Rocket Propulsion' 



By Ralph S. Cooper 



Los Alamos Scientific Laboratory 

 Los Alamos, New Mexico 



[With 1 plate] 



In the exploration of space, propulsion — the means of getting 

 there — has always been the crucial problem. Inspection of any of our 

 space vehicles shows that the bulk (over 90 percent) of their volume 

 and weight is devoted to the propulsion systems, mainly to the pro- 

 pellant itself. The extent of space exploration in the future will 

 depend primarily upon the sizes and efficiencies of the propulsion 

 systems that will be developed. 



One might wonder whether large-scale space operations are eco- 

 nomically feasible in teiTns of their apparently high energy require- 

 ments. But in fact, the electrical energy used by a typical American 

 household durmg 1 month is sufficient to put about 75 pounds into 

 orbit about the earth. The same amount of energy is contained in 

 only 6 gallons (50 pounds) of gasoline plus the oxygen (150 pounds) 

 needed to burn it. Kockets, being far from 100 percent efficient in 

 transferring the energy to the payload, require about 5 to 10 times as 

 much as this, but still the requirements are not unreasonable. Fur- 

 thermore, atomic nuclei represent a very compact, almost limitless, 

 source of energy if we can find ways to utilize them efficiently. 



VELOCITY REQUIREMENTS 



Space travel is dynamic in the sense that velocities rather than 

 positions are significant. The important effect of propulsion is to 

 change the vehicle velocity, which then results in an appropriate 

 change in position, and thus one usually expresses the propulsion 

 requirements for various missions in terms of a velocity. For ex- 

 ample, the velocity required for a low earth orbit is about 26,000 feet 

 per second (or 18,000 miles per hour). In addition, one must lift 

 the vehicle to some height and overcome certain gravitational and 



1 Reprinted by permission from Bulletin of the Atomic Scientists for March 1962. Copy- 

 right 1962 by the Educational Foundation for Nuclear Science, 935 East 60th Street, 

 Chicago 37, lU. 



672-174—63 21 299 



