European space freighter checks avoidance feature
BY STEPHEN CLARK
Posted: March 16, 2008
Europe's Jules Verne space station transporter successfully completed a critical engine firing early Friday, proving it can steer clear of the orbiting complex if struck by a major problem during final approach.
The hour-and-a-half process demonstrated Jules Verne's collision avoidance maneuver, or CAM, a firing of four of the ship's attitude control thrusters that would push the craft away from the station at a relative velocity of around 11 miles per hour.
"It's good to have this tool in our back pocket," said John Ellwood, the mission's project manager.
Jules Verne, the first of five Automated Transfer Vehicles to service the space station, began its pursuit of the outpost this week after engineers overcame a propulsion system snafu that took out a quarter of the ship's thrusters shortly after its March 9 launch.
The ATV was more than 10,000 miles behind the space station during Friday's test, so controllers commanded the craft to move away from an imaginary point in space.
The test began on time at 0757 GMT Friday (3:57 a.m. EDT), when engineers at the ATV control center in Toulouse, France, uplinked a "red button CAM" command to Jules Verne, said Bob Chesson, head of the European Space Agency's human spaceflight and exploration operations.
During actual rendezvous operations, such a CAM burn can be ordered by the ground, the ATV's on-board computer, or the station crew.
The ship shut down its normal control system and relied on a Monitoring and Safing Unit, a "last-chance" computer with no backup to take over if something went wrong.
The control center transitioned the control system back to a fail-safe computer, then to the normal operational computer at 0935 GMT (5:35 a.m. EDT), wrapping up the essential test.
"The performance was absolutely flawless," Ellwood said. "We know now that it is completely safe for us to go to the station because we always have an independent way to get away from it."
A handful of small phasing burns are scheduled during the next five days to move the craft to its temporary parking spot 1,200 miles in front of the station. Nearly a dozen larger firings are scheduled in the hours before Jules Verne's arrival at the holding point around 1200 GMT (8:00 a.m. EDT) Wednesday.
"We are now basically in baby-sitting mode until March 18, when we do a mid-course correction to set up transition to (the) parking orbit," Chesson said.