One of my most useful references doesn’t sound all that relevant. Gail Marcus’s Nuclear Firsts might seem like a Guinness Book of Records but is chock full of entrancing facts. For example:
The first nuclear reactor to operate on a spacecraft was launched on the SNAP-10 satellite developed as part of this program. SNAP-10A was launched by an ATLAS Agena D rocket on April 3, 1965, and maintained a polar, low-earth orbit (500 nautical miles) for 43 days. . . . The reactor itself operated successfully. However, after 43 days, an onboard voltage regulator failed. The failure was unrelated to reactor operation, but the failure caused the reactor core to be ejected into a higher orbit. The reactor was left in a 700-nautical-mile (1300-km) earth orbit, and is expected to remain in orbit for 4,000 years.
Marcus, Gail H. 2010. Nuclear Firsts: Milestones on the Road to Nuclear Power Development. American Nuclear Society, Chicago, Illinois, p. 199.