When Japan’s Institute of Space and Astronomical Science (ISAS) came to NASA seeking technical help on Muses-C, it offered NASA the chance to fill out the lander’s unused cargo space. The Americans thought of sending a complement of scientific instruments, but decided that if these were attached to the lander they would merely duplicate the Japanese effort. Better to send a rover to explore other parts of Nereus.
Just one hitch: Muses-C has only two pounds’ worth of extra cargo capacity, with half needed for computer and communication equipment to enable NASA to “talk” directly with the rover. Ergo the next step in miniaturization: a one-pound “nanorover.” (This is a term of art, since nanotechnology usually refers to work at the molecular level. But what else do you call a machine one-twentieth the size of a “microrover?”) The nanorover’s science instruments will be more sophisticated than the relatively gigantic Sojourner’s: an infrared spectrometer for reading chemical signatures by infrared rays, an imaging camera with eight-position filter wheels for reading various light spectra, and perhaps an x-ray spectrometer. But the machine will have a much simpler chassis. A current prototype has only two wheels, on which it will skid and even flip over (and then right itself). On an asteroid, where impacts are glancingly light, such careening won’t be the disaster it would be on a full-sized planet. In low gravity, where stopping is difficult, such movements are inevitable anyway.
An asteroid presents even more fearsome temperature challenges than Mars. Brian Wilcox, JPL’s robotics group supervisor, notes that Sojourner operated only when it was warm-after its gel insulation had trapped enough heat each day. But insulating is futile on something as small as a nanorover, with its proportionally high surface area. And asteroid explorers must brace for 250-degree Celsius temperature fluctuations from day to night. Electrical components are typically rated only up to an automobile’s temperature range-about 120 degrees. Finding components that can handle minus-125 degrees is a main challenge, says JPL systems engineer Rick Welch, who has worked on the nanorover. The appropriate parts tend to be CMOS-complementary metal-oxide semiconductor-electronics, which maintain conductivity and work at extremely low temperatures. The asteroid rover will be a night crawler; “during the [scorching] day, we’ll just turn it off,” he notes.