NASA originally planned to send a mission to the Hubble on Oct. 14 to service the telescope, and then postponed plans until February. The agency said Thursday that engineers must fix a replacement data-handling unit first.
"We now have done enough analysis of all the things that need to happen with the flight spare unit to know that we cannot be ready for a February launch," NASA's astrophysics division director, Jon Morse, said in a statement from NASA headquarters in Washington.
"The February date was an initial estimate, assuming minimal hardware preparations and test durations that are no longer viewed as realistic. We've communicated our assessment to the space shuttle program so it can adjust near-term plans. We will work closely with the shuttle program to develop details for a new launch opportunity," Morse said.
The spare part, called the Science Instrument Command and Data Handling system, has been stored at the Goddard Space Flight Center for backup since 1991.
Engineers will continue to test and examine the part through mid-December to identify and correct problems. After that, NASA will test the unit for electromagnetic interference and ensure that it can withstand vibrations and extended time in a thermal vacuum chamber. NASA said final testing and delivery to the Kennedy Space Center in Florida is likely to take place in April.
"Getting ourselves in a position to be ready to launch the Hubble mission will involve many steps, and a significant one took place earlier today," Hubble program manager Preston Burch said in a statement from Goddard.
"We held a flight-certification peer-review meeting where every aspect for doing this effort -- the inspections needed, all the tests to be conducted, the certification process and the final flight preparations -- was examined. The conclusion was that we indeed have a very good plan in place," said Burch.
Workers still have to lubricate some of the parts, test motors on the Flight Support System, and install new batteries.
"The equipment we are dealing with has a flight-proven design," Burch said. "The original unit on Hubble ran for more than 18 years. We have a lot of spare parts if we encounter problems, and we have most of the same test equipment that was used with the original unit. We also have a lot of experience on our Hubble electrical replica, which uses the engineering model data handling unit."
NASA has successfully restarted the Hubble's main camera, the Wide Field Planetary Camera 2, and produced calibration images from the Advanced Camera for Surveys' Solar Blind Channel. The telescope resumed science observations Thursday, when the camera released an image.