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Cargo module mounted to space station for unloading BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: August 31, 2009 
NASA's Mission Management Team met Monday and cleared the shuttle Discovery's nose cap and wing leading edge panels for re-entry as is. An assessment of the shuttle's heat shield tiles is continuing, but there are no signs of any serious problems and engineers hope to wrap up the analysis by Wednesday at the latest. "We really have a very clean vehicle and the mission's going very well for us," said MMT Chairman LeRoy Cain. "We didn't have too many issues to talk about per se." Aboard the orbiting shuttle-station complex, meanwhile, astronauts Michael Barratt and Discovery pilot Kevin Ford used the lab's robot arm to carefully pull a 13.5-ton cargo module out of the shuttle's cargo bay for attachment on the Harmony module's Earth-facing port. Unberthing occurred around 4:45 p.m. EDT. A little more than an hour later, at 5:56 p.m., the Leonardo module was firmly bolted in place. It took several hours to complete leak checks and work to pressurize a vestibule between Harmony and the cargo module, but the astronauts ran ahead of schedule and opened the module at 11:54 p.m., an hour and a half earlier than expected. The only problem of any significance so far during Discovery's mission is the loss of the shuttle's six vernier steering jets due to a leak in one thruster that was detected after launch. The vernier jets, two in the shuttle's nose and four in the aft, are normally used during final approach to the space station, to help maneuver the shuttle-station "stack" and maintain the lab's orientation, or attitude. During docking Sunday, commander Frederick Sturckow guided the shuttle to a precision linkup using the ship's larger primary thrusters. After Discovery's docking to the front end of the station Sunday, however, Russian maneuvering jets were used to yaw the combined 945,000-pound stack 180 degrees, putting the Russian Zvezda command module in the direction of travel and Discovery at the back. The maneuver, normally conducted with the vernier jets, is intended to minimize shuttle heat shield exposure to micrometeoroid impacts. "The big maneuver that took place after we docked, we had to do that on the Russian segment thrusters because of our loss of verniers," Cain said. "The propellant usage there was more than had been expected or predicted. ... As a result of that, we're going and looking at a lot of the attitude maneuvers and attitude holds we have remaining in the docked mission and seeing what we can do to try and mitigate the use of the Russian thrusters and their propellant." Russian flight controllers budgeted about 66 pounds of propellant for the entire mission, Cain said, assuming the shuttle's vernier jets would be available. "We far exceeded that in this one maneuver that we did," he said. The shuttle's primary thrusters, which generate 870 pounds of thrust when ignited, can be used to maintain the station's orientation when the gyroscopes are not available, but engineers have not yet certified plans to use the big thrusters for the post-docking maneuver or the reverse maneuver before undocking. "In the simulation runs that were done, there were no issues with structures or contamination of any of the station components or subsystems," Cain said. "The issue with the auto pilot for those larger maneuvers ... was getting into the final attitude. The maneuver would kick off fine, it would proceed fine and progress well. Once it got to the right attitude and was firing thrusters to stop the rates in the various axes is when it was having trouble converging on the final attitude and doing that in a way that was considered controllable." He said engineers believe the primary jet digital autopilot routines can be fine tuned and "we might end up with a configuration that would be acceptable for us to do this maneuver. Beyond that, there might be an option for us to do the maneuver in this ALT-DAP configuration and when we get close to the final attitude, maybe at that point switch over to one of the other attitude control, attitude hold subsystems." But that remains to be seen. In the meantime, Cain characterized the shuttle's loss of vernier jets as a relatively minor issue and said that even though more Russian fuel was used than expected after docking Sunday, there was no danger of running out or even running low. "We have options, and we're looking at the various options because we can," he said. "We're nowhere near any kind of impending issue with the propellant budget on the shuttle or the station in any way at all. It's just we're trying to be smart about what we're doing."
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MONDAY NIGHT'S MISSION STATUS BRIEFING 