Hayabusa: Mission Accomplished

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The determination by the Japan Aerospace Exploration Agency (JAXA) that dust particles recovered from the Hayabusa probe’s sample return capsule came from the asteroid Itokawa is icing on the cake for a mission that has been a resounding success on several different levels. Hayabusa was JAXA’s first mission to an asteroid and the first by any space agency to return samples from an asteroid’s surface. These achievements, noteworthy in their right, are downright remarkable considering what JAXA had to overcome to pull it all off.

Hayabusa was beset with technical difficulties almost from the start of the mission. The probe lost the use of one of its four ion thruster engines right after its 2003 launch and suffered a power problem en route to Itokawa that JAXA officials warned put the entire mission in jeopardy. In November 2005, Hayabusa managed to land on Itokawa despite having lost two of its three attitude control systems. Then, after the probe lifted off the asteroid’s surface, it became disoriented due to a fuel leak in an attitude control engine and went incommunicado for two months.

Had the mission ended there, JAXA could have declared victory for its up close encounter with Itokawa and the scientific data that yielded. Somehow, communications with Hayabusa were restored — no easy feat given its distance from Earth plus a host of unknowns — but by then the probe’s attitude control system had broken down, forcing JAXA engineers to devise a new means of attitude control using the ion propulsion system and solar light pressure. In 2007, Hayabusa began limping back toward Earth on a new schedule, with the use of only two of its original four ion engines.

The spacecraft was in the home stretch of its return journey in November 2009 when what one JAXA official characterized as the biggest crisis of the mission occurred: One of the two remaining ion thrusters failed abruptly while the other suffered a degradation in performance as it neared the end of its design life. Demonstrating resourcefulness often associated with the expression “failure is not an option,” JAXA came up with a solution that cobbled together working components from two of the crippled ion engines, providing, in effect, a single healthy engine. It was this propulsion configuration that put Hayabusa in position for its return to Earth. The probe’s sample return capsule successfully landed in the Australian desert in June, some three years later than originally planned.

Planetary missions are extremely difficult, as evidenced by the fact that experienced and highly capable spacefaring nations like China and India have only gotten their feet wet with lunar orbiters in the last three years. To rendezvous with an asteroid, collect a sample and successfully return that material to Earth adds several layers of engineering difficulty.

Some Hayabusa mission objectives were not achieved. Notably, a lander that was to separate from the main probe and land on Itokawa missed its target. Further, the fact that the mission encountered so many technical difficulties suggests that JAXA could have benefited from more extensive testing on some of the spacecraft components. Still, Hayabusa, according to JAXA, broke a world record for the longest operation of an ion engine, the source of most of the mission’s problems.

More generally, Hayabusa’s accomplishments are such that the negatives are barely worth mentioning, except to the extent that they brought out the best in JAXA’s technical teams. JAXA, which like all space agencies has experienced failures over the years that prompted internal reviews of its engineering and management practices, demonstrated amazing resourcefulness and ingenuity in making Hayabusa a success. In doing so the agency has made an important contribution to science while setting an example that all spacefaring nations — old and new, big and small — can look up to.