Shuttle boss talks inspection vs. landing day debate
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 20, 2006
The decision earlier this week to add a spacewalk to Discovery's mission and still preserve a final heat shield inspection today forced NASA managers to delay re-entry one day to Friday and in so doing, give up one of three end-of-mission landing opportunities. With only two available landing days - Friday and Saturday - NASA flight rules require a landing attempt Friday, even if that means diverting the shuttle to California or New Mexico. The latter option is a worst-case scenario that could expose the orbiter to sub-freezing weather for two days, possibly damaging thruster seals and water lines, and delay the ship's return to Florida by four to six weeks.
The latest forecast from the Spaceflight Meteorology Group at the Johnson Space Center in Houston calls for a chance of showers and low clouds at the Kennedy Space Center on Friday and high crosswinds at Edwards Air Force Base in California's Mojave Desert. The forecast for Northrup Strip at White Sands Space Harbor, N.M., where only one shuttle has ever landed, calls for acceptable conditions.
The weather improves at Edwards Saturday and deteriorates in New Mexico. The weather at Kennedy is expected to remain no-go. But NASA flight rules preclude waving off Friday if any one of the sites is acceptable because of the possibility of a mechanical or electrical problem that might require troubleshooting. That means a landing in New Mexico Friday, NASA's first since the third shuttle flight in 1982, is a possibility, depending on how the weather plays out.
Even so, shuttle Program Manager Wayne Hale said the decision to retain today's heat shield inspection was a no brainer.
"I have to tell you there are a lot of folks who think this is really extraordinarily critical," Hale told CBS News in an interview Monday at the Johnson Space Center. "I haven't quite gone to that level, but we're evolving in our thinking. The crew office has been very strong in desiring a late inspection."
A detailed heat shield inspection was conducted earlier in the mission to look for any damage that might have been incurred during launch. The goal of the late inspection is to look for signs of micrometeoroid and orbital debris damage - MMOD - that might have occurred since the first inspection was completed.
NASA engineers currently put the odds of an MMOD impact that could cause entry-critical damage at around 1-in-200 to 1-in-250. That's roughly equivalent to the same level of risk faced by the astronauts during launch.
"There is a pretty good statistical database now on this debris that is too small to be tracked by the Space Command radars and yet large enough to cause a serious problem," Hale said. "And in fact, we do see a number of MMOD hits on the orbiter every time we fly, small stuff that does maintenance-type, non-critical damage, which is consistent with all these statistical models."
To help improve the odds, NASA now re-orients the station-shuttle complex during docked operations to turn the orbiter's heat shield away from the direction of motion.
"Attitude plays a big role," Hale said. "We changed the attitude to more or less shield the shuttle, we're flying 180 degrees around from where we used to fly, which helps. And the numbers, it's something on the order of a 1-in-200 chance of incurring critical damage if you did nothing. If you do a late inspection and you assume a certain probability of detection, which the guys have studied, and then you say we have this repair technique that we have a high degree of confidence in - not 100 percent, so you put a knock-down factor in that - gets the odds down to around 1-in-320-ish if all that's effective."
Discovery's reinforced carbon carbon nose cap and RCC wing leading edge panels experience the most extreme heating during re-entry - more than 3,000 degrees Fahrenheit. Earlier in the mission, after the initial inspection was completed, sensors in the outboard left wing detected what many engineers believe was an MMOD impact. The astronauts took a look with a robot arm television camera and no obvious signs of damage were spotted. But the incident seems to have played a role in the ensuing debate about retaining the late inspection.
"This flight in particular has been somewhat complicated by this report we have off the wing leading edge sensor that said we probably, not guaranteed but probably, had an MMOD strike somewhere on that outboard lower left wing. And we've looked at it with the camera views that we could, which give you some kind of resolution but not the best resolution. There's a large portion of the community, by the way, that feels that's a closed issue, that we had the resolution we would have needed to see critical damage. But like all these things, there is a debate. ... I think we'd all like to take another look. And the question is, how hard do you want to take that extra look?"
NASA's options are limited by the amount of hydrogen and oxygen Discovery is carrying to generate electricity and a pre-launch decision to add a docked day to the flight because of the mission's complexity and the possibility a day would be needed to correct problems activating the lab's permanent power system.
As such, Discovery's flight is classified as a 12-plus-zero-plus-two-day mission, i.e., a 12-day flight with two weather contingency days. There is not be enough hydrogen and oxygen on board to extend the mission itself beyond 12 days and still preserve two backup landing days.
Going into Discovery's mission, late inspection was not listed as a major mission objective and managers agreed up front to take it off the board if the astronauts ran into problems with the station's electrical and cooling systems that might require an additional day for troubleshooting or an unplanned spacewalk.
When NASA did, in fact, add a spacewalk to the mission to retract a balky solar panel, many shuttle observers assumed late inspection would be taken out of the timeline. Late inspection, in fact, did not even show up on a list of pre-flight mission priorities. But NASA's Mission Management Team opted to retain late inspection and give up a landing day instead.
"We knew when we wrote the rules pre-flight that there was a large part of the community that believes late inspection is absolutely mandatory to provide safety to the crew," Hale said. "It's a priority, it was just written down differently than what we're talking about today. It was always a priority."
It was not an issue under the original flight plan, which called for undocking Monday, late inspection Tuesday and a landing Thursday at the Kennedy Space Center, with Friday and Saturday as weather backups. But the flight plan was thrown into disarray when the astronauts ran into problems retracting a solar array on the international space station.
By adding a spacewalk to the mission, NASA managers had to make a difficult decision.
"I think our thinking is evolving," Hale said of the late inspection turn around. "That's what you're seeing, our thinking is evolving here. One of the things I'm very interested in is to get some ground truth, to get Discovery back home ... look at the whole wing and say was there really something that happened out there or was this just a thermal creaking of the joints kind of thing? So we're trying to understand the whole process."
Depending on what the engineers find, NASA's thinking about MMOD and the relative priority of future late inspections might be altered. But in the near term, Hale said, there was no real choice.
"Our thinking is evolving and I've got to tell you from where I sit, if MMOD is going to be our number one risk, or number two, we have to do whatever we can to mitigate that risk," he said. "And so you look at the other side and say OK, what (does) having that weather day buy me? It buys me another day or another certain percentage chance to get back to the Kennedy Space Center, principally.
"It's not so much that we won't find a safe place to land, it's can I get back to the Kennedy Space Center as opposed to being out west somewhere where I've got a longer turnaround? It's a schedule thing. So when I see it's a safety versus a schedule (thing), then the preponderance of evidence has got to be on the safety. I'm not here to tell you that this is necessarily where we're going to wind up for the long term, but I am telling you that we are still weighing this and our thinking is evolving on the late inspection."
But by keeping late inspection in Discovery's flight plan, NASA managers had to extend the flight a day and give up one of the three end-of-mission landing days. And with just two landing days available, that means an attempt to get Discovery down - somewhere - on Friday.
The fact that NASA is even willing to consider a landing in New Mexico to ensure late inspection is an obvious indicator of NASA's post-Columbia willingness to put safety first.
That point is driven home when one considers what a landing in New Mexico would mean to the space agency.
The only pre-positioned equipment at White Sands is a shuttle tow bar, a tractor for towing the orbiter to a servicing area, a set of stairs to position by the ship's side hatch and a motor home to serve as an "astrovan."
After landing on the gypsum runway, the crew would power down the shuttle's electrical systems, exit and depart the area. Discovery would be towed to a concrete pad that is somewhat out of the wind to minimize damage cause by blowing gypsum dust.
And then the shuttle would simply sit, awaiting equipment and personnel from Kennedy and Edwards. With no power or heated purge air, Discovery would be exposed to sub-freezing temperatures for two days, possibly causing thruster seals to rupture. That would require time-consuming repairs back at Kennedy should that actually occur.
Once power and purge air are available, engineers would service the shuttle's hydraulic system and rocket engine valves and position the ship's three main engines for attachment of an aerodynamic cone required for the ferry flight back to Florida. The cone itself would have to be disassembled at Edwards, shipped to White Sands and then re-assembled.
Likewise, engineers would have to move and re-assemble a huge harness-like device to eventually pick the shuttle up for attachment to its 747 transport jet. The huge cranes required to do the heavy lifting would have to be shipped in and assembled on site.
It typically takes a week to 10 days at Edwards, where all the equipment is pre-positioned, to ready a shuttle for shipment back to Florida. The work costs about $1 million. At White Sands, engineers would need four to six weeks to get the job done, roughly the same time that would be needed to get a shuttle back from Spain or France after an emergency landing during launch. The cost of a New Mexico turnaround is not known, but officials say it would be "significantly more" than $1 million.
"The back-of-the-envelope turn-around time based on bar charts and schedules is 45 days," Hale said. "They have a convoy that will get the astronauts off safely and the vehicle powered down and they can tow the vehicle off the gypsum lakebeds to a concrete pad in an area that is protected from the winds. And they can put covers on to keep gypsum dust out, which is what happened on STS-3 (in March 1982). But then we've got to get everybody out there to do all the normal turnaround and most of all, the lift to put it on the 747.
"We have a contract that we've kept alive out there so we know what it takes to go get the cranes and all of that. But it would be a considerably longer operation than at Edwards. Again, that's just a schedule thing."
Discovery already was scheduled to be taken off flight status after this mission for a major inspection and overhaul. The shuttle Endeavour, coming out of its own orbiter maintenance and down period, or OMDP, will serve as the emergency rescue vehicle for the next shuttle flight in March.
But Discovery's next flight is STS-122, a high-priority mission scheduled for launch next October to carry the European Space Agency's Columbus research module into orbit. While NASA likely could make up any lost time getting Discovery back to Florida, the schedule is tight and the Columbus launch date would be in clear jeopardy if Discovery ends up in New Mexico.
"I haven't reviewed those schedules in detail ... but I would tell you it doesn't matter," Hale said. "If we need to go to Edwards or we need to go to White Sands and it's the day we need to land, we'll do it and then we will deal with the consequences and change our plans accordingly."
Based on historical weather data, there is just a 1 percent chance of bad weather closing all three landing sites in late December. There is only an 8 percent chance of Kennedy and Edwards both being down at the same time due to weather.
One wild card in the discussion about Discovery's eventual landing site may be a new set of tires installed on the space shuttle. NASA flight rules currently forbid landings in crosswinds greater than 15 knots. That limit can be raised to 17 knots if there is no turbulence.
But Discovery is equipped with a new type of landing gear tire that is capable of handling the stress of 20-knot crosswind landings. It's not yet clear whether the Mission Management Team might reconsider the crosswind landing limit Friday. The current forecast calls for a crosswind of 18 knots.
A landing at Edwards, however, still poses a major problem for Hale and the hundreds of engineers and technicians who would have to service the orbiter.
"My concern about extending the flight a day and potentially landing at Edwards is a workforce morale issue because we worked very hard to get this vehicle off early so we could get it down on the ground to give everybody off Christmas," he said. "And now by extending a day, and certainly if we land out west, we're going to have about 350 folks that are not just going to have to work Christmas but be 3,000 miles away from their families for a couple of weeks around Christmas.
"I really wanted to give folks the holiday with their families and I sure hope it works out that way because of workforce morale, the tension, you know, esprit de corps kind of thing. When I tell my wife I'm going to have to go to California to be with them on Christmas day, I may be looking for a new place to live!
"Having said that, that is all secondary to safely wrapping up this flight," Hale added. "We'll do what we've got to do."