Early last month, DARPA issued an RFP for the next phase of their Demonstration Rocket for Agile Cislunar Operations (DRACO) nuclear thermal engine program. This follows on their selection, one year ago, of an early engine design by General Atomics and two spacecraft concepts from Blue Origin and Lockheed Martin. Now they’re moving on to the development and assembly of the engine through a new open RFP (not limited to the aforementioned companies). They hope to have a test flight in 2026, with NASA participating out of interest for use with future crewed deep space missions, as nuclear thermal propulsion can achieve both the required high thrust-to-weight ratio and 2-5 times the efficiency of a chemical engine. One key challenge with nuclear reactors in space is the risk of contaminating Earth. While systems are designed to be safe even in the case of a launch failure, once they’ve been activated, an accidental re-entry could be a radiological disaster. We’ve written about this DARPA program a number of times, as well as NASA’s related efforts and NIAC awards. We also took a dive into the history of nuclear reactors in space in Issue 85 (which we feel is worth a re-read). Relatedly, the DIU just funded two in-space nuclear power research projects as well.