. 24/7 Space News .

Subscribe to our free daily newsletters

Lots Of Little Errors Caused DART Spacecraft Mishap

DART, the NASA experiment that 'almost' worked. Image credit: NASA
by Phil Berardelli
SpaceDaily U.S. Editor
Washington DC (SPX) May 17, 2006
NASA officials released a summary report Tuesday identifying the causes of a collision on April 15, 2005, between the experimental Demonstration of Autonomous Rendezvous Technology spacecraft and its intended rendezvous target, MUBLCOM, an inactive military communications satellite.

A five-month investigation following the mishap found that DART had used up its pressurized nitrogen gas maneuvering fuel before it could complete the rendezvous. The investigation board determined that excessive thruster firings in response to incorrect navigational data caused the spacecraft to run out of thruster fuel during its approach, so it could not avoid the low-velocity collision with MUBLCOM.

"There were a lot of causes," Scott Croomes, who chaired the eight-member board, told reporters during a teleconference at NASA's Marshall Space Flight Center in Huntsville, Ala.

Croomes said the spacecraft's global-positioning receiver suffered from a "factory error," which caused DART to reset its position and speed continually, and thereby discard the real-time GPS data that could have kept it on a precise course for the rendezvous and avoided the collision.

Because of the error, DART's receiver consistently produced a velocity reading that was biased by about 0.6 meters per second from what it should have been. The spacecraft's onboard software could not reconcile the error with the real-time data, and hence kept firing the thrusters and using up its fuel.

The investigation board also found that although the DART team at Orbital Sciences Corp. � the spacecraft's builder - knew about the error, they never attempted to correct it. This proved to be a critical misstep, because the software model that simulated the receiver during preflight testing assumed the receiver measured velocity perfectly, and that assumption was transferred to the spacecraft's software.

Combined with other errors and complications, the miscalibration caused DART to collide with MUBLCOM, the NASA board found � although the collision was minor. DART missed its 6.3 meter target envelope by less than 2 meters.

DART's design did include a collision-avoidance mechanism, but the software was dependent on the same navigational data source as the guidance system, so it was ineffective.

"The reasons for this inadequately-designed logic include the unanticipated potential for navigational errors and a lack of adequate design review," the board concluded in the summary report.

"This almost worked," Croomes told reporters. "Had any one of those causes not been there, (the rendezvous) would have worked."

After its launch, during which DART was carried by a Pegasus XL rocket dropped from a lift aircraft at Vandenberg Air Force Base, Calif., NASA found that the spacecraft performed nominally during the first eight hours of its mission ? including the beginning of the rendezvous phase.

Only when DART began to approach MUBLCOM did ground controllers notice the anomalies in the spacecraft's navigation system. DART ended up nudging MUBLCOM, boosting its orbit by 1.2 nautical miles, but leaving the rendezvous satellite undamaged.

NASA's Exploration Systems Mission Directorate, which funded the project and produced the report and summary, said in a statement that both satellites remain in low-Earth orbits that do not threaten other spacecraft, and eventually they will burn up upon re-entry into Earth's atmosphere.

NASA released only a summary report because the full report contains information protected by U.S. International Traffic in Arms Regulations. That information contains details about the military's navigation and communications technology.

Related Links
DART mishap report

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

Robots Embedded At School In Quest To Bond With Humans
Tokyo, (AFP) Apr 16, 2006
Playtime over, a toddler says nighty-night and spreads a blanket on the floor on top of his silver-colored friend. It is an everyday scene at one US nursery school, where robots are immersed among children to find out what it takes for machines and humans to develop long-term relationships.

  • International Workshop Eyes Cooperative Solar System Exploration
  • Japan space sneakers are ultra-high heels
  • NASA Testing Heat Shield Samples For CEV
  • NASA Awards Boeing S-3B Viking Modification Contract

  • Mars Drilling Tests Will Seek Knowledge And Resources
  • Opportunity Within Sight Of Victoria
  • Spirit Takes A Winter Break From Travels But Remains Busy
  • Opportunity Encounters Rolling Ripples

  • Arianespace Inks More Launch Contracts
  • Ariane 5 Mission Takes Next Assembly Step
  • Sea Launch Contracts To Launch EchoStar XI
  • Saab Ericsson Space To Equip More Ariane 5 Launchers

  • NASA Looks At Hurricane Cloud Tops For Windy Clues
  • Raytheon Tests Advanced Space-Based Weather Sensor
  • Tibet Provides Passage For Chemicals To Reach The Stratosphere
  • ESA To Host Atmospheric Science Conference

  • New Model Could Explain Eccentric Triton Orbit
  • New Horizons Taking Exploration To Edge Of Sol
  • Xena Poses A Bright Mystery
  • Tenth Planet Only Slightly Bigger Than Pluto

  • Stardust Analysis Update
  • EADS Astrium To Build Gaia Satellite
  • VLT Spies Twin Supernovae
  • Light So Fast It Actually Goes Backwards

  • India Hoping To To Unveil Space Prowess Before NASA
  • China To Launch Satellites For Lunar Surveying
  • NASA Announces Lunar Lander Analog Competition Agreement
  • Scientists Working To Help Astronauts To Breath Moon Dust

  • Sat-Nav Directs British Ambulance Off-Course
  • ESA Satellite Workshop Forecasts Navigation Advances
  • Spirent Federal GPS Simulation System Selected by Naval Air Systems Command
  • Iridium Will Supply Satellite Links For ARGO Tracker

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement