NASA’s JPL looks to boost power from nuclear batteries
NASA’s Curiosity rover took this self-portrait. The “fins” of the MMRTG are clearly visible. Photo Credit: NASA
Radioisotope thermoelectric generators (RTGs) have been the power source for many of the most ambitious exploration missions in NASA’s history, powering spacecraft in areas too remote, or too impractical, for solar panels to provide sufficient electricity. A new development to this power-generating workhorse may soon substantially improve the capabilities of the RTG, possibly benefiting both interplanetary missions and daily life here on Earth.
In an Oct. 13, 2016, release, NASA’s Jet Propulsion Laboratory (JPL) outlined the potential to increase the efficiency of the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), and make it hardier in the process.
“NASA needs reliable long-term power systems to advance exploration of the Solar System,” said Jean-Pierre Fleurial, supervisor for the thermal energy conversion research and advancement group at JPL.
JPL materials engineer Samad Firdosy holds a module made of four thermocouples. Photo Credit: NASA / JPL-Caltech
To that end, JPL engineers look to make use of a class of materials known as skutterudites. These minerals have the electrical conductivity of a metal while maintaining the thermal insulation characteristics of glass.
Skutterudites hold the promise of increasing the available power to a spacecraft by nearly 50 percent at the end of its 17-year design life, as compared with current MMRTGs.
“We needed to design high-temperature compounds with the best mix of electrical and heat transfer properties,” said Sabah Bux, a technologist at JPL who works on thermoelectric materials. “Skutterudites, with their complex structures composed of heavy atoms like antimony, allow us to do that.”
Should the enhanced MMRTG (eMMRTG) be developed, it would contain the same 768 thermocouples as the MMRTG used in Curiosity’s power generating system, though they would be made of the skutterudite material instead of the tellurium-based thermocouples in current systems.
The increased efficiency of an eMMRTG means that a mission can make use of less radioactive material, like plutonium, allowing for greater mission flexibility.
With the rest of the eMMRTG being essentially the same as its less-efficient MMRTG sibling, development of the generator should be relatively straightforward.
“Only minimal changes to the existing MMRTG design are needed to get these results,” noted Fleurial.
The new eMMRTG passed its first major NASA review in 2015, and should it fare as well in its 2017 and 2018 reviews, the generator could power the next New Frontiers-class mission.
RTG Technology
Though an RTG may ultimately derive its power from nuclear materials, it is not a traditional nuclear power system. Rather than utilizing the splitting of single atoms (fission) or the joining of two atoms (fusion) to drive steam-powered power generators, RTGs rely on the natural decay of radioactive materials to produce heat.
This heat is passed to one side of a thermocouple, which is made of two thermoelectric materials joined at one end. The area where the materials are joined, called the “shoe”, generates an electric voltage from the two dissimilar thermal states. These thermocouples are joined end-to-end, creating one long circuit and generate enough power to suit the needs of robotic explorers like NASA’s Curiosity rover and the New Horizons spacecraft.
However, one need not be an interplanetary voyager to make use of the technologies being developed for the eMMRTG.
In 2015, JPL licensed several patents on high-temperature thermoelectric materials to Evident Technologies. The Troy, New York, company currently provides similar materials for terrestrial applications.
“We feel that there is an unmet need for customers who want to convert high-temperature heat into electricity,” stated Clint Ballinger, CEO of Evident Technologies.
Being able to harness the waste heat and convert it to electricity could provide substantial benefits in fuel and energy efficiencies for both consumer and industrial applications.
“We are excited to capitalize on these NASA advances and plan to launch commercial products very soon,” said Ballinger.
Video courtesy of NASA JPL
Curt Godwin
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.
