Artificial-gravity B NTR crew transfer vehicle for Mars.
The NASA Glenn Research Center is involved in systems and mission analysis studies for Prometheus and the President’s Vision for Space Exploration. In support of this effort, engineers at Glenn have been studying the application of nuclear thermal rocket (NTR) engines to human missions to Mars.
The NTR is one of the leading propulsion options for future NASA human exploration missions because of its high specific impulse capability (Isp ~875 to 950 sec) and attractive engine thrust-to-weight ratio (>3). Because only a relatively small amount of enriched uranium-235 fuel is consumed in an NTR during the primary propulsion maneuvers of a typical Mars mission, engines configured for both propulsive thrust and modest power generation (referred to as bimodal operation) provide the basis for a robust, power-rich stage with efficient propulsive capture capability.
A family of modular bimodal NTR (BNTR) space-transfer-vehicle concepts has been developed that utilize a common core stage powered by three ~15-klbf engines that produce 50 kWe of total electrical power for crew life support, high-data-rate communications with Earth, and an active refrigeration system for long-term, zero-boiloff liquid hydrogen (LH2) storage. Candidate nuclear fuels for BNTR engines include uranium carbide (UC2) particles with a chemicalvapor-deposited coating in graphite and uranium-carbide zirconiumcarbide (UC-ZrC) in graphite, which were developed during the Nuclear Engine for Rocket Vehicle Application (NERVA) program, as well as uranium oxide (UO2) in tungsten (W) metal cermet. These fuels, which are listed in order of increasing temperature capability, can produce hot hydrogen exhaust ranging from ~2550 to 2900 K. Each engine has its own closed-cycle Brayton rotating unit, capable of generating up to 25 kWe, that provides an engine-out capability. Under nominal conditions, each Brayton rotating unit would operate at two-thirds of the rated power (~17 kWe).
Compared with other propulsion options currently being studied, Mars mission architectures using BNTR transfer vehicles require fewer transportation system elements. This makes space operations simpler and reduces mission mass and risk.
In addition, artificial gravity capability can be easily integrated into the BNTR vehicle design to ensure crew health and fitness on long-duration missions. On a representative crew transfer vehicle, the bimodal core stage is connected to an inflatable TransHab (transfer habitat) module via an innovative saddle truss that is open underneath to allow the inline LH2 propellant tank to be easily jettisoned following the trans-Mars injection burn. After the tank is released, the crew transfer vehicle initiates vehicle rotation at ~4 rpm to provide the crew with a Mars gravity environment (~0.38 times Earth gravity, gE) during the outbound transit. A higher rotation rate of ~6 rpm would provide about 0.8gE during the return leg of the mission to help reacclimate the crew to Earth’s gravity. A variant of the LH2 NTR option, known as the LOx-augmented NTR (or LANTR), would add an oxygen afterburner nozzle to the BNTR if variable thrust, variable Isp, or stage volume reduction was needed.
Borowski, S.K.; Dudzinski, L.A.; and McGuire, M.L.: Bimodal Nuclear Thermal Rocket (NTR) Propulsion for Power-Rich, Artificial Gravity Human Exploration Missions to Mars. IAA–01–IAA.13.3.05, 2001.
Borowski, Stanley K.; Dudzinski, Leonard A.; and McGuire, Melissa L.: Artificial Gravity Vehicle Design Option for NASA’s Human Mars Mission Using “Bimodal” NTR Propulsion. AIAA Paper 99–2545, 1999.
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Glenn contacts: Dr. Stanley K. Borowski, 216–977–7091, Stanley.K.Borowski@nasa.gov; and Melissa L. McGuire, 216–977–7128, Melissa.L.McGuire@nasa.gov
Authors: Dr. Stanley K. Borowski, Melissa L. McGuire, and Leonard A. Dudzinski
Headquarters program office: Exploration Systems
Programs/Projects: Project Prometheus, Exploration Systems Artificial-gravity BNTR crew transfer vehicle for Mars.
Last updated: July 15, 2005 1:54 PM
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