Shuttle Endeavour aims for Monday morning launch
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: May 14, 2011
KENNEDY SPACE CENTER, FL-With the shuttle Endeavour's countdown proceeding smoothly toward launch Monday, NASA managers carried out a final processing review Saturday and said they were confident the electrical glitch that grounded the ship April 29 has been safely resolved. There are no other technical problems of any significance and forecasters are continuing to predict a 70 percent chance of good weather at launch time Monday.
"We took our time to walk through the issue that caused the launch scrub last time, the APU-1 heater problem, to make sure we truly understood our resolution and our fix, that everybody had a chance to see that. ... And everybody was fine with that."
Early Saturday, engineers pumped liquid oxygen and hydrogen aboard to power Endeavour's three electricity-producing fuel cells. If all goes well, a protective gantry will be pulled away from the shuttle around noon Sunday, exposing the ship to view and setting the stage for fueling.
Working by remote control, engineers plan to begin pumping a half-million gallons of liquid oxygen and hydrogen rocket fuel into Endeavour's external tank starting at 11:36 p.m. EDT (GMT-4) Sunday. The procedure should be complete by 2:36 a.m. Monday.
After a final weather briefing, commander Mark Kelly and his crewmates -- pilot Gregory H. Johnson, Michael Fincke, Gregory Chamitoff, Andrew Feustel and European Space Agency astronaut Roberto Vittori -- plan to head for the launch pad to begin strapping in around 5:41 a.m.
Liftoff is targeted for 8:56:26 a.m., the opening of a five-minute launch window marking roughly the moment when Earth's rotation carries the pad into the plane of the space station's orbit. Launch Director Mike Leinbach said law enforcement authorities are predicting up to a half-million spectators for Endeavour's final launching.
"You'll recall for the first launch attempt on that Friday afternoon, the estimate was between 500,000 and 750,000," he said. "So they're not quite expecting that big surge, but it'll still be a heck of a traffic jam after launch."
Weather permitting, of course.
Shuttle weather officer Kathy Winters said stormy weather was expected to pass through the area overnight Saturday, clearing out through the day Sunday. The forecast calls for a 70 percent chance of acceptable weather at launch time Monday, with the only concerns being possibly high crosswinds and low ceilings at the shuttle's emergency runway. A major problem during the first few minutes of flight could force Kelly and Johnson to attempt an emergency return-to-launch-site abort and NASA flight rules require generally clear skies and light crosswinds.
Stormy weather is expected to move through the area again on Tuesday, lowering the odds of a launch to just 40 percent, but conditions are expected to improve to 80 percent "go" on Wednesday.
The primary goals of the 134th shuttle mission are to deliver the $2 billion Alpha Magnetic Spectrometer particle physics detector to the International Space Station, along with a pallet of critical spare parts and components being stockpiled to protect against failures after the shuttle fleet is retired. Four spacewalks are planned to perform needed maintenance and upgrades.
Assuming an on-time launch, Kelly will guide Endeavour to a docking a the station's forward port around 6:15 a.m. Wednesday. The spare parts pallet, known as External Logistics Carrier No. 3, will be attached to the left side of the station's power truss a few hours after docking while AMS will be attached to the right side of the truss the next day.
Endeavour is scheduled to undock from the lab complex around 11:53 p.m. May 29, setting up a landing back at the Kennedy Space Center around 2:32 a.m. on June 1. That same morning, engineers will be hauling the shuttle Atlantis to the launch pad for the shuttle program's 135th and final flight. Launch is currently targeted for the second week in July.
NASA attempted to get Endeavour off the ground April 29, but a presumed short circuit knocked out power to a set of hydraulic system fuel line heaters and the countdown was called off. Engineers believe damaged insulation on a thermostat connector triggered an undetected short circuit during testing last June that blew fuse elements in a power switching circuit used by the heaters in question.
The circuit was not powered up again until the day of launch, when engineers noticed the B-string heaters were not responding as required. The countdown was called off and NASA launched an extensive engineering evaluation.
Playing it safe, the aft load control assembly power distribution box that included the blown fuse elements was replaced, along with thermostats and associated wiring. Extensive tests show the circuitry is working normally and engineers do not anticipate any additional problems with the system.
Engineers discovered the damaged thermostat insulation after reviewing data from last June that showed a previously undetected current spike during a test involving that same thermostat. While they have not been able to conclusively prove the insulation problem caused the short, no other problems have been found that could explain what happened.
"The only piece that's missing is the molten metal you'd see as an arc jumped from the bare wire to whatever ground point it had," Moses said. "But we were actually at the time heating this thermostat up with a heat gun that has a metal tip on it. If we inadvertently managed to touch that metal tip to the wire, it would have melted directly through the insulator, come into direct contact with the wire and shorted without an arc jumping the gap.
"So we postulate that's what happened. You could be a lawyer (and) say that we haven't exactly proven that was exactly it, but in our minds we are good to go and we have no problems expected with this APU heater any more in this count."
MISSION STATUS CENTER