HOUSTON — NASA’s plans to test the technology for an automated rendezvous in space may have been doomed from the start, the SpaceRef Web site reported Tuesday. The payload, called DART, might have become crippled before it even reached outer space.
A NASA announcement on Monday merely stated that "a review of projected loads data, or the G-forces the payload experiences upon ignition of the Pegasus second stage, is being re-evaluated to ensure mission success." But the wording suggested that without such a review, success was in doubt.
The Pegasus air-launched rocket, built and launched by Virginia-based Orbital Sciences Corp., had been slated to send NASA's 800-pound (364-kilogram) DART satellite into orbit on Tuesday for a test rendezvous with an experimental military satellite. Citing NASA and aerospace industry sources, SpaceRef's Keith Cowing reported that alterations made in the Pegasus about a year ago could have broken the DART spacecraft during its launch, frustrating the mission and severely setting back the potentially valuable rendezvous capability.
Cowing, a former NASA manager, is the editor of SpaceRef.com as well as NASAWatch.com —two independent Web sites that are closely watched by aerospace insiders.
Contractor defends procedures
Responding to an inquiry from MSNBC.com, Orbital spokesman Barry Benesky said his company had followed "the standard procedure" for reliable space operations.
"As in any launch campaign, you review data all along, sometimes right up until launch day," Benesky said. "In this case, some data came to light — late in the game, certainly — so with caution and diligence, we're not going to proceed to launch."
Benesky couldn't recall any past case where a launch was called off so close to the launch date on the basis of review of old data. "It is unusually late" this time, he conceded. But he insisted that in the end, launch managers did the right thing: "We told the customer, and together we decided to take some time to review it."
DART stands for “Demonstration of Autonomous Rendezvous Technology,” and the dartboard metaphor is apt. The project aims for a target in space that could open a wide range of beneficial applications. It is the type of expand-the-envelope technology development mission that NASA needs more of in order to build a base for more ambitious space projects.
The planned launching last week was delayed several times — first by weather, then by an instrument problem on the target satellite, and then by the fortuitous discovery of loose debris inside the payload container atop the rocket.
But these frustrations may have the ultimate in space silver linings. That’s because NASA didn't find out about the potentially fatal flaw in the booster until after the third delay, Cowing reported.
“About a year ago,” Cowing wrote, “Orbital's Launch Division changed the stage two igniter in the Pegasus launch vehicle that would be used to launch DART. They eventually determined that the launch environment would be different and that it would present a larger launch load.”
During ascent, the changes could have subjected the DART spacecraft to stresses it was not designed to withstand, he said. The launch “would have damaged the DART spacecraft,” Cowing wrote.
Cowing quoted his sources as saying officials at Orbital Sciences initially had assured NASA engineers that there was no need to worry. The report raised questions along the lines of "what did they know and when did they know it," but Benesky denied that any reliability information had been covered up.
"We are 100 percent open and transparent, on all products, at all times, with all customers," he said.
The review process could take weeks, and one outcome would be a decision that the DART payload is safe to launch as is, Benesky said. Alternately, more tests might be required to determine this with confidence. In the worst cases, modifications to the booster or even the payload hardware might be needed, resulting in a much longer delay.
In one sense, the 800-pound DART robot's planned rendezvous with a retired military satellite might look like a small-scale retread of operations performed for decades by U.S. and Russian space vehicles. But DART's space technology could be applied to far more wide-ranging missions.
All American rendezvous missions since the first one in December 1965 have been guided manually, by astronaut crews. In contrast, Russian space missions (beginning in 1967) were automated — although on piloted spaceflights, cosmonauts often stepped in to correct malfunctions.
Eventually, the Russian system was perfected: More than 100 robot resupply flights to space stations have been conducted with Progress spacecraft over the past 25 years, and every single mission has succeeded. The biggest blemish on the Progress' record — the 1997 collision with the Mir space station — came during a high-risk test of a docking maneuver using remote control by a cosmonaut. The Progress had already docked successfully and was off-loaded before undocking for this extra experiment.
DART uses a technique more advanced than the U.S. and Russian approaches currently in use. The docking system doesn't need a crew's guiding hands, nor does it require a cooperative target sending out homing signals, as the Russian system does.
Russia's robotic dockings require the target to carry a radio transponder that echoes pulses from the chaser vehicle, in order to provide measurements of range, speed and direction. If the complex equipment fails, or if the target spacecraft has died, it won’t work. Such a scenario actually arose in 1985 when the Salyut 6 space station went dead. A manually controlled rendezvous had to be quickly thrown together — the only such mission in Russian space history.
So, unlike existing systems, the DART approach can in theory be used for automated rendezvous missions with targets that are entirely passive, such as derelict satellites requiring repair. No docking system currently in use can be modified to perform such a mission.
Not quite there yet
This test mission would still fall short of the ultimate goal, however. The target satellite has been equipped with laser reflectors to enhance the accuracy of DART’s laser range-finder. Furthermore, a Global Positioning Satellite receiver on the target transmits readings that DART can pick up and compare to its own GPS data, producing highly accurate information about its relative position and velocity.
Potential applications for more advanced versions involve missions far from Earth, where total autonomy is demanded due to the excessive round-trip time of radio signals from Earth that aid current systems. Among the examples: assembling a supply depot at an interplanetary balance point a million miles from Earth, or picking up a sample of Mars rocks fired into Martian orbit by a lander probe for transfer to an Earth-return capsule.
In the nearer term, NASA needs practice in robot rendezvous missions in order to conduct its robotic Hubble Space Telescope rescue flight about two years from now. In the same time period, the U.S. Air Force will be performing automated docking and undocking space tests to prove out techniques for resupplying large and expensive reconnaissance satellites with fuel to prolong their lives.