310 ANNUAL REPORT SMITHSONIAN INSTITUTION, 196 2 



Table 2. — High-thrust ■propulsion system parameters 



Solid 



Liquid 

 RP-Oj 



High energy 

 Hj-Oj 



Nuclear 

 Hj 



Exhaust velocity, ft. /sec . 

 Percent dead weight 



000 



8 



10, 000 

 5 



13, 500 



7 



27, 000 

 15 



representative parameters for four propulsion systems currently 

 under development. The gross weights of vehicles to send a 10,000- 

 pound payload on various missions are given in table 3. A 10,000- 

 pound pay load was chosen for consistency and as a reasonable manned 

 vehicle size, although the more difficult missions may require greater 

 payload for radiation shielding and life support systems. Results are 

 scalable to other payloads. The necessity for staging leads logically 

 to the use of early, low-power versions of advanced propulsion sys- 

 tems in upper stages resulting in hybrid vehicles with intermediate 

 performance. Each replacement of a chemical by a nuclear stage 

 leads to reductions of two and one-half in vehicle gross weight as can 

 be seen in table 4 for the lunar mission. Thus the booster size can be 

 reduced and the payload increased considerably with nuclear upper 

 stages. For manned vehicles, a chemical last stage would be desirable 

 to act as an escape vehicle, and for the shielding its propellant would 

 provide. 



There are no unclassified performance figures available for the 

 nuclear explosion scheme, and low-thrust nuclear-electric propulsion 

 perfonnance depends crucially on the specific weight of the power 

 plant. If the desired values can be achieved, orbital start electric 

 spacecraft could carry about one-third of their gross weight as pay- 

 load on interplanetary round trips. 



To summarize the situation, most of these propulsion systems can 

 be used exclusively for any vehicle, but combinations will be used 

 which reflect their attributes and state of the art. Liquid propellant 

 rockets will be the most used of the 1960's, with high-energy propel- 



Table 3. — Performance of high-thrust systems 



