Shuttle Atlantis tentatively cleared for Nov. 16 launch
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 30, 2009
NASA managers met at the Kennedy Space Center Thursday and tentatively cleared the shuttle Atlantis for launch Nov. 16 on a three-spacewalk mission to deliver nearly 15 tons of spare parts and supplies to the International Space Station.
"In terms of being the flight that brings up all the spares for station, this is really full," said Bill Gerstenmaier, NASA's director of space operations. "They've done a tremendous job of really outfitting station with all the spares that are going to be needed, essentially through its lifetime. This flight, and a couple of the other shuttle flights that come later, really set us up very well for kind of the end of the shuttle servicing era."
NASA was able to reserve two days on the U.S. Air Force Eastern range - Nov. 16 and 17 - in a launch window that extends, in theory, through Nov. 19 and possibly Nov. 20. NASA got the launch slot after the Air Force agreed to delay, if necessary, launch of a United Launch Alliance Delta 4 rocket carrying a military communications satellite.
As it now stands, a ULA Atlas 5 rocket carrying an Intelsat communications station is scheduled for launch Nov. 14, with Nov. 15 as a backup. If the Atlas takes off on time, Atlantis will have a shot at launching on Nov. 16 with the Delta 4 following suit on Nov. 18. If the Atlas is delayed a day, the shuttle will slip to Nov. 17 and the Delta to Nov. 19.
If Atlantis doesn't get off by Nov. 17 - and if the Air Force agrees to another delay for the Delta 4 - the shuttle could have additional launch opportunities Nov. 18 and 19. But as it now stands, NASA only has two days to get Atlantis off the ground. After that, the shuttle launch would slip to Dec. 6 because of heating constraints related to the space station's orbit.
Mike Moses, shuttle integration manager at the Kennedy Space Center, said Atlantis is in good shape and should be ready for flight by Nov. 16 if engineers can close out a handful of open issues.
One on-going investigation involves the effects of vibrations and acoustics associated with startup of the shuttle's three hydrogen-fueled main engines. Another involves the strength of key brackets used to secure the shuttle's potty inside the crew module against worst-case crash loads.
The engine startup acoustics issue first came to light after the October 1998 shuttle flight that launched former Sen. John Glenn back into orbit. During liftoff, the door covering the shuttle's braking parachute fell off, prompting an investigation that ultimately led to liftoff acoustics.
Additional instrumentation was added to subsequent flights and the data seemed to show sound levels were in the expected range. But in a subsequent analysis, engineers realized the way the sensors were being calibrated did not adequately take into account how the vibration of the pressure transducers themselves interacted with the sound they were supposed to measure.
More accurate calibration showed the acoustic environment at engine startup "was a lot more severe than we thought," Moses said. "It was definitely above what our design limit was."
Engineers then began analyzing shuttle structures to make sure they could safely withstand the unexpected acoustic environment.
"At the end of the day, we had one tile, literally one tile, that did not have a factor of safety greater than 1.4," Moses said. "And we're going to go bond some gap fillers around there so the load gets shared across a couple of tiles and that'll take care of that one tile.
"The systems underneath the structure, like all the plumbing lines and the wiring and all that, we vibe test that but we don't vibrate it to failure like we would on a primary structural member. So the teams are looking at that to see where their limits are, how they're certified and to see what margins they have. And we've cleared all but a few subsystems. They just need a little more time to go through the math on the subsystems. But those should clear within the next week or two."
One area of concern concerns bolts that hold maneuvering jet extensions, called "stingers," on the back of the shuttle's orbital maneuvering system rocket pods.
"The stinger is the little part that sticks out of the back where all the RCS (reaction control system) thrusters are housed," Moses said. "It's held onto the OMS pod with four separate attach bolts. One of them carries a load in three separate axes at launch. That one shows some negative margins and we have some homework to do."
But the safety factor built into the shuttle design assumed a worst-case acoustic environment for every launch and engineers now know the environment is highly variable.
"The acoustic environment back there is a very dynamic thing and it's very hard to know that you're getting that same environment every single time," Moses said. "In fact, you don't get that environment every single time. How you take that and then apply that to a lifetime projection on your parts is where we're doing our math to make sure we're not being too conservative, we're not being too aggressive with our calculations."
Boroscope inspections of the bolt in question show no cracks, at least to the limits of the instrument's resolution. Engineers also are tearing down qualification hardware built in the early days of the shuttle program that was subjected to vibrations simulating 100 missions to look for any signs of undue stress.
"So that's the big work in front of us," Moses said.
Other topics covered during Thursday's executive-level flight readiness review included the threat of impacts from debris eroding off thermal blanket around the nozzles of the shuttle's solid-fuel boosters - engineers do not believe it poses a significant threat - and an on-going assessment of the foam insulation used on the shuttle's external tank.
An unusual amount of foam loss from the central intertank region of the shuttle's external tank earlier this year prompted additional testing, but Moses said Atlantis' tank appears to be in good shape. Likewise, non-destructive examination shows the foam used to cover so-called ice-frost ramps that hold external pressurization lines in place is solid, without the voids that can lead to foam shedding.
"So a real good story from the ET team," Moses said.
Atlantis will be flying with an additional camera in the cockpit that will be looking up during ascent, toward the ice-frost ramps on the liquid oxygen section of the tank, to give engineers a bird's eye view of how the foam behaves during the shuttle's climb out of the dense lower atmosphere.
"We'll be able to see four or five of the ice-frost ramps out of window No. 4 and that'll be very interesting data for us, it'll help us understand when the ice-frost ramps degrade and how they come apart," said Gerstenmaier. "Very likely, we should expect to see some foam shedding, some popcorn coming off of those regions. So if you see it in the video during ascent, I wouldn't be surprised by that."
As for the shuttle's toilet, Moses said the issue involves a bracket used to help anchor it to the crew module structure. The module is design to withstand crash loads of up to 20 times the force of gravity, or 20 Gs, but engineers discovered cracks from high-cycle fatigue in toilet brackets from two other shuttles.
Playing it safe, engineers replaced the bracket in Atlantis. But in the analysis, it was determined that the bracket was "under designed and cannot handle a crash load," Moses said. "We want anything in the crew compartment to be able to withstand a 20-G crash load."
For Atlantis' flight, engineers were able to show that a new bracket was unlikely to fail in a single flight even if a crack developed.
"I think we're going to do some ultimate, actual load testing and show we're probably somewhere above 10Gs, probably not quite at 20 Gs," Moses said. "So we're going to take a waiver to say we're not going to quite make our 20 Gs but for the normal design case and for a pretty severe crash landing, we'll be fine with this bracket."
For future flights, NASA plans to use a redesigned bracket.
"The simplest redesign is just to make it out of titanium instead of aluminum," Moses said. "When you look at it, it's actually a pretty thin, flimsy little part and it has to withhold something like 12,000 pounds of force in a 20-G crash load."
The Atlantis astronauts - commander Charles Hobaugh, pilot Barry Wilmore, Leland Melvin and spacewalkers Robert Satcher, Michael Foreman and Randolph Bresnik - plan to strap in aboard the shuttle Nov. 3 for a dress-rehearsal countdown that will set the stage for launch.