February 1960: SNAP - the dawn of nuclear satellite propulsion

On June 29, 1961 Transit IV-A became the first spacecraft to carry a radioisotope power supply into space, and in February of the previous year The Engineer was given a brief glimpse into the development of the nuclear power source.

Transit IV-A was one of several artificial Earth satellites designed at fabricated by Johns Hopkins University Applied Physics Laboratory (APL) in Maryland, USA as part of the ARPA-funded Transit programme, which established the basis for the wide acceptance of satellite navigation systems. As well as carrying a radioisotope power supply, Transit IV-A was notable also for breaking an APL mission-duration record and confirming that the Earth’s equator is elliptical.

A year before launch, The American Scene section of The Engineer took at look at the prototype of a lightweight, high-temperature nuclear reactor designed to generate heat to produce 3kW of electric power for spacecraft.

The reactor, dubbed the SNAP Experimental Reactor, weighed approximately 220lb without shielding and was fuelled with enriched uranium. Our American editor filed a report after it had been test-operated at design power and temperature.