Unbowed by Robot Loss, Japan's Asteroid Probe Readies For Touchdown
Despite a glitch in deploying a mini-robot onto asteroid Itokawa, Japanese space officials plan to proceed in a milestone-making touchdown on the space rock to obtain samples of the object for return to Earth.
The problems encountered Nov. 12 with the release by Japan's Hayabusa space probe of its camera-toting robot highlight the difficulty of this kind of mission. The robot probe, called the MIcro/Nano Experimental Robot Vehicle for Asteroid (MINERVA), was lost upon release from the mother ship Hayabusa.
MINERVA was successfully released, but the device appeared to start drifting away from the asteroid's surface, according to a release from the Japan Aerospace Exploration Agency (JAXA). The robot was expected to land and hop around on the asteroid's surface collecting data with three small color cameras.
Now, Hayabusa ground controllers are preparing to carry out a first touchdown on asteroid Itokawa on November 19 and a second touchdown on November 25. The mission is being run by the Institute of Space and Astronautical Science (ISAS), a space science research division arm of JAXA.
Loss of MINERVA
Japan's Hayabusa probe is now roughly 2 miles (3.5 kilometers) from Itokawa. The mission is being carried out nearly 180 million miles (288,923,070 kilometers) away from Earth.
On November 12--during a trial run to check out descent landing procedures--the Hayabusa probe closed in on its asteroid target, reaching an altitude of about 180 feet (55 meters) from the space rock. The rehearsal included use of an onboard Laser Ranging Finder (LRF). It was successfully verified that the device is ready to handle the upcoming touchdown maneuvers.
The separation of the ultra-small MINERVA robot took place during the rehearsal. Ground controllers were able to confirm its deployment, with communications established with the free-floating robot. The ejection of MINERVA was also confirmed by the obstacle detection sensor onboard Hayabusa, according to JAXA officials.
Separation of MINERVA was performed via command from ground control. However, during the ten minutes or so until the separation actually took place, JAXA said, the position of Hayabusa had drifted to a higher spot over the asteroid - an altitude of about 656 feet (200 meters). That being the case, MINERVA failed to plop itself down onto the surface of Itokawa.
Gravity of the situation
What happened to MINERVA is a lesson learned for future asteroid work, said Donald Yeomans, Supervisor of the Solar System Dynamics Group at the Jet Propulsion Laboratory (JPL) in Pasadena, California.
"While this MINERVA technology test anomaly certainly does not take away from the outstanding Hayabusa science results at Itokawa, it does underscore just how difficult it will be to land upon, or drop off any instrument packages on very small solar system objects that have very little gravity of their own," Yeomans told SPACE.com. The velocity required to escape the surface of such a small beast of a rock like Itokawa is only about 13 centimeters per sec or about 0.3 miles per hour, he noted.
"Small asteroids would have very little influence on a landing package and because of the distances involved you can't joystick the package down in real time," Yeomans pointed out. "To place a package on the asteroid's surface, the spacecraft needs to be autonomous and very smart."
Yeomans said that Hayabusa was ascending with a velocity just greater than the asteroid's escape velocity when MINERVA was released. "So rather than heading for the asteroid's surface, it drifted slowly away and is now, I suppose, in solar orbit."
Hayabusa communicated with MINERVA for 212 minutes before losing signal, Yeomans said, and that MINERVA did manage to image part of a Hayabusa solar panel as it drifted away.
"It seems MINERVA was ready to do its part if only given the chance," Yeomans suggested.
Set of samples
The upcoming touchdown attempts of Hayabusa are sure to offer more tips on dealing with asteroids in the future.
Hayabusa's asteroid sampling device is installed on the base of the probe. A funnel-type tube called a horn will sense contact with the Itokawa's surface.
During this brief contact, Hayabusa will fire a small metal ball at the surface at high speed. Pieces stirred up by the impact are to be collected within a canister attached at the top of the horn. Specimens are to be taken from two different locations on the asteroid, with material collected enclosed in individual parts of the canister.
This container is then transferred into a reentry capsule mounted on the side panel of the Hayabusa spacecraft.
If all goes according to plan, the space probe would depart the asteroid by early next month on a course that returns it to Earth in June 2007. The sample-carrying canister is designed to parachute into a desert landing locale in Woomera, Australia.
Hayabusa was rocketed into space from Japan's Kagoshima Space Center on May 9, 2003. The spacecraft arrived at asteroid Itokawa on September 12 of this year.
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