1. engineering sources, and basic engineering calculations. The preponderance of the nuclear fusion engineering data was obtained from U.S. Department of Energy's (DOE) terrestrial power and scientific research programs, while much of the propulsion system engineering data was derived from NASA expendable launch vehicle and conceptual nuclear thermal rocket (NTR) design studies. Only limited NASA fusion space propulsion system data existsbeyond whatwas accomplished since the termination ofthe 20 yearnuclear fusion program at NASA GRC (LeRC) in 1978.
2. Fusion propulsion systems are expected to operate at high enough Ispand a to produce accelerations greater than the local acceleration due to solar gravity atEarth's orbit (0.6milli-g;where 1milli-g = 32.1739 10° ft/sec2)M. The normally thought of conies of minimum energy trajectories followed by today's chemical systems degenerate into nearly straight line, radial transfers at these high acceleration levels with continuous thrust. A "field-free space" approximation can be invoked to greatly simplify the usually complex orbital mechanics. Gravity losses and optimum steering concerns can be neglected without introducing too much error, obviating the need for computationally intensive, numerically integrated solutions to support preliminary analysis. In addition, a "launch at anytime" approach to mission design is a luxury that can usually be assumed for fusion systems so long as the thrust to weight is great enough compared to the local acceleration dueto solar gravity. As will be shown, despite an initial thrust to weight of only 1.68 milli-g , the Discovery /Ts trajectory was reasonablyclosetothat of aradialtransfer.
3. Using these definitions and constant total mass flow rate (m-dot^, the total flow rate of propellant and reactor fuel and gc= 32.1739 Ibmft/(lbfsec2)), the jet thrust power (Pjet), thrust (F), Isp, and exhaust velocity (c) canallbesolved forusingthefamiliar Equation (3):