Earth return of asteroid sampling craft delayed
BY STEPHEN CLARK
Posted: December 14, 2005
The hard-luck craft that pushed teams to the edge for more than three months will leave Earth-bound controllers hanging on for several more years after managers finally concluded it was no longer possible to bring the Hayabusa probe home as planned in 2007.
The most recent crisis began late last week when a sudden attitude change was observed, which broke off communications with Earth. Engineers attribute the abrupt change to the out-gassing of previously leaked fuel. The disruption occurred as Hayabusa was in a slow spin to establish attitude control as work was performed to bring chemical thruster systems back online after being knocked out in the preceding weeks.
Hayabusa's design allows it to stabilize within a few months with a spinning motion around one axis, keeping hopes high for its eventual recovery. Managers have transitioned the project team from operational to rescue mode for a period of up to one year - enough time to realistically have a shot at bring the probe back to normal operations. Before then, Hayabusa may not have the ability to simultaneously communicate with controllers and charge batteries using solar power because both require accurate pointing toward Earth and Sun.
Risks of losing Hayabusa after prolonged periods of no communications are low because the craft remains near Itokawa - a known position almost 180 million miles away on the opposite side of the solar system. The spacecraft is expected to soon begin to power down to save electricity, but the software is designed to restart key systems when commands are received from Earth.
The wildly uncontrolled attitude means controllers are unable to ignite the ion engines, which are designed as a low thrust, but highly efficient means of propulsion. The powerplants use xenon gas and electricity, and were used prolifically for over 25,000 hours of operating time during the outward journey from Earth to Itokawa from its 2003 launch until last summer.
Because of this, Hayabusa's return capsule will have to wait until June 2010 to make its parachuted landing in the Australian outback, assuming efforts to recover the $100 million probe are successful by around February 2007. Senior managers believe there is a high probability of recovery, ranging between sixty and seventy percent by early 2007 according to their studies.
Officials say the chemical thrusters are not required on the trip home, and that a new method devised in the past few weeks using xenon gas for attitude control is likely to be a viable backup.
As one of Japan's first ventures into solar system exploration, Hayabusa has served a dual purpose not only as a scientific platform to study asteroid Itokawa and retrieve samples from its surface, but also as a testbed for technologies that are key to future space missions.
Included in its repertoire are cutting edge ion engines, an autonomous navigation system, and an innovative sample collection device that was to gather small amounts of rock and dust from the potato-shaped asteroid. Science instruments such as near infrared and X-ray spectrometers were trained on Itokawa during a two-month long survey that ended in early November to determine its composition, while other payloads mapped the entire asteroid in fine detail.
Hayabusa also inadvertently achieved a historic first in space exploration in November when it spent up to thirty minutes on the surface of Itokawa before climbing away in an abort, which left the probe dozens of miles away before it was brought back under control. This event marked the first time any spacecraft had successfully taken off from an asteroid, or any celestial body other than the Moon.
The landing occurred at the end of the first approach to gather samples from the asteroid, but a sensor detecting potentially unsafe obstacles in the path of the craft triggered an abort of the sampling procedure, while the descent continued.
A second attempt on November 26 was initially called a success, but during the ascent away from Itokawa, Hayabusa was struck by the first in a nearly deadly series of blows that cut off communications between the spacecraft and ground controllers, put the thruster system out of commission, drained battery power, and leaked precious chemical propellant. The successful sample collection run was later determined to likely have been a failure, once recorded data was beamed back to Earth as conditions aboard Hayabusa became more stable. See our full account of these events here.