Managers say they don't mind launching later in the month, but they are very keen to fly before the closing of the first launch period on June 3. The dates are based on several technical considerations, including new safety rules implemented after the Columbia accident.
For example, for the first two post-Columbia flights, NASA will only launch the shuttle during daylight hours so that cameras will have a clear view of the liftoff and any debris that might fall off and hit the orbiter. Likewise, the agency wants the separation of the external fuel tank, which occurs 8 1/2 minutes after launch, to take place during daylight.
Columbia was hit by a piece of falling foam insulation from the shuttle's fuel tank, but NASA didn't have a clear view of the strike. The impact broke a hole into the leading edge of the shuttle's left wing, but the damage was not discovered until Columbia attempted to return to Earth 16 days later.
As the shuttle flew through the atmosphere, superheated gases blasted inside the damaged wing, leading to the ship's destruction and the deaths of its seven astronauts.
If Discovery can be launched this spring, it would clear the schedule for NASA's second post-Columbia mission in July.
Provided all goes well, the agency would look to ease some of its restrictive launch options, clearing the way for the resumption of International Space Station construction missions in December, said Michael Kostelnik, NASA's deputy associate administrator for space shuttle and space station.
If Discovery misses its spring launch opportunity and launches in July, NASA has only a matter of days through the rest of the year that would be suitable for launching with all the flight restrictions, Kostelnik added.
"Flying in May is a big win for the program, assuming that it is a good flight," Kostelnik said. "Then we fly in July and if we see a repeat of what we saw in (Discovery) — we'll be back where we need to be."
In addition to routine pre-launch flight preparations, NASA plans to conduct a test of the shuttle's newly designed fuel tank on April 14.
The real show-stopper, however, could be the findings of the task force set up to oversee NASA's implementation of the Columbia Accident Board recommendations. The board postponed its final report pending completion of a NASA in-house review.
"I would be hard-pressed to fly if the (task force) said we shouldn't," said shuttle deputy program manager Wayne Hale.
Since the accident, the country's entire human space program has been recast, with the shuttle now set as the first step in a decades-long project to return astronauts to the moon and eventually send crews to Mars.
"If we can't fly the shuttle safely and complete the space station, then we won't be doing anything else," Hale said.
