Wednesday, July 29, 2015

Hayabusa 2: On its Way to an Asteroid

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 ( 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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