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NASA’s TransFormers Could Make Harsh Lunar Environments Robot Friendly

Robots using mirrors to reflect sunlight at other robots could enable exploration of craters and caves

6 min read

NASA’s TransFormers Could Make Harsh Lunar Environments Robot Friendly
This artist’s concept shows a group of TransFormer robots on the rim of the Lunar South Pole crater projecting sunlight to an exploration rover.
Image: JPL

Right now, planetary rovers have two options for power: a solar-based power system or a radioisotope thermoelectric generator (RTG). Solar is common because it’s cheap, reliable, and will run almost indefinitely. RTGs are expensive and bulky, but they provide a lot of power and will do so reliably for decades.

The problem with solar power, and it’s a huge problem, is that there are all sorts of situations in which it simply does not work, nighttime being the one you’re most familiar with. In more exotic environments (like Mars) solar-powered robots have suffered from dust as well as from inadequate power during the winter, or while they’re traversing slopes that tilt them away from direct sunlight. And there are lots of places that solar-powered robots cannot go, including caves and other areas that are permanently shadowed.

Does this mean that to explore these places, we need to send in big, expensive robots with big, expensive RTGs? Maybe not. Maybe we can instead transform the areas that we want to explore into ones that are more favorable for exploration by using robots with mirrors to turn permanent night into permanent day.

In space, for most practical purposes, there’s very little difference between shadow and night. In either case, you’ve got something in between you and the sun that’s substantial enough to prevent light from making it through. Whether you’re talking about a crater on the Moon that is in permanent shadow, or a cave on Mars, the fundamental problem is the same, which is that the environment is unfavorable for a solar powered robot.

At JPL, a team of researchers is being funded by NASA’s Innovative Advanced Concepts program to develop a way of bringing light into extreme environments using mobile robotic mirrors called TransFormers (herein abbreviated TFs). Here’s what the concept looks like:

imgTFs power rovers in craters (above) and caves (below).Image: JPL

It’s a bit blurry, but what’s going on here is that you’ve got mobile robots with giant mirrors attached to them perched on the rim of a lunar crater. They continuously adjust the angle of the mirrors to reflect sunlight down into the crater, which is otherwise in shadow. This allows a solar-powered rover to operate down there, and in addition to providing energy, the light also allows the rover to see and helps keep it warm.

In terms of scale, modeling suggests that you could power a rover 10 kilometers into a deeply shaded lunar crater with a TF robot holding a mirror about 40 meters in diameter (yep, that’s a big mirror). With a little bit of focusing, this would reflect 300 watts per square meter, enough to keep an Curiosity-sized rover happy. And as the rover drives around, the TFs would adjust the angle of their mirrors to make sure that wherever the rover is, it’s smack in the middle of a warm and bright and happy spot of reflected sunlight. This same sort of thing should also work in more complex environments like caves, although you’ll need multiple TFs reflecting sunlight along passages and around corners. Looking way, way ahead, exploring caves is especially important because they’re the logical place to put an initial base on the Moon or Mars.

The TFs themselves are designed to be cheap. Utilizing origami-style folding, the idea is that you could pack one (including its 1,200-square-meter mirror) into a cubic meter of space, with a mass of less than 100 kilograms. Especially compared to RTGs, a TF system would be way cheaper (a single RTG costs about $45 million), and you could use it over and over again to provide power to lots of different missions. Furthermore, RTGs weigh enough that you couldn’t stick one on a small (and cheapish) rover: rather than having something Opportunity, sized, you’d need something Curiosity sized or larger, further increasing cost and complexity (not to mention the extra safety precautions, because of the radioactive fuel to power the RTG).

When we’re ready for our first TF mission, it’ll probably be to a shadowed crater on the Moon where we think there might be volatiles (like water) at or close to the surface. The most likely scenario is to send a mobile TF and an exploration robot to a location near the crater, and then drive them to it (perhaps with the rover towing the TF to simplify things). The TF will set itself up on the crater rim, and then beam sunlight at the rover as it makes its way into the crater:

imgTop left: The rover makes its way out of the landing module, transporting a compactly folded TF, and approaches the rim. Top right: The TF unfolds to reflect sunlight into the crater—it is placed at a location that provides line-of-sight coverage of the planned exploration path. The TF also adjusts its position/posture for improved stability. A crosslet origami unfolding is depicted. Bottom left: The exploration rover starts its descent into the crater. The TF continuously tracks the rover, lighting its path with the reflected sunlight. As the rover reaches areas with ambient temperatures below 100 Kelvin, it is powered and warmed by the TF projected energy. Bottom right: The TF continuously adapts its reflector shape, precisely tracking the moving rover, pointing the reflected energy onto its solar arrays, and controlling the beam as required for the rover to examine its surroundings and to take measurements.Image: JPL

So, how close are we to getting something like this to work? First of all, we know it does work, because we’ve done it on Earth for years: reflected sunlight has been used to illuminate and direct tunnel digging operations, and there’s a village in Norway (and one in Italy) located in deep valleys where large heliostats are used to bring in sunlight during the winter. Getting this technology into space is, like getting any technology into space, a challenge. But NASA has just approved a mission called the Lunar Flashlight mission, which will be sending a 6U Cubesat into lunar orbit with an 80-square-meter solar sail designed to double as a reflective surface that will project sunlight into a shadowed lunar crater from orbit:


Image: NASA
This artist’s concept shows the Lunar Flashlight solar sail reflecting sunlight into a shaded crater on the Moon.

As far as the TransFormers concept specifically, we’re looking at component technologies that are currently at TRL 3 or better, with integration at TRL 1 or 2. So, there’s a lot of work to do before we even see a prototype of a TF. But that’s the whole point of NASA’s Innovative Advanced Concepts program: taking wildly futuristic ideas and giving them the resources to actually happen.

While these scenarios are futuristic, the benefits of TFs as a means to control microenvironments are clear and present. TFs enable new classes of missions of high scientific and exploration value in the relative close proximity to Earth, at low costs, without RTGs. TFs also provide an avenue for missions with many rovers, less burdened by power and heat loads, with low cost since they were built to terrestrial grade components—they would operate in climatized landscapes—and with less concern of failure since they are multiples. This truly opens the door for cooperative robotic operations, from scientific exploration to exploitation of resources.

NASA-developed TFs at the Lunar South Pole, or wherever points of high interest emerge, will be able to serve the mission of all NASA partners. This will be the first asset of true benefit for many; designed for a sufficient lifetime and strategically located, it would start an essential infrastructure on the Moon, and serve as a model for later expansion to other places.

For a lot more information, here’s JPL’s 2014 NIAC Phase I Final Report on the TransFormers concept (pdf). They’re now onto NIAC Phase 2, which means we’ll be hearing a lot more about this in a year or so.

[ NASA ] via [ PopSci ]

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