|
|
An Orbital Sciences-built Pegasus XL rocket successfully orbited NASA's autonomous DART spacecraft on April 15,2004 during an air-launch staged from a Stargazer L-1011 carrier aircraft flying over the Pacific Ocean. Credit: NASA TV. |
UPDATE: Story first posted 11:00 a.m.
WASHINGTON - NASA officials have confirmed that the DART rendezvous spacecraft bumped into its target satellite 760 kilometers above the Earth during an April 15 mission that ended early when the $110 million experimental spacecraft ran out of fuel faster than expected.
"The DART spacecraft did make contact with the target satellite during the rendezvous phase of the mission and boosted it into a slightly higher orbit," NASA spokeswoman Kim Newton said April 22.
Newton said neither DART (Demonstration of Autonomous Rendezvous Technology) nor its target satellite, a retired U.S. military spacecraft dubbed Multiple Path Beyond Line of Site Communication (Mublcom) satellite, appeared to have been damaged in the incident.
"There is no evidence that the DART spacecraft or the Mublcom satellite received any damage at contact," she said.
The DART program was managed by NASA's Marshall Space Flight Center in Huntsville, Ala. The spacecraft itself was built and launched by Orbital Sciences Corp., a Dulles, Va.-based NASA contractor.
Orbital Sciences also built Mublcom, a 48-kilogram experimental communications satellite that was built for the Pentagon's Defense Advanced Research Projects Agency and launched in 1999 aboard a Pegasus rocket, the same kind of rocket that carried DART aloft April 15.
DART, was designed to approach within 5 meters of Mublcom without any guidance from spacecraft operators on the ground and perform a series of maneuvers. The entire mission was expected to last less than 24 hours.
NASA initially reported that the self-guided DART spacecraft closed to within about 100 meters of Mublcom before DART's onboard computer detected that it had prematurely exhausted its onboard propellant. The computer then called off the approach.
In an April 16 conference call with reporters, DART Program Manager Jim Snoddy said that once DART exhausted its fuel, the spacecraft executed a pre-programmed plan to back off from the target and place itself in a retirement orbit meant to ensure its eventual re-entry into the Earth's atmosphere. Snoddy said DART accomplished some but not all of its mission objectives and that NASA would be convening a mishap investigation board to determine what caused DART's mission to end early.
NASA has since revised its understanding of what happened during DART and Mublcom's close encounter.
The first indication that DART hit Mublcom came from ground controllers at Orbital Sciences who detected that the military satellite was in a slightly higher orbit than it was before its encounter with DART, according to Newton.
Newton said Marshall officials first found out late in the day on April 20 that Mublcom's orbit appeared to have changed. She said the change of altitude was confirmed by the U.S. Air Force Space Command's NORAD tracking station.
NASA received only a limited amount of telemetry data from DART while the mission was still in progress. Newton said a further detailed review of DART on-orbit mission data confirmed that the spacecraft made contact with its target.
Newton said after contact, "DART went on to complete its planned retirement phase and is still working, and communications from Mublcom show that it is still fully functional."
DART is in a planned retirement orbit intended to keep the spacecraft aloft for years to come. The spacecraft is being tracked by the ground and is expected to re-enter the atmosphere and burn up sometime within the next 25 years, Newton said.
NASA has picked Marshall engineer Scott Croomes to lead the DART mishap investigation board.
Croomes, the deputy manager of Marshall's test laboratory, said during a brief interview April 22 that the rest of the board members would be announced by NASA headquarters by the end of the day.
"We are just in the initial stages of getting the team together and we anticipate getting into full swing next week," he said.
Croomes said the board is required to report back to NASA headquarters within 75 days.
Orbital Sciences President J.R. Thompson, during an April 21 conference call on the company's first-quarter earnings, told analysts that DART may have hit Mublcom.
"There is some data to suggest that indeed it got a lot closer [than 100 meters], and perhaps even touched the target," Thompson said. "All other DART systems performed as expected."
Thompson said DART's fuel supply was used more quickly than planned "due to excessive propulsion system thrusting caused by noisy GPS system inputs," a conclusion that would suggest DART's GPS-based navigation system did not receive clear information once the mission began.
NASA originally developed the DART mission to test technologies for the Orbital Space Plane project, which has been canceled. However, space agency officials have said they consider autonomous rendezvous capabilities important to missions as diverse as Mars sample return, satellite servicing and delivering cargo to the international space station.
NASA proponents of servicing the Hubble Space Telescope robotically frequently pointed to the DART mission as a confidence-building demonstration of some of the approach and rendezvous technologies that would be needed to fix Hubble without astronauts.
A National Academy of Sciences panel, in a report issued late last year, said it felt many of the technologies needed to mount a robotic Hubble repair mission were not ready.
NASA Administrator Mike Griffin said much the same thing April 18 during his first press conference, pronouncing the robotic servicing option "off the table."
Peter B. de Selding contributed to this report.
