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N A S A F A C T SVol. II, No.9

An Educational Services Publication of theNational Aeronautics and Space Administration

MARINER IV

Mariner IV spacecraft.

The United States has launched an unmannedspacecraft in the first American experiment toexplore space farther from the sun than earth'sorbit. The spacecraft, called Mariner IV, isequipped to report on space phenomena that it

encounters and, if all goes well, to provide mankind with the first close look at Mars. The experiment also provides engineering experiencein operation of spacecraft during prolongedflights away from the sun.

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Two views of the Mariner IVspacecraft, showing locations of principal parts.

Page 2SCIENTIF IC INVESTIGATIONS

Mariner is equipped to carry out a broadange of investigations in interplanetary spaceand near Mars. The investigations include:

1. Ionization Chamber-The Mariner IV ion-ization chamber is a five-inch diameter spherefilled with argon gas. It is designed to measurethe intensity of high-energy radiation, particu-larly cosmic rays. When cosmic ray particles(nuclei of hydrogen or helium atoms, nuclei ofatoms heavier than hydrogen or helium, or elec-trons-originating principally outside of the solarsystem) penetrate the sphere, they strip electronsfrom the argon gas atoms, creating a trail ofargon ions. The degree of ionization yields ameasurement of the energy of the particles. AGeiger-Mueller Tube associated with the chamberfurnishes a count of particles. Together, theinstruments provide information on the densityand energy levels of cosmic rays.

2. Trapped Radiation Detector-The principalpurpose of this instrument is to report the exist-ence, if any, of a radiation belt around Marssimilar to the Van Allen Radiation Region aroundthe earth. The Van Allen Region consists oftomic particles (chiefly electrons and protons)apped in the lines of force of earth's magnetic

field. The detector also reports on radiation ininterplanetary space.

3. Cosmic Ray Telescope-This instrumentanalyzes in detail portions of the cosmic rayenergy range covered by the ionization chamber(above). It also detects particles with lowerenergy. The instrument derives its name fromthe fact that its three detectors are arranged likethe series of lenses in a telescope. The degreeof a particle's penetration-i.e. through one,

L OW-G A IN OMNI-A N TE NN A

IO N C HA MB ER MAGNETOMETERC OSM IC D UST

P RO PU L SIO N A SS EM B LY

T HE RM AL C ON TR OL L OU VE RS~ SOLAR PRESSURE VANE

NASA FACTS Vol. II, No.9two, or three detectors-yields information relctive to its energy.

4. Magnetometer-This instrument providesinformation on the strength and direction ofmagnetic fields in interplanetary space. It isalso designed to determine the existence andnature of a magnetic field, if any, around Mars.Mariner II reported that magnetic fields werenearly always present in interplanetary space.

5. Micrometeoroid Detector-The micromete-oroid detector provides information on the dis-tribution and momentum of tiny particles ofmatter in space. Mariner II reported relativelyfew micrometeoroids between earth and Venus.Mariner IV may encounter more meteoroids thanMariner II because it is flying toward the aster-oids, one presumed source of micrometeoroids.In addition, Mariner IV passed through threemeteoroid streams. In December 1964, thespacecraft flew through the Geminid and Ursidmeteor streams. In March 1965, it passedthrough the Tuttle-Giacobini-Kresak stream.(The asteroids are a swarm of small celestibodies in solar orbit, largely between the orbiof Mars and Jupiter. The three meteor streamsare believed to be composed of particles oncemaking up the nucleus of a comet. Both as-teroids and comets have been said to be sourcesof meteoroids.)

6. Solar Plasma Probe-This instrument wasincluded in Mariner IV's series of experimentsto measure the density, velocity, temperature,and direction of the solar plasma betweenearth and Mars. Mariner II showed the plasmato be a predominant feature of the interplanetaryspace environment through which the spacecraft

C AN OP US S EN SO R

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NASA FACTS Vol. II, No.9_w. Theplasma significantly influenced cosmicrays and magnetic fields. Solar plasma is a~boiling off of the sun's atmosphere. It is a highvelocity, high temperature electrified gas (hydro-gen or helium).

7. Occultation Experiment-The trajectory, orflight path, of Mariner IV will carry the space-craft behind Mars relative to earth. Themannerin which Mariner's radio transmissions are dis-torted by the Martian atmosphere as the space-craft flies behind the planet can indicate theatmosphere's density.

8. Television Camera-Mariner is expectedto reach the vicinity of Mars at 9: 11 p.m. EDT,July 14, 1965, and draw as near as about 5,000miles to the planet. While passing Mars, Mar-iner's television cameras will snap up to 22 blackand white close-ups of the Martian surface forlater telecast to earth. The strip of pictures isexpected to show terrain features as much as50 times smaller than those visible from earth.

SPACECRAFT DESCRIPTIONMariner IV is basically an octagonally shaped

structure 50 inches across. In and on this struc-ture are attached the solar panels that generateelectric power for spacecraft operation, communi-cation equipment, experiments, a rocket enginefor course changes, an orientation and stabiliza-tion system, and other components.On earth, Mariner IV weighs 575 pounds. In

space, with appendages deployed, Mariner spans22 feet 7 1 1 2 inches across its solar panels andsolar vanes (see below) and extends 9 11 2 feetfrom the base of the octagonal structure to thetip of the omni-antenna (an antenna that radiatesradio signals in all directions).Mariner IV has four solar panels as compared

to the two with which Mariner" and the Rangerlunar spacecraft were equipped. This is in-tended to compensate for the decreasing inten-sity of sunlight with increasing distance from thesun. At the orbit of Mars, sunlight is only halfas bright as at the orbit of earth.

The panels hold a total of 28,224 solar cellsat convert sunlight to electric power. In addi-ion, Mariner is equipped with a storage batterywhich provides power when the panels are notfacing the sun (as during a course correction)and serves as a back-up during peak power de-

--_----------- - ---~--~-~

Aerodynamic shroud, which protected Mariner IVduring launchthrough the atmosphere, is tested.

mands. The battery is recharged by the solarpanels.

Solar pressure vanes attached to the ends ofthe solar panels balance out the faint pressureof the solar radiation by increasing or decreas-ing the area of the craft that faces the sun.They are an auxiliary attitude, or orientation,control system.

The primary attitude control system consists

MARINERIIIMariner III, launched toward Mars on November 5,

1964, failed when a new kind of shroud did notjettison as planned. The shroud covers a spacecraftand protects it from aerodynamic forces, such as therush of air, created during launch.Engineers designed, built, and tested another kind

of shroud for Mariner IV. This shroud operatedproperly.

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NASA FACTS Vol. II, No.9age 4

Solar panels of Mariner IVare attached.

nitrogen gas jets linked to three gyroscopes,n sensors, and a Canopus star sensor. Thestem is designed to keep the high-gain antennan antenna that focusses radio beams in agle direction, thereby providing maximumength for receivers) pointed to earth, the solarnels facing the sun, and the television cameraed at Mars when Mariner reaches the planet'sinity. This attitude also provides a referenceint from which the craft can be reoriented forcourse guidance.The sun sensor is a light-sensitive device thatnerates an electric impulse when Mariner'slar panels are not receiving maximum sunlight.

The pulse activates gas jets, which turn the craftto the sun.

The Canopus sensor is a photomultiplier tube.In such an instrument, light striking a grid knocksoff electrons which in turn knock off more elec-trons in succeeding grids. This results in am-plification of the light in the form of a measur-able electric current.

The sensor is set to respond to light in theintensity range of the star Canopus. However,the lower end of this range grazes the brightnessof other celestial objects. Moreover loss of thelock on Canopus could be caused by dust par-ticles drifting between the sensor and Canopus

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NASA FACTS Vol. II, No.9and reflecting a flash of sunlight into the sensor.As a result, planners incorporated into MarinerIV a system by which it could be commandedfrom earth to search for Canopus.

Canopus is the second brightest star in thesky, exceeded in brilliance only by Sirius. Itis about 100 light years or 600 trillion miles-from earth. It is a Southern Hemisphere star,visible no farther north than about 30 degreeslatitude North (Florida).

The star was chosen as a reference point be-cause it is located at about a 90 degree anglefrom the sun (another reference point) and isrelatively isolated from other bright stars.

This is the first use of Canopus as a referencepoint. Mariner IV does not use earth as a refer-ence point as did Mariner II and the Rangerlunar spacecraft. One reason is that the earthis in front of and shadowed by the sun relativeto Mariner IV.Ground personnel know when the Canopuslock is achieved by analyzing the radio signalsinto which the electric currents of the star sensorhave been converted. The signals should matcha predicted value for Canopus.Altogether, Mariner IV is made up of 138,000

components. For Mariner to accomplish all ofits goals, the components must remain functionalfor a minimum period of about nine months asthe spacecraft hurtles approximately 350 millionmiles through the hostile environment of space.

FIRST JOURNEY FROM THE SUNThe Mariner experiment is the first in which

American spacecraft have been launched in aflight away from the sun. As a result, the ex-periment provides the first experience in buildingand operating spacecraft for such missions.

Mariner IV began its approximately 350-million-mile journey when its Atlas-Agena boosterlaunched it into a low earth orbit at a speed ofabout 18,000 miles per hour (mph). At theproper location in this orbit, the still attachedAgena second stage ignited and propelledMariner toward Mars at 25,598 mph.

This speed relative to earth is not maintained.For example, at a distance of 122,000 miles,Mariner is pulling away from earth at a rate ofabout 8,000 mph. Although earth's gravitycan never pull Mariner back to earth, its influ-nce does slow Mariner down.

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Atlas-Agena booster launches Mariner IV.

At this point, however, the important speedis that of Mariner relative to the sun. Marineris hurtling through space at a speed of about74,000 mph relative to the sun in an orbit thaintersects the orbits of Mars and earth. (Earth'orbital velocity relative to the sun is about66,000 mph; Mars' 54,000 mph.)

A planned event of the Mariner IV flight ismidcourse correction of its trajectory. This inecessary because an error of just one mile pehour, for example, in the execution of the launccan result in a 9,OOO-mile miss of the target.Mariner is equipped with a 50-pound thrusrocket motor which can be fired tpice for courscorrections. (Rocket motors 'of Ranger andMadne, II could be r"ed only once.) J

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Page 6 NASA FACTS Vol. II, No.9

Mariner IVmidcourse maneuver.

At the time of its midcourse maneuver on De-cember 5, 1964, Mariner was 1,267,613 milesfrom earth. Its velocity was 7,019 mph rela-tive to earth and 74,108 mph relative to thesun. If it continued on its original flight path,it would pass Mars at a distance of about151,000 miles, too far to provide significantnformation about the planet.For the maneuver, Mariner IV executed the

following commands radioed from earth: pitchturn of minus 39.2 degrees; a roll of 156.08degrees; and rocket firing for 20.06 seconds(see illustration).

The maneuver added 28 mph to Mariner'sspeed relative to earth. Because of the vastdistance involved, it changed Mariner's arrivaldate at Mars orbit from July 16, 1965, to July 14,1965. Instead of passing 151,000 miles infront of Mars, Mariner will pass about 5,000miles behind Mars.After the maneuver, Mariner locked on the

star Gamma Velorum, near Canopus which isthe Mariner star sensor's proper reference point.On December 17, Mariner, on command fromearth, rolled, searched for, and reacquiredCanopus.

LAUNCH WINDOWA launch window is defined as a period of time

during which a craft can be launched and meet itsobjective. The launch window for Mars shots occursevery 25 months and lasts several weeks.

BEFORE MIDCOURSE MANEUVEII :M AR IN ER W OU LD H AV E P AS SE D151000 MILESFROM MAilS ONJULY 16, 1965 AT 8:24 PM EST

Results of Mariner IVmidcourse maneuver.

Mariner is ai~ed to pass rather than land onMars. If Mariner struck Mars, it would haverelatively little time for close-up observation andsending this information to earth. Moreover, itcould land earth microorganisms on the planet,a prospect that scientists are anxious to avoid.

Earth and Mars are about 134 million milesapart when Mariner makes its planetary observa-tions. Mariner snaps each picture of the Mar-tian surface in a fraction of a second. Then,Mariner transforms the pictures into electricalimpulses that are recorded on magnetic tape, inmuch the same way as television studios tapeshows for future presentation. Because of thelimited power available on Mariner and the gre

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NASA FACTSVol. II, No.9MARINER TRAJECTORY TO MARS

MARS AT LAUNCH

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30DAYSey' .. I {O~I .' J ..... ., 90 ". "60""- .,/( .., '"""\ . ..: \ ..... ~120 210 . 228 DAYS

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ars through a telescope on earth. Mariner IVmay providepographic pictures as much as 50 times more detailed than

those made from earth.right polar caps which are thought to be madep of thin layers of frost. The darkening ob-erved when the polar caps appear to meltuld indicate vegetation responding to rnois-reo However, since certain inorganic sub-ances such as salt also darken when wet, thereas that darken could be salt flats.Some astronomers have noted strange spotsn the Martian surface that change size and

hape as if they were alive. Still others havelaimed to see "canals" which would have toe the work of intelligent beings. However,ther scientists consider the "canals" subjective

Spectographic observations, through whichatter is identified by its absorption and emis-ion of light, suggest existence of organic ma-rials. However, scientists know that organicaterials could arise through non-biologicalrocesses. Moreover, the spectroscopic studiesveal none of the characteristics of green chlo-NASAFACTSformat is designed for bulletin-board displayuncut, or for 8 x 10Y2looseleaf notebook insertion whencut along dotted lines and folded along solid lines. Fornotebook ring insertion, punch at solid dots in the margins.

NASA FACTS Vol. II, No.9rophyll. And studies show that the dark areaswarm up during the Martian day and cool offduring the Martian night as rapidly as otherareas. These would not be typical of plant lifeas we know it.

Analyses of the planet's atmosphere hav -produced conflicting results. Generally, it isbelieved high in carbon dioxide and nitrogenand low in oxygen and water vapor. Its den-sity at the Martian surface is estimated at any-where from 10 to 100 millibars. This is aboutone to 10 percent of the pressure at earth's sur-face. More definite information on density ofthe Martian atmosphere is essential for designof craft intended for soft landings on thatplanet.

Among the puzzling Martian phenomena isthe blue haze which generally envelops theplanet and which from time to time mysteriouslydisappears.Science has gathered many facts about Mars.Its mean distance from the sun is calculated at141 million miles, compared to earth's 93 millionmiles. Its temperatures at the equator rangefrom 50 degrees Fahrenheit at the Martian noonto 90 degrees below zero Fahrenheit at night.(Such a temperature range does not make lifeprohibitive.)

The Martian year, or time for Mars to circlthe sun, is 687 days. The Martian day, or timfor a complete rotation on its axis, is 24 hours37 minutes, almost the same as earth's. Likeearth too, Mars tilts on its axis and, therefore,has seasons.

Mars has a diameter of 4,140 miles, abouthalf that of earth. Its gravity pull is .38 thatof earth, meaning a 100-pound object on earthwould weigh 38 pounds on Mars.

It has two small satellites: Phobos (diameter12 miles) and Deimos (diameter 6 miles). Theirsmall sizes, low altitudes (less than 15,000 miles),and peculiarity of their movements around Marshave led to much speculation about their natureand origin.NASAFACTSis an educational publlcaton of NASA'sDivisionof Educational Programs and Services. It will be mailed toaddressees who request it from: NASA,Educational Publica-tions Distribution Center, AFEE-l, Washington, D.C.,20546.

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