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TABLE 2.4-c

8-CYLINDER GILLESPIE ROCKET HASS TABULITION, MUTUALLY ADJUSTED FOR MARS AND VENUS SHIPS. ROUID TRIP TO VENUS, CIRCULAR CAPTURE; 3 PEOPLE, OPEN-CYCLE ECOLOGY. ONS SHIP, ONE STAGE FOR DEPARTURE FROM NEAR-PARABOLIC EARTH ORBIT AND CAPTURE AT VENUS; ONE STAGE FOR DEPARTURE FROM VENIS. RETANKING REQUIRED ON VEMIS CIRCULAR ORBIT. 145-17-280 DAYS; MASS FRACTIONS, 0.851 x 0.35 & 0.38

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16062

Lv Venus, 0.20 x 0.38 x 46964
Rejcct tanko ctc, 0.08 x 30902.
Reject crginc, 0.02 x 0.5€ x 46964
Reject waste, 5.4545/15 x (7.7 + 280) days
Reject cabin
Enter atm. at Earth, 3400 kg + 5600 kg H20

30902 2472

13590

13120

470 1620

11500

9000 2500

o 9000

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TABLE 2.4-d

8-CYLINDER GILLESPIE ROCKET

MASS TABULATION, INJTUALLY ADJUSTED FOR HARS AND VEX3 SHIPS.
ROUND TRIP TO MARS, CIRCULAR CAPTURE; 3 PECPLE, OPEN-CYCLE ECOLOGY.
ONE SHIP, ONE STAGE FOR DEPARTURE FROM NEAR-PARABOLIC EARTH ORBIT
AND CAPTURE AT LAPS; ONE STAGE FOR DEPARTURE FROM MARS. RETANKING
REQUIRED ON MARS CIRCULAR ORBIT.
385-100-385 DAYS; ASS FRACTIONS, 0.702 x 0.41 & 0.41.:

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Mass on near-parabolic orbit at Earth
Two x thrce tankers, each 36264
Lv Earth, 0903 x 0.702 x 145056
Reject waste, 5.451,545 x 325 days
Circular capture, 0.99 x 0.41 x mass
Reject tanks etc., 0.08 x 108110
Rojcct cngine, same as at Venus
Reject waste, 5.454545 x 100 days
Reject part of waste water
Transfer propellant oxygen
Roject control package.
Rëject special tank, same as at Venus
Reject excess propellant

36264
0 · 36264

O 145056 -108792 145056 -108792 91952 53104 91952 53106 83852 2100 91.952 36102 53750 36946 55006 271453 8649 28297 8649 26338 ?115 272.82 1115 25793 545 27182

0 22693

3100 27182' 44829 -2?136 5016 22136 44829

11046 1000 44829

O 1863 2183 44829

0

Ö 1863

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TADLE 2.4-0

.28

SELECTED SAIPLE SHIP MUSSES, HUTUALLI ADJUSTED

900

OHE 3-STAGE SAIP, CIRCULAR CAPTURE AT EITNER-
VENUS 'OR MARS (800-DAY & VENUS SKDY TO HARS):
INCLUDES HIRI-LANDER AT MARS

800

700

ONE 3-STAGE SHIP, CIRCULAR CAPTURE AT EITHER
VEHUS OR MARS (800-DAI & VENTUS SIBI TO MARS)
SEPARATE FREICHTEN TO MARS, LARGE LANDER

600

17:0 2-STAGĖ SIIPS, CIRCULAR CAPTUNE AT TITS
OITE 2-STAGE SIIP, ECCENTRIC CAPTURE AT MIS
(800-DAY TRIP TO MUM)

500

:

ISADDD SHIP, METRIC TOIS ON EARTH PAFKING 0:3IT (CIRCULAR)

400

TWO 3-STAGE SHIPS, CIRCULAR CAPTURE AT EITHER
VEITUS OR H.13 (800-DAY & VEITUS SIBI TO MARS)
SEPARATE FREIGHTER TO MARS, MEDIUM LANDER

300

200

OIE 2-STAGE SHIP, ECCENTRIC CAPTURE AT MARS (950-DAY TRIP); ROUID-TRIP VENUS PLIBY SATURN V, ROOID-TRIP VENUS FLYBY

100

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do. Figure 2.4 shows the problem. The plotted points correspond to Hohmann transfers., Shorter trips require more propulsion at both ends of the journcy. The check list of missions, Section 4, shows that 263 metric tons is a good selection. À largco size is unnecessary, and a br.aller size would require more refuelling. A few missions would be precluded, except by multiple retanking on orbit.

case.

A fair question at this point is whether another means of propulsion might lead to a more economical or a more capable rocket. It has often been stated that nuclear propulsion is mandatory for manned exploration of he planets. The chemically powered space ship already described in this section shows that such is not the

For any mission in the solar system, nuclear propulsion has marginal advantages and disadvantages relative to chemical propulsion. Such advantages as may exist would hardly justify the cost, delay, and uncertainty of a development progrom. Solid rockets are sometidies advocated as cxpendable first stages. Hoilever, it is difficult to show that any expendable first stage is competitive with the increase in size required to give an equivalent capability to a single-stage-to-orbit, hydrogen-oxygen rocket. Microtirust electric propulsion to the planets is interesting.

It has been proposed for one-way trips to the outer planets, but it is not really competitive with the chemical rocket described in this section. It has also been proposed for manned round trips to Mars. If the ratio of total mass of the rocket to the jet poser could be made less than about 11 kg/kW, electric propulsion combined with chemical propulsion would reduce the round trip time to less than 500 days, and make it possible to start the trip in either direction almost at will. llowever, such a ratio is definitely outside the limits of present engineering knowledge. Almost within the limits would be 19 kg/kw. This capability is worthless for Mars trips, but would cut the round trip time to any of the outer planets, including Pluto, to about five years. The possibility presented for manncá trips to the outer planets in future decades may or may not be considered a justification to continue a low-level developuient program in elcctric propulsion,

24-215 O -78 - 52

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F43. 2.4 CAPABILITIES OF REFERENCE SHIP TO OUTER PLAITETS

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