Deep inside some of NASA’s most famous space probes lie plutonium-filled hearts beating to warm and power robots, including a twin. Voyager spacecraft, Cassini before his daring breakthrough through the rings of Saturn and New Horizons trekking along the rubble of the Kuiper belt.
But after the Cold War, the US stopped producing its own plutonium. For a time, NASA was able to carry out its missions solely using existing or imported plutonium. But thanks to changes in the space agency’s partnership with the Department of Energy, fresh American plutonium left Earth again inside NASA’s Mars spacecraft last summer. Persistence all-terrain vehicle – and more missions will do so in the coming years. And this is vital for scientists studying the outer solar system.
“Our journey of discovery requires us to be able to decouple ourselves from our own solar system,” said Abigail Rymer, a space physicist at the Johns Hopkins University Applied Physics Laboratory in Maryland and a member of the Outer Planets Assessment Panel, which advises NASA. Space.com. “We must be able to take our home with us; our power supply should not depend on our own star. The further we go, the more believable it becomes. “
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There are only a few familiar and reliable ways to power a spaceship; plutonium and sunlight are the most common choices. But as the probe moves further into the solar system and further from the Sun, sunlight quickly loses its power: Juno For example, a spacecraft currently orbiting Jupiter requires solar-powered technology to survive without nuclear technology, Rymer said.
So, if you want to send a spaceship to the giant planets of our solar system and beyond, or to other dark places such as permanently dark regions deep in craters near the poles of the moon, you probably need nuclear power. This preference isn’t just about sunlight; Nuclear power also helps spacecraft withstand threats such as cold temperatures and high radiation.
“It allows us to explore where sunlight is not getting, but it also allows us to explore harsh conditions, and that’s because we can take heat with us,” – June Zakrysek, Program Manager for Radioisotope Power Systems (RPS) at NASA. at the Glenn Research Center in Ohio, Space.com reported. “It is reliability and factors that are really important to our missions, and we would not be able to complete some missions without it.”
NASA’s next plutonium-powered spacecraft will be Dragonfly rotorcraft mission launched in 2027 to Saturn’s strange moon Titanium, which the NASA says receives about 1% of the sunlight from the Earth. Due to Dragonfly’s nuclear power source, the spacecraft is likely to freeze amid liquid methane and towering ice-water rocks long before it fails, Zakrysek said.
Dragonfly belongs to the class of NASA missions dubbed New frontiers, the more ambitious level of the agency’s planetary science expedition proposals that NASA is accepting from scientists outside of its centers. The fact that NASA even considered Dragonfly – much less chose it – speaks to the agency’s progress in working with the DOE to increase the supply of plutonium available to mission developers.
Zakraisek said that in a selection campaign for the previous New Frontiers mission, NASA stipulated that the spacecraft should operate without nuclear power, as the agency was not confident that the partnership would have enough plutonium to support the new mission. (IN OSIRIS-REx during this round, the mission to explore the near-Earth asteroid Bennu was selected.)
Zakrysek called the availability of fuel for the recent selection “a big deal.” “The fact that we no longer make mission-limiting decisions based on RPS. [radioisotope power systems] “This is important,” she said. “This seems to make scientists a little happier.”
The move is partly due to NASA’s decision to assess its plutonium requirements annually over the next decade, which gives the partnership additional training to secure the necessary supplies, she said. It also stems from the Department of Energy’s decision to produce plutonium for spacecraft at a constant rate – a dramatic change from the previous process.
“NASA would walk up to the department and tell us, ‘Hey, we have a mission coming up,’” Tracy Bishop, deputy assistant secretary for nuclear infrastructure programs at the Department of Energy, told Space.com. “We’ll take equipment out of standby, go and hire new personnel, retrain equipment and processes, produce fuel, support RPS development – and once the mission is complete, we’ll shut down the capabilities and put them on cold standby until the next addition.”
This system was designed in part because NASA spacecraft are only used by the DOE for this material, plutonium oxide, also called plutonium-238… And a spacecraft may not be what is first thought about when asked about plutonium. “Our use is by far the least known of those for which plutonium is used,” Rymer said. (Plutonium used in nuclear weapons and reactors contains an extra neutron compared to plutonium used in space travel.)
But in 2017, NASA and the Department of Energy decided that the intermittent process was too risky for a spacecraft that couldn’t launch without plutonium-238. Bishop said that with the new stable production system, the agency hopes to cut production times by two years, which could take up to ten years.
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The plutonium aboard the Perseverance rover speaks to the impact of this new approach. The Department of Energy had no plans to supply this spacecraft with fuel. But the first plutonium from the new production process was ready and had to be evaluated anyway, so once the agency determined it was NASA compliant, program officials decided to go ahead and finish preparing the material a couple of years ahead of schedule to test the systems. … Bishop said. She noted that the success of the project has increased the DOE’s confidence that it can meet NASA’s future fuel needs.
“It’s very easy to turn the dial a little if the projection of the mission changes from the disc off and now you have to turn it on and wait for it to warm up and go into the process,” she said. “It’s more of a fine tuning now.”
While the DOE is ramping up plutonium production, NASA is working to develop the next generation of power systems that will contain this plutonium, with the work focusing on two different approaches, Zakraisek said.
One, called a dynamic radioisotope energy source, can be three or four times more efficient than the current standard, the multipurpose radioisotope thermoelectric generator (MMRTG). However, a dynamic system is tricky because, as the name suggests, it includes moving parts.
“Space is difficult, and it is really difficult for moving systems,” Zakrysek said. She noted that NASA is currently working on the design of such a system that could potentially be ready for a test flight to the moon towards the end of the decade.
The second approach builds on NASA’s own legacy, based on the nuclear power systems of the very first spacecraft. This system would be an improved, more efficient version of the general purpose RTGs (GPHS) that were flown in Galileo, Cassini and New Horizons. Zakrysek said such an energy source would be especially attractive for larger missions heading to Neptune or Uranus.
Coincidentally, Rymer has led a team exploring exactly how such a hypothetical mission might study Neptune and its biggest moon, Triton… She described the intricate process of trying to “shave every watt and gram we can” of tools to meet the limitations of launching capabilities and power supplies without sacrificing scientific goals.
“It’s a huge effort because it’s one of the things we can control,” she said. “Physics tells you how much energy you need to survive to get to your goal, but we have scientists and engineers who can optimize how much energy you need to use when you get there, so we really devote quite a bit to this. attention “.
Based on current production schedules, if the Dragonfly mission were the only previous nuclear powered spacecraft, there would be hardly enough plutonium to power the hypothetical Neptune / Triton mission.
However, there is a chance that another mission will join the queue. NASA will soon announce which of four finalists he chose in less Opening class missions. (This program includes spacecraft such as the Lunar Reconnaissance Orbiter and the Martian geological lander InSight, as well as future missions on the asteroids Lucy and Psyche.)
One of the four finalists, Trident, will explore Triton and rely on two nuclear power units. Chances are, if this mission is chosen, NASA will skip the larger Neptune / Triton idea to avoid duplication of scientific work, but there are many other distant worlds worth exploring. And the ongoing specter of scarcity points to limitations that scientists still need to keep in mind when considering future spacecraft.
It’s just a limitation that NASA hopes to remove through a retooling partnership with the Department of Energy.
“If plutonium were produced continuously, we would have a large stockpile of this plutonium,” Rymer said. “I hope this will be the situation in which we will find ourselves in a few years.”
Email Meghan Bartels at mbartels@ or follow her on Twitter @meghanbartels. follow us on Twitter @Spacedotcom and on Facebook.