NASA has decided that a robotic servicing mission to the Hubble Space Telescope (HST) is feasible and may decide to release a request for proposals (RFP) for such a mission by the fall, according to Associate Administrator for Space Science Ed Weiler.

NASA Administrator Sean O'Keefe sparked a controversy in January when he canceled the final planned space shuttle servicing mission to HST, saying it would violate the safety recommendations of the Columbia Accident Investigation Board (CAIB). Originally scheduled for 2005, the final servicing mission was to have replaced the telescope's crucial gyros and batteries and installed a new main camera and spectrograph.

Instead, NASA has been exploring other means of keeping the telescope operating for as long as possible, including robotic servicing. NASA's Goddard Space Flight Center in Greenbelt, Md., which operates the Hubble, released a request for information (RFI) about such a mission in February and received approximately 26 responses, according to Weiler.

"There look like there are some promising ideas on how we might be able to do a significant portion of a shuttle servicing mission without a shuttle, without astronauts, and thus taking the safety and risk issue off the table," Weiler said during a teleconference April 21.

Goddard is leading a NASA-wide team exploring the various robotic servicing options, and should have decided on a way forward by early June, Weiler said. If a mission should be approved, Goddard probably would manage it.

The most critical consumable on the Hubble is its onboard battery power. Without recharging or replacement, the batteries will run out by 2007 or 2008, rendering the telescope useless. Also crucial are Hubble's gyros, which allow for accurate pointing of its telescope.

Servicing priorities

The robotic servicing would involve a small spacecraft rendezvousing with Hubble and attaching itself to it. At the very least, the smaller spacecraft could be used to ensure that Hubble re-enters the atmosphere safely, according to Weiler.

In addition, "I think we're beginning to get pretty confident that the concept of batteries and gyros [being replaced or renewed] may be doable," Weiler said.

Schemes under consideration range from physically replacing the batteries to providing Hubble with an external power source that would reside in the smaller spacecraft. The servicing spacecraft might be able to feed power to Hubble through an umbilical attachment point on the telescope that has been used to secure it in the shuttle's payload bay during servicing missions, Weiler said. With its batteries recharged or replaced, Hubble probably could be kept operational until its orbit finally decays in 2013, he said.

More complex tasks, such as replacing the main camera, also are being considered, although NASA is being careful not to make the mission too ambitious and risk accidents that could render HST inoperative.

"Think of this nightmare scenario," Weiler said. "You put the instrument in for some reason, and you can't get the doors closed and you've got a light leak. Now all the instruments on Hubble are useless. That would be a bad day."

In part to satisfy the concerns of outspoken Hubble advocate Sen. Barbara Mikulski (D-Md.), NASA has asked the National Academy of Sciences (NAS) to offer its opinion on various options for extending Hubble's life. That response is expected in September.

Although it will seek input from the NAS along the way, NASA can't afford to wait for its response before beginning planning for the robotic servicing, Weiler said.

"We won't have to select and start funding contractors until after the Academy reports ... but we have to get the RFP ball rolling and proposals in to be evaluated so that when the academy report comes out, we will have the ability to take swift and determined action," Weiler said. "If we're going to do a robotic mission [in 2007-2008], we've got to get people under contract this fall."