With its exciting operations at asteroid Itokawa in late 2005, Japan's Hayabusa showed the time has come for on-site exploration of near-Earth asteroids and comets. Dennis Ebbets and his colleagues at Ball Aerospace and Technologies Corp. in Boulder, Colorado, presented a novel design concept for such missions at this week's American Astronomical Society meeting in Seattle.
The group suggests a standardized, spherical landing probe about 11.8 inches (300 millimeters) across — slightly smaller than a soccer ball — with a mass of about 26 pounds (12 kilograms). The probe would supply a basic suite of spacecraft functions — such as battery power, thrusters, data management, and communication with an orbiting spacecraft — to support different science payloads up to about 8 pounds (3.5 kg).
Here's how it might work. An orbiting carrier spacecraft drops one or more probes at interesting locations on an asteroid or comet. The probes fall from a height of 22 miles (36 kilometers) for nearly 3 hours and strike the surface. The impact itself would allow onboard accelerometers to measure surface properties, and seismic instruments could measure the impacts of additional probes.
After touchdown, the probe's shell opens up and three hinged petals deploy. No matter what the spacecraft's landing orientation, opening the petals guarantees the probe will upright itself into its operational position.
All of the experiments reside in a central equipment stack. A camera might then acquire a 360° wraparound image of the landing site, and instruments like an X-ray spectrometer could determine the chemical content of the surface.
After returning half a gigabyte of science data to the orbiting spacecraft, the probe could use cold-gas thrusters to kick itself into a 5-minute flight to explore a new locale. It would then close up its petals and re-impact the surface. This way, a single probe could explore several sites. When the probe's battery power dwindles, the orbiting spacecraft could trigger explosives on the probe to blast a crater, reveal the subsurface, and generate seismic waves any sister probes could detect.
Ebbets says there are many asteroid candidates available to such a mission. Launched on a Delta II rocket, spacecraft could reach these targets in 1 to 3 years. And, he says, the costs fall comfortably within the cap of NASA's Discovery-class missions.