1. This standard derivation assumes one-dimensional flow, a perfect gas, and negligible entropy increase—all fairly reasonable assumptions. See, for example,
v Ronald W. Humble et al., Space Propulsion Analysis and Design (New York: The McGraw Hill Companies, Inc., 1995), p. 101.
v Ascher H. Shapiro, The Dynamics and Thermodynamics of Compressible Fluid Flow, Vol. 1 (New York: The Ronald Press Company, 1953), p. 80.
2. One might question whether launch velocities of 32 miles per second were possible. The Paris gun, shown in Figure 215 on page 395, launched 210-pound rounds at one mile per second after accelerating over a distance of only 92 feet. Imagine what nuclear powered accelerations over a 60-mile distance might have achieved. The fluttering crust also produced cyclic water hammers.