NASA managers reviewing laser scans of Discovery's nose cap and wing leading edge panels have found no signs of any micrometeoroid impacts and have officially cleared the shuttle for re-entry Monday, weather permitting, to close out a space station repair and resupply mission.
In a brief chat with shuttle commander Steve Lindsey, mission control also said engineers believe a leaking hydraulic power unit that was tested earlier today can be safely used during re-entry and landing at the Kennedy Space Center.
Entry flight director Steve Stich has decided not to staff NASA's backup landing site at Edwards Air Force Base, Calif., Monday and instead to focus on Florida only. The crew will have two landing opportunities on successive orbits, the first leading to a touchdown at 9:14 a.m. and the second around 10:50 a.m.
If they can't make it back to Florida Monday because of weather or any other problems, Discovery will remain in orbit an extra day and likely land Tuesday in either Florida or California.
"After finishing the review for the port and starboard wings and the nose cap, they did not see anything new so they all look pretty good," astronaut Steve Frick radioed from the Johnson Space Center. "For weather ... the clouds shouldn't be an issue tomorrow, however there's still a chance of showers for the first rev and a little higher chance probably for the second rev. There's a front extending off into the Atlantic and depending on how it moves tonight, it may be close enough to cause some showers in the area. So we'll be looking real close at that. Edwards is looking real good both tomorrow and Tuesday if we need it."
"OK, we copy that," Lindsey said. "And is the vehicle cleared for entry?"
"That's affirm, I'm being told I can use that word. You are cleared for entry."
"OK, thanks," Lindsey said. "And a question about tomorrow. Will we land no matter what? Or will we just go for KSC tomorrow?"
"Tomorrow is KSC only," Frick replied. "For Tuesday, we'll look at other sites. But for tomorrow, we're just calling up KSC. However, the weather does look good for the West Coast for at least the next two days."
"OK, copy that."
Frick then passed on the latest thinking about APU 1, the hydraulic power unit in Discovery's engine compartment that is leaking either nitrogen gas or toxic hydrazine fuel. Engineers believe the small leak is nitrogen, used to pressurize the tank, and that more than enough will be available for entry.
While they cannot rule out a more hazardous hydrazine leak, results from a test run earlier today indicate APU 1 can safely be used for a normal re-entry and landing.
"They are feeling more and more confident it's likely not an internal ... hydrazine leak," Frick said. "There's always the chance, but we're feeling a little bit more comfortable with it. So the plan for APU 1 tomorrow will be nominal ops, we're not going to try to start it early or do anything unusual to burn extra hydrazine out of there. We'll be looking at it close like we did to day during FCS (flight control system) checkout. And it looked just fine today."
"OK, we copy that," Lindsey said. "Sounds great, thanks."