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Inside the Air Force
March 2, 2001

Military looks to solar power for spacecraft


Budget constraints and recent advances in solar cell technologies have ended what one industry analyst calls the Defense Department's longstanding “flirtation” with developing nuclear power sources for spacecraft, according to industry and Pentagon sources.

“The military had an ongoing flirtation with nuclear power for nearly 50 years, and now they are saying it is over,” said Steven Aftergood, senior research analyst at the non-profit Federation of American Scientists, a think tank based in Washington, DC.

Nuclear power offers at least a 100-fold increase in power generation over traditional technologies -- such as solar power or heat-based power -- which explains DOD's affinity for the technology as it relies more and more on space-based assets for its operations, according to Aftergood.

However, he notes that the Pentagon's recently released Space Technology Guide does not mention nuclear power, an omission he describes as a “real shift in DOD policy,” or at least a significant departure.

The National Space Policy and the Defense Department's space policy remain the same, said Pentagon spokeswoman Susan Hansen.

“Both policies preclude the use of nuclear power in Earth orbit without the specific approval of the president. Any requests for approval must take into account public safety, economic considerations, treaty obligations and U.S. national security and foreign policy interests,” Hansen wrote in a statement for Inside the Air Force. “Those policies have been in place for quite some time and have not changed.”

DOD created the Space Technology Guide in response to Congress' request for an overarching guide of investments in key technologies needed for national security space purposes. Congress requested the guide in the fiscal year 2000 defense authorization act, and the Defense Department released it earlier this month (ITAF, Feb. 9, p16).

The guide includes a list of “key enabling technologies” for national security space that identifies a need for investment in advances for solid rocket motors, electric and plasma thrusters and solar and chemical power generation. Nuclear power does not appear on the list.

In a query submitted to Charles Williams, who works on such issues in the office of the assistant secretary of defense for command, control, communications and intelligence, Aftergood suggested that the official omission of nuclear power in the guide could be the result of political pressures or technical considerations.

In his response to Aftergood, Williams said that while politics and technical challenges were factors, the key reasons for the subject's removal from the guide were funding and public safety.

“In the STG, the Congress asked for an investment strategy for space technology. Given the severely constrained funding available for space technology development, funds for nuclear power devices would not make the priority cut,” Williams wrote.

“Even if we could produce them economically, the mission costs would be unaffordable because of the measures necessary for safety.

“These scarce resources are needed to fund technologies that provide real, accountable leverage to meet future mission requirements,” he continued. “These economic and technical reasons obviate any need to pursue nuclear power options.”

Additionally, Hansen noted “there is no DOD requirement for nuclear power sources for spacecraft. All of our space-based power needs are being met with alternative methods, such as vastly improved and more efficient solar cells, new battery technologies, and future power technologies such as flywheels.”

Advances in solar cells are also “more than sufficient to maintain ample power supplies,” Williams added.

Before these alternate technologies matured, however, the Pentagon frequently funded research efforts into nuclear reactors for satellites. As recently as 1991, the Pentagon funded classified work on a nuclear-powered rocket engine program called Timberwind that was part of the Strategic Defense Initiative, Aftergood said.

Prior to Timberwind, DOD dabbled in various programs -- some as a partner with the Energy Department or NASA -- to produce space-based nuclear reactors. Timberwind evolved out of such programs as SP-100, on which Aftergood said DOD spent about $500 million, and the Multi-Megawatt program, which is considered a basis for much of the modern understanding of space-based nuclear power technology. DOD also participated in a program that in 1965 launched an experimental reactor into space; the reactor malfunctioned 43 days later, Aftergood said.

Although the National Space Policy and the Defense Department's space policy require presidential approval for the launch of payloads containing nuclear reactors, that stipulation has not prevented DOD's involvement in such projects, Aftergood said. In his four years in office, former President George Bush approved two such launches.

While recent advances in other technologies provide the Defense Department with a more politically correct and safer source of energy preferable for use on spacecraft on Earth orbit, Williams noted in his correspondence to Aftergood that “the only type of mission where space nuclear power would be needed is an interplanetary one, such as NASA's Cassini mission to Saturn.” On such a long journey, solar and battery power could not alone power a spacecraft, William said. Indeed, Aftergood said he expects NASA to continue investing in space-based nuclear power alternatives for spacecraft.

However, the Defense Department's Earth-focused mission precludes further involvement on a practical basis, he added. -- Amy Butler

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