A host of errors prevented NASA’s DART spacecraft from completing its mission to rendezvous with a military satellite last year, the mishap’s chief investigator said May 16.
Scott Croomes, the NASA engineer who chaired the DART Mishap Investigation Board, said the mission’s failure stemmed from a combination of spacecraft navigation errors traced back to missteps by the vehicle’s Orbital Sciences Corp.-led design team.
“There was not one single cause,” Croomes told reporters during a May 16 teleconference. “It was not a smoking gun, but the parts that made up the gun. Any one of which, had it not been there … the gun would not have fired.”
NASA’s $110 million DART — or Demonstration of Autonomous Rendezvous Technology — mission launched April 15, 2005, on a 24-hour mission to meet and fly around an aging military communications satellite dubbed Mublcom . But the mission ended less than 11 hours later after DART collided with Mublcom instead of performing a series of precise maneuvers around the small spacecraft.
“What we found in the investigation is that this almost worked,” said Croomes, who also serves as test laboratory deputy manager at NASA’s Marshall Space Flight Center in Huntsville, Al a. “I think there are quite a few lessons available for other programs.”
Croomes led a 4.5-month, $1 million investigation into the mishap, though NASA has said the official 70-page report will not be released publicly because it contains sensitive material protected by International Traffic in Arms Regulations (ITAR). The space agency instead released a 10-page summary of the investigation board’s findings May 15, about eight months after the initial report was completed. Croomes said the summary leaves out technical details about DART’s navigation system that were deemed ITAR-sensitive.
ITAR restrictions were also partly to blame for DART’s failure to complete its mission.
Croomes said the technology export control regulations made it difficult for Orbital Sciences to talk freely with Surrey Satellite Technology, Ltd ., the United Kingdom-based firm that supplied DART’s GPS receiver. The receiver misstated DART’s velocity by about .6 meters per second, which in and of itself would not have been a problem if DART’s software designers had adequately accounted for the receiver’s bias, Croomes said. But the software model the team used to simulate the receiver during testing assumed the receiver measured velocity perfectly.
“I don’t want to speculate too far into what might have been, Croomes said. “If there had been the ability to communicate about expected performance, that would have enhanced chances of this being a successful mission.”
In addition to software glitches that led to DART’s navigation errors, investigators found a lack of adequate experience and training among the spacecraft’s development team. Spacecraft designers also failed to draw on the available expertise provided for the mission, the mishap summary reported.
“The outcome could have been different had they heeded the advice of their paid experts,” Croomes said of the DART designers. “They were available and being paid for.”
Part of the problem, Croomes said, lay in DART’s origin as a high-risk, low-budget mission, which left much of the details of the spacecraft’s design and construction up to its prime contractor, the Dulles, V a.-based Orbital Sciences, which built the 362-kilogram vehicle for NASA’s Marshall Space Flight Center . But over time, DART’s mission took on greater importance as an early technology milestone for NASA’s Vision of Space Exploration, and should have received additional risk-management oversight by NASA officials, investigators found.
Orbital Sciences Corp. proposed the DART mission as a $47 million technology demonstration in 2001 under NASA’s Space Launch Initiative, a multibillion effort to foster the development of a second-generation reusable launch vehicle to serve commercial and government markets. NASA elected to stick with DART even as the agency dropped the grander ambitions of the Space Launch Initiative in late 2002 in pursuit of the Orbital Space Plane, envisioned as a winged capsule that would launch atop an expendable rocket. DART also survived the cancellation of the Orbital Space Plane, which was dropped in favor of the multipurpose Crew Exploration Vehicle that President George W. Bush called for in his January 2004 Vision for Space Exploration speech.
By the time DART launched in 2005, about a year later than initially planned, the mission cost $110 million. Croomes said part of the cost increase was due to NASA’s switch to full cost accounting, which added, among other expenses, the salaries of NASA civil servants assigned to DART.
Orbital Sciences also built the Mublcom satellite and the Pegasus XL rocket that launched DART into orbit. Orbital officials did not comment on the newly released mishap summary itself, but added that while DART did not accomplish all of its goals, the mission did yield several lessons for future autonomous spacecraft systems.
“It was a challenging, experimental mission to begin with and it was all new technology,” Orbital Sciences spokesman Barry Beneski said. “Finding out what went wrong and why is an important part of the process to learn so that next time the technology is tested out, we’ll get even better at it.”
Croomes said NASA should not allow the DART mission mishap to prevent subsequent tests of autonomous spacecraft rendezvous systems.
“This was the first time the United States attempted an autonomous mission like this,” Croomes said. “NASA should not shrink back from attempting things that are difficult.”
NASA spokeswoman Kim Newton said the agency’s investment in autonomous rendezvous and docking technology would continue, although NASA is not currently planning any dedicated spaceflight demonstrations of the technology.
She also said NASA is developing a report for Congress “over the next month” that will detail the agency’s plans for automated rendezvous, proximity operations and docking in space.
Staff writer Brian Berger contributed to this article from Washington. Comments: tmalik@space.com