August 26, 1920J 



NATURE 



809 



A Method of Reaching Extreme Altitudes. 

 By Robert H. Goddard, Professor of Physics, Clark College, Worcester, Mass. 



IT is the purpose of the present article to state 

 the general principles and possibilities of the 

 method of reaching great altitudes with multiple 

 charge rockets, from which the exploded gases 

 are ejected with high efficiency. 



Fundamental Principle. 



The basic idea of the method, briefly stated in 

 general terms, is this : Given a mass of explosive 

 material of as great energy content as possible, 

 what height can be reached if a large fraction of 

 this material is shot downwards, on exploding, 

 with as high a speed as possible? It is evident, 

 intuitively, that the height will be great if the 

 fraction of material that remains is small and 

 the velocity of ejection of the gases is high. 



A theoretical treatment of the subject shows 

 that, provided the speed of ejection of the gases 

 is high, and the proportion of propellant is large, 

 the initial masses necessary to raise a given mass 

 to great heights are surprisingly small, but are 

 enormously large if these conditions are not 

 satisfied. 



Principles to be Applied in Practice. 



(i) In order to apply practically the general 

 principle above stated, there are three conditions 

 that must be realised experimentally : First, the 

 gases produced by the explosion must be ejected 

 downwards with the greatest efficiency possible. 

 This requirement must be met by burning the 

 explosive in a strong combustion chamber, to 

 which a tapered nozzle is attached, in order to 

 obtain the work of expansion of the gases. 



The apparatus used in the first experiments is 

 shown in Fig. i, in which P is the charge of 

 dense smokeless powder, and B is the wadding. 

 Three steel plugs were used, to vary the size of 

 the powder chamber. The velocity of the gases 



highest velocity being nearly 8000 ft.-sec, pro- 

 duced by the chamber shown in Fig. 2, whereas 



Fir,. I.— Chamber used in early experiments. 



was measured by supporting the chamber in a 

 ballistic pendulum, and observing the motion of 

 the recoil. 



It was found, by experiment, that the energy 



of motion of the ejected gases as compared with 



the heat energy of the powder could be increased 



very greatly over that for ordinary rockets, the 



NO. 2652, VOL. 105] 



B 



nearlj- 8ooo ft. per sec. 



for ordinary rockets the velocity is but 1000 ft.- 

 sec. Incidentally, the energy of motion of the 

 gases in the case under discus- 

 sion is more than 64 per cent, of 

 the heat energy of the powder, 

 whereas for ordinary rockets the 

 efficiency thus defined is but 2 

 per cent. 



An interesting way of empha- 

 sising the magnitude of the velo- 

 city, 8000 ft.-sec, is to compare 

 it with the "velocity of 

 escape," or the "parabolic 

 velocity " of planets. This 

 velocity of escape is the velo- 

 chy a body would require, pro- 

 jected upwards from a planet, in order to escape 

 to infinity, and is a perfectly definite velocity, 

 depending only upon the mass and diameter of 

 the planet. For the moon the velocity is 1-5 

 miles per second, and for the planet Mars 30 

 miles per second. Thus if the chamber shown in 

 Fig. 2 were placed upon the surface of the moon 



