Batteries: thermoelectric and photoelectric – Thermoelectric – Nuclear energy type
Reexamination Certificate
2000-06-06
2001-12-11
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Nuclear energy type
Reexamination Certificate
active
06329587
ABSTRACT:
This invention relates to a power generator, and, more particularly, to a semiconductor power source that is powered by a fission source of heavy ions and alpha particles.
BACKGROUND OF THE INVENTION
Long-duration space missions require electrical power sources for on-board systems. The electrical power sources must operate reliably for long periods of time using little fuel. Such electrical power sources are to be distinguished from the propulsive engines. Long-duration space missions include, for example, deep-space missions, interplanetary missions, and long-term earth-orbit missions. The electrical power sources must also be relatively light in weight, as they must be initially lifted to orbit.
Solar electrical power sources are widely and successfully used for earth-orbit missions, such as geosynchronous communications satellites. The solar power sources are not practical for deep-space missions and for many lower-orbit missions.
Another approach to such a long-term power source has been small nuclear reactors. A variation of the conventional nuclear reactor favored at the present time for some applications is the Radioisotope Thermoelectric Generator (RTG), which uses the heat produced by fission of fuel to heat a thermopile. The thermopile includes an array of thermocouples which produce an electrical voltage responsive to the heating. In each of these cases, the fuel mass requirement is relatively large. The current version of the RTG utilizes about 10 kilograms of uranium to produce about 60 amperes of current. That is, a large weight of fissionable material must be launched into space on a booster rocket. In addition to the amount of weight that must be lifted, there is an environmental concern with the amount of uranium that is potentially scattered in the event of a booster failure. Additionally, the large amount of excess waste heat generated by such power sources must be radiated into space by large radiators located on the spacecraft, which add to the weight of the spacecraft. An effort is made to radiate the heat uniformly, but there have been indications that slight asymmetries in the amounts of heat radiated in different directions can lead to changes in the velocity of the spacecraft, throwing it off its intended course or orbit.
There is a need for an improved approach to the generation of electrical power for long-duration space missions, particularly deep-space missions. The approach must meet the power requirements, and desirably would overcome or minimize the problems associated with existing power sources. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a power generator that produces electrical power using a small amount of fissioning fuel. The power generator is founded on a layered structure utilizing semiconductor technology. It is compact and may be packaged and encapsulated in a small volume, and is also light in weight. There are no moving parts, and accordingly the power generator is highly reliable. A relatively small amount of waste heat is produced, reducing the problems associated with radiation of the waste heat as compared with conventional electric power sources.
In accordance with the invention, a power generator has a current-generating cell comprising a layer of a fission source of heavy ions and alpha particles, and two semiconductor structures, one on each side of the layer of the fission source. Each semiconductor structure produces electron-hole pairs upon impingement of heavy ions and alpha particles thereon. There are two metal contact layers, each metal contact layer contacting a respective one of the semiconductor structures at a location remote from the layer of the fission source. The power generator also includes a voltage source in electrical communication with the two metal contact layers to apply a collection voltage across the current-generating cell, and two current collector leads, each current collector lead being in electrical communication with a respective one of the two metal contact layers.
The layer of the fission source is preferably either Pu
238
or Cf
252
, and most preferably Pu
238
. Each semiconductor structure may comprise an intrinsic layer, and at least one doped layer contacting the intrinsic layer. The at least one doped layer is a p-type semiconductor or an n-type semiconductor. Preferably each semiconductor structure comprises a doped silicon structure, most preferably wherein there is at least one doped layer contacting an intrinsic layer. The at least one doped layer is a p-type semiconductor or an n-type semiconductor. Examples include layered P-I, N-I, and P-I-N type structures. (In these conventional abbreviations, P stands for p-type, N stands for n-type, and I stands for intrinsic.) In one specific example of interest, the semiconductor structure is a P-I-N structure having a layer of p-type silicon adjacent to the layer of the fission source, a layer of intrinsic silicon adjacent to and contacting the layer of p-type silicon, and a layer of n-type silicon adjacent to and contacting the layer of intrinsic silicon and remote from the layer of p-type silicon.
The voltage source is preferably a thermopile operating from heat produced by the current-generating cell.
At least two current-generating cells as described may be electrically interconnected in series and/or in parallel through their current collector leads to generate the required voltage and current.
The present approach produces electrical current by collection of the electron-hole pairs produced by ionization reactions in the semiconductor materials resulting from bombardment by heavy ions and alpha particles. The power generator is preferably embodied in a thin structure much like a thin-film microelectronic device. A layer of the fission source is sandwiched between the thin semiconductor structures that produce electron-hole pairs upon impingement of the heavy ions and alpha particles. Metal contact layers externally contact the semiconductor structures to serve as electrodes for application of the collection voltage and collection of the electron-hole pairs as a useful current. The typical total thickness of each current-generating cell is about 5 millimeters, so that numbers of such cells may be packed together and arrayed in the manner of microelectronic devices.
The present approach is to be distinguished from the known Radioisotope Thermoelectric Generator (RTG). The RTG uses heat produced by a fissionable mass to heat a thermopile. The thermopile produces the required current. By contrast, in the present approach the required current is produced by electronic interaction of emitted heavy ions and alpha particles with the semiconductor structure. A thermopile may be present, but it produces only the biasing collection voltage applied to the cell and is not the primary current source. Thus, the heat required to operate the thermopile is very small as compared with that required in the RTG. A battery or other voltage source may be used instead of the thermopile to supply the biasing voltage.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
REFERENCES:
Q-Metrics, “Radioisotope Thermolelectric Generator (RTG)”, (1996) pp. 1-2 no month provided.
SpaceViews-Cassini, “The RTG Debate”, May 1, 2000, pp. 1-3.
Katz, “A Possible Explanation”, Oct. 20, 1998, pp. 1.
SpaceViews, “RTG Heat May Account For Anomalous Spacecraft Acceleration”, Oct. 1, 1998, pp. 1-2.
RTG Programs, RTG Program is “Go”, Sep. 30, 1994, pp. 1-2.
Space Link, “Facts About RTG Misconceptions” Sep. 19, 1989, pp. 1-4.
Gorgos Kathryn
Gudmestad T.
Hughes Electronics Corporation
Parsons Thomas H
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