Jules Verne practices close approach to space station
BY STEPHEN CLARK
Posted: March 31, 2008
Resembling an X-wing fighter from a science fiction film, the European Jules Verne cargo freighter flew just 36 feet from the international space station Monday using the world's most advanced space autopilot system.
"I'm known for my understatements, but the only word that comes to mind about today is impressive," said John Ellwood, the Automated Transfer Vehicle's project manager at the European Space Agency.
But the dramatic rendezvous was completed flawlessly, and the giant spaceship flew in tight formation with the complex for more than 30 minutes.
"This demonstration day confirms the performance of the vehicle is even better than we had hoped for," said Nicolas Chamussy, the ATV project manager for lead contractor EADS Astrium.
Engineers evaluated the condition of loose thermal insulation blankets covering the outer shell of the spacecraft, which they believe are causing temperature fluctuations inside the ship.
"These were in exactly the positions that our thermal analysis had predicted," Ellwood said. "At the moment, we do not envisage that this will have any impact on Thursday's planned docking."
Jules Verne's thermal control system has been using more power than anticipated, but officials do not expect the problem to pose any major consequences.
"We have addressed with our ISS partners the increase in power we might need to maintain the temperatures and we foresee no problems," Ellwood said.
Jules Verne, the first of at least five craft Europe intends to dispatch to the station, pressed closer to the station using precise navigation data derived from the ship's two videometers.
The videometers, working simultaneously with one in standby mode, fire pulses of laser light toward the station one-to-ten times per second.
Acting as space mirrors, 26 reflectors positioned on the back end of the station's Zvezda service module beamed the laser light back to the sensors on Jules Verne, creating unique light patterns captured on the ATV's cameras. The craft's advanced computers used the patterns to autonomously determine its orientation, closing rate and distance from the space station.
Two other instruments known as telegoniometers served as watchdogs during the final rendezvous, ready to take over if something went wrong with the primary system.
The telegoniometers, similar to police radar guns, emit laser light at a different wavelength toward the Zvezda reflectors up to 10,000 times per second. The light's travel time between Jules Verne and the station allow the craft determine its range, while the direction of the station is given by the angles of two built-in mirrors rotating to the aim the laser at its target.
The freighter, loaded with more than five tons of supplies for the station, resumed driving toward the complex at approximately 1547 GMT (11:47 a.m. EDT).
The ATV control center ordered Jules Verne to hold nearly 500 feet from the station a few minutes later. Engineers then told the bus-sized spacecraft to retreat about 100 feet, followed by a resume command for the ship to continue its approach.
These planned tests were critical demonstrations to prove the ground can manually intervene to correct a botched rendezvous.
"These are maneuvers that we could require if things don't go correctly during the rendezvous," said Bob Chesson, head of the European Space Agency's human spaceflight and exploration operations.
Marked by external tracking lights, Jules Verne approached the station under the cloak of darkness, its shadowy figure eerily appearing out of the night shortly before orbital sunrise.
Jules Verne halted at the S4 hold point 62 feet from the rear of the outpost at about 1617 GMT (12:17 p.m. EDT) to give officials a chance to review the progress of the testing before approving a final push to a distance of 36 feet from the station.
The 34-foot-long ship precisely aligned its Russian-built docking cone with the corresponding port at the aft end of Zvezda. Jules Verne aims for a corridor just one-half inch wide at the point of docking.
Russian cosmonaut Yuri Malenchenko, operating from a control panel inside Zvezda, sent crew commands for Jules Verne to retreat, putting Jules Verne in reverse to return to a distance of 62 feet from the complex.
Malenchenko sent an escape command at 1652 GMT (12:52 p.m. EDT) as the duo passed over the western coast of Africa.
"There is a 'go' to send escape, and after the escape command monitor the situation according to the reverse side of the corridor," a Russian flight controller said to the station crew from a control center near Moscow.
"Copy," Malenchenko replied. "And we're ready to send the escape command."
"Go ahead and send the escape command," the control center radioed.
"The escape command has been sent," Malenchenko said. "The three indications are on. There is the confirmation of the escape."
Jules Verne rapidly backed away from the station after receiving the order, reaching a point a half-mile away from the outpost less than 10 minutes later.
The ship will spend the next three days in free flight, positioning itself for the beginning of docking operations early Thursday.
Thursday's rendezvous will get underway at 1033 GMT (6:33 a.m. EDT), and docking is scheduled for 1441 GMT (10:41 a.m. EDT).
Although there were no clear problems encountered during Monday's demo, engineers will spend the next 48 hours crunching data from the ATV to present to senior officials during a mission management team meeting Wednesday.
Based on the vetted results from Monday's tests, the managers will decide whether to attempt docking as planned Thursday.