DART (spacecraft)

DART, or Demonstration for Autonomous Rendezvous Technology, is a NASA sponsored project. The goal was to develop and demonstrate an automated navigation and rendezvous capability in a NASA spacecraft. Currently, only the Russian Space Agency and JAXA have autonomous space craft navigation. Orbital Sciences Corporation was the prime contractor for construction, launch and operation the DART vehicle with a project cost of $95 million dollars. DART was originally scheduled for launch October 25 2004, but launch was postponed for launch loads analysis and instead performed on April 15, 2005.

After launch, DART successfully orbited and within hours made a rendezvous with the target MUBLCOM (Multiple-Path Beyond-Line-of-Sight Communications) satellite. The automated systems aboard DART successfully acquired MUBLCOM and began autonomously approaching it. During proximity operations, multiple malfunctions in navigation, propellant management and collision avoidance programming led to a soft collision with the target spacecraft and premature departure and retirement of the DART spacecraft.

DART had no capability for interactive piloting from the ground or for uploading new programming after launch, thus all on-orbit operations were directed by DART itself based upon pre-programmed criteria. The initial mission was to occur over about 24 hours but its premature failure occurred after only about 11 hours.

Mission objectives

Automatic orbital transfer maneuvers

The DART craft was launched on a Pegasus rocket into a polar, circular parking orbit (760 × 770 km). The space craft then autonomously navigated with orbit transfer maneuvers to reach MUBLCOM satellite. No navigational information was relayed to the vehicle after launch; it navigated autonomously and with GPS.

Proximity operations with AVGS

Once the spacecraft had navigated to the target satellite, it was to have performed a series of close proximity maneuvers. The maneuvers would have demonstrated the capabilities of the AVGS (Advanced Video Guidance Sensor). It was planned to demonstrate station keeping, docking axis approach, circumnavigation, and a collision avoidance maneuver. DART would have then departed the vicinity and retired to a final orbit. The entire sequence was to have been accomplished under autonomous control.

Additional demonstrations

* Safe operations
* Validate ground test results of the AVGS and proximity-operations algorithms
* Provide hardware capabilities for future missions by validating the AVGS in the space environment

The craft

* 2 meters long, 1 meter wide, 360 kg (with fuel)
* 16 nitrogen-fueled thrusters
* Contract awarded: June 2001
* Pegasus fourth stage (integral part of the DART craft), three hydrazine-fueled thrusters, and the reaction control system includes six nitrogen-fueled thrusters
* International Designator: 2005-014-A

The target

* MUBLCOM (Multiple-Path Beyond-Line-of-Sight Communications) satellite
* Orbital Sciences Corporation prototype communications relay satellite
* c. 49 kg satellite launched from Vandenberg Air Force Base 18 May 1999
* International Designator: 1999-026-B

Mishap investigation board

NASA convened a mishap investigation board to determine the reason for the DART spacecraft anomaly. First reports pointed to the spacecraft running out of fuel before concluding its mission. [http://www.spaceflightnow.com/pegasus/dart/ (Spaceflightnow)]

On April 14 2006 NASA announced that they would not release the investigation's report, citing that the report includes details protected by the International Traffic in Arms Regulations.

On May 15 2006 NASA released a public summary of the DART mishap investigation board report [http://www.nasa.gov/mission_pages/dart/main/index.html (NASA press release)] . NASA revealed that a critical navigation failure occurring when the DART and MUBLCOM spacecraft were about 200 meters apart precluded the full activation of the AVGS, and allowed DART to approach MUBLCOM without accurate ranging information. A later failure of the collision avoidance system, which was relying upon inaccurate position and velocity information, allowed DART to ultimately collide with MUBLCOM at a relative speed of approximately 1.5 meters per second. Both spacecraft survived the collision without apparent damage. Throughout the autonomous proximity operations, DART used its limited propellant faster than anticipated, which caused "a premature end to the mission" 3 minutes 49 seconds after the collision. DART initiated its retirement programming, removed itself from the vicinity of MUBLCOM, and prepared for deorbit. After the collision, MUBLCOM "regained its operational status after an automatic system reset".

The DART Mishap Investigation Board determined that of the 27 defined mission objectives, only 11 were partially or fully met, these relating to the launch, early orbit, rendezvous, and departure and retirement phases. None of the 14 objectives related to the proximity operations phase were met.

Current status

As of May 2006, DART remains in its polar retirement orbit of about 390 × 470 km, and MUBLCOM remains in a polar orbit of 740 × 750 km.

See also

*Attitude control
*Spacecraft

External links

* [http://www.msfc.nasa.gov/news/dart/ DART at Marshall Space Flight Center]
* [http://www.orbital.com/AdvancedSpace/AdvancedLaunchSystems/DART/ Orbital DART site]
* [http://www.nasa.gov/mission_pages/dart/media/05-051.html NASA Press release about the DART mishap] 16 April 2005
* [http://www.nasa.gov/pdf/148072main_DART_mishap_overview.pdf Mishap overview and description of the cause] 15 May 2006
* [http://www.cnn.com/2006/TECH/space/05/15/spacecraft.mishap.ap/index.html CNN DART mishap story] Dead link|date=July 2008 15 May 2006
* [http://www.nasa.gov/pdf/167813main_RP-06-119_05-020-E_DART_Report_Final_Dec_27.pdf DART Mishap Investigation Board Final Report] January 4, 2007