[9] In 2001, the Safe affordable fission engine was under development, with a tested 30 kW nuclear heat source intended to lead to the development of a 400 kW thermal reactor with Brayton cycle gas turbines to produce electric power.
[citation needed] Project Prometheus was an early 2000s NASA study on nuclear electric spacecraft.
[citation needed] Kilopower is the latest NASA reactor development program, but is intended for surface use only.
March 2016 - First batch of nuclear fuel received[citation needed] A pebble bed reactor using high mass-flow gaseous nitrogen coolant near normal atmospheric pressures is a possible heat source.
Nuclear fuel would be highly enriched uranium encapsulated in low-boron graphite balls probably 5–10 cm in diameter.
This reduces the risk of an unplanned release of radioactive elements, including fission products.