For space agencies and the commercial space industry, the priorities of the next two decades are clear. First, astronauts will be sent to the Moon for the first time since the Apollo Era, followed by the creation of permanent infrastructure that will allow them to say there for extended periods. Then, the first crewed missions will be sent to Mars, with follow-up missions every 26 months, culminating in the creation of surface habitats (and maybe a permanent base). To meet these objectives, space agencies are investigating next-generation propulsion, power, and life support systems.
This includes solar-electric propulsion (SEP), where solar energy is used to power extremely fuel-efficient Hall-Effect thrusters. Similarly, they are looking into nuclear thermal propulsion (NTP) and compact nuclear reactors, allowing for shorter transit times and providing a steady power supply for Lunar and Martian habitats. Beyond NASA, the UK Space Agency (UKSA) has partnered with Rolls-Royce to develop nuclear systems for space exploration. In a recent tweet, the international auto and aerospace giant provided a teaser of what their “micro-reactor” will look like.
Thermoelectric generators have been integral to long-range space exploration for decades. The first missions to rely on them include the Viking 1 and 2 orbiters and landers that were the first to explore the surface of Mars. The Voyager 1 and 2 probes, currently in interstellar space, also relied on thermoelectric reactors that allowed them to remain in operation for more than 45 years. In recent decades, multi-mission radioisotope thermoelectric generators (MMRTG) have enabled missions like the New Horizons probe and the Curiosity and Perseverance rovers.
Looking toward the future of space and the exploration goals of NASA, the ESA, China, and others, researchers are considering nuclear technologies that have been thoroughly tested since the early space age – like the Nuclear Engine for Rocket Vehicle Application (NERVA). More recent efforts have led to programs like NASA’s Kilopower Reactor Using Stirling TechnologY (KRUSTY) and the NASA/DARP effort to realize a spacecraft that would rely on nuclear-thermal propulsion (NTP). Not to be left behind, the UKSA (an integral part of the ESA) has partnered with Britain’s chief aerospace developer.
The partnership was announced in December 2021, with Rolls-Royce stating that they had signed a contract with the UKSA to study nuclear power options for future space missions. The resulting technology will provide propulsion and power systems for long-duration missions far from Earth, where solar power is not always an option. This includes the South Pole-Aitken Basin, where NASA, the ESA, China, and Russia are all planning on building surface habitats in the coming years. In this region, a single “lunar night” lasts fourteen days, followed by another fourteen days of perpetual sunlight.
During a Martian year (which lasts roughly 687 Earth days), the distance between Mars and the Sun ranges from 1.38 to 1.66 times the distance between the Earth and the Sun. As a result, Mars receives about half the energy Earth does, and seasonal dust storms can lead to heavily-overcast skies that can play havoc with solar panels. Some examples include the Opportunity rover, which remained in continuous operation on Mars for 15 years until a global dust storm in 2018 ended the mission. More recently, the InSight lander ceased operations due to the build-up of dust on its solar panels.
Another issue with sending crewed missions to Mars is the transit times involved. The current mission architecture for NASA and the China National Space Agency (CNSA) is to launch missions every 26 months to coincide with Mars and Earth being at their closest points in their orbit (aka. a Mars Opposition). Using conventional technology, these missions will take (at minimum) six months to reach the Red Planet. During that time, the crews will be exposed to elevated levels of solar and cosmic radiation and living in microgravity.
As per the agreement, Rolls-Royce is developing a “micro-reactor” to enable nuclear propulsion and surface base power. The concept was unveiled in October 2021 at the International Astronautical Congress (IAC) conference in Dubai. As they described in a press release, the system would be capable of providing power in the “watts to megawatts” range, and the technology would have applications in space and here at home. They further stated that they planned to have a prototype micro-reactor prepared for 2029. Abi Clayton, the Director for Future Programs at Rolls-Royce, said at the time:
“Alongside the micro-reactor technology, we are also providing our nuclear knowledge in the development of Radioisotope Power Systems, and the space opportunities of converting ‘decay heat’ into electrical energy via thermoelectric generators or moving parts. This is a very exciting time for the Future Programmes team and the development of nuclear power across Rolls-Royce.”
The early mockup shown in the tweet is the same design as the mini-reactor presented at the IAC 2021. This time, however, the company provided a few more details about how it will operate, writing, “A Rolls-Royce Micro-Reactor is designed to use an inherently safe and extremely robust fuel form. Each uranium particle is encapsulated in multiple protective layers that act as a containment system, allowing it to withstand extreme conditions.”
Other teasers, like the many videos and artist impressions featured on the Rolls-Royce Space website, show the many applications and roles they hope this technology will have. These include reactors that would power surface habitats on the Moon and Mars (to which they include resource acquisition and use) and fast-transit nuclear spacecraft that will explore beyond the Earth-Moon system and even beyond Mars. Other potential applications include hypersonic space planes, small satellites, and on-orbit assembly.
While the details of the micro-reactor are still limited, it is clear that the UKSA and Rolls-Royce are intent on being an active part of the future of space exploration and the commercialization of space. Said Amanda Solloway MP, Parliamentary Under Secretary of State and Minister for Science, Research and Innovation:
“As we build back better from the pandemic, it is partnerships like this between business, industry and government that will help to create jobs and bring forward pioneering innovations that will advance UK spaceflight. Nuclear power presents transformative possibilities for space exploration and the innovative study we are conducting with Rolls-Royce on this could help to propel our next generation of astronauts into space faster and for longer, significantly increasing our knowledge of the universe.”
Further Reading: Rolls-Royce Space