International Space Station Not Damaged But Some Of Its ‘Fatigue’ Life Consumed In Rough Vibrations During Reboost
NASA Postpones Three Space Maneuvers As Gremlins Run Rampant, But One Problem Already Solved And Liftoff Achieved
If it’s true that bad luck comes in sets of threes, then NASA must be in line for a spectacular run of good luck, after glitches caused postponements of three separate space maneuvers.
First, a problem part forced a delay in launching Space Shuttle Discovery on the STS-119 Mission to the International Space Station (ISS). Then a severe vibration problem during maneuvering of the space station may have stressed its structure, forcing a delay in any further repositioning.
Finally, a system problem had to be remedied before NASA could light the fuse on a Delta II rocket carrying the NOAA-N satellite to successful orbit. (Please see separate story in this issue.)
These were the details as NASA experts and technicians gamely coped with evil spirits:
Discovery Discovers Glitch
Bill Gerstenmaier, associate NASA administrator for space operations, said in an evening news conference after a flight readiness review last week that the shuttle would lift off no earlier than Feb. 19. Later, NASA extended that, saying launch will be no sooner than Sunday, Feb. 22. That means that at this point, there is no official launch date.
The villain here is a lip flow control valve. Space agency officials didn’t realize until recently that part of the small valve can break off in a manner that can pose a threat, perhaps doing damage to space shuttle/external fuel tank plumbing.
While most checklist items were cleared for flight in the hours-long review, the flow control valve issue is still an open item, John Shannon, space shuttle program manager.
He said the tip of the valve “liberated,” or broke off, which surprised NASA experts. It seems vibration caused the break, caused by the flow of pressure through the valve.
Shannon likened a bit of the valve breaking off to the 40 mph wind forces that once collapsed a bridge in Washington state on Nov. 7, 1940, four months after its completion.
NASA engineers had “a failure of imagination” by not realizing what damage could occur if a piece of the valve broke off and went whipping through a system that provides pressure in the tank. It all might depend on where a “little poppet” might hit.
To answer that worry, NASA ordered experts at White Sands Missile Missile Range, N.M., Glenn Research Center in Ohio, and Stennis Space Center in Mississippi to experiment with shooting little pieces of valves into mockups of the plumbing.
So NASA shuttle program experts and leaders will meet Friday, Feb. 13, to assess progress in the sleuthing effort, and decide then whether to go ahead with another flight readiness review on Feb. 18. When the review occurs, it will set the final shuttle launch date.
There are three valves that channel gaseous hydrogen from the shuttle’s main engines to the external fuel tank, to pressurize the tank. One of these valves in Space Shuttle Endeavour was found to be damaged after its mission in November.
NASA sent the valve back to its manufacturer, Shannon said.
As a precaution, Discovery’s three gaseous hydrogen valves were removed, inspected and reinstalled. They have undergone an electron microscope inspection to look for cracks, he said. “The valves are in great shape,” Shannon told the media. “We’ve got the right valves in place,” Gerstenmaier said. But experts, to be safe, want to check what would happen if a bit of one of those valves breaks off and goes sailing through the plumbing.
But NASA isn’t sure just how rapidly they might be damaged, and whether that could happen just in the course of a single flight.
Shannon said NASA will put astronaut safety first, saying that results of the investigation will determine when Discovery is fit to fly.
“We’ll just let the [investigation results] drive us” in deciding when to launch Discovery, Shannon said.
The flow control valve headache is the only problem barring launch, he added. “With this once exception, we’re ready to fly,” he said.
Space Station: Shaken, Not Hurt
As for the space station, the problem arose during a routine maneuver that has been performed countless times. Called a reboost, the maneuver involves using thrusters to push the space station from a decayed (fallen) orbit back up to a normal orbit.
The boost was needed to position the station to receive a visiting spacecraft.
During that reboost burn of the thrusters, there was “quite a bit more vibration” than normal, Suffredini said. Apparently the thrusters cut off abruptly instead of gradually, causing the vibration.
“We did exceed” the normal amount of vibration during a reboost. The crew “never felt the [ISS] shaking like this,” he said, though they didn’t hear any creaking from the structure.
A video taken by a camera in the space station during the boost vibration showed objects moving up and down several inches for perhaps half a minute.
The net effect is that the shuttle still may have enough structural solidity to serve out its design life, which has an excess margin built in, but that excess was reduced by some amount during the vibration. In other words, the vibration shortened the useful life of the space station.
That violent vibration, or shaking, “put more cycles on [the station] than planned,” and did shorten the ISS lifespan, but not significantly, Suffredini said. “There was some fatigue life we did use up,” he explained. Yet the vibration left the station in good enough shape that it hasn’t violated its 15-year fatigue life, he added.
NASA leaders hope to win congressional approval of extending the ISS mission beyond a current 2015 cutoff.
The next reboost of the ISS won’t occur until March, when it will be needed to accommodate an arriving Russian Soyuz spacecraft.
The station is taking shape, and will be close to its final appearance once Discovery blasts off and carries the S-6 (Starboard-6) truss aloft to be attached to the space station. The truss is “tucked away in the [shuttle] cargo bay, ready to go,” said Mike Suffredini, space station manager.
More work is needed on the station system that recycles astronauts urine, sweat and exhaled breath vapor into potable (drinkable) water.
Crew member will change out a distillation assembly and bring it back to Earth for failure analysis.
During the mission, crew members will use the system to relieve themselves, and then experts will monitor how well it purifies the liquid and turns it into potable water.
NASA wants all the system components that have operated individually to be checked to ensure they work together properly.
One problem is that the system provided a water sample withy a high bacteria count, with more than 50 parts per million of coliform organisms. Escherichia coli bacteria are found in the human colon, and can contaminate water supplies, lakes, streams and other items.
Discovery will bring up iodine that will be used to flush the system and hopefully resolve the problem.
All this is critical to plans for the space station crew capacity to double to six members, from the current three, and for any crew to survive with drinking water in space once the space shuttle fleet stops flying next year on orders from former President Bush.
The shuttle fleet has been ferrying large amounts of water to the station, but after shuttles are grounded, NASA won’t have a human-carrying spacecraft until the next- generation Orion-Ares system begins manned flights in 2015, which will be a far smaller spacecraft than the shuttles. And the spacecraft flying to the space station in that five- year gap also will be far smaller than the shuttles.
Many other systems required to accommodate the shift to a six-person crew have been installed on the station and work well.
They include exercise stations, new expanded crew quarters, a galley and warming plates, a total organic carbon analyzer, an oxygen generator and more.
Separately, detective work has continued as experts attempt to determine why two consecutive Soyuz spacecraft suffered steep ballistic reentry paths to landing, with explosive bolts failing to detach unneeded structural panels from the spacecraft.
Russian engineers test-fired explosive bolts that crews brought back to Earth from a Soyuz docked to the space station, and those bolds “worked fine,” Gerstenmaier said. That leaves the ballistic rentries, which injured two space travelers, as an “unexplained anomaly,” he said.
During the half-decade gap between U.S. shuttle flights and the first manned Orion-Ares flights, American astronauts will have to depend on Russians and their Soyuz spacecraft to fly to the space station.