Shuttle boss optimistic about Discovery hydraulics issue
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 14, 2006
Editor's Note... This story has been updated with the results of today's Mission Management Team meeting to discuss APU landing strategy. MMT Chairman John Shannon provided additional details, but our earlier story is essentially unchanged. Engineers continue to study a variety of options on the assumption hydraulic power system No. 1 has a small hydrazine leak. APU 1 will be fired up during a routine flight control system checkout Sunday. If the leak rate doesn't get worse, the unit likely will be used during entry Monday. If it does worsen, engineers will run the unit until the fuel is exhausted and Discovery will return to Earth with just two operational APUs. Quotes and details from Shannon have been added below.
Astronauts Lisa Nowak and Stephanie Wilson, dubbed the "robo chicks" by mission control, used the space station's robot arm to detach a 10-ton cargo module from the lab complex and remount it in Discovery's cargo bay for return to Earth. Engineers, meanwhile, continue assessing the health of the shuttle's hydraulic system but senior managers are optimistic the issue will not have a major impact on Discovery's re-entry and landing Monday.
The shuttle has three auxiliary power units - APUs - to provide the hydraulic power needed to move the ship's wing flaps, rudder, brakes and runway steering system during re-entry and landing. Any one operational APU can provide the hydraulic power needed for a safe landing, but three are on board to provide redundancy and NASA has complex flight rules governing how APUs must be managed in the event of failures.
Earlier this week, engineers noticed a very small pressure decay in the fuel tank of APU 1. It could be leaking nitrogen gas used to pressurize the system or it could be leaking hydrazine. If it's the former, there are no problems for landing; at the current leak rate, more than enough nitrogen would be available to fully pressurize the fuel tank.
If the leak is hydrazine, however, engineers will need to convince themselves the leak won't get worse before proceeding with a "nominal" re-entry. While the shuttle can land with just one operational APU, hydrazine is a dangerous material and leaks are definitely frowned upon. In addition, APU 1 is the only hydraulic system that can deploy the shuttle's landing gear. If APU 1 is out of action, pilot Mark Kelly would have to manually fire pyrotechnic charges to deploy the gear.
Shuttle program manager Wayne Hale said in an interview with CBS News today that he's optimistic APU 1 will work normally during re-entry and landing Monday at the Kennedy Space Center. But the jury is out until engineers complete their analysis.
"We actually went through all the flight rules yesterday at the MMT (Mission Management Team meeting) and the rule would say if it's suspected to be hydrazine, which as we've said, this little bitty pressure decay could be a few drops of hydrazine leaking, from the letter of the law you have to declare that that APU could potentially not be there for landing.
"But losing one APU is still nominal end of mission," Hale said. "We might think real hard about the weather rules, you don't want tight weather wherever you're going. You look around at the weather a little bit for higher ceilings, lower crosswinds, all that kind of stuff and you pick the best place to go."
Forecasters with the Spaceflight Meteorology Group at the Johnson Space Center are predicting good weather at the Kennedy Space Center on Monday with showers more likely Tuesday.
"I've got this real optimistic weather forecast, which worries me four days out," Hale joked. "The forecast will change, and this one's only got one direction to change."
MMT Chairman John Shannon said it's unlikely engineers will be able to rule out a hydrazine leak in APU 1. As a result, the astronauts will fire up APU 1 on Sunday as part of a routine flight control system checkout. After the test, engineers will monitor the fuel tank pressure. If the leak stays the same, APU 1 likely will be used in the normal fashion for re-entry Monday.
If the leak worsens, however, Shannon said the astronauts will be told to restart APU 1 and run the unit until all the hydrazine is exhausted. They would then fly back to Earth with just two operational APUs, which Shannon said was a "certified" procedure.
"The consensus of the team was the best thing to do with this small a leak rate is to go run it for flight control system checkout on Sunday morning," Shannon said. "Then we'll shut it down and we'll go look at the pressure trace. I fully expect to see we won't have any change at all and if that's true, I would expect we'll use it for a nominal entry.
"If we did see a change in the decay rate, it got higher - it has a long way to go to get above flammmability limits - but if it changed, that would say it's not really a stable situation and the operations team would go ahead and burn it off in orbit and get all the hydrazine out of that tank. We'd re-enter on two APUs.
"Two APUs is fine, it's certified," Shannon said. "It's not as good as three APUs. You'd lose some things with hydraulic system No. 1 not being active, the most important probably is that you don't hydraulically deploy your landing gear, you end up doing a pyro deploy. ... While that is perfectly certified and it is dually redundant, you'd rather do a hydraulic deploy."
An analysis shows that at the current leak rate, even if it's hydrazine, there is no ignition threat. But Hale agreed with Shannon that "the potential for a hydrazine leak is a very serious concern."
"What I am feeling very good about is the team has put a full court press on understanding what's going on and what the potential outcomes are and put together a plan to deal with it as best we can. We're going to get another report at today's MMT.
"So far, the news would indicate that if this is indeed a hydrazine leak, and again, we can't tell, but if indeed it's a hydrazine leak and stays at this level, it will pose no credible hazard to us. The real key question is, how good do we feel about the potential this will not get worse?"
According to NASA's flight rules, a presumed hydrazine leak is grounds for declaring an APU failed, Hale said, "but the real operative rule says, and I can't quote you the words exactly, but it says with a credible expectation of combustion. Again, at this leak level, there's no credible expectation of combustion. I would say there's a very good chance the crew will come down to a nominal entry. However, the jury is still out, the folks are still doing the analysis. If they come back and say we need to go, after we undock, and burn it off ... until the tank bottoms out ... that's a decision we still have a couple of days to talk about."
A senior manager familiar with the discussions told CBS News the flight rules assumed a leak of liquid hydrazine. In this case, the leak rate is so small the presumed hydrazine vaporizes instantly and is vented to space.
Shannon agreed late today, saying the engineers who wrote the flight rules said they were intended for much larger leaks. Sensors show APU 1's plumbing is tight downstream of a set of fuel valves. The presumed leak, therefore, is many feet away from the APU itself and far from any hot spots that could provide an ignition source.
Otherwise, Discovery's nearly trouble-free mission has increased Hale's optimism about launching the shuttle Atlantis around Aug. 28 to restart space station assembly. The only wild cards today are the APU issue and whether any extensive inspections or work are required on Atlantis; resolution of a shuttle cooling system issue that may or may not be a problem; and troubleshooting to explain slightly higher pressures in main engine No. 3 during a post-shutdown purge.
NASA's official launch window for Atlantis opens Aug. 28 and closes around Sept. 13. But because of a potential conflict between the planned launch of a Russian Soyuz capsule carrying the station's next crew, NASA may be forced to close the shuttle window Sept. 9 or even a few days earlier. Hale said he has asked the shuttle team to look into the possibility of launching the next mission a day or two earlier than Aug. 28 if possible.
Resuming space station assembly represents a major step forward for NASA and managers are elated with the results of Discovery's flight.
"All in all, it was just a great mission," said Rick LaBrode, lead space station flight director. "This is just a roaring success for the station team and we're ready to proceed with assembly ops."
The shuttle-station crew transferred more than 7,000 pounds of equipment and supplies from the Leonardo cargo module to the space station. For return to Earth, the module was loaded with around 4,600 pounds of no-longer-needed equipment and trash. Another 1,800 pounds or so of equipment was transferred from Discovery's crew cabin to the station, along with 171 gallons of fresh water, a by product of the shuttle's fuel cell system.
"This particular flight, we've transferred more payload cargo than any other shuttle flight," LaBrode said.
The astronauts planned to spend the afternoon using the shuttle's robot arm and a long sensor boom to closely inspect Discovery's left wing leading edge for any signs of impact damage from micrometeoroids. The flight plan called for the shuttle's nose cape and right wing leading edge to be inspected Saturday, after Discovery undocks from the international space station.
Nowak and Wilson ran into problems with the space station's robot arm that took time to resolve. The port wing inspections were delayed and rather than forcing the crew to work into their sleep preparations, flight director Norm Knight gave commander Steven Lindsey the option of eliminating the inspections all together.
"The program does not consider this mandatory," astronaut Lee Archambault radioed from mission control. "It's highly desireable, but not mandatory. We don't want to push you into this."
But Lindsey said he and pilot Mark Kelly would press ahead with the port wing inspection as planned to get it out of the way today.
Assuming no problems are found after the inspections are completed post undocking Saturday, the shuttle crew will depart the area and begin packing up for re-entry and landing Monday. The Spaceflight Meteorology Group ss predicting light winds and scattered clouds at landing time.
Here are all the deorbit ignition and landing times for Discovery's crew through next Wednesday at the Kennedy Space Center (KSC), Edwards Air Force Base, Calif. (EDW) and Northrup, N.M. (NOR). "Rev" refers to the shuttle's orbit (all times in EDT and subject to change):
SITE..REV...DEORBIT......LANDING (updated times) Monday, July 17 KSC...202...08:11 a.m...09:14 a.m. (planned) NOR...203...09:35 a.m...10:39 a.m. KSC...203...09:40 a.m...10:42 a.m. EDW...204...11:09 a.m...12:11 p.m. NOR...204...11:11 a.m...12:13 p.m. EDW...205...12:45 p.m...01:46 p.m. Tuesday, July 18 KSC...218...08:18 a.m...09:21 a.m. EDW...219...09:47 a.m...10:51 a.m. NOR...219...09:49 a.m...10:52 a.m. KSC...219...09:54 a.m...10:56 a.m. EDW...220...11:23 a.m...12:25 p.m. NOR...220...11:25 a.m...12:27 p.m. EDW...221...12:59 p.m...02:00 P.m. Wednesday, July 19 KSC...233...06:56 a.m...08:00 a.m. KSC...234...08:32 a.m...09:35 a.m. EDW...235...10:01 a.m...11:04 a.m. NOR...235...10:03 a.m...11:06 a.m. EDW...236...11:37 a.m...12:39 p.m. NOR...236...11:40 a.m...12:41 p.m.