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Jules Verne gets clearance for approach and docking BY STEPHEN CLARK SPACEFLIGHT NOW Posted: April 2, 2008 Fresh off an "impressive" display of proficiency for the European Jules Verne cargo ship's space-age autopilot system, senior international space station officials met today and confirmed plans for the craft's docking to the complex Thursday.
Managers from the station's international partners convened a senior-level meeting Wednesday to evaluate the Automated Transfer Vehicle's performance during Monday's test, the second of two "demo days" designed to exercise Jules Verne's high-tech systems before the ship is allowed to link up with the station. "Essentially we have now exercised all ATV systems except the docking system itself, although on Monday we did extend the probe. Consequently we know that there are no flaws in the design concepts, that practically everything is working, that the operations concepts are good, and the operations teams are capable of executing the operations in time. I would therefore say that most of the risks have already been burned off," said Bob Chesson, head of the European Space Agency's human spaceflight and exploration operations. "Of course there is always the risk of a random failure, and we still have to exercise the docking system," Chesson said. The docking system, a "probe and drogue" design long used by Russian Soyuz and Progress spacecraft, has been through hundreds of dockings over four decades of service. "In the end, we're using the docking mechanism of the Russian segment, so the final thing is a proven system," said Alan Thirkettle, ESA's space station program manager. Demonstrations on Saturday proved the ATV could autonomously fly toward the station using its long-range GPS navigation system. The docking dress rehearsal Monday focused on testing Jules Verne's videometers and telegoniometers, laser sensors that provide data to the ship's flight computers to determine its range, closing rate and orientation. "We have proven that Jules Verne's systems are safe, reliable and ready to dock to the station," said John Ellwood, ATV project manager. "Everyone has worked very hard to get to this point, and we have also proven that the team on the ground is fully ready for tomorrow's first attempt." The conference was a key step planned before the mission to review any problems encountered during the demonstration. Chesson said the ship's systems "all performed better than we could have hoped for." The only issue with Jules Verne involves uplifted thermal blankets on the craft's outer shell causing unexpected temperature fluctuations inside the spacecraft. The ship is drawing more power from its electrical system to compensate for the varying temperatures, but officials don't consider it serious. Wednesday's meeting adjourned with a "go" for Jules Verne's docking with the station. "I would say we have reduced the risk already by over 90 percent," Chesson said. "We are extremely confident of completing the last (36 feet) tomorrow." Chesson said conservative settings on safety monitoring software designed to keep an eye on the rendezvous could stop the approach even if there is no major anomaly. "We are always close to violating safety corridors," Chesson said. "During ground testing we have often triggered escape maneuvers due to limit violations even though nothing was wrong. This is still a possibility during the final rendezvous and docking and after (2.2 miles) we will not have time to recover the system and still go for docking. "This being said, because of the superb performance of the guidance and navigation system, and also our experience with operating the vehicle ... we do not expect false escapes, but there is still a possibility." See our detailed timeline of Thursday's rendezvous and docking here. Scheduled to begin at 1033 GMT (6:33 a.m. EDT) Thursday, the final rendezvous phase will commence as the cargo freighter flies toward the station using relative GPS navigation from a distance of 24.2 miles. The timeline calls for Jules Verne to arrive at the S2 hold point 2.2 miles behind the complex at 1205 GMT (8:05 a.m. EDT). Jules Verne will turn on its external tracking lights and activate the Kurs rendezvous radar, a venerable Russian instrument that will provide supplemental data during the approach. The craft will leave the S2 hold point at 1237 GMT (8:37 a.m. EDT) for a 40-minute automated flight to a temporary parking spot about 817 feet off the station's rear. Duplicating activities successfully demonstrated Monday, Jules Verne will activate its optical rendezvous instruments while holding a length of nearly three football fields behind the complex. Two videometers, working simultaneously with one in standby mode, will 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 will beam the laser light back to the sensors on Jules Verne, creating unique light patterns captured on the ATV's cameras. The patterns will allow the ATV to autonomously determine its orientation, closing rate and distance from the space station. Two other sensors known as telegoniometers will serve as watchdogs during the final rendezvous. The telegoniometers, similar to police radar guns, will also emit laser light at a different wavelength up to 10,000 times per second toward the reflectors. The light's travel time between Jules Verne and the station will determine range, while the direction of the station will be given by the angles of two built-in mirrors rotating to aim the laser at its target. "We're the first vehicle which will completely automatically, using optical sensors, dock with the space station," Ellwood said. The space tug will resume approaching the station at 1354 GMT (9:54 a.m. EDT) and fly to a point 62 feet from the Zvezda's aft docking port, where it will arrive at about 1415 GMT (10:15 a.m. EDT). Jules Verne will fire its maneuvering jets to precisely align its Russian-built docking probe with its target on Zvezda. The ship will aim for a narrow corridor just one-half inch wide, about the diameter of a Euro coin or a U.S. dime. Jules Verne will move within 36 feet of the station by about 1433 GMT (10:33 a.m. EDT). The ship will pause for about five minutes before ground controllers give a final go-ahead for docking. Station flight engineer Yuri Malenchenko, a veteran Russian cosmonaut, will occupy a command console inside Zvezda throughout the rendezvous sequence. The control panel allows Malenchenko to send orders to Jules Verne though a proximity communications antenna. The crew can command the ATV to hold, resume and retreat to correct minor errors in the ship's approach. In the case of a more serious problem, Malenchenko can send an escape or collision avoidance command for Jules Verne to rapidly depart the station's vicinity. Malenchenko, assisted by station commander Peggy Whitson, will monitor the approach through a network of video cameras tracking the ATV. Engineers at the ATV control center in Toulouse, France, also have the ability to intervene if any problems develop. The station residents and the ground control team demonstrated giving such orders during both rendezvous trials. The crew can send an abort command until the ATV reaches three feet from its docking target. After that point, an emergency maneuver could do more harm than good, according to Chesson. Engine plumes from Jules Verne's thrusters could damage the station when they are fired at close range. Known as the Crew Hands-Off Point, or CHOP, the abort limit line also takes into account the crew's reaction time, Chesson said. Closing at a relative velocity of about one-sixth of a mile per hour, the ship is scheduled to pull into the station's rear port at 1441 GMT (10:41 a.m. EDT). Zvezda's docking mechanism will immediately grasp Jules Verne at the moment of first contact, forming a temporary physical link between the two craft. "We do a sort of a dance with the space station. They're under their own control system. We're under our control system. We're like a pair dancing on the floor. We come in very, very slowly so that we do not collide," Ellwood said. If any issues preclude docking Thursday, the next opportunity to link up with the complex would come Saturday, according to ESA. The ATV's docking probe will retract a few minutes later to bring the two craft together. Eight latches will begin driving at 1515 GMT (11:15 a.m. EDT) to form a long-term connection, and the automatic sequence will mate electrical and fluid lines. The station crew plans to open the 31-inch hatch to Jules Verne's pressurized cargo carrier Friday morning to install atmosphere scrubbers to cleanse the air inside the module. Final ingress is on tap for Saturday morning, according to ESA officials. "This is when the ATV mission in support of the international space station really starts," Chesson said. Over the next four months, the station crew will gradually unload more 2,500 pounds of supplies from the cargo module. Jules Verne will also transfer water, oxygen and refueling propellant to tanks in the Russian segment of the space station.
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VIDEO:
PREVIEW OF DEMONSTRATION DAY 2 