Hayabusa - Changes in Mission Plan

Changes in Mission Plan

The Hayabusa mission profile has been modified several times, both before and after launch.

• The spacecraft was originally intended to launch in July 2002 to the asteroid 4660 Nereus (the asteroid (10302) 1989 ML was considered as an alternative target). However, a July 2000 failure of Japan's M-5 rocket forced a delay in the launch, putting both Nereus and 1989 ML out of reach. As a result, the target asteroid was changed to 1998 SF₃₆, which was soon thereafter named for Japanese rocket pioneer Hideo Itokawa.
• Hayabusa was to deploy a small rover supplied by NASA and developed by JPL, called Muses-CN, onto the surface of the asteroid, but the rover was canceled by NASA in November 2000 due to budget constraints.
• In 2002, launch was postponed from December 2002 to May 2003 to recheck the O-rings of its reaction control system since one of them had been found to be using a different material than specified.
• In 2003, while Hayabusa was en-route to Itokawa, a large solar flare damaged the solar cells aboard the spacecraft. This reduction in electrical power reduced the efficiency of the ion engines, thus delaying the arrival at Itokawa from June to September 2005. Since orbital mechanics dictated that the spacecraft still had to leave the asteroid by November 2005, the amount of the time it was able to spend at Itokawa was greatly reduced and the number of landings on the asteroid was reduced from three to two.
• In 2005, two reaction wheels that govern the attitude movement of Hayabusa failed; the X-axis wheel failed on July 31, and the Y-axis on October 2. After the latter failure, the spacecraft was still able to turn on its X and Y axes with its thrusters. JAXA claimed that since global mapping of Itokawa had been completed, this was not a major problem, but the mission plan was altered. The failed reaction wheels were manufactured by Ithaco Space Systems, Inc, New York, which was later acquired by Goodrich Company.
• The 4 November 2005, 'rehearsal' landing on Itokawa failed, and was rescheduled.
• The original decision to sample two different sites on the asteroid was changed when one of the sites, Woomera Desert, was found to be too rocky for a safe landing.
• The 12 November 2005, release of the MINERVA miniprobe ended in failure.