NASA's program executive for Hubble, Michael Moore, said Aug. 24 that a final decision was in the hands of NASA Administrator Mike Griffin, who is expected to rule soon.
Griffin's special assistant, Chris Shank, however, told attendees of the Mars Society's annual conference in Boulder, Colo., Aug. 13 that the special deorbit module would likely be deleted from NASA's to-do list for the mission. "It does not look like a propulsion module will be necessary for a shuttle servicing mission," he said.
Hubble has no propulsion system, and NASA safety guidelines mandate that the school bus-size spacecraft not be allowed to re-enter the Earth's atmosphere on its own. NASA once entertained the idea of retrieving Hubble with a shuttle and bringing the spacecraft back to Earth for display in a museum. But since the February 2003 shuttle disaster, NASA has settled on attaching a deorbit propulsion module that would allow flight controllers on the ground to time Hubble's re-entry so that the spacecraft breaks up over an uninhabited stretch of ocean.
Moore said in an interview that extensive analysis has shown that Hubble is unlikely to re-enter on its own before 2020. "All of the analysis gives us more confidence that we have quite a bit of time before natural re-entry," Moore said.
Nicholas Johnson, NASA Orbital Debris program manager at Johnson Space Center in Houston, said boosting Hubble's altitude at the conclusion of a shuttle servicing mission would buy NASA even more time.
Moore said not including a deorbit propulsion module on the proposed Hubble servicing mission would save NASA roughly $170 million in development costs, but budget is just one factor in the decision. He said NASA also has considered the mission risk entailed in flying a propulsion module that has never been tested and the schedule risk that comes from adding a major development to the proposed servicing mission at this late stage.
"All of the hardware for the nominal SM-4 mission is in hand," he said, referring to NASA's designation for the long-proposed service call to Hubble. "There is programmatic risk involved in adding a major element like this."
Deleting the propulsion module from the proposed Hubble servicing mission does not eliminate the need for an eventual controlled deorbit for the telescope. But Moore said finding the right technical solution should prove easier in the future. "As we speak there are other programs that are working very hard on the kind of technologies that would be needed," Moore said.
NASA spent much of 2004 pursuing a robotic mission to service Hubble, but rejected that option as too risky given the fairly immature state of the needed technologies. A National Academies of Science panel late last year recommended that NASA scrap the robotic option and reinstate the shuttle servicing mission instead. In April 2005, during his first week on the job, Griffin said the robotic option was off the table and that NASA would proceed on the assumption that approval ultimately would be granted for one last shuttle mission to Hubble.
Griffin, however, has not committed to conducting a Hubble servicing mission, saying a decision would be made only after the space shuttle successfully completes its first two flights since the Columbia accident. The first of those two flights, STS-114, was a mixed success. While many new systems and procedures worked well, Discovery's external fuel tank shed unacceptable large pieces of insulating foam, prompting NASA to ground the fleet until the problem is solved. NASA currently does not expect to attempt a second flight before March.
Moore said preparations for a Hubble servicing mission continues at Goddard Space Flight Center, Greenbelt, Md., on the assumption that the mission ultimately will be approved.
NASA is targeting late 2007 for conducting the mission. Moore said the repair job, which will outfit Hubble with fresh batteries, gyroscopes and two new instruments, is expected to cost around $240 million, not including the cost of a shuttle flight. Once repaired, Hubble would be expected to last well beyond 2010.