Radioisotope thermoelectric generators (RTGs) are the power plants of the interplanetary spacecraft. Or at least they have been for going on 50 years now. But they have significant drawbacks, the primary one being that they're heavy. Even modern-day RTG designs run into the hundreds of kilograms, making them useful for large-scale missions like Perseverance but prohibitively large for any small-scale mission that wants to get to the outer planets. Solar sails aren't much better, with a combined solar sail and battery system, like the one on Juno, coming in at more than twice the weight of a similarly powered RTG.

To solve this problem, a group of engineers from the Aerospace Corporation and the US Department of Energy's Oak Ridge National Lab came up with a way to take the underlying idea of an RTG and shrink it dramatically to the point where it could not potentially be used for much smaller missions.

Multiple space agencies plan to send astronauts, cosmonauts, and taikonauts to the moon in the coming years, with the long-term goal of establishing a permanent human presence there. This includes the NASA-led Artemis Program, which aims to create a "sustained program of lunar exploration and development" by the decade's end. There's also the competing Russo-Chinese International Lunar Research Station (ILRS) effort to create a series of facilities "on the surface and/or in orbit of the moon" that will enable lucrative research.

Beyond these government-agency-led programs, there are many companies and non-government organizations (NGOs) hoping to conduct regular trips to the moon, either for the sake of "lunar tourism" and mining or to build an "International Moon Village" that would act as a spiritual successor to the International Space Station (ISS). These plans will require a lot of cargo and freight moving between Earth and the moon well into the next decade, which is no easy task.