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Test on newly installed valves pushes liftoff date to Feb. 22

NASA’s planned launch of the space shuttle Discovery this month has slipped a few more days to Feb. 22 due to extra time needed to finish tests related to newly installed valves on the spacecraft, agency officials said Friday.

Discovery was slated to launch no earlier than Feb. 19 pending the completion of tests to ensure the shuttle’s three fuel flow control valves are safe to fly. But work at several NASA centers to evaluate the valves in time for a Tuesday meeting by shuttle managers is taking longer than planned, and shifted the launch to no earlier than Feb. 22, according to an update released late Friday.

Mission managers are now expected to discuss the valve test results on Feb. 13, and then meet again on Feb. 18 to review the Feb. 22 launch target, said NASA spokesperson Kyle Herring at the agency’s Johnson Space Center in Houston. That process, however, is wholly dependent on the progress and results of the valve tests, he added.

Earlier this week, NASA delayed Discovery’s initial Feb. 12 launch date by at least a week due to concerns with the spacecraft’s flow control valves.

There are three flow control valves on Discovery — one for each main engine — designed to route gaseous hydrogen from the engines to a propellant tank in the orbiter’s external tank to maintain proper pressurization during the launch into space.

During NASA’s last space shuttle launch in November, one of the valves aboard the Endeavour orbiter was damaged, sending a small chip about the size of a thumbnail tip into the plumbing lines leading back to the external tank. Endeavour successfully reached orbit and maintained fuel tank pressure despite the glitch. Engineers found a crack in the suspect valve after Endeavour returned to Earth.

An initial analysis suggests that acoustic vibrations may have led to high-cycle fatigue of a valve component that pops up and down like a lawn sprinkler head, NASA’s space shuttle program manager John Shannon told reporters late Tuesday. Similar valves aboard Discovery were replaced with ones that have flown previously and are known to be in good shape, he added.

Even so, mission managers ordered a round of tests to better understand how metallic chips from the valves could affect plumbing lines leading back into Discovery’s fuel tank during flight.

“We want to make sure we’ve got this right,” said NASA’s space operations chief Bill Gerstenmaier late Tuesday. “So we think standing down a little bit of time, and letting the folks do a little more work is a good thing.”

Commanded by veteran spaceflyer Lee Archambault, Discovery’s STS-119 mission is NASA’s first of up to six shuttle flights scheduled for 2009. The two-week mission includes four spacewalks to deliver the last set of U.S.-built solar arrays to the International Space Station and replace a member of the orbiting laboratory’s Expedition 18 crew.

A series of additional space station construction flights, as well the final shuttle mission to overhaul the Hubble Space Telescope, are also slated to launch this year.

Astronauts living aboard the International Space Station were surprised by the unexpectedly strong vibrations that rattled their orbiting lab last month, but don’t believe the event damaged their $100 billion outpost. Space station commander Michael Fincke of NASA said the Jan. 14 vibrations shook objects loose from the walls during a scheduled engine burn, but it did not immediately spark concerns over the health of the spacecraft.  “We were definitely surprised,” Fincke told SPACE.com Thursday via a video link. “It’s not usual during a reboost to see anything come off the walls.” Video from a camera inside the space station showed equipment doors and other objects shaking back and forth.

The vibrations on Jan. 14 occurred during what was expected to be a routine Russian thruster firing to boost the space station into a higher orbit. During the two-minute, 22-second maneuver, sensors aboard the space station picked up vibrations that exceeded acceptable limits.

Michael Suffredini, NASA’s space station program manager, said Tuesday that a subsequent analysis has shown that the vibrations did not shorten the orbiting lab’s 15-year design lifetime. Space station flight controllers, however, did cancel another planned thruster firing slated for Wednesday pending more study.

“Fortunately, the results of the analysis so far shows that we haven’t hurt the space station,” Fincke said. “But we certainly could have, so we’re definitely going to be very careful next time.”

Fincke described the engine burn as the strongest thrust he and his two crewmates had felt since they launched into space last fall aboard a Russian Soyuz rocket and NASA space shuttle. Whenever Fincke let go of a handhold in the station, the rest of the ship would noticeably move around him as he floated in weightlessness.

“At the time it was quite amazing,” Fincke said. “Then the harmonic vibrations started to kick in and we saw things shaking off the walls. That was surprising, but it didn’t last very long.” The astronauts then had to fly through the space station’s cabin collecting loose items and reattaching them to the outpost’s walls, he added.

Shuttle Discovery’s delay

With the vibration event behind them, the space station crew is preparing the orbiting lab for the arrival of a new Russian cargo ship and the space shuttle Discovery later this month. The unmanned cargo ship Progress 32 is slated to launch early next week and dock at the station on Feb. 13. But the planned Feb. 12 launch of Discovery has been delayed at least one week as engineers evaluate a fuel flow control valve concern.

For space station flight engineer Sandra Magnus, also of NASA, Discovery’s delay means a longer stay in orbit. Magnus arrived at the orbiting lab last November and will return home aboard Discovery.

“Of course, with shuttle schedules you never really want to get your heart set on a specific date because it’s a very flexible program,” Magnus told SPACE.com. “Another week is fine, they’ll make the right decision when to launch the shuttle and I’ll go home whenever it arrives.”

Discovery is now slated to launch no earlier than Feb. 19 to deliver the last set of U.S. solar arrays and Magnus’s replacement, Japanese astronaut Koichi Wakata.

Earlier this week, Magnus raided the space station’s pantry to put together some special treats during Sunday’s Super Bowl showdown between the Pittsburgh Steelers and Arizona Cardinals. Fincke, a Pittsburgh, Pa.-native who grew up in Emsworth, is a vocal Steelers fan who beamed down video messages of support to spur his team on during the NFL playoffs and their Super Bowl win.

“We really didn’t have a party, but Sandy did. She put together some really amazing dips and other Super Bowl treats that we normally would have on the ground,” Fincke said. “It made the day even more special.”

Vigorous vibrations caught on video during orbital reboost last month

HOUSTON – A faulty rocket command sequence aboard the international space station caused the 300-ton structure to shake back and forth vigorously for two minutes last month, during what was supposed to be a routine, gentle orbital adjustment. Space experts in Houston and Moscow have spent the last two weeks searching for the cause of the shaking and doing a damage assessment.

Under the worst-case scenario, such vibrations could rattle the station so much over the long term that the structure might begin to crack and leak. One of the solar arrays might bend out of position, affecting the station’s power-generating system. Experts cautioned that it was too early to determine how likely or unlikely these scenarios might be.

Partly as a result of last month’s anomaly, a second rocket burn originally scheduled for Wednesday has been canceled. Since the maneuvers had been intended to line up the station’s path to receive future visiting spacecraft, the dates of those missions are now in doubt. A Russian Soyuz visit in late March already has been postponed a day.

The original rocket firing on Jan. 14 involved two 440-pound (200-kilogram) thrust engines attached to the station’s Russian-built Zvezda service module at the trailing end of the station. The engines fired for 142 seconds under autopilot control to raise the station’s orbit slightly. The purpose was to shift the station’s ground track into a proper path to facilitate rendezvous with future visiting spacecraft.

In the past, such firings had given the station a gentle push, enough to send free-floating objects adrift toward the cabin’s back end in 30 or 40 seconds. Reboosts also have been performed with smaller thrusters aboard Progress cargo ships, as well as with the small maneuvering jets on docked space shuttles. Those firings are usually so gentle that crews don’t notice – they even can sleep through them.

But during the Jan. 14 firing, something went seriously awry. The station’s solar power wings began swaying back and forth alarmingly. More dramatically, an interior camera captured views of wall-mounted equipment and cables flopping back and forth to a two-second beat, as the camera itself swayed on its mounting bracket.

Buildup of gyrations

It was quickly apparent that some periodic force had excited the space station’s structure at one of its resonant frequencies, leading to a buildup of gyrations rather than a damping down. As with the traditional “soldiers marching across a bridge” story, and the all-too-real Tacoma Narrows bridge collapse in 1940, resonance buildup in a large structure can quickly lead to serious consequences.

Kelly Humphries, a spokesman at the Johnson Space Center in Houston, told msnbc.com in an e-mail that the space station’s structure “has been cleared for tomorrow’s burn, but the burn has been canceled.” Other sources told msnbc.com that the clearance was granted only for use of the much gentler small engines on a docked Progress. Use of the larger engines, and their autopilot control software, remains suspended. The sources spoke on condition of anonymity because they were not authorized to discuss the limitation publicly.

Humphries said that the latest burn cancellation was a good idea for other reasons. “This will help us conserve propellant and set up better for the 2JA mission [a shuttle flight scheduled for launch on May 15], where we were trying to deal with too much altitude,” he wrote.

These are real benefits, sources told msnbc.com, but they would never have caused the cancellation of the burn if the original overshaking hadn’t occurred.

Delayed reports

The shaking was not discussed publicly when it happened, but 10 days afterward, the anomaly was described as “higher-than-usual structural oscillations” in one of NASA’s routine station status reports. The report said the next reboost would be put on “temporary hold until results … have been reviewed in depth”.

Two days later, another status report said the Russians determined that the shaking was brought on after “an error in parameter settings” was uploaded to the engine control system for the Zvezda module.

The Russian engines are hinge-mounted to allow a small variation in thrust pointing direction, and somehow the autopilot began swinging the engine up and down seeking the “sweet spot” for thrusting, but always overshooting and repeatedly reversing direction. By unfortunate coincidence, that back-and-forth swinging had a period close to the station’s resonant frequency. So, like a child pushing periodically on the back of her swing-mounted playmate, the swings became wilder and wilder.

How bad was the shaking?

The thrashing of the long solar array wings reached a degree “five times greater than allowed,” one source told msnbc.com in an e-mail. Another source said the swaying was the “biggest I’ve ever seen… Outside the certified limits of ISS structure…”

The extent of the damage or structural weakening induced by the shaking is “very much still in work,” a third source said in an e-mail. The attach points of the long booms, and the docking interfaces between pressurized modules, are particularly susceptible to accumulated flex-induced fatigue. In the latter case, loss of pressure integrity is a potential consequence.

This source said two “million-dollar questions” had to be answered soon. First, data gathered from accelerometers and stress sensors on the structure must be analyzed to see how bad the overloads were. Second, why were the Russian commands for the automated rocket burn approved without adequate simulation and testing?

A review of such issues has been going on for the past couple of weeks without any breaks, sources said.

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