March 2015
Japan’s second asteroid
sampling mission is under way. Hayabusa 2 was launched from the
Tanegashima Space Center in January on its 6-year trip to the Near Earth
Asteroid (NEA) named 1999 JU3. The
mission is a follow-up to the ambitious but trouble-plagued Hayabusa 1 flight of 2003-2010, which
aspired to grab a substantial sample of the NEA Itokawa, but suffered several
failures, including malfunction of its sampling equipment. Hayabusa
1 nonetheless returned successfully to Earth bearing traces of asteroid
dust on its surface.
Hayabusa
2
carries, in addition to a sample-acquisition system, four small probes, one of
which is patterned after the Philae probe that recently landed on Comet 67P/Churyumov-Gerasimenko. These probes are capable of “hopping” about
on the asteroid surface; indeed, the main spacecraft is intended to land and
collect samples in three different places.
The present target
asteroid, despite its uninteresting name, has particular attraction for people
interested in the discovery and use of the native resources of space: it is a
very dark rock, similar in its reflectivity and spectrum to the carbonaceous
chondrite meteorites. These meteorites
contain up to 20% water by weight, plus about 6% of tarry organic polymers and
interesting amounts of many other compounds of the volatile elements hydrogen,
carbon, oxygen, sulfur, nitrogen, chlorine, and so on. The dominant minerals are water-bearing
clays, magnetite, and a variety of metal sulfides loosely cemented by the
organic gunk that coats the mineral grains.
The CI chondrite meteorites also contain veins of various water-soluble
and water-bearing minerals, mostly sulfates and carbonates, that run through
the otherwise very black groundmass.
Moderate heating releases water vapor; strong heating drives off a rich
variety of gases and causes the organic matter to react with the oxygen-rich
mineral magnetite to “burn” the organic matter and release copious amounts of
carbon oxides and water. All told,
strong heating of CI material drives off ~40% of the total mass of the
meteorite as gases of H, C, O, N, S, and Cl compounds.
1999 JU3 is about 920
meters (0.6 miles) in diameter, with a total mass of about 1 billion tonnes,
which upon heating would release some 400 million tonnes of volatiles. By way of comparison, a fully-fueled Saturn V rocket or Space Shuttle contains about 2000 tonnes of rocket propellant: 1999
JU3 contains enough hydrogen, carbon, and oxygen to fuel 200,000 such flights.
Deep Space Industries
(deepspaceindustries.com) is presently studying processes for turning the volatiles extracted from
carbonaceous asteroids into fuels and oxidizer for future space missions, and
into air and water for life-support and agricultural uses by future
spacefarers. The byproducts from
extraction of volatiles, including metals, are also of great economic interest.
Plans to manufacture these products await the successful return of samples to
Earth.
Return of Hayabusa 2 from the asteroid will
commence in late 2019, with entry into Earth’s atmosphere and recovery of the
return capsule scheduled for December 2020 in the interior of Australia.
Hayabusa
2
is a difficult and challenging mission.
The Japanese Space Agency JAXA is to be congratulated for learning
valuable lessons from their earlier asteroid mission and designing an ambitious
and well-conceived successor. I wish
them the very best of luck.
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