An article in R&D Magazine today, reprinted from the Center for Space Nuclear Research, part of the U.S. Department of Energy’s Idaho National Laboratory, describes one of the CSNR’s design projects — for a fleet of nuclear-powered “Mars Hoppers” that could map the whole Martian surface in a matter of a few years, much faster than ground-based rovers could.
The hoppers would be about as big as an adult Emperor Penguin and would use Radioisotope Thermoelectric Generators (RTGs) run through a Sterling Engine to power the onboard instruments. The RTG/Sterling outfit would also run a device that draws in the thin Martian atmosphere and compresses it to create tanks of propellant, eliminating the need for the hopper to carry its own. Heat is then stored in a beryllium core, which the hopper uses to activate the rockets when it’s time to move. The system would allow the thing, when it finishes mapping a site, to “hop” about half a mile in the air and travel up to 9 miles away to map the next site. This process would be much more efficient than using a rover design, which moves at a crawl:
The twin Mars rovers Spirit and Opportunity have outlasted their planned three-month lifetime and given us our closest look yet at the Martian surface. But the solar-powered rovers have covered only 21 miles of Martian terrain in their combined 11 years of operation, leaving most of the surface unexplored…
A single rocket launch from Earth could deploy several hoppers at once. A few dozen hoppers could map the entire Martian surface in a few years, Howe says. Hoppers could also serve as a network of weather stations monitoring the Martian climate and could collect a trove of air, rock and soil samples to send back to Earth.
I’m far from convinced on that last point — getting something back to Earth from Mars is a much taller order than bouncing around the low-gravity, low-atmosphere surface where you don’t have to worry about radioactive contamination. Going to Mars and back, even with a robot, is way more than twice the trouble of just going to Mars.
But what I really love is the idea of having a bunch of universities contribute:
The scientific community will ultimately decide what the hoppers will carry, says [CSNR director Steven Howe.] While the Mars rovers employ an armada of tools such as cameras, drills and spectrometers that allow them to photograph, sample and analyze the Martian environment, small hoppers might only carry one or a few tools apiece.
Howe envisions having different universities around the world competing to design their own hopper payloads and experiments. “You can have 10 to 20 universities from around the world, hopping around Mars,” he says.
Radioisotope Thermoelectric Generators are the same technology used in the Cassini-Huygens Probe, which freaked people out when it hurtled past Earth a few years ago on its gravity-assisted way to the outer solar system. RTGs provide power through the thermal energy released in radioactive decay. They are used in space probes because they’re one of a very, very few viable choices:
Unlike solar panels, radioisotopes produce steady power even at night or when obscured by Martian dust storms. And unlike chemical fuel, which can burn only once, the same block of radioisotope fuel could be used to launch a hopper over and over again and run its scientific instruments for a decade or more.
In deep-space probes, RTGs are used because probes like Cassini travel so far from the sun that solar power isn’t an option past a certain point.
The Soviet Union used RTGs for lighthouses throughout the Arctic and in its Siberian territories — more than 1,000 of them — which were designed for a 10-year life (and many of them are out in the field after 30+ years). (In 2001, some Georgian woodsmen found one and slept near it as a heat source. This was not a good idea.) The US Air Force still uses RTGs at “sensing stations” in Alaska.
The Soviet lighthouses and USAF RTGs use Strontium-90; Cassini used plutonium. Polonium, americium, curium, prometheum and cobalt isotopes have also been studied.