The Japan Aerospace Exploration Agency’s HAYABUSA asteroid explorer (pre-launch mission name: MUSES-C) represents a scientific triumph for a nation that is rapidly becoming a major player in the field of space exploration. Despite technical problems that threatened to jeopardize the mission, HAYABUSA managed to achieve a landing on the surface of the asteroid Itokawa, possibly capturing a sample of the surface material, and put itself on a return course for Earth. It is a huge achievement for JAXA and a major scientific landmark. The sample material will be invaluable to the scientific community, and the mission was the debut of sample return technology that will pave the way for similar missions on other bodies in the solar system in the future.
HAYABUSA was launched on May 9, 2003 on an M-V-5 launch vehicle from Uchinoura Space Center on Kyushu Island, Japan. About a year later, the probe modified its orbit by performing a flyby of Earth, and was sent on a trajectory for its destination. It arrived at Itokawa on September 12, 2005.
It was a perilous journey. Along the way, HAYABUSA had to endure two solar flares, one of which damaged its solar panels, resulting in a delay in arrival. Despite the problems, the mission was a technological success, premiering an array of new devices that will also be used on future space missions. The craft is a beautiful piece of equipment, featuring four ion drive propulsion units and an autonomous guidance system allowing the probe to guide itself without directions from Earth. Its flyby of Earth was the first such maneuver to be achieved using only ion drive as the propulsion.
(For the rest of this article, you must bear in mind that there was a 30-minute signal delay, so the events that are related here in a few paragraphs actually took place over many worried hours, with much nail-biting by the mission control crew.)
So far, so good. HAYABUSA had arrived a little battered, but still capable of performing its mission. It made observations of the asteroid from a few kilometers out. (Itokawa looks a bit like a cucumber: elongated and slightly bent, with little lumps here and there on its surface.) The next part of the mission was to deploy a small hopping robot to rove over the asteroid’s surface. On rough terrain, hopping is sometimes a better way to get around than rolling. It was hoped that this little device would be able to get to places that the larger unit couldn’t.
Unfortunately, this part of the mission was a failure. A technical malfunction caused the hopper to fire in the wrong direction, missing the asteroid completely. It’s still out there somewhere, whizzing around the sun: an artificial asteroid. That was a disappointment, but the main part of the mission was still to come. HAYABUSA prepared for its landing on the surface of Itokawa.
At this point, there was a malfunction that almost ended the mission prematurely. HAYABUSA made two landing attempts, and on the second one, a leak developed in a fluid line within the probe, causing a cascade of damage. After that, there was a period of confusion.
The probe continued to approach the asteroid. The moment of landing came and went, and the probe kept signaling that it was descending. Why was it still descending? Had it missed the asteroid completely, or was the signal simply incorrect? The mission control team decided to give the probe instructions for an emergency ascent in the direction of Earth. It was a gamble, since they were not sure of the status of their probe and were not even certain if it could respond, but it was their only chance.
To their enormous relief, it worked. Communication was reestablished with the probe, which sent an update relating the exact sequence of events:
The first landing attempt was aborted by the probe itself, because it detected an obstacle during the descent and recognized it as a danger. On the second landing attempt, apparently the signal indicating that the probe was still descending after the expected landing time was incorrect. The landing was successful, and the probe remained on the surface of the asteroid for about half an hour. The probe then lifted off from the asteroid.
It was at this point that the leak in the fluid line had developed, resulting in a period of signal loss. During this time, the probe’s onboard computer had rebooted once, causing the loss of all data that was stored at that time. This left the central question unanswered: did HAYABUSA successfully collect its sample of asteroid dust? The team members pored over their data, and there were conflicting press reports which first indicated that the sample had been taken, then that it had not.
The plan had been for HAYABUSA to fire one or two pellets into the ground, throwing up a plume of dust which would be captured and stored in the probe’s sample container. In examining the data from the probe, the scientists were unable to determine if this had been carried out. However, it was ascertained that during the 30 minutes that HAYABUSA was on Itokawa, its sample collector was open and in contact with the ground. It is hoped that even if the pellets were not fired as planned, some dust from the surface may have been disturbed by the landing and drifted into the container. Even a microscopic amount would be of enormous scientific importance.
The problems were not over for HAYABUSA. A malfunction developed in the craft’s ion drive, raising the possibility that it might not be able to put itself into orbit for return to Earth. (We can guess that this may be related to the original fluid leak.) In a heroic save, the team managed to link parts of two of the craft’s four ion engines, thus achieving the thrust of one engine. The reduction in thrust would delay the probe’s return to Earth, originally planned for 2007, until June of 2010.
That day is coming in just a few months now, and provided that the probe’s return to Earth is successful, we will finally learn if it contains the dust of an asteroid. Even if it doesn’t, the Japan Aeronautical Exploration Agency has earned praise from the scientific community for their heroic and ingenious efforts in overcoming the many obstacles that this mission faced. Regardless of the result of the HAYABUSA mission, Japan has suddenly moved into the forefront of space exploration.
Watch for an update at this site when HAYABUSA returns to Earth in June.
Sources:
Website of the Japan Aerospace Exploration Agency (JAXA): jaxa.jp/projects/sat/muses_c/index_e.html
Current Status of the Asteroid Explorer HAYABUSA in Space Daily: Your Portal to Space, February 6, 2009: spacedaily.com/reports/Current_Status_Of_The_Asteroid_Explorer_Hayabusa_999.html
Space Topics: HAYABUSA (Muses-C) at website of the Planetary Society: planetary.org/explore/topics/hayabusa/
Cain, Fraser: HAYABUSA Successfully Collects an Asteroid Sample in Universe Today: universetoday.com/2005/11/29/hayabusa-successfully-collects-an-asteroid-sample/