Thermionics Quo Vadis? An Assessment of the DTRA's Advanced Thermionics Research and Development Program (2001) / Chapter Skim
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4 Solar Thermionics
4 Solar Thermionics
Pages 33-42
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From page 33... ...
In this chapter, the committee discusses potential missions that could use concentrated solar energy as the heat source for a thermionic power conversion system in both standard and hybrid systems. 33 POTENTIAL SOLAR THERMIONIC MISSIONS Solar thermionic converters do not involve many of the problematic technical issues associated with nuclear thermionic conversion, nor does solar conversion technology have to contend with the social controversy surrounding the use of nuclear power systems.
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From page 34... ...
The solar thermionic power conversion system could be used in a dual mode power and electric propulsion configuration. The power conversion system is first used for electric propulsion to maneuver a spacecraft into the proper orbit.
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From page 35... ...
HIGH-POWER, ADVANCED, LOW-MASS CONCEPT For a solar power conversion system using thermionics, solar energy is concentrated into a heat receiver using either reflective or refractive optics. This heat receiver then serves as the heat source for a group of thermionic converters that provide power to the spacecraft.
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From page 36... ...
This process repeats until essentially all of the solar energy is absorbed inside the heat receiver. The aperture would be kept small to minimize both heat loss and the loss of reflected solar energy back out of the aperture.
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From page 37... ...
Based on space vehicle market trends over the past 10 years, the 50 kilowatt design proposed for the HPALM concept appears to be a potentially viable option. The solar thermionic system also appears to have a power density advantage when scaling to higher power levels, while a photovoltaic system has the advantage when scaling down.
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From page 38... ...
A thermal energy storage device would be incorporated into the heat receiver, and energy for operating the spacecraft during eclipse would be stored in a phase change material. Such a material melts as heat is added, then refreezes when the heat is used during eclipse.
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From page 39... ...
Without a heat receiver, the solar energy would be concentrated on different parts of the heat receiver cavity at different points of an orbit, thus creating hot spots in the cavity. If there is no thermal energy storage system to act as a buffer between the concentrated solar energy and the thermionic convert ers, they may produce different amounts of power de pending on the amount of solar energy directed on any one converter.
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From page 40... ...
The committee felt it needed to review the tests in detail since the poor START test results indicated that there was some fundamental failure of the thermionic converter technology. STRING THERMIONIC ASSEMBLY RESEARCH TESTBED TESTS AT THE NEW MEXICO ENGINEERING RESEARCH INSTITUTE The SOTV program is a follow-on to the hydrogen fueled Integrated Solar Upper Stage (ISUS ~ Orbital Vehicle program started in 1994, and the START tests were initiated under that program.
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From page 41... ...
The committee examined the START tests in detail and found problems with the testing, analysis, design, and test fixture fabrication in the START series that should be carefully accounted for in any future tests. Because these problems bring into question the validity of the data that were collected, the committee determined that the viability of thermionic power conversion technology should not be judged based on these tests.
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From page 42... ...
Previous experience in testing thermionic devices indicates that converters can be made to work in seriesconnected circuits to develop a usable voltage level. The committee therefore recommends that the future sponsoring agency look closely at the START tests in order to identify and make use of the lessons learned and increase the probability of a successful test in the future.
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