91-040

TO PLANETS USING NUCLEAR-ELECTRIC THRUST TO L1, THEN CHEMICAL TO

OBTAIN LUNAR FUEL, SHIELDING, SUPPLIES, AND EARTH GRAVITY ASSISTThomas M. Morse

5

ConsultantMooresville, N.C. 28115. USA

ABSTRACTastronomy sites. (4) Develop Mars bases. (5) Learn

Method uses unshielded nuclear-electric thrust for more about the planets and their moons.

the OTV to ferry an unmanned spaceship from LEO to Why via moon instead of direct to Mars? A mission

LI. Spaceship has 3 chemical engines, but empty fuel using solely chemical fuel, direct or indirect, is

tanks. Takes 3-5 months to reach LI via spiral impractical because of large weight and cost. Safe

trajectory of Earth. Lunar tankers await in LI with robotic nuclear-electric thrust, activated in LEO,

shielding, fuel. etc. MC robotically removes OTV will enable economical means of hauling unmanned

from spaceship and parks it in Ll. Mars lander and spaceships and heavy mining-manufacturing equipment

crew is launched to LEO and proceeds under own to the moon, and to haul tankers of reserve fuel and

chemical power to LI. Lander docks with spaceship. power supplies to Mars orbit. Chemical fuels and

Crew boards. Spaceship has solar panel to power other supplies, manufactured on the moon from lunar

robotic arcjets and solar-electric station-keeper sources, will enable fast manned missions to Mars

thrusters. Tanker is brought alongside and fuel is from LEO, via the moon or L1, in about the same

pumped to fill tanks of both ships. Shielding is elapsed time, and at far less cost, than would

placed around outside a small compartment for crew nuclear-thermal thrust direct from LEO. Direct

refuge from solar flares. Landers 3 engines have missions from Earth to Mars, using nuclear-thermal

enough thrust to escape Mars; spaceship has half as thrust, will probably never occur, for economic and

much thrust, but enough fuel to run for days, and perceived environmental reasons, if the primary

more stored in Mars orbit. Engines not used during architecture laid out in America's "SPACE EXPLORA-

free-fall except to stay on a course that will clear TION INITIATIVE" (SEI) is followed. ((Note: Trips

Earth by 250-400km. Lander's thrust is used sparing- to Mars using nuclear-thermal thrust in a manner

ly to: (1) aid gravity assist to collision course economically and environmentally acceptable, is dis-

with Mars. (2) ensure Earth escape, and (3) braking. cussed near end of this paper.))

Spaceship's thrust is used for a long period leaving A space station in LEO isn't immediately required

Earth. Aerobraking in Mars landing is not so import- for this nuclear-electric-chemical mission to Mars,

ant with plenty of low-gravity fuel. Return to LI where manned part of the mission does not take long,

takes 5 months. Spaceship parks. in LI until next artificial gravity is provided by simple centrifuge,

trip. Crew returns to LEO in lander. Total manned and radiation shielding is obtained from the moon.

round-trip travel time is one year. which compares The need for these will be well understood by then

favorably with nuclear-thermal planned for SEI. Cost as a result of tests made earlier in an orbiter, and

is far less. Only crew and fuel is launched to LEO on the moon, to prove concepts and equipment.

on later trips, at still less cost; nuclear-reactor A finally, President Bush has directed NASA, in

is kept away from Earth. OTVs haul tankers to Mars. cooperation with other nations, to go via the moon.

and beam power to bases from geostationary orbit. A NE METHOD OF PROPULSION FOR THE NEAR FUTUREA NEW METHOD OF PROPULSION FOR THE NEAR FUTURE

NOMENCLATURE AND DESCRIPTIONSDirect missions to the planets, even stars, using

OTV Orbital Transfer Vehicle. nuclear fusion particle (proton) thrust may be poss-

LEO Low Earth Orbit. ible, but is many generations in the future.

MC Mission Control for telerobotics. Probably, in the not too distant future, a new

ERV Earth Return Vehicle. propulsion method will be developed. Nuclear, solar

Spec. Impulse Engine thrust in pounds, divided by energy will be beamed by laser or maser from space,

propellant flow rate in pounds/sec. moon, or Earth, to the spaceship and converted to

Thrust/weight The ratio of engine thrust to engine electric thrust. It would not be too different from

weight. using nuclear or solar with electric thrusters, in

Delta-V Velocity change required to change the method discussed herein. Using laser beamed

orbits and course, to achieve power would be much superior because the manned

destination. Is expressed in km/s. spaceship would not have to carry the mass of the

m.t. Metric tons. nuclear reactor and required shielding. A spaceship

N Newton. Equals 0.2248 pound thrust, could go direct to any planet. High velocities could

be attained, since the thrust, while low, would be

INTRODUCTION present almost continuously. The thrust could alsobe used for braking, changing course, and for the

A lunar base should be well developed before we return trip. To those readers taught that all light

attempt a Mars mission. To go to Mars prematurely diminishes in strength with the square of the dist-

will delay development of both moon and Mars. Devel- ance from the source, that does not apply to coher-

oping lunar bases will benefit Earth more, especial- ent laser or maser beams. In space, coherent light

Iv the environment. Thirty years from now, methods remains in the same narrow beam forever without

of beaming solar-nuclear power to Earth are likely, losing strength, or, until it strikes an object such

and in fifty years, obtaining clean nuclear fusion as the solar panel of a spaceship. The solar panel,

from lunar helium-3 is likely. Lunar observatories as now made, is only about 30% efficient, but if

will enable astronomers to explain the universe, used with receptor fields resonant to the wave-

Spaceships will be built on the moon. length of the coherent light, it can be about 80%

We must avoid space projects that accomplish efficient. For this mission, however, it is assumed

little, yet cost-delay the main goals, which are: that this type of thrust is not yet developed.

(1) Solve most environmental problems of Earth. (2)

Develop lunar bases. (3) Build variety of lunar REASONS FOR HASTE IN ESTABLISHING LUNAR BASES

There are good reasons for haste in establishinglunar bases. By hindsight, it should have been our

*Member Planet. Soc., Space Study Inst.. Nat'l Space first priority after the lunar missions. Instead, we

Soc.; Plan. Engr. AT&T Tech. (Retired). Member AIAA. were sidetracked by too many unrelated programs, andby exotic visions of missions direct to Mars.

1

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t.,es: , a; nt lu r.: ^..br ,v !

".t"": time con.: 1,i Z.

.017n ''I )U,1C. ,,- con. ;- m 1n t. Ij .«* y'0 ta n s c e ; s t b e ' L i -. - 3,,, o r s t e o n : T a s t lqr r I 1re,_r l solut on to [pollutiCn :t E rth O se_.'n o supp s, also avors L .

r-, ,,r ro e. Nu.c!e - r fusIn Nl l 1 -- . lv- , Li-h ! - ir is e l i

r to m.tch the .re irture t a z ' t ,

L'y e ner- gy from th sun ealm.,! t, EF:a th. cr b s - tr :vU 'F Fror [1, constant C c;,nilatlon Cd; be ln-ir;-pFIJn clean fL:.ion ater 1l (Hi- t- Earth fr-. ti

( F

L. os c n c in-

moon. Environrmentalsts n-d sr a i. as w do. t ined with both lujnar base and Earth, but ir luri:ctU-iT. comr;-Jnction with a Iunr base can be ro-ti,-lunar bases are mainditorv f-or ,1. A lcar pbrobe

t t commi;c a f ' tion itch lunt.r bande can e r-Ith ,-

in polar orbit would be irexensive. and is badv d to a seconds each it and, at the thneeded now to t-ll us wha marials e on or b- ntem, a very ih lundr orbit still restrictneath, the surfa-e. Is ice theP What fuels can be com;unication with a lunar base to less than one-i tt ethird the time. whije com..nicaticn with Erth ismad. available? What materi!s can be used to

t hi

r d t he

time. wh l

.] c o m

m.,nicaticn wilh Earth isconstruct, siTId. and insul ate Can we build reduced tc, about half the time.

leoe fr-i una(r )mter s Spaceships Fiallv. from LI. th- OTV can beam p.wue' to 1lunar base at all times.

THE NUCLEAR-ELECTRIC-CHEM ICAL MISS.IN.MATIN THiF OTV TO SPACECHIF IN LEL' PARKING THE SPAClEHIP I L, _AN

DISENGAGING AND) PARKING THE UTV

For the first lea of this mission, we need anunmanned spaceship in LEO with 3 low power chemical As it nears L1, the spaceship-OTV urit is rat.engines. The main fuel tanks are empty, but the en- 10

b y C,

u sin the a secess. Then, by uskin the

Qines are connected to small tanks that are filled. thrust of the OTV, as necessary for brakino, thTwo small solar-electric thrusters are on board to spaceship-OTV gently coasts into position at l.

provide station keeping in Lagrange point LI. later. L is elongated between Earth and moon. PeopleSuch a lightweight ship can be placed in LEO by one rcal

L1b a

l i b r a to o Lcrange oire t but i is f r

modified shuttle, or equivalent fr o

m beinq a

p oi

n t. I

t is centered about 5e.300 km.modified shuttle, or equivalent, from the moon, directly in line between Earth si

A relatively lightweight, unmanned, unshielded, fr o m t h

e mo o n ,

di

r e c t ly i line between Earth ndmoon. But 48,000 km. from the moon, on lihr. a ha.!non-activated nuclear-electric thrust OTV will be m n

t 000 km. from the mo on lin a baplaced in LEO. close to the spaceship, by a similar i

s till

a l mo s t n t h e "point", with only a slih'

tendency to fall toward moae. L is the ls eeor,lift vehicle. Both spaceship and OTV will be equi- tendency the gravities of Earth and moon cnsicelped with arcjets for robotic control of their atti- h e r e t he gavities of Earth and moon ancel.tudes by signals from MC on Earth. The spaceship'sC checks the distance, by laser measurement, tsolar-electric thrusters, and the OTV's nuclear- the moon, and for alignment between Earth and mnon

electric thrusters are also remotely controlled by The spaceship-OTV is parked 48,000 km. from moon, .

MC. As such, the OTV-spaceship can robotically be distance which may be automatically maintained bymated together in LEO, and disengaged when necessary the paby using n a ith frequent auto-measureientwithout the aid of astronauts or of a space station. and, by using nuclear-electric thrust occasionally

to maintain (station-keep) position.

FERRYING THE UNMANNED SPACESHIP TO L1ST U S The OTV is disengaged from the spaceship by MC

Before this mission takes place, a lunar base using telerobotic control, and parked safely ne-arerthe center of Li. The OTV. like the spaceship. iswill have been established. Nuclear-electric propel- abe to atot llOTV. like the spaceship isled OTVs will have ferried up most of the equipment

a b l e t o automatically station-keep in Ll.needed for a base on the moon. Therefore, ferrying USING OT TO BEAM POER TO MAS FROM GEOSYNthe unmanned spaceship will be routine. A spiral UING OTV TO BEA POER TO FRO YNtrajectory of Earth is mandated by the low thrust.and necessitates a trip time of 3 to 5 months, Unless needed for base power on the moon. the riT;and necessitates a trip time of 3 to 5 months, would remain in Li only until a base was built ordepending upon the thrust available, by then, from w

o u l d r e mai

n i

n Lt only untl a b a s e

was b u i l t o n

the one megawatt nuclear-electric OTV. One reason "a r s

, a t

whic h t i me

"C wo u l

d o r d e r

the OT V

tofor using the slow nuclear-electric OTV instead of proceed to a geosync orbit of Mars. P:wer beaminrfor using the slow nuclear-electric OTV, instead ofa rocket to lift the ship to Ll is the big savin laser equipment, installed before OTV lef- Earth.a rocket to lift the ship to Li, is the big savin would be used to beam power from th one rwin fuel and cost the OTV affords. Another reason. w

o u l d b e u s e d to b e a m p o

we r f r o m

tse one rna'e.the OTV is more dependable. Since the trip to L1 is suclear rea tor, to the M ars base .Alternativel.unmanned, we do not care how long it takes. Still such power beaming equipment were not evailace.another reason for using the OTV is that it will be shielded (b lunar shielding) OTV will be takerused, later, to supply electric power to bases on

t h e surface

o f a r s , using rockets f-r lower:;athe moon or Mars, thus saving still more funds. , S.MARS LANDER. WITH ASTRONAUTS. IS LAUNCHED FRM EtA;-[;:

WHICH IS THE BETTER PARKING PLACE, LI OR LUNAR ORBIT The spaceship has no wlngs, and the Mare lar.d..r

In the vicinity of the moon. where over 95% of probably will not have any. The only protuberancosEarth gravity is overcome. MC has the choice of on

t e spaceship will be engines on its aft end. t

parking the spaceship in gravity-free L1, or. in a solar panels on its nose, a docking facility on it:

medium high lunar orbit. An Earth, or lunar gravity "belly" toard h the nose, and antennae for ccnun t b -assist, in changing course toward an intercept of

tE o n o n o n e " si

d e " s he re they are "visible" o btMars. can be obtained almost equally well from Eat

h and Emoon as spaceshi normally sits i h p leither location. However. L1 appears to be the best

a n d Ea r t h a r e a a y vsble through rtparking place for the following reasons, mostly in the top and bottom of the ship.relating to ease of rendezvous with supply craft. A shuttle will probably be used to launch Marscommunications, and safety: lander. with astronauts, from Earth to high LEO. Thle

(1) From L1, the spaceship keeps a constant posi- Mars lander will proceed under own chemical power,tion. with respect to a lunar base, but if in lunar and will

r e a c h the spaceship in two or three da .

orbit, the spaceship's position is always changing. They will dock on the spaceship, with the lander's

(2) In virtually gravity-free Ll, since forces are three chemical engines facing aft. Docking is ratheralmost neutralized, the point to which one moves is simple in L because the lander goes where it is

aimed, due to gravity and other forces being practi-

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91-040

,3;itr-^iii' u-s nt t M- , h7 , l.-r a , 1 .-" .- : -::, "

The- . .- ck out;' the ba't-rv, "- s i k.-rt c'..i: :.1

i"the 'i-.lAr parels.- Tl.e -Ce, ;:I 1 lat : a,' id ' * 1 -

sol-i! car.els as soon is theyv a-, r, c-".'. ,. 'r; ;r:-::oion T.- astrorait not f MC th.it : "*' a: t -.i:

c'.'er ninua! cor.trol ct the spf', eshi Th- I .n.checks t. at th.v have c introl of the ar c '-t.. r: ' " '

the t; ow F.,wer s .lr-elect ri thru-st-s: . :il

e:n.ble them -o mar.euv'er th sh:p without t.- m3inchemnial thrust. enines. Th ,v then operate ea "h ofthe three ch-m-icil thru t 1nes3. separ at: ,. at

Icw power for short 'per-iod. W .en theyv h.a'%- fuilVchecked out the spac,ship, the astroaut, n.,tit'

rMof tha.t fact. arid thenili ot. i th,- luiI .s t.;

they ire ready to k-oni caro . -

PRI UIPNG UP S rPLIiES F1 i M THi MOC; " ' : '

A li:nar supply tanker is already wait:rn ir. L.filled with fuel and other supplies from th.- ir.One could expect that there will be LOX a;; i ;[H' inthe tanker ready to be pumped over to tar.k, -f thespaceship and Mars lander. In a short while the Flaure 1 Sh u- lc3Itiorns of the f i ve

tanker is brought ilongside, and pumpirng berains. lbration po;-, . LI-L5, of the Earth-r:o-,n

There may also be strap-on tanks. designed to fit system. Thru patlhwavs to Mars from Mn,.o ,' -re

the curvature of the spaceship and lander, in places shown. One path leaves a lunar orbit direct

where there is nothing else to intertere. It is also for Mars. Arnother path leaves LI. goinc in

likely that there will be water, and, perhaps. food. front of moon. f-r lunalr cravity assist. A

Solar panels will have been made on the moon to fit third goes behind Earth for gravity assist.

the needs of the spaceship and lander. --

A small compartment will be inside the spaceship, engines of the Mars lander will be used only momen-just large enough to hold the entire crew, and a few tarily. if needed, during the latter part of thesupplies, during solar flares. Shielding for this fall to ensure proper miss distance. After the nearcompartment will be strapped on to the outside of miss of Earth, at almost escape velocity, both thethe ship. This shielding may simply consist of plain lander's. and spaceship's engines are used as longlunar regolith, or, it may be made of special metal. as necessary (arrows Fig. 1) t ensure that themined, separated, and formed to fit on the moon. spaceship will end up on a collision course with

Someday, almost everything required for a space Mars, and that escape velocity is reached. Aftermission, even spaceships, will be built on the moon. that, the lander's engines will be shut down. After

the close encounter, the spaceship passes by EarthLEAVING MOON FOR EARTH GRAVITY ASSIST ON WAY TO MARS in less than an hour. The spaceship's engines will

continue to accr lerate the ship for a period, theFigure 1 shows three possibilities for leaving length of which will depend upon many options. such

moon enroute to Mars, as follows: as: (1) how much fuel was brought from the moon. (2)First Method: Spaceship leaves lunar orbit direct, whether it is planned to use the engines for brakingSecond Method: Spaceship leaves LI for lunar gravity after the coast period, and (3) whether a preparkedassist on way to Mars. tanker was sent ahead to Mars orbit.Third Method: Spaceship leaves Ll for Earth gravity The Mars lander's engines have twice as muchassist on way to Mars. thrust as the spaceship's engines, because the land-

At first glance, the first method, leaving lunar er needs to lift off from Mars, and also must leaveorbit direct, may look best. However, from an orbit high LEO for 1.- . Studies have shown that, in gener-around the moon, a large course change is required al. the less pouwr engines have, the more conservingof a now relatively massive spaceship to intercept of fuel they are , so it is wise to use low powerMars. This would require more fuel and nullify gain. engines that will run for days, where it is feas-

The second method has quite a bit of merit. By ible. Since there is no friction in space, acceler-making a relatively slow passage in front of the tion continues as long as the engines are operated.moon from L1 (arrows Fig. 1), without using much Acceleration to a higher velocity than needed.fuel, the moon's gravity has a long time to change shortens the mission, which is very desirable, butthe course substantially. The spaceship can pass it requires braking after the coast period by theclose to front of moon also. since the moon has no spaceship's engines, which may be undesirable. Theatmosphere. Depending on where the moon is in its spaceship would have to be rotated 1800. by theorbit, it might be the best method. Using 31unar arcjets, to use the engines for braking. Such brak-gravity assist was treated in a previous paper in assumes a plentiful supply of low-gravity fuel.

Third method gains a gravity assist from Earth.Leaving the parking location at L1, the astronauts ARRIVAL AND LANDING ON MARSfirst use the combination of arcjets and the space-ship's low power chemical engines, to start out on When the astronauts arrive vicinity of Mars. theythe course that takes them behind Earth, as shown in will either go to one of its moons, or, more likely.dashed lines (Fig. 1), until Earth's gravity begins to the preparked tanker, to refuel. Then they willto take over, and the spaceship, with lander, starts g to a low Mars orbit for reconnaisance. The crewfree-falling on a course that will take them behind has a good idea of the best landinu sites fromEarth. Thereafter. as they accelerate toward Earth, previous reconn and robotic landings. A cre of four

spaceship's engines are used sparingly, in coniun- will board the lander, and it will be readied fortion with arcjets. to correct course as necessary, entry and landing. By then it will be known whichso that spaceship passes Earth by the calculated types of aerobraking to use. if any. Aerobraking tomiss distance, somewhere between 250-400 km., to conserve fuel will not be so inportant by then.ensure they will experience no drag due to atmos- since they will have plenty of low-gravity fuel.phere. MC is in communication, and monitoring theircourse during the whole maneuver. The more powerful

3

91-040

The arcjets will be used near the surface, to nose GRAVITY WELLSup the ship so that the engines can let down gently o --- -. o-on the landing legs. A land rover vehicle will carry ' ' . ,",b '"" Q 0them over the surface. They use it to gather samples .' ', , "from borings deep below the surface. Soundings willdetermine the depth of the crust, and if water orice is present.

By that time, small individual thrust rocketswill be available for moving swiftly above the sur-h LEOface within a radius of about 25 km. Q Hh LE .''...

A small habitat will probably be built fromMartian materials. This habitat will be filled withbreathable air, procured partly from the Martianatmosphere, and mixed with oxygen. Heat for the hab-itat will be obtained by burning fuel.

The astronauts can stay on Mars no longer thanthree months this first mission. When they have allthe specimens wanted, they load the specimens into EARTHthe lander and thrust off, either to another site.or to return to the spaceship, where they dock. The Fiqure 2: Shows gravity wells of Earth.spaceship-lander then returns to the orbiting tanker moon and Mars. Also, shows Earth gravity infor refueling, and more supplies for the trip to L. hh LEO where Mars lde r will be parked.

ty i n

high LEO where Mars lander ill be parked.SPACESHIP AND LANDER RETURN TO LNote that gravity at high LEO is the same asSPACESHIP AND LANDER RTURN TO L Mars, requiring the same thrust to lift-off.

The trip back to LI takes 5 months. In L1, space-ship equipment will be checked with MC for properfunctioning, including: auto-station-keep, solar fast nuclear-thermal rocket.panels-batteries, auto-communication, and telero- After a ship has climbed Earth's gravity well.botic. The spaceship is left on auto-station-keep Figure 2, it does not take much chemical fuel tofunction, parked in LI. (In about a year, the space- propel it to the vicinity of Mars. The needed hiahship will again be joined by astronauts and taken on LEO is over half way out of Earth's gravity well. Itthe next mission.) is the climb (descent) from Earth to LEO. and the

descent (climb) from low Mars orbit to Mars, thatRETURN TO LEO IN MARS LANDER requires the greater amount of fuel. and that is

where the nuclear-thermal rocket architecture, asThe crew returns to high LEO in the Mars lander. planned for SEI. will use chemical enaines. with

The lander is met in LEO by the version of the Earth-weight chemical fuel. Chemical fuel to lift toshuttle then available. The astronauts are returned high LEO: (1) the great mass of the nuclear engine,to Earth, leaving the lander parked in high LEO with propellant, (2) the spaceship, with astronautsuntil the next mission. and supplies, and (3) the Mars lander with fuel. A

nuclear-thermal propelled spaceship would not landRETURN TO MARS ON SUBSEQUENT MISSIONS on the moon (or near it), or park at LI, in the SEI

scenario, as now planned. The moon would serve someOn the first mission to Mars, it was necessary to purpose, however, in training crews for Mars mis-

lift a relatively lightweight, unmanned, unfueled sions, but the big advantages would not be gainedspaceship, and also an unmanned, unshielded, non- from use of low gravity lunar propellant and mater-activated OTV, from Earth to LEO. On subsequent mis- ial, nor from an Earth or lunar gravity assist. Duesions. it is only necessary to lift the crew, with to the great mass to be ferried to high LEO, asupplies and enough fuel, to the Mars lander so it nuclear-thermal mission has already cost more thancan reach LI from high LEO. (This is important in the nuclear-electric-chemical mission by the time itsaving money.) The Mars lander proceeds under its has reached LEO, and by the time it has gone as farown power to L1 and docks with the spaceship. The as the moon, the cost of the nuclear-thermal missiontwo ships, together, are then refueled and supplied would have far exceeded the cost of the low-cost un-by tankers from the moon. From LI, they get an Earth manned nuclear-electric OTV, and Mars lander trips(or lunar) gravity assist and proceed to Mars. (For to moon. This was on just the first mission. On sub-later missions, the spaceship may be designed so it sequent missions, the cost differential mounts morecan land on the moon and Mars.) swiftly in favor of the nuclear-electric-chemical

On subsequent missions, most of the crew will architecture. Example: the massive manned, shielded,stay on Mars, while two crew members take the space- nuclear-thermal spaceship has to return to, andship back to LI (or to moon), and then proceed in depart from, high LEO each mission, but the muchthe Mars lander (or the ERV) to high LEO. Since the lighter, unmanned, unshielded nuclear-electric OTVtotal elapsed time, from start of one mission to the and spaceship has to depart high LEO only on thenext, is about 2.2 years, only about one year will first mission. The OTV and spaceship never return toelapse between the return of one crew to Earth, and LEO from L1, or from the moon or the vicinity ofthe leaving of the next crew from Earth. Mars, as case may be. This is a tremendous advantage

On Mars, power will be beamed down from a nuclear for the nuclear-electric-chemical architecture. Whenelectric OTV in geosync orbit. Other OTVs, aided by using the nuclear-electric-chemical scenario, onlyrockets, will haul heavy equipment for expansion. the much lighter Mars lander returns to high LEO

from space each mission. The chemical spaceship isCOMPARING NUCLEAR-ELECTRIC-CHEMICAL left in L

l (or on moon), and used repeatedly on

WITH NUCLEAR-THERMAL PROPULSION later missions, with low-gravity fuel and supplies.The dangerous nuclear-reactor and engine, of the

One is reminded of the story of "THE HARE AND THE nuclear-thermal system, is left orbiting around inTORTOISE" when comparing nuclear-thermal with LEO for years.

nuclear-electric thrust. In case you missed the We have reason to expect a long-lived spaceshipstory as a child, the moral is that the swift do not in L1 (or on the moon), judging by the decades longalways win the race. For example, the slow, non- lives of spacecraft in outer space, but, parked inmanned, nuclear-electric OTV could ferry a 50 ton high LEO, the nuclear-thermal spaceship may have aspaceship to the moon, for much less cost than the shorter life due to space debris, meteorites, and a

4

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perceived nuclear threat to Earth by a large percent and the ship would also be able to land on Mars. The

of people. There is possible danger of damage from Mars lander would be unnecessary. Instead, an ERV

secondary radiation in the Van Allen belt. would be left parked on the moon, or at LI, durir.

But that is not all. The nuclear-electric OTV is the trip to Mars. This would have the added advant-

an excellent source of base power. Hopefully. it can age of not requiring the spaceship to be left in

be used to beam power to the moon from Li. and to Mars orbit during long stays, with its occupants

Mars from geosynchronous orbit. It can be landed, subjected to space radiation. On the return from

with aid of rockets, if necessary, for direct power Mars, the nuclear-thermal rocketship would be parked

use. The nuclear-thermal engine, on the other hand. on the moon (or at LI) until the next mission and

cannot be readily used for base power. Without the the crew would return to LEO in the ERV. On subse-

nuclear-electric OTV, billions of dollars sill have quent trips, the crew would be taken from Earth to

to be spent for power sources for Mars and moon. LEO by shuttle, and thence by ERV to the moon or LI.

One criticism expected of the foregoing compari- The important advantages of this scenario are

son is that the huge cost of developing the moon. (1) the nuclear-thermal reactor is not left for long

over a period decades, is not figured into the cost intervals in LEO to frighten some people on Earth.

of the nuclear-electric-chemical architecture. The (2) lunar material is used whenever possible; and

answer is that the moon will stand alone in its (3) there is no need to take a Mars lander to Mars.

development. The moon will be developed, in any

case, for what it has to offer Earth. To not use its It is assumed that a single gaseous element will

many features would be unwise. If nuclear-electric- be available on the moon to serve as propellant for

chemical development helps the moon. that is fine. the nuclear-thermal engine. We know that oxygen is

One could just as logically cite the huge cost of available in large amounts, but oxygen reacts or

the nuclear-thermal Rover (NERVA) engine development burns readily with most elements under conditions of

since the late 1950's, which, if finally adopted, high pressure-temperature. It may not be compatible

will continue until the nuclear-thermal engine has with the walls of the compression chamber. Hydrogen

been proven, or disproven, in space. is present on the lunar surface in small quantities

The nuclear-thermal engine does not promise an that may be sufficient. Helium is not plentiful. An

increase in power, with development, without a element, or combination of elements, may be found

corresponding increase in mass. The nuclear-electric that inhibits oxygen from reacting readily.

thrusters, on the other hand, have been proven many It is doubtful whether the nuclear-thermal engine

times in space, and the future promises more power- can compete with nuclear-electric-chemical, and its

ful thrusters without much increase in mass. It will various related developments. Both architectures

be aided by developments in related MagnetoPlasma- need further study and development before anyone can

Dynamic (MPD). and also related microwave plasma, be sure. The wrong choice may bankrupt America, or,

thrusters. Development of the related laser beamed regrettably, end our space program.

power thruster would greatly reduce mass.A CENTRIFUGE FOR ARTIFICIAL GRAVITY ON MARS MISSION

COMPARISON OF SALIENT FEATORES OF CHEM..

N-E AND N-T PROPULSION TO MARS The Soviet experience, as well as our own, is

that artificial gravity equipment is necessary on

NUCLEAR- NUCLEAR- trips of long duration. A simple centrifuge, which

CHEMICAL ELECTRIC(Chem) THERMAL can hold three astronauts, should suffice. It will

Spec. Impulse:" 475sec 5,000-9.000sec 924sec occupy little space in the cabin, and can provide

Thrust: 150 m.t. 80-N 250 m.t. from 0-1g. It is believed that 0.6g will be found

Thrust/weight: Very good Very poor Good adequate, if used by each astronaut for at least

Init.Mass LEO: 1250 m.t. 270 m.t. 750 m.t. eight hours daily. Each astronaut will be compart-

Init.Trips LEO: 5 3(incl Mars 1.) 3 mented separately, but can communicate. Some scien-

Later Trips LEO; 4 1 2 tists say that a small centrifuge can't be used

RoundTrip Time** 460 days 360 days*** 320 days because coriolis effect, chiefly on the brain and

Lift Veh. Req.:# 250 m.t. 90 m.t. 250 m.t. inner ears, would cause dizziness. Based upon my own

*Refer to INSTRUCTIONS on first page. experiences, there will be no dizziness, or other

**Not counting days spent on Mars. ill effects, because the inner ears and both halves

***Includes only manned part of trip. Also, of the brain, will be kept close to the same dis-

L1 Delta-V, and Earth gravity assist. tance from the axis of rotation, and because he/she

#For reference, lunar Apollo had 140 m.t. will not see any surroundings that are not moving

with the astronaut. To his/her mind, they will not

In the above table, it is evident that we are be moving. Artificial gravity will be applied while

dealing with two vastly different types of nuclear astronaut is sleeping, reading, hearing music, etc.

thrust. From some figures, nuclear-thermal looks

best, but careful analysis shows strongly that REFERENCES

nuclear-electric-chemical is far less costly, and

requires only 40 more days roundtrip time for the 1. Stafford, T.P., Lt. Gen., USAF(Ret.), The Synthe-

manned Mars mission, sis Group: "America's Space Exploration Initiative

(SEI)", pp.1-114. May 1991. Order "The Synthesis

PROPOSED MISSION TO MARS SCENARIO FOR NUCLEAR- Group Reports" from Sup't. of Documents. U.S. Gov.

THERMAL ROCKET THAT ENABLES A MUCH REDUCED COST Printing Office, Washington. D.C. 20402.

AND AVOIDS THE PERCEIVED THREAT TO EARTH2. Rawlin, V.K. and Patterson, M.J.: "High Power Ion

The idea is to go to Mars via LI (or the moon) in Thruster Performance", NASA TM-100127, Jan. '87.

basically the same manner described for the nuclear-

electric-chemical spaceship, except the OTV, and, 3. Morse. T.: "The Best May to Planets is Via Cis-

perhaps, the Mars lander, would not be used. The lunar Libration Point Using Electric and Chemical

nuclear-thermal rocket would only carry enough pro- Propulsion", AIAA 90-2115, 26th Joint Prop. Conf.,

pellant to take the rocket from LEO to L1 (or to the July 16-18, 1990.

moon), where it is parked while propellant, fuel,

solar flare shielding, solar panels, etc.. are taken 4. Holdridge. J., Shepard. K., Hueter, U., and Sum-

on board for the mission. An alternative would be to rall, P.: "An Infrastructure Assessment of Alter-

land the rocketship on the moon to load supplies on native Mars Transfer Vehicles", AIAA 90-1999, 26th

board, rather than rendezvous in LI. With this Joint Prop. Conf., July 16-18, 1990.

alternative, the design would include landing legs.

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