptune: encounter scheduled for 1989

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nasa facts how we get pictures from space

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