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Preprint UCRL-JC-135315 Water Rocket - Electrolysis Propulsion and Fuel Cell Power F. Mitlitsky, A. H. Weisberg, P. H. CatYet-, M.D. Dittman, 63. Myers, R. W. Humble, J. T. Kare This article was submitted to American Institute of Aeronautics and Astronautics Space Technology Conference and Exposition, Albuquerque, NM, September 28-30, 1999 July 24,1999 U.S. Department of Energy Approved for public release; further dissemination unlimited DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. AIAA-994609 WATER ROCKET - ELECTROLYSIS PROPULSION AND FUEL CELL POWER F. Mitlitsky*, A.H. Weisberg*, P.H. Carter*, M.D. Dittman*, and B. Myers’, Lawrence Livermore National Laboratory, L-174, Livermore, CA 94551-0808; [email protected] R.W. Humble* Astronautics Department, United StatesAir Force Academy, Colorado Springs, CO J.T. Kare* Kare Technical Consulting, San Ramon, CA Abstract many mission scenarios, solar cells can be used Water Rocket is the collective name for an integrated set of opportunistically to produce propellants (or generate technologies that offer new options for spacecraft reactants to store electrical energy), so that Water Rocket propulsion, power, energy storage, and structure. Low can be implemented without adding solar cells beyond pressure water stored on the spacecraft is electrolyzed to payload requirements. The pressure vessels required for generate, separate, and pressurize gaseous hydrogen and storing propellants (or reactants) often will be strong oxygen. These gases, stored in lightweight pressure tanks, enough to serve as vehicle structure. Mass savings from can be burned to generatethrust or recombined to produce subsystems with multiple functions expand the range of electric power. As a rocket propulsion system, Water missions for which Water Rocket is advantageous. The Rocket provides the highest feasible chemical specific core of that range comes from the best chemical Isp impulse (-400 seconds). Even higher specific impulse available from storable propellants. This range of propulsion can be achieved by combining Water Rocket applications is a new niche for spacecraft, allowing the with other advancedpropulsion technologies, such as arcjet rapid maneuvers of chemical thrusters but obtaining the or electric thrusters. With innovative pressure tank energy for propulsion by accumulating solar power. technology, Water Rocket’s specific energy [Wh/kg] can exceedthat of the best foreseeablebatteries by an order of A Water Rocket spacevehicle may be totally inert and non- magnitude, and the tanks can often serve as vehicle hazardous at launch. Minimal insulation and redundant structural elements. For pulsed power applications, Water layers of leak sealing make a Water Rocket designed to Rocket propellants can be used to drive very high power launch unpressurizedentirely harmless to other equipment, density generators, such as MHD devices or detonation- and essentially unregulated. Thus Water Rocket enables driven pulse generators. A space vehicle using Water rapid prototyping and space testing of space vehicles Rocket propulsion can be totally inert and non-hazardous without long delays caused by range safety (or Shuttle during assemblyand launch. These features are particularly safety) concerns. This is particularly important for the important for the timely development and flight timely developmentof microsats and nanosats. qualification of new classes of spacecraft, such as microsats, nanosats,and refuelable spacecraft. Water Rocket’s capability for high Isp propulsion, combined with the low mass overhead required to store Introduction unpressurizedwater, can take secondary payloads through New options for spacecraft propulsion, power, energy large total-AV missions. As long as the totaldV storage, and structure are enabled by an integrated suite of requirement of a mission can be broken up into several technologiesknown as Water Rocket. High Isp propellants bums, allowing gas tanks to be refilled several times during can be generated,separated, and pressurized on-the-fly by a mission, Water Rocket outperforms (in preliminary, the electrolysis of low pressure water. Water can also be unbiased comparisons) conventional chemical propulsion the medium for high energy density electrical energy (due to propellant mass savings) for total-missiondv storage. The same hardware and resources are used for above -1.3 km/s. This is particularly attractive in orbit propulsion and energy storage, allowing operational water transfer, satellite repositioning, lunar, and Earth-escaping allocation decisions to be made during the mission. In missions. * Member AIAA + AssociateFellow AIAA Copyright (c) 1999by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 1 American Institute of Aeronauticsand Astronautics L AIAA-99-4609 .“” URFC Electronics Bladder Expulsion Tank lStructure Proton Exch gH, igo, Maneuvering Thruster Electrolyzer (Charge) Figure 1. Schematic of Water Rocket and Unitized Regenerative Fuel Cell (URFC) Besides enabling high total-AV missions for secondary l Unitized re&enerative fuel cell (URFC) is both a payloads and enabling missions with energy storage propellant generator when operated as an electrolyrer, requirements that would demand excessive battery weight, and an electrical power producer, when operated as a Water Rocket is the best approach to refuelable spacecraft fuel cell becausewater is very easy to handle. Several key aspects . URFC specific energy (Whikg) offers up to an order of of Water Rocket systemsare summarizedbelow: magnitude improvement over batteries l Mass fractions can be dramatically improved for Low pressure water electrolyres into HI/O, gases at systemsrequiring relatively massive batteries pressures up to several ksi; no moving parts are l Integration of structure and tankage allows additional required using some zero-g electrochemical stack massfraction improvement designs Vacuum specific impulse (Isp vat.) of >380 seconds is A schematic of Water Rocket and URFC operation is feasible for near-stoichiomehic gH,/gO, engines shown in Figure 1. (stoichiometric for water is 2 moles of Hz for each mole of 0, or oxidizer/fuel mass retio=7.94) Lawrence Livermore National Laboratory (LLNL) initiated Several km/s mission AV is feasible, mission AV above the design and development of a Water Rocket Propulsion -1.3 km/s advantageous Subsystem in 1998, with the assistanceof: the Air Force Multiple hot burns of tens to hundreds of meters/s ResearchLaboratory (AFRL), the United States Air Force increaseWater Rocket advantages Academy (USAFA), the European Air Force Office of Developed, stable, long life designs for gH,/gOl Research and Development (EAORD), and NASA Glenn enginescan provide a wide range of thrust levels Research Center (GRC), and various industrial partners, Non-toxic propellants and unpressurized tanks create a including United Technologies Hamilton Standard Division non-hazardousspace vehicle at launch (HS), Schafer Corporation, Thiokol Corporation, Aero Tee Integration costs and delays are minimal for inert, non- Laboratories Inc. (ATL), RAND Corporation, and hazardous-at-launchWater Rockets Southern ResearchInstitute (SRI), and several consultants. Water is ideal for indefinite storage, at low pressure, with minimal container massoverhead 2 American Institute of Aeronautics and Astronautics AIAA-99.4609 Plumbing to Engine ~lPr+r”tv7er”eslg”rd fnr IN”.g QH, 00: Encnne ksigned by Suppkd by Hamtlton Standard LLttL. AFRL. and IlASh L&C Figure 2. Solar Powered Water Rocket Brassboard Demonstration at AFRL Edwards AFB, CA on 1116198 USAF). This team also determined the state-of-the-art (SOA) for the key componentsof Water Rocket Systems, and initiated a program plan that could develop and demonstratethe technologies required for a flight-worthy system. Examples of the appropriate component technologies were assembled and integrated for the first time. This team put together and operated a functionally complete Water Rocket hardware brassboard in November 1998, which demonstrated solar-powered electrolytic gas generation using a zero-g capable electrolyzer, pressurizedstorage of the electrolyzed gases, and combustion of those gasesin a 1. I Newton (0.25 lb0 thruster (Figure 2). A close-up photo of the zero-g capablestatic feed electrolyzer is shown in Figure 3. AFRL provided a wealth of information related to Figure 3. Zero-g Capable Static Feed Electrolyzer gH,/gO, engine development and testing. AFRL designed several important elements in the prototype engine used LLNL facilitated copious communication within this for the brassboard.