An artist's illustration of DARPA's Orbital Express spacecraft in orbit, with the ASTRO servicing vehicle (left) bearing down on NextSat.
WASHINGTON ? The U.S. Air Force will deactivate the Pentagon?s Orbital Express satellites the week of July 2, eliminating any chance of NASA using the experimental spacecraft to test robotic techniques applicable to future Mars sample return missions.
Orbital Express is a roughly $300 million satellite-refueling demonstration led by the U.S. Defense Advanced Research Projects Agency (DARPA). It consists of a pair of unmanned spacecraft that were launched in March aboard an Atlas 5 rocket to conduct a series of experiments over a planned 90-day period. NASA contributed about $25 million to the project back in 2001 and engineers at the space agency's Marshall Space Flight Center helped develop the spacecraft's automated guidance system.
Sources familiar with the situation said NASA and DARPA had been quietly appealing to the Air Force to keep Orbital Express on orbit a while longer, but were turned down.
But NASA spokesman Dwayne Brown said June 29 that there was no disagreement between NASA and the Air Force about ending the Orbital Express mission.
?There is no dispute,? Brown said. ?We elected not to pay to do an extended mission.?
According to e-mails obtained by Space News, the two Orbital Express spacecraft completed their final rendezvous and capture maneuver shortly after midnight June 29. It was the second successful grapple of NextSat by the Autonomous Space Transport Robotic Operations (ASTRO) servicing spacecraft.
?Orbital Express will perform a mated scenario this weekend, demonstrating the ASTRO spacecraft?s ability to remove and re-insert a spare flight computer with its robotic arm. Once complete, DARPA?s demonstration is done,? U.S. Air Force Lt. Col. Fred G. Kennedy, DARPA?s Orbital Express program manager, wrote in a June 29 e-mail to several senior DARPA officials including Tony Tether, the agency?s director.
Tether forwarded Kennedy?s status report to nearly two dozen U.S. government officials, including Air Force Secretary Michael Wynne and NASA Administrator Michael Griffin, explaining that the mission was about to complete its final objective and would be decommissioned at the request of the Air Force.
?This is the last scenario for Orbital Express which has now set historical records for the U.S. space effort,? Tether wrote. ?It was hoped that OE would continue for NASA missions. However the Air Force is unable to support any further Orbital Express missions; rationale unknown at least to me but offers of paying the ground station cost for the next three weeks were rejected.?
?Orbital Express will be ?de-orbited? sometime next week,? Tether concluded.
Wynne, responding to Tether in an e-mail copied to the same long list of recipients, said he considers the upcoming decommissioning of Orbital Express a settled issue.
?As I understand it; it was explained that the science aspects of the mission were appreciated and completed. There is no intention to maintain this in orbit forever, and the offers of resources and the risk they offset from other opportunities for learning about space operations have been evaluated. Great work by DARPA,? Wynne wrote, adding: ?I thus do not know what problem we are trying to solve now??
DARPA spokeswoman Jan Walker, reached by telephone and e-mail June 29, would not immediately comment.
- VIDEO: The View from Orbital Express
- Orbital Express: Prototype Satellites Primed for In-Flight Service
- All About Satellites