Even if no obvious signs of foam shedding or damage show up in the initial imagery or wing leading edge data, CAIB recommendation 3.4-3 calls for NASA to "provide a capability to obtain and downlink high-resolution images of the underside of the orbiter wing leading edge and forward section of both wings' thermal protection system." The Discovery astronauts are going to spend their second day in space carefully inspecting the leading edges of both wings, along with the RCC 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.

Thomas will unlimber the shuttle's 50-foot-long robot arm and lock it onto the OBSS. Thomas, Kelly and Camarda then will spend the entire day maneuvering the boom back and forth along the leading edges of both wings, using an OBSS television camera and a laser sensor to inspect every square inch of the RCC panels. The astronauts also will use the boom to inspect the nose cap.

Maximum speed of the boom survey: 2 inches per second.

"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."

A year ago, Hill said, engineers thought entry critical damage "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.

"What we found out in more recent arc jet tests, in the last couple or three months - this is the thing that's key - if (RCC coating is intact), our conventional wisdom is good, we don't care, internal delamination's not an issue.

"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. 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.

"With our increased knowledge of the transport model, there's only very few parts of the leading edge where we're really at risk of taking an impact that can do that," Hill said.

Flight Day 2 highlights:

   DAY..EDT........DD...HH...MM...EVENT
   
   07/14/05
   Thu  05:51 AM...00...14...00...STS crew wakeup
   Thu  08:06 AM...00...16...15...SRMS powerup
   Thu  08:08 AM...00...16...17...NC-2 rendezvous rocket firing
   									(165.7/155.3 nm)
   Thu  08:21 AM...00...16...30...Centerline camera installation
   Thu  08:21 AM...00...16...30...SRMS checkout
   Thu  08:51 AM...00...17...00...Ergometer setup
   Thu  09:06 AM...00...17...15...Orbiter boom survey system (OBSS) unberth
   Thu  09:21 AM...00...17...30...PGSC setup (2)
   Thu  09:21 AM...00...17...30...KU-band antenna deploy
   Thu  10:31 AM...00...18...40...Rendezvous tools checkout (part 1)
   Thu  10:36 AM...00...18...45...OBSS thermal protection system (TPS)
   									survey
   Thu  10:51 AM...00...19...00...Contingency water container (CWC) setup
   Thu  11:01 AM...00...19...10...SAFER jet backpack checkout
   Thu  11:31 AM...00...19...40...Lawrence exercises
   Thu  11:31 AM...00...19...40...Spacewalk power tool checkout
   Thu  12:01 PM...00...20...10...Crew meals begin
   Thu  01:01 PM...00...21...10...Airlock prep
   Thu  01:51 PM...00...22...00...EMU (spacesuit) checkout prep
   Thu  02:06 PM...00...22...15...Docking ring extension
   Thu  02:36 PM...00...22...45...OBSS survey resumes
   Thu  03:36 PM...00...23...45...EMU (spacesuit) checkout (MS1&2)
   Thu  04:01 PM...01...00...10...OBSS berthing
   Thu  04:46 PM...01...00...55...SRMS survey
   Thu  05:21 PM...01...01...30...NPC rendezvous rocket firing
   									(165.8/155.1 nm)
   Thu  06:16 PM...01...02...25...NC-3 rendezvous rocket firing
   									(165.8/155.1 nm)
   Thu  08:51 PM...01...05...00...STS crew sleep begins

PREVIEW REPORT PART 6 --->