As science and technology advance, we are asking our space missions to deliver more and more results. NASA’s MSL Curiosity and Perseverance rovers illustrate this fact. Perseverance is an exceptionally sophisticated collection of technologies. These advanced rovers require a lot of power to perform their tasks, which means bulky and expensive power sources.
Space exploration is an increasingly energy-consuming endeavor. Orbiters and fly-by missions can perform their tasks using solar energy, at least as far away as Jupiter. And ion drives can take spacecraft to more distant areas. But to really understand distant worlds like the moons of Jupiter and Saturn, or even more distant Pluto, we’ll eventually need to land a rover and/or lander on them, just like we did on Mars.
Those missions need more power to operate, and that usually means MMRTGs (multi-mission radioisotope thermoelectric generators.) But they are bulky, heavy and expensive, three undesirable qualities for spacecraft. Each cost more than $100 million. Is there a better solution?
Stephen Polly thinks so.
Polly is a research scientist at the NanoPower Research Laboratories at the Rochester Institute of Technology. His work focuses on something most of us have probably never heard of: the development, growth, characterization and integration of III-V materials by metal-organic vapor phase epitaxy (MOVPE).
While that sounds complicated to non-specialists, space enthusiasts can easily relate to the idea that all his work has led to: a potentially new way to generate energy space missions.
Polly is working on what could be a revolutionary way to power spacecraft on long journeys to the outer planets. It is called a thermoradiative cell (TRC) and it is similar to an MMRTG. It uses a radioisotope as an energy source.
Polly relies on a technology called metal organic vapor phase epitaxy (MOVPE). It uses chemical vapors to produce thin polycrystalline films. It is a industrial process used in optoelectronics to make things like light emitting diodes (LEDs.) Polly’s work uses MOVPE to make thermoradiative cells (TRCs).
TRCs use a radioisotope like MMRTGs do and are based on heat from radioactive decay, but there is a difference. The decay heats the TRC, which then emits light. The light then reaches a photovoltaic cell, which in turn produces electricity. It’s kind of a combination between an MMRTG and solar energy.
But Polly’s idea is much smaller, which is a holy grail in aerospace engineering. “This device, powered by a radioisotope heat source, will allow for an increase in mass-specific power (~30 vs. ~3 W/kg) and a three orders of magnitude decrease in volume (~0.2 vs. ~212 L) compared to a conventional radioisotope thermal generator (MMRTG) for multiple missions,” Polly explained in a brief press release.
Polly writes that these devices could revolutionize our lives space Research activities. It could lead to a proliferation of smaller spacecraft that don’t need to deploy large solar arrays or carry bulky, heavy MMRTGs. Due to technological progress, scientific loads are constantly getting smaller, so if the power source can shrink alongside them, CubeSats could become much more useful.
This allows small satellite missions to go directly to the outer planets as well as operations in permanent shadows such as polar lunar craters,” explains Polly. The first use of the technology could be a mission to Uranus. “We will analyze a thermoradiative converter to power a CubeSat (or fleet of CubeSats) that can ride on a Flagship Uranus mission, perform information transfer tasks for atmospheric probes, and get a parallax view of the planet and moons.
We’re all there for the ride – or at least our intellects and imaginations – when we send spacecraft out into the solar system to explore nature. If Polly’s work comes to fruition and spacecraft can be built using smaller, more effective energy sources, the ride will be even more interesting.
Polly’s idea is a Phase One Selection in NIAC, the NASA Innovative Advanced Concepts Program. He has been given money to further develop the idea.
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