Sensor boom to scan shuttle during inspections today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 27, 2005
The Discovery astronauts geared up for a detailed inspection of the shuttle's reinforced carbon carbon nose cap and wing leading edge panels today. The post-Columbia safety survey is designed to spot any entry-critical damage to the areas of the shuttle that experience the most extreme heating during the return to Earth.
Image analysts on the ground, meanwhile, continued assessing the potential significance of at least three debris events spotted during Discovery's launch Tuesday.
The shuttle's external tank suffered a bird hit seconds after liftoff and the apparent loss of a relatively large piece of foam or some other type of debris just after the ship's solid-fuel boosters were jettisoned two minutes and five seconds into flight.
A minute or so earlier, imagery from a new camera mounted on the external tank showed a piece of a black heat shield tile on the edge of a nose landing gear door cracking off and flying away. Mission operations manager John Shannon said Tuesday it would take engineers several days to complete their assessments of the shuttle's condition and that it was premature to speculate about whether any one of the events might, or might not, turn out to be significant.
Lead flight director Paul Hill, speaking well before launch, said he fully expected to see tile damage during Discovery's mission.
"We will likely have coating loss or chips on the bottom of the vehicle that are well within the capability of the (thermal protection system) to bring us to the ground," he said. "It is the nature of having a glass-covered thermal protection system on the bottom of the orbiter. But a we've demonstrated on more than 100 flights, chipped coating on tile, it still performs like a champ. That material will bring us down to the ground, it's very robust. We understand what types of damage change that equation."
With post-Columbia imagery upgrades, Hill said, "we are now going to have all these fabulous pictures of the bottom of the vehicle. We're going to see a lot of white dings, many or all of which I expect we will have in our flight history as cases we have landed with and were absolutely no impact. But we have talked about this a lot, now we're going to be presented with all of this and there is this concern that folks will over react, that we see little things that clearly are within the capability of the vehicle to bring us to the ground but now that we can see it, we may over react.
"There's been a lot of concern about whether or not we'll over react and that would paralyze us for making all of the right decisions during the flight or maybe jumping the gun and repairing a vehicle when we didn't need to repair the vehicle."
But Hill said based on the team's performance during multiple simulations, "we're not going to over react, we are capable of seeing a lot of damage and crossing out the ones that are clearly within our capability and then focusing on the ones that are either right on the edge and we need more data or we're just not happy with it.
"I think we've demonstrated that the community is capable of hearing that story, assessing the data and making good, technical decisions and not making emotion-driven decisions."
Columbia was brought down during re-entry two-and-a-half years ago by a hole in the leading edge of its left wing. The Discovery astronauts plan to spend a large part of their second day in space carefully inspecting the leading edges of both their wings, along with the reinforced carbon carbon nose cap of the shuttle, using a new 50-foot-long boom mounted on the starboard side of the payload bay known as the orbiter boom sensor system, or OBSS.
Engineers on the ground, meanwhile, will assess data from new sensors mounted directly behind the leading edge panels that are capable of registering the force of an impact. The wing leading edge sensor data was downlinked overnight.
Astronaut Andrew Thomas will use the shuttle's 50-foot-long robot arm to pick up the equally long OBSS. Starting around 5:30 a.m., Thomas, assisted by pilot James Kelly and Charles Camarda, will maneuver the boom back and forth, using an OBSS television camera and a laser sensor to inspect the wing leading edges and the nose cap.
"Getting the boom, lifting it up out of the payload bay and positioning it to start the survey is all done essentially manually," Thomas told CBS News in a pre-launch interview. "I'll be doing that. Berthing it will be done manually. But once you've got it in the initial position to start the survey, then we invoke computer control sequences which will drive it automatically. And we kind of need to. This thing is 50 feet long, so a small deflection at the end of the arm would be a huge deflection at the end of the boom and you have the risk of hitting structure. So that parts all automated."
Asked what the survey might show, Thomas said "I don't think we'll see too much."
"You know, we have to do this," he said. "They've done all this work on the tank and you have to confirm that what they've done on the tank is as expected. Any debris that's released from the tank is understood and controlled. And the only way you can do that is by these detailed surveys. This flight and the next flight are the ones that are largely going to do that. So we have to do it.
"You point out a risk, though, that there will be sites that will be false alarms, false positives which will exercise the management structure that's on the ground to look at damage sites, compare them to pre flight and make judgments about their importance or otherwise. That's actually not a bad thing to do, though. Because this is the first time it's being done and we need to exercise those procedures.
"I can see, for example, that we will get a call for some targeted inspections of certain sites. ... And I think that's a good thing to do, too, because it exercises the whole organization chain."
Given the launch day debris events, that seems like a safe bet. Here is an updated timeline of today's events (in mission elapsed time and EDT)
07/27/05 Wed 03:09 AM...00...16...30...Centerline camera installation Wed 03:39 AM...00...17...00...Ergometer setup Wed 03:54 AM...00...17...15...Orbiter boom survey system (OBSS) unberth Wed 04:09 AM...00...17...30...Laptop computer setup completed Wed 04:09 AM...00...17...30...KU-band antenna deploy Wed 04;39 AM...00...18...00...OMS pod photo survey Wed 05:19 AM...00...18...40...Rendezvous tools checkout Wed 05:24 AM...00...18...45...OBSS: Starboard wing LDRI survey begins Wed 05:49 AM...00...19...10...SAFER jet backpack checkout Wed 06:19 AM...00...19...40...Lawrence exercises Wed 06:19 AM...00...19...40...Spacewalk power tool checkout Wed 06:49 AM...00...20...10...Crew meals begin Wed 06:49 AM...00...20...10...OBSS: Nosecap survey begins Wed 07:49 AM...00...21...10...Airlock prep Wed 08:29 AM...00...21...50...OBSS: Nosecap survey complete Wed 08:39 AM...00...22...00...EMU (spacesuit) checkout Wed 08:54 AM...00...22...15...Docking ring extension Wed 09:24 AM...00...22...45...OBSS: Port wing LDRI survey begins Wed 10:24 AM...00...23...45...EMU checkout continues Wed 10:49 AM...01...00...10...OBSS: Port wing survey complete Wed 10:49 AM...01...00...10...OBSS berthing Wed 11:44 AM...01...01...05...SRMS survey Wed 12:59 PM...01...02...20...LDRI downlink Wed 01:04 PM...01...02...25...NC-3 rendezvous burn Wed 03:39 PM...01...05...00...STS crew sleep begins Wed 11:39 PM...01...13...00...STS crew wakeup Wed 11:39 PM...01...13...00...ISS crew wakeup
A year ago, Hill said in an earlier interview with CBS News, engineers thought entry critical damage to the leading edge panels "required a penetration of the RCC, not just coating damage or even small damage to the substrate on the outside."
"More recent arc jet testing has us worried that coating damage alone, if it's large enough and if we had internal damage - delamination - between the layers, that the combination of those two could be entry critical."
In the early years of the shuttle program, Hill said, tests indicated the leading edge RCC panels could tolerate penetrations a quarter of an inch across. But that testing was with a clean hole punched in the panel, which is what one would expect with a hypervelocity impact in space. But during launch, impact velocities would be much lower and any resulting penetrations would be more ragged.
Engineers then began wondering if lower-velocity impacts might be entry critical. Subjecting RCC panels to re-entry heating in an arc jet furnace, engineers discovered that as long as a protective coating remained intact, internal delamination would not cause any major problems.
"But if the coating is gone and underneath that coating you're delaminated, then picture the RCC itself from a side view like a cross section. Now you've got this bubble or this void in between layers," Hill explained. "What you've done is, you've significantly reduced the density of this RCC that's exposed to the heat load. So it burns faster.
"So now instead of being this more solid material that's hard to light, kind of like if you take a piece of hard wood like oak and you hold a match to that oak, it won't light typically. But if you shave off some splinters of that oak, you can get them to flash. Damned if that's not what we found in a handful of RCC runs for uncoated RCC."
For the tests, engineers deliberately damaged an RCC panel by pushing on it with a metal cylinder. After confirming the panel developed delamination as a result, "they put that bad boy under the arc jet and it burned like there was no tomorrow. The whole area that covered the delamination burned off like a fuse."
If it is credible that the shuttle could take an impact that has enough energy to cause delamination and loss of coating, "then that does not have to be very big to be catastrophic," Hill said. "From an RCC damage perspective, that looks like a penetration. So now the question is, do we believe that testing? Have we done enough of those tests to be sure that is an entry critical damage form? And then, is it credible for us to take an impact that could cause that kind of damage?"
One OBSS laser sensor, known as the laser dynamic range imager, or LDRI, dwill be used to inspect the wing leading edge panels and the shuttle's nose cap. A second sensor, known as the laser camera system, or LCS, may be used later to focus on a suspect area or to collect additional data.
"If you think about the laser, the way we're recording the data is similar to recording video," Hill said. "Imagine standing on the side of a soccer field watching one of your kids play soccer with a camcorder. And you're panning that camera real fast so you can watch him run down the field. But when you play it back at home, you can't make out hide nor hair because everything is blurred. That's the problem we've got. We've got a translation constraint. If we move too fast, we blur the image, which directly affects the resolution and we can't see the small stuff we're looking for."
See the Status Center for full play-by-play coverage.