NASA Facts Space Launch Vehicles

8/7/2019 NASA Facts Space Launch Vehicles

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The basic ;p rinciple, applicable to the rocketengine and explaining the work of the launchvehicle, was recognized by Sir Isaac Newtonnearly 250 years ago when he defined and wrotethe laws of motion. His third states: "For everyaction there is an equal and opposite reaction."As fuel burns in a rocket engine chamber, thegases created in the burning expand and escapethrough its chamber nozzle at high velocity, creat-ing reaction or thrust in the opposite direction.

While there are a number of advanced types ofrocket engines in development such as nuclearand electric propulsion, rocket engines now inuse all burn a chemical fuel, either liquid orsolid.

There are certain advantages in both types offuel. Solid fuel engines are quite simple andthe fuel may be stored for long periods of timein the rocket. Liquid engines are very complexand generally their fuel must be loaded just beforefiring. The primary advantage of liquid fuels,however, is that they are more controllable thansolids. Liquid fuei engines are easily stopped andstarted, whereas solid fuel engines present moredifficulty in this regard.

In a liquid rocket, the fuel and oxidizer arecarried in separate tanks and burned in the com-bustion chamber. Kerosene is used in rocketboosters such as Atlas, Delta and Saturn. TheTitan II vehicle uses aerozine, a 50-50 mixture ofunsymmetrical dimethyl hydrazine (LJDMH) andhydrazine. Common oxidizers are liquid oxygen,inhibited red fuming nitric acid (IRFNA- and nitro-gen tetroxide. In recent years the developmentof high-energy propellant technology has led tothe operational use of liquid hydrogen as in thecase of the Centaur engine and upper stages ofSaturn. Development of other chemical combina-tions, for even higher energy, is under way.

Solid rocket motors are used primarily for sound-ing and military rockets and other experimentaltest purposes. However, solid rocket motor tech-nology is advancing rapidly and some engines nowcan produce as much as three million poundsthrust. Advanced methods for starting and stop-ping them are also in development.

In a solid rocket, the propellant is cast into asolid mass of mixed fuel and oxidizer and isbonded to or supported inside the motor case.The propellant cast, called a grain, usually has ahole running down its center. Burning takes place

along the exposed surface of the grain and pro-gresses radially toward the case. Fuels used ipsolid propellants are asphalts, waxes, oils, plastics,metals, rubber, and resins. Their oxidizers areoften common nitrates and perchlorates.

Most rockets are now built in stages so that, asthe propellants are consumed, the empty stagescan be separated and dropped away. The re-mainder of the launch vehicle, after stage separa-tion, is much lighter and can continue on its courseusing smaller engines and less fuel.

The earth's gravity exerts the greatest pull atground level and, of course, the launch vehicleand its payload at launch time has no momentum.Also, the total weight is greatest at launch becausethe vehicle propellant tanks are loaded.

To overcome the greatest gravitational forces.The first stage has the greatest amount of totalthrust. The thrust then is usually less in the sec-ond, third and fourth stages, or however manystages the rocket contains. As the pull of gravitydiminishes with distance from the earth and asvelocity increases, the other stages are fired andthen separated to lighten the load, until only thespeeding payload remains.

Aside from the basic problem of getting enoughthrust for a long enough time to counteract gravityfor a particular weight, the rocket engineer mustalso control the rocket's flight and give it onlyenough velocity for the chosen flight path. Thenearer the satellite's planned orbit is to the earth,the stronger the gravitational pull, and thereforethe greater the velocity needed to keep the satel-lite in orbit. At 200 miles from the earth, a satel-lite needs a velocity of about 17,500 m.p.h. tostay in orbit. At 250,000 miles from the earthapproximately the distance of the moonit needs2,000 m.p.h. When a payload reaches a velocityof 24,600 m.p.h. after launch, it completely over-comes the earth's gravitational pull, escapes earth-orbit and goes into a solar orbit.

A satellite's path around the earth generally iselliptical rather than circular. With exceedinglyprecise guidance and velocity control, a spacecraftcan be put into circular orbit, but the slightestdeviation in velocity will produce an ellipse.,Earth satellites often are put into elliptical orbitsdeliberately, so as to produce a variety of alti-tudes and data .2

If an escaping spacecraft is given a greatervelocity than the earth's orbital velocity aroundthe sun, it may achieve an orbit with a greater

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mean" distance from the sun. With the correctvelocity and guidance, it can be made to reach anouter" planet (i.e., farther from the sun thanthe earth) such as Mars. But if the spacecraftis launched against the earth's rotation aroundthe sun, it falls toward the sun and achieves asmaller orbit. With proper guidance, it couldreach Venus or Mercury.

The flight path chosen for a payload and thepayload weight determine what capabilities arerequired of the particular launch vehicle. Ob-viously, it would not make sense to use a movingvan to deliver a few parcels. Similarly, it wouldbe impractical to use a Saturn vehicle to orbit asmall, light-weight group of scientific instruments.That is why this country has developed a familyof reliable launch vehicles of various sizes, shapes,and capabilities. First, this policy is economical.Second, the more experience we have with a fewparticular kinds of vehicles, the more reliable theybecome. The aim is to use the smallest numberof vehicles consistent with the full scope of spacemissions now foreseen.

Each member of the launch vehicle familyhas been assigned appropriate missions. Theserange from scientific research and exploration to,and including, manned space flight projects.

At present, NASA launch vehicles include Scout,Delta, Thor-Agena, Atlas-Agena, Atlas-Centaur,Uprated Saturn I, and Saturn V. The famous Mer-cury-Atlas launch vehicle of Project Mercury andthe Gemini Launch vehicle (Titan II) in ProjectGemini have completed their missions.

I O rbits for the Projects Mercury and G emini f l ightsgenerally were ell iptical. For example, F aith 7, with M er-cury Astronaut Gordon Cooper, had an orbit with a perigee(nearest to earth) of 100 miles, and apogee (farthest fromearth) of 166 m iles. The Gemini spacecraft, after dockingwith the Agena stage, used the Agena propulsion systemsto change its orbit significantly. In Gemini XI the Agenarocket was fired to raise the apogee from an initial 177miles to 850 miles, a new alt i tude record. The Ap ol lospacecraft has its own propulsion system, w hich gives itthe ability to make orbital changes.

2 Explorer XV II I, launched November 27, 196 3, achievedan orbit with a perigee of 12 0 m iles and an apogee of23,0 00 miles.

SCOUTScout, the smallest of the basic launch vehicles,

is a reliable and relatively inexpensive launchvehicle for payloads weighing up to 240 pounds.It is used for unmanned small satellite missions,high-altitude probes, and re-entry experiments.

Scout has four stages, is 68 feet high (less thespacecraft), and has a maximum diameter of 4 feetat its widest cross section.

Guidance is provided by a strapped-down gyrosystem, and the vehicle is controlled by a com-bination of aerodynamic surfaces, jet vanes, andhydrogen peroxide jets.

The only U.S. launch vehicle with solid propel-lants exclusively, the Scout has a first-stage thrustof 88,000 pounds. It can put a 400-pound payloadinto the lower levels of space, put 240 pounds intoa 300-nautical mile orbit, or can carry a 100-poundscientific probe about 7,000 miles away from theearth.

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!k`_i^ .A_`DELTA

Delta has two liquid-fueled stages topped by asolid-fuel stage. Ninety feet high and 8 feet indiameter at the base (excluding fins), it can boost550 pounds into a 500-nautical-mile earth orbit.Its gross weight is 114,200 pounds, and the totalthrust of the first stage is 170,000 pounds.

Delta is a workhorse NASA vehicle for a widerange of small-payload satellite missions and spaceprobles. It launched the first Orbiting Solar Ob-servatory, some of the Tiros weather satellites,and has been used in the communications-satelliteEcho I, Telstar, Relay, and Syncom programs.

First launched by NASA in May 1960, Delta hasa long list of successful firings to its credit.

Its first stage is a modified Thor, its seconda modified and improved stage from the Vanguardand Thor-Able programs, and its third stage isthe spin-stabilized, solid-propellant Altair. TheAltair is also derived from the earlier Vanguardand Thor-Able vehicles. Delta thus utilizes provenengines, modified to gain high reliability and per-form a variety of missions.

THOR-AGENAThor-Agena is a two-stage vehicle that can senq

1,150 pounds into an earth orbit of 100 nauticalmiles, or 600 pounds into a 1,200-mile orbit.

Both stages burn liquid propellants, and thetotal thrust of both stages is 186,000 pounds. Thevehicle is 76 feet high (without spacecraft) and 8feet wide (without the fins). NASA launched itsfirst Thor-Agena in September 1962.The second stage is the restartable Agena,which permits great precision in selecting an orbit.Agena was developed by the Air Force as a secondstage for use in its own programs. Early in 1960NASA decided to use it in combination with Thorand Atlas rather than develop a similar vehicle.The NASA version of Agena, developing 16,000pounds thrust, is modified so that various types ofpayloads can be bolted to the front end.

Thor-Agena is used by NASA for meteorological,communications, and scientific satellites, includ-ing the Orbiting Geophysical Observatory, Nimbus,Sert Il, and Pageos programs.

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ATLAS-AG ENAThe Atlas-Agena is a two-stage all-liquid-propel-

lant vehicle capable of putting 5,950 pounds ina 100-nautical mile earth orbit and of sending in-strumented payloads of 950 pounds to the moonand 600 pounds to Mars or Venus. It is 88.3 feethigh (less the spacecraft) and 10 feet in diameter.Total thrust is 404,000 pounds.

The Atlas booster, developed from the Air ForceAtlas intercontinental ballistic missile, won famein the Mercury manned space flight program. Thefirst NASA Atlas-Agena launch was in August, 1961(Ranger 1).

NASA uses the Atlas-Agena to launch a varietyof scientific payloads. It can orbit large earthsatellites and place into escape trajectories, lunarprobes and interplanetary and planetary explora-tion spacecraft. When used as the launching ve-hicle for a satellite, the entire Agena stage, afterseparation of the spacecraft, also becomes a satel-l ite.

This vehicle consists of an Atlas first stage andan Agena second stage. With its standard three-engine propulsion system plus two small vernier'rockets, the Atlas weighs about 260,000 pounds.The second, or Agena, stage has a 16,000-pound-thrust engine that can be stopped and started inspace.

Components of the Atlas-Agena guidance sys-tem are the inertial guidance system, timing de-vices, a velocity meter, and an infrared horizonsensor. During powered flight, pitch and yaw con-trol is maintained by gimbaling the rocket motor.During coast periods, high-pressure jets are used.

In a typical lunar application (for example, theRanger VII launched in July 1964) the Atlas' fiveengines burn for about 2 1/2 minutes before theouter engines cut off and drop away. The smallercenter engine and vernier engines continue firingfor another 2 minutes, taking the vehicle to analtitude of 80 miles. The two small 1,000-pound-thrust vernier engines continue firing after centerengine cutoff long enough to trim velocity. Anon-board computer commands the Atlas airborneguidance system to start the timer on the Agenastage.

After the verniers cut off, the Atlas-Agena coastsfor a few seconds. Then the spring-loaded aero-dynamic shroud protecting the payload is dis-carded. Explosive charges separate the Agenafrom the Atlas first stage. The Agena goes througha pitch maneuver to bring it into horizontal aline-

ment with the earth's surface. Then the timersignals the propulsion system and ignition occurs.

During the 2 1/2 minutes of powered flight, theAgena is controlled by the hydraulic control sys-tem. When the engines cut off, the payload is ina circular parking orbit approximately 100 milesabove the earth. After a 14-minute coast period,the Agena engine re-ignites and powers the payloadfor another 1 112 minutes, placing it in the lunartrajectory. Some 2 1/2 minutes after engine cutoffthe Agena and the payload separates, and thespacecraft continues alone.

The vehicle with which the Gemini spacecraftrendezvoused in space was the Agena, a 1,700-pound Air Force upper stage modified to fit therequirements of Project Gemini. The changes in-cluded addition of a secondary propulsion system,modifications to the primary propulsion system toprovide restart capability, electronics modificationsfor command and docking, a systems status panelwhich told the astronauts the status of the Agenasystems, and an adapter for docking operations.

s V erniers are small rocket engines used primarily toobtain a fine adjustment in the v elocity and trajectory ofa space vehicle or m issile.5


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ATLAS-CENTAURAtlas-Centaur, with an Atlas first stage and a

Centaur second stage, is the most advanced of theAtlas-based series of launch vehicles. This 100-foot-long, 300,000-pound vehicle is capable ofsending approximately 8,500 pounds into lowearth orbit, 2,150 pounds to the moon, and 1,300pounds to Venus and Mars.

The two-stage liquid-fueled vehicle develops atotal thrust of more than 400,000 pounds. (Atlasdevelops 388,000 pounds thrust and the Centaurdevelops 30,000 pounds thrust). The Atlas-Centaurcombination is a high-performance, general-purpose launch vehicle for use by NASA and theDepartment of Defense. The Centaur program haspioneered research to develop a rocket vehicle thatcan utilize high-energy liquid hydrogen as fuel.It has provided much of the basic high energyknowledge req uired for the design of the upperstages of Saturn vehicles and propulsion systemswhich will use the same fuel.

Atlas-Centaur can fly unmanned lunar and plane-tary spacecraft beyond the capabilities of the Atlas-Agena launch vehicles. It launched the highlysuccessful Surveyor spacecraft that soft-landed onthe lunra surface and relayed photographs backto earth.

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GEMINI-TITANThe powerful Titan 11 was selected as the launch

vehicle to boost the Gemini two-man spacecraftinto orbit. It was first used successfully in theunmanned flight of Gemini on April 8, 1964.

It was chosen for the Gemini mission becauseof its payload capability and importantly becauseits propellants are non explosivea feature per-mitting use of an ejection-seat escape system in-stead of the rocket escape tower of Mercury. Allengines operate on a mixture in which the fuel is ablend of unsymmetrical dimethylhydrazine (re-ferred to as (UDMH) and hydrazine, and the oxi-dizer is nitrogen tetroxide. The mixture is hyper-golic, meaning that when the fuel and oxidizer arebrought together the combination ignites spon-taneously, without need for an ignition system.

The propellants can also be stored for sometime in Titan's fuel tanks. As a result, the launchvehicle can be readied for use on comparativelyshort notice and need not be drained of fuel if alaunch is postponed.

Titan II has a 430,000-pound-thrust first stageand a 100,000-pound-thrust second stage. It is90 feet high (less payload) and 10 feet in diameterat the base.

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UPRATED SATURN IThe original Saturn launch vehicle project was

conceived in 1948 to provide early capability forlarge payloads. The decision to arrange the enginesand tanks in clusters allowed the use of equipmentalready developed for earlier rockets as well as themachine tools that produced them. Thus, the firststage of the two-stage Saturn I was a cluster ofeight H-1 engines, each capable of generating188,000 pounds of thrust. The second stage of theearly version had six liquid-oxygen, liquid-hydrogenRL-10 engines, each generating 15,000 pounds ofthrust.

Saturn I is part of a family of heavyweight lift-ing launch vehicles, used first in the Apollo pro-gram. The first ten vehicles, called Saturn I, werelaunched for research and development purposes,and also placed into earth orbit engineering testmodels of the command and service modules ofthe Apollo spacecraft. The last three Saturn I'splaced meteoroid technology satellites into earthorbit to examine the size and distribution of par-ticles in space near the earth.

The first Saturn I was launched successively inOctober, 1961, with only the first stage live. Whena live second stage was used for the first time, inJanuary, 1964, the fifth Saturn I placed 37,900pounds into earth orbit.

Beginning with the eleventh flight, a new, morepowerful second stage was used on the Saturn I.This new second stage has a single 200,000-poundthrust liquid hydrogen-liquid oxygen J-2 engine,replacing the six-engine stage used in the earlyvehicles. The first stage of the Uprated Saturnhas the same eight liquid oxygen-kerosene enginesused previously, but with total thrust uprated to1.6 million pounds.

Saturn I's first-stage thrust of 1.6 million poundsmay be compared with the 360,000 pounds ofthrust of the Atlas vehicles that launched the Mer-cury astronauts into earth orbital flights.

The Uprated Saturn I mated to the Apollo space-craft and its launch escape system stands 225 feethigh. It can orbit 40,000 pounds and will be usedto launch manned and unmanned modules of theApollo spacecraft into earth orbit.

On its first flight, in January, 1966, the UpratedSaturn I was used to test the Apollo command/service modules in a suborbital mission. Afterthree test flights, the improved launch vehicle wasdeclared ready for manned Apollo missions.

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LAUNCH ESCAPESYSTEM

COMMAND MODULE

SERVICE MODULE

LUNARMODULE

INSTRUMENTU N I TFUEL TANK

LOX TANK

S - I V 8STAGE1 ] ENGINE (I)

FUEL TANK

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SATURN VThe three-stage Saturn V stands 363 feet highwith its Apollo spacecraft in place, and has a

liftoff weight of more than 6.1 million pounds. Thefirst stage is powered by five F-1 engines whichburn kerosene and liquid oxygen. The five enginesconsume 15 tons of propellant a second and pro-duce 7.5 million pounds of thrust.

On a trip to the moon, the first stage enginesburn for about 2 1/2 minutes, boosting the Apolloastronauts to an altitude of 36 miles and a veloc-ity of about 6,000 miles per hour. The first stagethen drops away, and the second stage ignites.The second stage is powered by five J-2 engines,each producing 200,000 pounds thrust. Thesehydrogen-oxygen engines, burning for 6 1/2 minutes,push the spacecraft to an altitude of about 100miles and near-orbital velocity. Its mission com-pleted, the second stage is separated and fallsback to earth.

The third stage of the Saturn V, the same asthe second stage of the uprated Saturn I, has asingle J-2 engine which develops 200,000 poundsthrust. This stage ignites to give Apollo spacecraftthe final shove that places it into earth orbit, at analtitude of about 115 miles. Then the engine shutsdown, while the spacecraft is checked out, andthe proper moment is awaited for continuing thetrip to the moon. At the precise moment, the thirdstage engine is reignited. It burns for about 61/2minutes, accelerating the spacecraft from its earthorbital speed of 17,400 miles an hour to about24,600 miles an hour, the velocity needed toovercome earth's gravity.

The Saturn V can place a payload of 285,000pounds into earth orbit or send almost 98,000pounds to the moon. This heavy payload capa-bility will be used in both manned and unmannedmissions for the continuing exploration of space.

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