Nuclear Powered Space Missions - Past and Future
by Regina Hagen

August 11, 1998


  1. See Chapter 7, Literature List for references. Page numbers are given for formatted and page-oriented documents. DoE develops and produces all RTGs used by DoD and NASA.

  2. So far, no nuclear powered space missions seem to have been launched by other countries. However, the European Space Agency as well as individual universities and research institutes from other countries used U.S. and Russian space missions to send their own experiments/instruments/probes into space.

  3. Invaluable information about the use of nuclear power in space by NASA as well as by the U.S. military can be found in many articles as well as in a book and a video by journalistic professor Karl Grossman. For the purpose of this article, however, it seemed to make sense to not quote him but official sources. Some of Karl Grossman's publications are listed at the end of Chapter 7, Literature List.

  4. Different information about RTG safety features can be found in the articles of Karl Grossman and Michio Kaku in this Working Paper.

  5. Various DoE and NASA documents give different numbers of previous nuclear powered space missions, namely between 21 and 25. Chapter 3: Past Missions - a Chronology lists 30 corresponding missions.

  6. Translation of the quotation by the author of this article.

  7. The amount and enrichment of the U-238 in the Soviet RORSAT nuclear reactors stated by Harro Zimmer is confirmed by the Bellona Report, see [NILSEN].

  8. For more details about the coolant debris, see the information for Kosmos 1176.

  9. Translation of the quotation by the author of this article.

  10. For further information about solar cells development for deep space missions, see Gerhard Strobl's article in IANUS 5/1998 Working Paper "Energy supply for deep space missions", Martin B. Kalinowski (Ed).

  11. Plutonium-238 is not identical to the weapons-grade plutonium-239 used for nuclear weapons. For details about the effects and toxicity of Pu-238 see the articles of Karl Grossman, Michio Kaku, and Roland Wolff in IANUS 5/1998 Working Paper "Energy supply for deep space missions", Martin B. Kalinowski (Ed).

  12. NASA's Cassini FEIS states the source term of all other missions it lists, but not for this reactor.

  13. For more details about the injection of reactors into higher orbit see the information given for Kosmos 198.

  14. The Kosmos missions are sometimes spelled Cosmos.

  15. Tyuratam is a launch site in Kazachstan. The Bellona Report [NILSEN] mentions that the Kosmos missions were launched from Plesetsk. The TRW Space Log 1996 [TRW], however, names Tyuratam for all Soviet nuclear powered space missions.

  16. HEU-235 = highly enriched uranium-235.

  17. In his book "The Wrong Stuff" (Common Courage Press, 1997), Karl Grossman mentions Kosmos 305 as one possible lunar mission which fell back to earth in 1969. As a second one he lists Kosmos 300, launched on Sept. 23, 1996. As this information was not confirmed by the information sources used for this article, Kosmos 300 is not listed here. It should be pointed out, however, that the TRW Space Log 1996 explicitly mentions two modules for Kosmos 305. Therefore, it may be concluded that this mission carried two reactors.

  18. One DoE list [USDOE/d, pages 15/16] also mentions Apollo 11 which was launched on July 16, 1969. It states 'ALRH' as the power source. The text continues to say that Apollo 11 was equipped with RHUs (Radioisotope Heater Units) for the seismic experimental package. Therefore it may be assumed that no RTG was on board for this mission.

  19. Apollo 13 did not reach the moon.

  20. Although the TRW Space Log 1996 [TRW] often gives information about the mission status, this is not the case for the two Topaz test missions Kosmos 1818 and Kosmos 1867.

  21. The Berlin database [ILR] does not include this information. However, there is no reason to believe life duration should be any different from the other Kosmos missions.

  22. Radioactive Heater Units (RHUs) were used on all Apollo and interplanetary missions. One recent example of RHU usage is the otherwise solar powered mission Sojourner/Pathfinder which landed on Mars on July 4, 1997.

  23. For further details about Cassini, see the articles by Karl Grossman and Michio Kaku in IANUS 5/1998 Working Paper "Energy supply for deep space missions", Martin B. Kalinowski (Ed).

  24. Private communication with a Russian space engineer; he quoted an ITAR-TASS press release of February 10, 1998.

  25. Although no origin is stated on the hardcopy available to the author of this article, it is safe to assume that the spreadsheet was created by DoE and lists the plutonium-238 inventory required to build the RTGs for the planned NASA missions. As the lists refers to requirements from 1992-2001, the spreadsheet has probably been created in 1992. Earlier compilation of the list is unlikely, as according to [JPL/CIT] a Pluto Flyby mission was first considered in 1992.

  26. Identical to the Europa Ocean Explorer mission.

  27. Identical to the Titan Biologic Explorer mission.

  28. A document by Malin Space Science Systems, Inc., also deals with financial issues. See Section 4.6.12 - Venus Lander.

  29. In a DoE statement from March 1998 [USDOE/e] the figure given for R&D (research and development) alone, i.e. without actually building any RTGs, is $40.5 million. See table.

  30. Additional information about Solar Concentrator Arrays can be found at NASA's home page for the Deep Space 1 mission, see In addition to using exclusively solar concentrators, Deep Space 1 will also use Solar Electric Propulsion (Ion Propulsion). For details see

  31. SEP = Solar Electric Propulsion

  32. Radioisotope Thermal Generators (RTGs) are not permitted on Discovery missions proposed to this AO. Other, smaller radioactive sources (such as radioactive heating units or instrument calibration sources) are permitted." [NASA/a]

  33. About the Outer Solar System Program, the Solar System Exploration Subcommittee writes:
    "Technology development progress should govern mission selection, with the goals of conducting the overall program at the lowest possible cost and maximizing science return from the individual missions. A set of decision gates will be laid out to indicate when mission targets must be selected and what criteria will be used. Generally the final selection will be made about 3 years prior to launch." [NASA/i]
    Although technology development is analyzed by the Subcommittee, non-nuclear power supply is not an issue. Instead, one of the technology criteria are that "all top-priority needs can be met by existing programs" [NASA/i].
    Other technology issues are lightweight, low-cost, high-performance chemical propulsion, sensor/detector and instrument development, and avionics development.

  34. 1 AU = 1 Astronomical Unit = the mean distance from the Earth to the Sun. So 80-90 AU equals 80 to 90 times the distance between Sun and Earth.

  35. "Nuclear or RTG electric propulsion" is very imprecise. Nuclear propulsion has been under consideration for many years, is not identical with the RTG technology used to provide electrical energy for instruments, however.

  36. For detailed information about the Mars missions, see

  37. 1 AU = 1 Astronomical Unit = the mean distance from the Earth to the Sun. So 10-20 AU equals 10-20 times the distance between Sun and Earth.

  38. This document also gives information about NASA's effort to use state-of the art and miniaturized technology to keep the mission small (and therefore cheaper as a smaller launch vehicle can be used.) The article explains that many of the "enabling technologies result from breakthroughs by the Ballistic Missile Defense Organization (BMDO)." [JPL/CIT]

  39. Cassini uses a Venus-Venus-Earth-Jupiter Gravity Assist (VVEJGA) trajectory.

  40. High natural background radiation is a mission problem in the Jupiter environment.

  41. These are the Mars missions; see Section 4.6.6.

  42. The MSSS document was written in 1996.

  43. Although ESA press releases back to 1993 are available in the Internet, this one is not provided online. Another press information numbered "07/94" is listed instead.

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