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Unprecedented coverage of slightly gentler ascent
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: June 29, 2006

When the shuttle Columbia returned to Earth on Feb. 1, 2003, no one knew the ship's left wing had suffered catastrophic impact damage during launch 16 days earlier. Long-range tracking cameras showed a chunk of foam debris from the shuttle's external tank breaking away from the tank's left bipod ramp 81.7 seconds after liftoff, but they did not show where the foam hit.

From the perspective of the only camera with a good view, the foam disappeared under the left wing followed by a shower of debris an instant later. Clearly, the foam hit the wing. But where? Engineers ultimately concluded it probably hit on the underside of the wing and, at most, damaged a few of the heat shield tiles in the area. No one believed the damage was catastrophic. But lacking good camera views, no one really knew.

As it turned out, the 1.67-pound chunk of foam hit the left wing's leading edge at a relative velocity of nearly 550 mph, blasting a 6- to 10-inch hole in the reinforced carbon carbon insulation. During re-entry, super-heated plasma burned its way inside, melting the left wing from the inside out and triggering a catastrophic structural failure. All seven crew members - commander Rick Husband, pilot William "Willie" McCool, flight engineer Kalpana Chawla, physician Laurel Clark, payload commander Mike Anderson, physician David Brown and Israeli flier Ilan Ramon - were killed.

Along with fixing the external tank foam - NASA eliminated the bipod ramp foam that was the actual cause of Columbia's demise - the space agency upgraded its tracking camera network at the Kennedy Space Center and Cape Canaveral Air Force Station to make sure any future damage is seen as soon as possible.

The ability to quickly spot any impact damage, giving engineers time to assess the consequences and possible repair options, is a large part of Griffin's justification for proceeding with flight.

At the launch pad, some 38 16mm cameras are mounted on the launch pad itself with three short-range camera sites around the pad perimeter featuring two 35mm cameras and one high definition TV camera each. Another 11 medium-range camera sites are positioned around the pad between one and six miles away, each one equipped with a 35mm camera and all but one equipped with an HDTV camera. Another 11 long-range camera sites are located between four and 40 miles of the pad. All long-range sites include 35mm cameras, two have 70mm cameras and 10 are equipped with HDTV.

From liftoff through the first 30 seconds of flight, objects an inch wide or larger can be seen. Between 30 seconds and one minute, the resolution drops to objects three inches in diameter or larger and from one minute to 90 seconds, it drops to objects eight inches or larger. Between 90 seconds and booster separation two minutes after liftoff, ground-based tracking cameras can detect objects 15 inches across and pinpoint an impact site to within five feet.

One WB-57 jet will be cruising 60,000 feet up, just north of Discovery's flight pat,h to photograph the shuttle using an infrared sensors and an HDTV camera attached to a powerful 11-inch telescope. The WB-57 will acquire most of its imagery in the minute leading up to solid-fuel booster separation (NASA operates two such jets, but one is grounded for maintenance).

Finally, a radar system is in place featuring one ground-based C-band and two ship-based Doppler X-band instruments to look for debris coming off the external tank.

For Discovery's flight, eight cameras mounted on the shuttle, its tank and twin boosters will provide close-up views of the external tank and the orbiter's belly during ascent.

As with Discovery's last flight a year ago, a camera mounted high up on the external tank looking down on the underside of the space shuttle will beam back live television views throughout the eight-and-a-half-minute climb to orbit.

But for this flight, four new cameras have been added, two near the top of each booster and two mounted near the back end of the powerful rockets. Each booster also carries another camera focused on a region of the tank known for losing small, popcorn-like pieces of foam.

Imagery from the six booster cams will be available after the spent rockets are recovered and towed back to Port Canaveral a few days after launch.

In addition, a digital camera mounted in a cavity where a propellant line enters the belly of the orbiter will photograph the tank as it separates in space.

As if all that wasn't enough, an X-band marine radar seven-tenths of a mile from the pad will be on the lookout for vultures and other large birds. During Discovery's launch last summer, a large vulture struck the external tank a few seconds after liftoff, rammed by the shuttle at some 70 mph. If any large birds are seen prior to Discovery's launch Saturday, the countdown can be halted briefly if necessary.

In short, if any impact damage occurs from any source, shuttle engineers expect to see it. NASA managers hope the radar systems, still somewhat experimental, eventually will provide enough resolution to permit acceptable debris coverage for night launches. But in the meantime, good lighting is required.

In the aftermath of Columbia, NASA managers decided to launch at least two missions in daylight to optimize photo documentation of the tank and the shuttle's heat shield. Complicating the matter, launch also had to be timed to ensure external tank separation in daylight half a world away.

Those lighting constraints and the requirement to launch into the plane of the space station's orbit severely limit when NASA can send up a space shuttle. Because of the problems experienced during Discovery's last flight, NASA is extending the daylight launch requirement to at least the next two missions. Here are the lighted launch windows for the rest of 2006:

July 1-19
Aug. 29 to Sept. 13
Oct. 26-29
Dec. 23-25

If the next two flights go well from a foam shedding standpoint, NASA will relax the daylight launch rule, permitting much more frequent launch opportunities. But for now, the windows are limited.

Once in orbit, the Lindsey and company will take over the inspection work, photographing the external tank as it tumbles away using a digital still camera and a movie camera. Data collected by the wing leading edge impact sensors also will be downlinked to mission control for detailed analysis.

Located on each wing's forward spar behind every reinforced carbon carbon panel, the 132 accelerometers will provide data telling flight controllers whether anything struck the leading edges during launch.

The sensor system generates two types of data: Peak and detailed.

"Think about what a stereo equalizer looks like," flight director Paul Hill said before Discovery's launch last summer. "You've seen these ones that, across the frequency band, as the signal bounces up and down, it leaves a hash mark. The system works kind of like that. It's recording very high rate frequency response data across the wing leading edge from all these accelerometers that are on the wing spar for every RCC panel. And it registers the peaks, the software pulls out where those little peaks are from T-0 all the way to after we've made it into orbit.

"The first thing we downlink is just the file that has all the peaks in it," Hill said. "That then tells us that we have a suspected impact somewhere and after we see that, then within an hour after the guys in the MER (mission evaluation room) see that and pick out the ones they think are potential impacts, then we put commands on board to downlink the detailed data around each one of those peaks."

On flight day two, the astronauts will spend six-and-a-half hours using Discovery's robot arm and a 50-foot extension known as the orbiter boom sensor system, or OBSS, to inspect the wing leading edge panels and the shuttle's reinforced carbon carbon nose cap in excruciating detail.

A laser sensor on the end of the boom is capable of spotting any wing leading edge damage that could pose a threat to the shuttle. The astronauts will start with the starboard, or right-side, wing leading edge, making six passes up and down the wing to cover all the angles. After scanning the nose cap, they will move on to the port wing and repeat the procedure.

A high-resolution camera is mounted on the end of the OBSS to take close-up photographs of any potential damage sites.

"The smallest damage of concern that we have is on the order of .08, eighty thousands of an inch, and that camera is certified to be able to show us that level of damage," said Steve Poulos, manager of the space shuttle projects office at the Johnson Space Center.

"So if we do have a need to go out and do a focused inspection, if we find something, whether it be from the ascent imagery, the radar, wing leading edge instrumentation, our flight day two scan with the laser dynamic range imager, if we find anything of any concern we have the ability to go back with that very high fidelity digital camera and screen out once and for all whether there's a real concern there or not."

But even that is not enough to satisfy the post-Columbia NASA.

During final approach to the space station, at a distance of about 600 feet directly below the lab complex, Lindsey will guide Discovery through a slow end-over-end flip known as a rotational pitch maneuver, or RPM. The maneuver will take about nine minutes to complete - three quarters of a degree per second - allowing station commander Pavel Vinogradov and flight engineer Jeffrey Williams to photograph the shuttle's belly using digital cameras equipped with 400mm and 800mm telephoto lenses.

It was during an identical flip during Discovery's flight last year that controllers spotted two so-called gap fillers protruding above the tile on Discovery's belly, prompting an impromptu spacewalk repair later in the mission. Since then, some 5,000 gap fillers have been removed and replaced.

Additional inspections will be carried out after Discovery docks with the space station to look for signs of damage from orbiting space debris, so-called micrometeoroid damage. These late inspections prevented normal off-duty time for the crew and NASA managers, concerned about over working the astronauts, decided not to baseline the third spacewalk unless the mission is extended a day.

The late inspections cannot be completed while docked to the station because of clearance issues between the OBSS and station structure. As a result, Discovery's crew will complete the work after undocking. Enough propellant will be available to permit a second rendezvous and re-docking if necessary.

"Our current estimate for (micrometeoroid) impact that might cause loss of crew and vehicle is about 1-in-210, something on that order," Poulos said. "When we do the late inspection, we're going to improve that number to at least 1-in-280 and as high as 1-in-350, based on the performance of the camera system itself."

Good imagery, radar and impact sensor data form one leg of Griffin's three-pronged justification for flight. The other two components are the crew's ability to repair minor damage and, in a worst-case scenario, the capability of the space station to support a combined crew of nine until a rescue flight can be mounted.

It would not be easy. The Russian Elektron oxygen generator has a history of malfunctions, there is only one toilet on board and supplies would be tight. Worse, the only way down in a major emergency would be a single three-seat Soyuz capsule.

But NASA and the Russians have pre-positioned additional supplies for just such a contingency, including food, water and lithium hydroxide to scrub carbon dioxide from the air, and even if the Elektron failed the day Discovery took off, the station could support the combined nine-member crew for at least 84 days.

"We're going to have cameras all over the vehicle, inside and outside the vehicle, we'll have ground stations, we'll have radar tracking, we'll have airplanes in the air looking at us and we're going to capture all that data going up," Lindsey said. "Once we get up there on orbit, we're going to separate the tank, we have external tank cameras just like STS-114 did, it's going to image the tank and then of course, we're going to do inspections. So if we have a problem with an ice-frost ramp, we're going to know about it.

"And if for some reason, in the very unlikely event it hits the orbiter and does damage and we need to do something about that damage, we have limited repair capabilities. And as a final last resort, we also have the safe-haven capability where we stay on station and wait for another vehicle to come get us. So we have a number of ways to mitigate this risk, some certified, some are not certified.

"We feel pretty comfortable flying as we are with the existing ice-frost ramp design," Lindsey said. "I supported the decision the program made in keeping them the same."

Until a new ice-frost ramp design is available, NASA engineers have redesigned Discovery's ascent profile to ease stress on the external tank's insulation, changing main engine throttle settings and lofting the shuttle's trajectory.

Just in case.

The so-called low-Q ascent profile is not new. NASA used it as recently as 1999 for a Hubble Space Telescope servicing mission.

But the normally used high-Q profile keeps the shuttle's main engines at a higher throttle setting during a phase of flight when the ship is climbing out of the dense lower atmosphere.

For Discovery's last mission, which flew high-Q, the shuttle's main engines throttled down to 72 percent power starting 38 seconds after launch. They stayed there for about 14 seconds before throttling back up to 104.5 percent. During the throttled-down phase of flight, the shuttle accelerated through the sound barrier and the ship was subjected to a maximum aerodynamic pressure of about 695 pounds per square foot.

For Discovery's upcoming flight, the engines will be throttled down to 67 percent power and remain there for about 24 seconds, or 10 seconds longer than the high-Q profile. At the same time, Discovery's trajectory will be lofted slightly to get it out of the lower atmosphere faster. Booster separation will occur at a slightly lower velocity and altitude.

The net effect is to reduce aerodynamic loads on the liquid oxygen feedline, the ice-frost ramps, the pressurization lines and cable try by about 7 percent at the expense of burning up about 1,180 pounds of additional propellant. The low-Q profile also exposes the crew to slightly greater abort risks.

For example, an engine failure early in flight could force the astronauts to attempt a risky return-to-launch site abort, or RTLS. During a high-Q flight, the RTLS window of vulnerability is about two minutes and 35 seconds long. For a low-Q ascent, RTLS vulnerability is two minutes and 45 seconds.

Likewise, vulnerability to aborts to emergency landing sites in Spain and France will be extended some 17 seconds. All in all, the low-Q profile increases a crew's risk of an abort by about 2 percent.

"What it really means is, as we approach supersonic speeds, when we get the maximum force on the vehicle, we usually throttle the main engines down so we can get through that heavier, thicker part of the atmosphere at a lower speed and accelerate more slowly until really, we're out of the atmosphere and there are no air loads on the vehicle. In the last 10 flights, 12 flights or so, we've been flying what's called a high-Q profile so we don't throttle down as much, we go faster, put more loads on the vehicle.

"Because our flight had some additional ascent performance - we were light enough we could carry say an extra 1,500 pounds to orbit - if we just gave up about a thousand pounds of that excess performance then we could throttle down sooner, stay throttled down longer and then throttle back up later, which would reduce the loads on the tank by somewhere around 7 to 10 percent.

"So imagine what it's like if you roll down the window in your car and you're going, say, 40 mph, and you stick your hand out the window you're going to get a certain force on your hand. If you then accelerate to 60 mph and you stick your hand out the window, you can tell there's a big difference. So doing this lower dynamic pressure, low-Q, it's less force on the tank, it buys a little bit more margin to deal with the uncertainties in the ice-frost ramps.

Pilot Kelly, who will be monitoring Discovery's main engines during the climb to space, said "it's almost transparent for us. The only thing for me that's different, instead of the engines throttling back to the 71 percent range, they throttle back to 67 percent. That's it. It changes abort boundaries, it changes the profile a little bit, it's a little bit more lofted. We've flown a lot more flights at low-Q than we have at high-Q."

PREVIEW REPORT PART 3 --->




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