Japan's Space Agency Is About to Land Bouncing Rovers on an Asteroid

Joe Pappalardo reports in Popular Mechanics,

This week the Japanese space agency’s asteroid-exploring spacecraft, Hayabusa2, will deploy a pair of rovers to explore the surface of an asteroid. It’s a mission of redemption as much as it is science, because the last time JAXA tried this, the mission ended in failure.

The Hayabusa2 probe left for asteroid Ryugu in December 2014 and is already well into its 1.5-year mission exploring the surface. It will return to Earth in 2020. The spacecraft is armed with a slew of sensors and probes, including a high-power ejector that will shoot a 0.5-gram tantalum bullet into the surface so it can study the ejected material.

Now JAXA is activating MINERVA-II1, a container holding a pair of octagonal, 2.5-pound rovers. (The acronym means “MIcro Nano Experimental Robot Vehicle for Asteroid.”) A few days ago, the JAXA Hayabusa team tweeted: “This week we will deploy the MINERVA-II1 rovers! Tomorrow (Sept 19) is the preparatory operation prior to the descent and on the 20th, the spacecraft will start descending towards Ryugu, The separation of MINERVA-II1 is scheduled for the 21st.”

If you picture the kind of wheeled rovers that NASA sends to Mars, don't. Asteroids are too small to have much gravity, so these rovers hop around in low gravity to get from place to place. Each probe has four rotating devices inside it. Those devices generate torque that propels the probes as they take 15-minute hops, traveling at about 15 meters per jump. Each rover has two cameras, a thermometer, and an accelerometer. It has optical and ultraviolet LEDs for illumination to measure dust particles.

An asteroid called Itokawa was the site of one of JAXA’s worst moments. On November 12, 2005 controllers on Earth issued the order for Habayusa1, the current probe's predecessor, to release the Minerva payloads. But because of a faulty altitude reading, the probes released while the spacecraft was too high. The Minerva canister flew off into space, the probes tucked inside for all time.

Now it’s time for the sequel. “Preparation for the spacecraft descent will take place today,” JAXA tweeted on Wednesday. “And from tomorrow the descent will begin.”

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