14 December 2006
When the New York Times mentioned in passing recently that polonium-210 had once been used to power U.S. spacecraft, it caused a furrowing of the brow among the seven or so people who dwell on the history of space nuclear power, since it is almost certainly not correct.
"President Eisenhower, eager to promote 'atoms for peace,' had the high heats of polonium 210 turned into electricity for satellites," wrote the estimable William J. Broad in a recent Times Week in Review piece ("Polonium, $22.50 Plus Tax," December 3). "But the batteries lost power relatively fast because of the material's short half-life, just 138 days. The United States made few such spacecraft."
Not so, according to Gary L. Bennett, who devoted much of his career at the Department of Energy and NASA to the development of space nuclear power sources.
"As far as I know, the U.S. never flew a spacecraft powered by polonium-210," Dr. Bennett told Secrecy News.
Dr. Bennett identified one documentary source that claimed otherwise, a history of isotope production at the Mound Laboratory in Ohio. It is consistent with the New York Times account, but he said it too was in error.
That Mound history described the use of polonium in an early radioisotope power supply called SNAP 3A:
"The first SNAP-3A, fueled with polonium-210, provided power to a satellite radio transmitter. The use of satellites powered by SNAP for global communication was first demonstrated under President Eisenhower in 1961, at which time the President's peace message was broadcast via a satellite containing a radio transmitter powered by the SNAP-3A RTG." See (at page 4):
But all other historical accounts agree that the first SNAP-3A was launched on June 29, 1961 (on the Transit 4A spacecraft), after President Eisenhower had left office, and it was fueled with plutonium-238, not polonium-210.
It is true that the SNAP-3A was originally designed with polonium fuel, because of Atomic Energy Commission restrictions on plutonium, according to a deeply researched official history of space nuclear power prepared for the Department of Energy.
A photograph of President Eisenhower in the Oval Office enthusiastically examining a polonium-fueled SNAP battery appeared on the front page of the Washington Evening Star on January 16, 1959. ("Nuclear critic Ralph Lapp complained that a highly lethal item had been placed on the President's desk.")
But "the AEC eventually relaxed its policy and agreed to provide the plutonium fuel and SNAP-3A, as a result, was converted from polonium-210 to plutonium-238," the official history stated (at page 23).
"Despite the president's enthusiasm [in January 1959], the first RTG [radioisotope thermoelectric generator] flight came two and a half years after the White House demonstration," the official DOE history states (page 18).
It was the plutonium-fueled version that was launched into space in June 1961, not the original polonium-fueled design.
See "Atomic Power in Space: A History," prepared for U.S. Department of Energy, March 1987 (188 pages, 8.5 MB):
Polonium-fueled radioisotope power or heater units were used on spacecraft launched by the former Soviet Union on a number of occasions, Dr. Bennett noted.