Chair Force Engineer

Monday, May 25, 2009

Hubble Disposal Revisited

With the crew of shuttle Atlantis having completed the last servicing mission on the venerable space telescope, I've revisited the question of what happens to the large Hubble spacecraft when its mission finally ends in a few years. A piece of space debris the size of post-shutdown Hubble poses an increased risk to people on earth during an uncontrolled re-entry.

The original Hubble disposal plan called for a shuttle mission to retrieve it and send it back to earth. But the winding down of the shuttle program ensured that Hubble would out-last the spacecraft that delivered her to orbit in 1990. Besides, the risk to astronauts in order to deliver Hubble to a museum on earth really can't be justified for most people.

Back when Sean O'Keefe supported a robotic servicing mission to Hubble, the addition of a deorbit stage was considered. At least a deorbit motor would permit Hubble to control its re-entry and minimize the risk to people on the ground. The deorbit motor was also considered for the current mission before being dropped. Instead, the STS-125 astronauts added the Soft Capture Mechanism, which should allow future spacecraft to pay Hubble a visit. A deorbit stage could also be launched, although it would require some form of terminal propulsion and gudance to safely dock with Hubble.

It's always possible that a future Orion spacecraft could dock with Hubble, re-boost it, and perform maintenance. But Orion is ill-suited for the task at hand. It has no payload bay for delivering spare parts to Hubble, and there's no arm to reposition spacewalking astronauts who would repair Hubble.

The long-term Hubble situation reminds me much of the fate of Skylab. While the first American space station was boosted into a higher orbit in hopes that it would still be around when the Space Shuttle first flew, it ended up re-entering and breaking apart over the Australian outback two years before the first Space Shuttle mission. Hopefully NASA will have an executable plan to safely deorbit Hubble at the end of it's life, unlike Skylab. And if anybody's holding out hope for Orion giving Hubble another reprieve, I think they'll be sorely mistaken.