Australian Sky & Telescope - June 2018

http://www.skyandtelescope.com.au 31

While the overall design philosophy for both missions may

be roughly similar (fly out to a primitive near-Earth asteroid,

rendezvous with the target and study it for a while, select

a good sampling site, collect the sample, and return it to

Earth), the specific sampling strategies for each are different

in their details.

Hayabusa 2 is the successor to Japan’s plucky Hayabusa

mission, which returned to Earth in June 2010 with tiny

samples of Itokawa. Launched from the Tanegashima Launch

Center on December 3, 2014, the Hayabusa 2 spacecraft

employs essentially the same configuration as its predecessor,

but with some novel technologies. The main body of the

spacecraft itself is about the size of a refrigerator, adorned

with two wing-like solar panel arrays that provide power for

the spacecraft’s instruments and ion engine.

After Hayabusa 2 arrives at Ryugu in June 2018, the

spacecraft will gradually approach the asteroid over 18

months or so as the mission team studies its mineral

composition, measures the temperature and thermal

properties of its surface, and searches for the best location to

sample. During this time the mother ship will deploy a small

lander called the Mobile Asteroid Surface Scout, or Mascot, as

well as three small, hopping rovers named Minerva-II.

The shoebox-size Mascot probe has its own camera, a

multi-colour microscope to closely examine the asteroid’s

surface materials, a radiometer to take Ryugu’s temperature,

and a magnetometer. Its battery should power a 16-hour or so

investigation of the surface.

The Minerva-II rovers are direct descendants of the

Minerva deployed toward Itokawa from the original Hayabusa

but which unfortunately failed to actually reach the asteroid’s

surface. There are two types of hopper: one larger, eight-sided

rover that’s roughly 20 cm tall, and a second, hexadecagonal

pair, each just 10 cm tall, or roughly the size of the palm

of your hand. They contain their own cameras and other

instruments similar to those on Mascot. Each probe has two

DC motors inside that work together to ‘hop’ the probes

across the surface. Combined with Mascot, the rovers will

reveal what the surface is like on a scale similar to what a

human explorer would experience poking around as a field

geologist, nicely complementing the global-scale observations

the main spacecraft gathers.

Finally, the mother ship will descend toward the surface to

collect its prize. A metre-long, metal sampling horn extends

down from the spacecraft’s underbelly. An aluminium

contact sensor and collapsible metal skirt will sense the

touchdown on Ryugu, setting off a sample collection process

that will shoot a 1-cm-size tantalum projectile into the bit

of surface inside the end of the sampling horn at a speed of

300 metres per second (1000 kph). The ejecta from the little

Not to scale

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HAYABUSA 2: JAXA; SAMPLING: GREGG DINDERMAN /

S&T