- Conference date: 7−11 Jan 1996
- Location: Albuquerque, New Mexico (USA)
Safe, reliable, low‐mass space power and propulsion systems could have numerous civilian and military applications. This paper discusses two fission‐powered concepts: the Heatpipe Power System (HPS), which provides power only; and the Heatpipe Bimodal System (HBS), which provides both power and thermal propulsion. Both concepts have 10 important features. First, only existing technology and recently tested fuel forms are used. Second, fuel can be removed whenever desired, which greatly facilitates system fabrication and handling. Third, full electrically heated system testing of all modes is possible, with minimal operations required to replace the heaters with fuel and to ready the system for launch. Fourth, the systems are passively subcritical during launch accidents. Fifth, a modular approach is used, and most technical issues can be resolved with inexpensive module tests. Sixth, bonds between dissimilar metals are minimized. Seventh, there are no single‐point failures during power mode operation. Eighth, the fuel burnup rate is quite low to help ensure ≳10‐yr system life. Ninth, there are no pumped coolant loops, and the systems can be shut down and restarted without coolant freeze/thaw concerns. Finally, full ground nuclear test is not needed, and development costs will be low. One design for a low‐power HPS uses SNAP‐10A‐style thermoelectric power converters to produce 5 kWe at a system mass of ∼500 kg. The unicouple thermoelectric converters have a hot‐shoe temperature of 1275 K and reject waste heat at 775 K. This type of thermoelectric converter has been used extensively by the space program and has demonstrated an operational lifetime of decades. A core with a larger number of smaller modules (same overall size) can be used to provide up to 500 kWt to a power conversion subsystem, and a slightly larger core using a higher heatpipe to fuel ratio can provide ≳1 MWt. The baseline HBS produces ≳50 N of thrust at a specific impulse ≳750 s, can operate for long periods of time (hundreds of hours, limited by propellant supply) in bimodal mode, produces ≳5 kWe in power or bimodal mode, has ≳10‐yr power mode life, and has a mass of ∼800 kg. HPS development cost (through flight unit fabrication, thermal testing, and zero‐power nuclear testing) should be less than $100M. The HBS development cost will be higher than HPS development cost because of the added complexity of the bimodal system.
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