OrbitalHub

NASA dicit:

The Swarm-Probe Enabling ATEG Reactor, or SPEAR, is a nuclear electric propulsion spacecraft that uses a new, lightweight reactor moderator and advanced thermoelectric generators (ATEGs) to greatly reduce overall core mass. This will subsequently require a reduction in operating temperatures and reduce the total power levels achievable by the core. However, the reduced mass will require reduced power for propulsion, resulting in a small, inexpensive nuclear electric spacecraft. This project will also demonstrate the operation of the ATEG conversion system through a series of lab bench tests by showing the improved characteristics of the new device.

Video credit: NASA