March 14, 2009
NASA has rescheduled the launch of Discovery for Sunday at 7:43 p.m., less than 15 minutes after official sunset.
After Wednesday's scrub, the big orange external tank was drained of hydrogen. They had to wait until Thursday afternoon to get access to the launch pad because of venting from the tank. (Hydrogen is very explosive--that's why it is used as rocket fuel!)
Once it was safe, workers carefully inspected the vent line at the shuttle interface. No obvious leaks were found, but all components were changed out just in case. The helium used for the leak checks was at ambient temperatures, so there is some concern that a leak could reoccur when the cryogenic liquid hydrogen is pumped back into the tank on Sunday afternoon.
If a leak or other problem scrubs the launch Sunday, they will try again on Monday or Tuesday--but one or more spacewalks will be cancelled. This is because the shuttle has to undock from the station by March 25 to avoid a conflict with the Soyuz launch that will bring up two new crewmembers. If they can't launch by Tuesday, the flight will be postponed until after April 7.
If they launch by Tuesday, the number of spacewalks that have to be scrubbed depends on whether or not the shuttle sustains debris damage during launch. If an initial inspection of the shuttle and launch videos show suspicious damage, then the crew must set time aside on orbit for what are called "focused" inspections. If the shuttle launch is delayed until Tuesday and a focused inspection is required, there would only be time for one spacewalk. That spacewalk would unload the S6 array from the cargo bay and mount it on the station.
If all but one spacewalk is scrubbed, it is not clear whether or not the station crew or a future shuttle crew would complete the complicated installation and deployment of the new array or when that would be done. How this would impact the plans to increase the crew size from 3 to 6 is also not clear.
Delaying into April would cause a domino effect that would delay the Hubble flight from May to June and delay the next station flight, too.
So fingers are crossed and prayers offered that the countdown goes smoothly for the Space Shuttle Discovery to liftoff near sunset on Sunday, March 15.
If you don't live in Florida to watch it live, or have the NASA cable channel to see it in hi def, you can watch the launch online at http://www.nasa.gov/multimedia/nasatv/index.html.
Posted by m_dyson at March 14, 2009 01:40 AM