http://www.space.com/missionlaunches/050422_dart_update.html
Fender Bender: NASA's DART Spacecraft Bumped Into Target Satellite
By Brian Berger
Space News Staff Writer
posted: 4:30 p.m.
ET
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.”
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