through the nozzle, especially at high expansion ratios, the static temperature in the stream falls remarkably low. The internal efficiency, the ratio of actual useful kinetic energy in the exhaust to the energy released in the chamber, is shown in Fig. 2 (2). A rocket with a high expansion ratio nozzle can easily achieve 80% internal efficiency. The external energy efficiency, the kinetic energy imparted to the payload compared to the total kinetic energy of the exhaust, is shown in Fig. 3 for a single-stage rocket (2). This figure illustrates both opportunity and dilemma. If the velocity increment to be achieved is about the same as the exhaust velocity, then, with good structural weight efficiency, an external efficiency as high as 40% can be achieved. If, as is required for Earth orbital velocities using chemical rockets, the velocity to be achieved is twice the exhaust velocity, then the overall efficiencies become very low. The structure must be very light, or nothing can be carried. This has led, of course, to the widespread use of staging. Chemical rocket exhaust velocities are too low for the achievement of orbital velocities. We operate too far to the left on the abscissa of Fig. 1 and too far-to the right on Fig. 3. It is safe to assume, given the current state of political affairs in this country, that it will be a long time before nuclear rockets are once again considered seriously. Nuclear energy in this country today has managed to achieve a social status somewhat lower than werewolves. This is ironic if one believes modern physical theory. If the astrophysists are correct in stating that all the heavy atoms in the universe were born in the tremendous nuclear explosions of supernovae, then the first ancestors of
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