NASA Technica Memorandum 05249 AIAA-91-3440 L HydrogedOxygen Auxiliary Propulsion Technology Brian D. Reed and Steven J. Schneider Lewis Research Center Cleveland, Ohio Prepared for the Conference on Advanced Space Exploration Initiative Technologies cosponsored by AIAA, NASA, and OAI Cleveland, Ohio, September 4-6, 1991 NASA HYDROGEN/OXYGEN AUXILIARY PROPULSION TECHNOLOGY Brian D. Reed and Steven J. Schneider National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 Abstract use hydrogen, oxygen, and water could lead to a simpler and more operationally efficient vehicle. This paper provides a survey of hydrogen-oxygen (H/O) auxiliary propulsion system (APS) concepts and In the past, the potential benefits of H/O propellants low-thrust H/O rocket technology. A review of H/O have made them attractive candidates for APS’s, includ- APS studies performed for the Space Shuttle, Space Tug, ing Space Shuttle and Space Station Freedom. However, Space Station Freedom, and Advanced Manned Launch they have yet to be implemented on an actual flight System programs is given. The survey also includes a system due, primarily, to concerns about the feasibility review of low-thrust H/O rocket technology programs, of developing the technology to implement the concepts. covering liquid H/O and gaseous H/O thrusters, ranging Various APS concepts using liquid, gaseous, and super- from 6600 N (1500 lbf) to 440 mN (0.1 lbf) thrust. critical H/O have been proposed over the years. Prob- Ignition concepts for H/O thrusters and high- lems, though, are usually encountered in the design of temperature, oxidation-resistant chamber materials are various concepts, such as large volume and high-pressure also reviewed. storage requirements for gaseous H/O, long-term cryo- genic storage and distribution, complexity and perfor- Introduction mance losses of propellant conditioning equipment, and uncertainties about thruster technology. Auxiliary propulsion is required on every launch vehicle, satellite, and spacecraft. Examples of auxiliary The primary propellant choice of APS’s has been propulsion include attitude control and orientation, monopropellant hydrazine or the bipropellant combina- stationkeeping, apogee insertion, rendezvous, docking, tion of monomethylhydrazine (MMH) and nitrogen separation, midcourse correction, and planetary retro. tetroxide (NTO). These Earth storable propellants have Auxiliary propulsion maneuvers can range from milli- the advantages of a long, successful flight history, long- second pulse trains to long, steady-state burns. Depend- term storability with minimal thermal control, high bulk ing on the application, thrust levels for auxiliary density, and either catalytic (monopropellant) or propulsion can range from 440 mN (0.1 lbf) to 27 kN hypergolic (bipropellant) ignition. Earth storable (6000 lbf). Thrusters in an auxiliary propulsion system propellants are also low performing compared with H/O, (APS) are usually located throughout the vehicle, are highly toxic, and have limited capability for integra- requiring a distribution network to supply propellants tion with other subsystems. The high reliability of Earth from the tanks. An APS must be able to provide storable systems has outweighed the potential benefits of frequent and rapid restarts, must have high cyclic life, H/O, because of the uncertainties associated with H/O and must have the flexibility to operate over a wide systems. However, the need for high performance in , range of environmental conditions, often with long quies- STV missions and an increased awareness of the impor- cent periods. tance of efficient servicing, checkout, and maintenance, have called attention to H/O APS. Currently, the primary candidate propellant com- bination for the APS of the space transfer vehicle (STV) This paper surveys H/O APS concepts and the H/O is hydrogen-oxygen (H/O) .‘I2 These propellants are thruster technology required to enable them. Included in attractive because of their high performance and their this review are concepts and technologies generated from nontoxic, noncorrosive nature and because of their H/O development programs for the Space Shuttle, the compatiblity with other subsystems, including the main proposed Space Tug, Space Station Freedom, and propulsion, power generation, and environmental control proposed advanced manned Earth-to-orbit vehicles. A and life support systems. Integrating subsystems that matrix matching references with H/O APS concepts is 1 given in Table I. A matrix of references and subjects in H/O thruster technology is given in Table 11. TABLE I.-REFERENCES FOR H/O APS CONCEPTS ~~ ~ Refer- Liquid Liquid stor- Gasous Super-critical ence storage age and gas- storage storage and electro- and feed eous feed and feed feed 3 X Shuttle 4 X Shuttle 5 Shuttle 7 Shuttle 8 Shuttle 9 X Shuttle 10 Space Tug 12 X Space Station 13 X Space Station 15 Space Station 17 X AMLS 32 33 Satellite 34 Satellite TABLE 11.-REFERENCES FOR H/O THRUSTER TECHNOLGY fa) Thruster Refer- Liquid hydrc en/oxygen Gaseous ydrogen/c Yeen ence 5500 N 110 N 5500 N 110 N < 22 N (1250 Ibf) (25 Ibf) (1500 Ibf) (25 Ibf) (5 Ibf) 3 X 6 X 11 X 18 X 19 X 20 X 21 X 22 X 23 X 24 X 25 X 26 X 27 X 28 X 29 X 30 X 32 X 33 X 34 X 35 X 36 X 2 TABLE 11.-CONCLUDED. [b) Ignition concepts and chamber materials Hydrogen-Oxygen Auxiliary Propulsion distribution system (see Fig. 1) using expansion bellows System Concepts accumulators and vacuum jacketed lines was proposed. 5 The pumps in this system would be located near the Space Shuttle storage tanks to avoid problems with cavitation caused by pressure drop and vaporization in the lines. Vacuum There was an extensive program’’‘ in the late 1960’s jacketed insulated lines would offer dual containment of and early 1970’s to develop H/O APS for the Space propellants. The expansion bellows accumulators would Shuttle. At the time, the Shuttle was envisioned to be accommodate the expansion of propellant due to heat a larger vehicle than the current version. The main soak. Recirculation fans in the distribution manifold propulsion tankage was internal to the orbiter vehicle. would prevent localized hot spots from vaporizing the The orbiter and the booster were to be flyback and reus- propellant. It was calculated5 that the oxygen manifold able. The Shuttle APS was to be composed of a liquid could accept 67.4 kJ/kg (29 Btu/lb) of heat before hydrogen and liquid oxygen orbital maneuvering system boiling of the propellant begins, while the hydrogen (OMS) for the orbiter and an H/O attitude control manifold could accept 36.3 kJ/kg (156 Btu/lb) of heat. system (later called the reaction control system (RCS)) This would allow for a seven-day Shuttle mission with for the orbiter and booster vehicles. little or no boiloff in the distribution manifold. A cryogenic H/O RCS was considered, but there were Pulsing of cryogenic propellants was also a technol- concerns about excessive heat leaks into the cryogenic ogy concern for a liquid H/O RCS.4 Heat soakback into distribution system causing two-phase (and therefore the injector manifold and feed system could lead to two- uncontrollable) flow to the thruster^.^ A cryogenic phase propellant flows. There were also concerns about 3 reliable low-temperature ignition. However, operation of An RCS using gaseous hydrogen and liquid oxygen liquid H/O thrusters in the pulse mode was demonstra- feed was proposed as a possible compromise between the ted,6 with successful ignition of liquid hydrogen and cryogenic and the liquid storage and gaseous feed sys- oxygen (as well as gaseous and two-phase) propellants tem~.~This concept eliminated the propellant con- with minimal amount of soakback to the feed system. ditioning equipment on the oxygen side, while avoiding Demonstration of pulsing liquid H/O thrusters, however, the distribution of liquid hydrogen, which is a deep came too late to impact the Shuttle APS program. cryogen. Ignition requirements with gaseous hydrogen and liquid oxygen were thought to be similar to the The primary candidates for Shuttle RCS were Pratt & Whitney RL-10 engine. systems with liquid storage and gaseous feed of propel- lant~.~~~After a preliminary screening, two gaseous feed Vehicle studies concluded that a smaller orbiter RCS concepts3 (one using high-chamber-pressure engines, vehicle with external, expendable main engine tankage the other using low-chamber-pressure engines) were would provide a more cost effective launch system. 4 examined in detail by McDonnell Douglas Astronautics This resulted in a reduction in shuttle size along with a Corp. and TRW Systems Group, Inc. reduction in RCS impulse requirements. An analysis showed that the downsized vehicle did not have sufficient In the high-chamber-pressure RCS concept^,^*^*^ the volume for the H/O OMS, and development of H/O propellants would be stored as liquids in low-pressure, technology was not considered justifiable without insulated tanks. Turbopumps, driven by gas generators, application to both OMS and RCS. A program decision would be used to raise propellant pressures. Heat was then made to design the APS for MMH and NTO exchangers, also driven by gas generators, would condi- propellants. The H/O technology development contin- tion the propellant. Different configurations using the ued in a limited fashion to provide a backup for the gas generators in series and in parallel with the turbo- MMH-NTO system. pumps and heat exchangers were investigated, as was the use of multiple gas generators. The propellants would be Space Tug stored in gaseous accumulators, to be fed to the thrusters at a regulated pressure. The accumulators would also In the 19'10'~~the Space Tug vehicle was proposed to supply propellants to the gas generators. Thrusters carry payloads from the Shuttle payload bay in low would operate at 2.07 to 3.45 MPa (SO0 to 500 psia) Earth orbit to high Earth orbit.