Late inspections of Discovery wings, nose cap completed
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 14, 2006
A quick-look assessment of post-undocking laser scans of the shuttle Discovery's nose cap and wing leading edges shows no obvious impact damage from space debris or micrometeoroids. Final clearance to proceed with landing Monday at the Kennedy Space Center will not be given until Sunday, however, after a detailed assessment is completed.
"From what they've looked at, there's nothing of any concern that we can report at this time," astronaut Lee Archambault radioed the crew from Houston late today. "So all looks good. Of course, the analysis will continue to crank out overnight and through tomorrow, and hopefully we'll have final words tomorrow."
"Thanks for the update," shuttle commander Steve Lindsey replied.
In the meantime, a key test is on tap early Sunday to assess the health of a hydraulic power unit that has a small leak in its fuel system. Lindsey and pilot Mark Kelly plan to fire up auxiliary power unit No. 1 around 3:58 a.m. Sunday as part of an otherwise routine flight control system check out.
APU 1 is on of three redundant powerplants in the shuttle's main engine compartment that generate the hydraulic pressure needed to move the ship's wing flaps, rudder, body flap and landing gear. The pressure in APU 1's hydrazine fuel tank has been dropping ever so slightly since launch July 4, indicating a leak of either nitrogen gas, used to pressurize the tank, or a leak of toxic hydrazine.
Because engineers cannot tell which material is leaking, mission managers have to assume it's hydrazine, an extremely hazardous material, and plan accordingly. Mission Management Team Chairman John Shannon says the team's strategy is unchanged from Saturday: If the leak doesn't get worse during the FCS checkout, APU 1 will be considered healthy enough for normal use during entry. If the leak worsens, the astronauts will simply run APU 1 until all of its fuel is exhausted and then return to Earth Monday with two operational APUs.
"The mission operations team put together their final plan," Shannon said. "The ops team will use APU 1 during the flight control system check out, they will run it the normal amount of time then they'll go assess it, make sure the leak rate did not change.
"If the leak rate changes at all, if it's perceptible to the ops team, they will burn it off, burn all the fuel out of that hydrazine system. We don't expect that to be the case. Assuming everything looks good after flight control system check out, that APU will be used as the first APU that's started pre deorbit burn and then used nominally throughout the entry."
Shannon said one member of the MMT dissented with the majority opinion, arguing "that maybe we did not know enough about the conditions back there and suggested we go ahead and burn it off for extra caution. But the other 31 people I polled were all in agreement that we go with the nominal plan."
The concern is that a major hydrazine leak could result in a fire late in re-entry under worst-case conditions. While engineers believe the leak is more likely nitrogen, which poses no threat, NASA's flight rules require conservatism to ensure the team errs on the side of caution.
A shuttle can safely land with just one operational APU, but APU 1 is required to deploy the ship's landing gear. If APU 1 isn't available for use Monday, Kelly will use a backup system to deploy the gear, firing pyrotechnic charges to blow the doors open and release the hooks that hold the gear in place. While that's never been done before, the system is redundant and Shannon said it would pose no problems for Discovery's crew.
APU 1 will be run for five to six minutes early Sunday to provide the power needed to check out the hydraulic system and movement of Discovery's aerosurfaces.
"It will be a good test for us, because it will start the APU up, it will run the APU, it will put it through some vibration, all the things we would expect to do prior to entry," Shannon said. "And then we'll just go and assess the leak.
"I would say it's going to take between six and 12 hours to see if the pressure decay rate has changed at all. If there's a significant change, then the ops team will go burn it off just because you would have lost confidence in the integrity of the system. I don't expect that to happen."
In addition to the FCS checkout and test firings of Discovery's maneuvering jets, Lindsey and Kelly also will carry out tests to troubleshoot an erratic controller in the ship's flash evaporator cooling system. The system, used to cool the shuttle's electronics after the ship's payload bay doors are closed, is difficult to test on the ground and NASA wants to collect as much data as possible to speed any possible repairs.
NASA hopes to launch the shuttle Atlantis around Aug. 28 on a long-awaited mission to restart assembly of the international space station. Discovery must be "turned around" quickly to serve as a potential rescue shuttle in case of problems that might prevent Atlantis from safely returning to Earth at the end of mission STS-115.
As reported here Friday, a conflict with the planned launch of a Russian Soyuz capsule carrying the station's next crew - Expedition 14 - has forced NASA to shorten Atlantis' launch window. As it now stands, according to station program manager Mike Suffredini, the window will open Aug. 28 - possibly as early as Aug. 27 if lighting permits - and close Sept. 7, nearly a week earlier than had been planned.
That's because NASA managers and their Russian counterparts want to ensure a separation between the shuttle's undocking and the arrival of the Soyuz to give the station crew time to make preparations and to adjust their body clocks to a different schedule.
For a variety of reasons, the Soyuz must take off by Sept. 18. Any later and the Soyuz carrying the station's outgoing crew would return to Earth about 10 days later in darkness. The Russians are using a recovery team with new personnel and want to ensure mostly daylight conditions for the recovery operation.
So the shuttle/Soyuz launch window will work like this: If Atlantis takes off between Aug. 28 and Sept. 3, the Soyuz carrying the Expedition 14 crew to the station will blast off from the Baikonur Cosmodrome Sept. 14. If Atlantis goes between Sept. 4 and Sept. 7, the Soyuz will take off Sept. 18. For a shuttle launch on Sept. 7, for example, Atlantis would dock with the lab complex Sept. 9 and undock Sept. 17. That would provide a three-day cushion between undocking and arrival of the Soyuz.
If Atlantis doesn't get off the ground by Sept. 7, NASA will stand down and the Soyuz launch will move back to Sept. 14. The next daylight launch window for the shuttle opens Oct. 26 and closes Oct. 29.