Atlantis fueling begins
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 9, 2007
Hoping for the best, engineers began pumping a half-million gallons of liquid oxygen and hydrogen rocket fuel into the shuttle Atlantis' external tank today for a second attempt to kick off a critical space station assembly mission. Launch is targeted for 3:21 p.m.
With forecasters predicting an 80 percent chance of good weather, engineers will be closely monitoring the performance of four hydrogen low-level engine cutoff - ECO - sensors at the base of the external tank, on the lookout for any signs of unusual behavior.
"Fueling of space shuttle Atlantis is underway," NASA commentator George Diller said at 6 a.m. "Confirmation that tanking and chilldown operations had actually begun (came) at 5:58. We expect to have some data on the ECO sensors within about the first 40 minutes of tanking."
Three of the four sensors did not respond properly during fueling Thursday, derailing the first attempt to launch Atlantis.
Because the system is suspect - and because repairs are not possible before the end of the current launch window Dec. 13 - all four sensors must work properly throughout the countdown today or the launch will be scrubbed again.
In addition, new instrumentation that provides voltage readings from the sensors, allowing flight controllers to monitor their health in realtime, must be working flawlessly for the countdown to proceed.
But if all goes well, commander Steve Frick and his six crewmates - pilot Alan Poindexter, flight engineer Rex Walheim, Leland Melvin, Stan Love and European astronauts Hans Schlegel and Leopold Eyharts will begin strapping in shortly after 12 p.m. for a launch attempt at 3:21:00 p.m.
Today's launch window is exactly one-minute long, closing at 3:22:00 p.m.
The goal of Atlantis' mission is to deliver the European Space Agency's Columbus research lab to the international space station along with Eyharts, who will replace Expedition 16 flight engineer Dan Tani.
Three spacewalks are planned to prepare Columbus for installation; to install two experiments on its hull; and to replace a spent nitrogen tank used to pressurize the station's ammonia cooling system. The nitrogen tank and a failed gyroscope will be moved back to the shuttle for return to Earth.
NASA managers plan to add a fourth spacewalk if possible to carry out additional inspections of the station's right side solar alpha rotary joint, a massive gear-driven mechanism that turns outboard solar arrays to keep them face on to the sun.
The starboard SARJ currently is locked in place because of recently discovered metallic contamination that indicates some sort of internal misalignment or other problem. NASA needs to restore the joint to normal operation as soon as possible to provide the electrical power necessary for the addition of a Japanese research module scheduled for launch next April.
The ECO sensors are part of a backup system intended to detect low fuel levels in time to prevent the shuttle's main engines from draining the tank after some other problem that might cause the powerplants to use up hydrogen faster than expected. Running out of fuel during engine operation likely would trigger a catastrophic failure.
In the wake of earlier problems with the cutoff sensors, NASA implemented a flight rule change that would permit a countdown to proceed if three of four sensors were operating normally and certain other conditions were met.
But engineers do not yet know what caused two sensors to "fail wet" during fueling Thursday or why a third sensor did the same during de-tanking operations. Because the system is suspect, the flight crew office proposed proceeding with launch Sunday if, and only if, all four sensors are operating normally.
The health of the sensors will be monitored throughout the countdown, using computer commands to simulate wet and dry conditions. The first such 'sim test" will occur early in the fueling process with additional checks planned at various points in the countdown. Voltage readings will be monitored all way to the T-minus 31-second mark when the shuttle's flight computers take over the countdown.
Using the new instrumentation, flight controllers will be able to determine whether any sensors fail after launch, allowing the crew to take action to preclude any potentially catastrophic downstream failures. Those options include aborting to a lower-than-planned orbit, dumping maneuvering fuel overboard to lighten the ship or diverting to an emergency landing in Spain or France.
But all of those scenarios would require multiple failures in unrelated systems. As such, program managers and engineers decided it was safe to proceed with launch.