Interest grows in nuclear propulsion for deep-space transportation
By Bryan Palaszewski and Kurt Polzin |December 2024
The Nuclear and Future Flight Propulsion Technical Committee works to advance the implementation and design of nonchemical, high-energy propulsion systems other than electric thruster systems.
In August, DARPA and NASA completed a preliminary design review of their DRACO spacecraft. The goal of the Demonstration Rocket for Agile Cislunar Operations program is to demonstrate in-space nuclear thermal propulsion, NTP. A Lockheed Martin-built spacecraft will be propelled by a nuclear reactor designed and fabricated by Virginia-based BWX Technologies. Progress was also made in fuel manufacturing risk-reduction testing, component environmental and functional testing and test article fabrication. Plans call for a United Launch Alliance Vulcan Centaur rocket to launch the DRACO spacecraft in 2027. The U.S. Space Force will oversee the launch, referred to as USSF-25.
For missions beyond DRACO, NASA continued to mature NTP technology under its Space Nuclear Propulsion project. Funded by NASA and the U.S. Department of Energy, California-based General Atomics and Ultra Safe Nuclear Corp. of Washington refined NTP reactor designs, performed several manufacturing demonstrations of reactor components and executed multiple test and evaluation campaigns in January, March and August. Among the tests, the companies exposed reactor fuel samples to a hot hydrogen gas environment at NASA’s Marshall Space Flight Center in Alabama, experimenting with various protective materials and features in tests where temperatures were rapidly increased to mimic the operating profile of an NTP engine.
Also under the Space Nuclear Propulsion project, the University of Alabama in Huntsville in January conducted a wide range of trade studies and sensitivity studies regarding utilizing NTP for robotic missions to the outer planets. This work studied missions to the outer gas giants using an NTP engine with a thrust in the range of 12.5-15 thousands of pounds force. The specific impulse analyses showed that a 13-klbf engine with a specific impulse as low was 850 seconds could propel flagship-class spacecraft to the outer gas giant planets on a direct-transfer trajectory, reaching the destination in some cases years earlier than previous missions that used gravity-assist trajectories. A separate study, conducted by Analytical Mechanics Associates of Denver, found that a 30-40 kilowatt-electric nuclear electric propulsion-powered spacecraft, possessing a high Earth departure velocity, could deliver a Cassini-sized payload to Saturn on a direct-transfer trajectory in seven years — or in significantly less time if the departure velocity is greater.
In January at AIAA’s SciTech Forum in Orlando, researchers from NASA Marshall, NASA’s Glenn Research Center and the U.S. Department of Energy presented a technology assessment for transformational space transportation options. Requested by NASA’s Space Technology Mission Directorate, the study recommended near-term or sustained investments to make meaningful progress toward maturation for far-term fast transit spaceflight.
In July, NASA analyses of atmospheric mining in the outer solar system, AMOSS, were presented at AIAA’s ASCEND conference in Las Vegas. AMOSS would allow the mining of nuclear fusion fuels from the atmospheres of Uranus and Neptune. In one concept, a nuclear-powered aerospacecraft would cruise in the atmosphere, capturing the helium-3 and deuterium for refinement into fuels that would power fusion rockets to various destinations in the solar system. To assist the mining, nuclear orbit transfer vehicles would be powered hydrogen mined from the water ice on the planet’s moons. Capturing the water ice and separating the water ice from the moon regolith are major challenges. For a 100-metric-ton water mining operation, if the water accounts for 75% of a 10-metric-ton payload machine, approximately 14 machines would be needed. Based on past analyses, the water ice fraction on the moons of Uranus could be very high, making mining more efficient. If the mass fraction of water in the regolith is below 10%, many hundreds of machines would be required.
