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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
Lv Venus, 0.20 x 0.38 x 46964
8-CYLINDER GILLESPIE ROCKET
MASS TABULATION, INJTUALLY ADJUSTED FOR HARS AND VEX3 SHIPS.
Mass on near-parabolic orbit at Earth
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
3100 27182' 44829 -2?136 5016 22136 44829
11046 1000 44829
O 1863 2183 44829
SELECTED SAIPLE SHIP MUSSES, HUTUALLI ADJUSTED
OHE 3-STAGE SAIP, CIRCULAR CAPTURE AT EITNER-
ONE 3-STAGE SHIP, CIRCULAR CAPTURE AT EITHER
17:0 2-STAGĖ SIIPS, CIRCULAR CAPTUNE AT TITS
ISADDD SHIP, METRIC TOIS ON EARTH PAFKING 0:3IT (CIRCULAR)
TWO 3-STAGE SHIPS, CIRCULAR CAPTURE AT EITHER
OIE 2-STAGE SHIP, ECCENTRIC CAPTURE AT MARS (950-DAY TRIP); ROUID-TRIP VENUS PLIBY SATURN V, ROOID-TRIP VENUS FLYBY
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.
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,
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