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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 62 



shock 

 absorbers 



pusher ^ 

 plate 



Figure 3. — A nuclear explosive-propelled vehicle. The nuclear explosive heats the pro- 

 pellant, which impinges on the "pusher plate," transferring momentum to the vehicle. 

 A set of shock absorbers smooths out the force on the payioad. 



that standpoint. To obtain the high thrust and high exhaust veloc- 

 ity, the reactor must run at much higher power and temperature than 

 do ordinary power reactors, but this is partially ameliorated by the 

 short lifetime (about 10 minutes) required of rocket reactors. Each 

 cubic foot of the reactor core must generate energy equivalent to the 

 electricity used in many thousands of homes. Furthermore, it must 

 do this while much of the reactor core, several cubic feet and several 

 thousand pounds, is at the temperature of an electric light bulb fila- 

 ment (2,000 to 3,000° C.) ! This is far above the melting points of 

 most common materials (such as steel, quartz sand, and most refrac- 

 toiy materials) and limits the choice of fuel elements to very few. 

 Graphite (the most familiar), tungsten (used in lamp filaments), and 

 a few metal carbides are about the only candidates. These must con- 

 tain the fissionable material in a refractory form such as uranium 

 oxide or carbide, which also have high melting points. 



