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Mission: Safety

Crew to inspect, test upgrades along with delivering ISS supplies

By Michael Coren
CNN

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Wing sensors on the shuttle will now monitor for debris impact during launch and in orbit.

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(CNN) -- Discovery's mission can be described in one word: safety.

Its top priority after launch will be ensuring the safety of its crew and testing ways to bring a damaged space shuttle back to Earth.

That's the goal of NASA's Return to Flight program, initiated after the loss of Columbia and its seven-member crew on re-entry in 2003.

"We've looked end-to-end at the shuttle to make improvements and make it safer than it has ever been," said Wayne Hale, deputy manager for the space shuttle program.

That capability is crucial as NASA's remaining fleet of three orbiters -- Atlantis, Discovery and Endeavour -- complete the half-finished international space station before they are decommissioned in 2010. A new "crew exploration vehicle" to replace the shuttle is being developed under President Bush's new exploration initiative known as Vision for Space Exploration.

Discovery will debut a number of redesigns, including the foam-clad fuel tank that damaged Columbia. It will also deliver much-needed supplies to the international space station, or ISS. Two and half years have passed since the space shuttle, with its school bus-sized payload bay, visited the station. Discovery will deliver a replacement gyroscope, an external storage platform and an Italian cargo carrier called Raffaello. The storage platform is needed for upcoming flights when it will be used to assembly the rest of the station.

For most of its scheduled 13-day mission, the crew will devote its time to inspecting and testing repairs for the shuttle's delicate silicon tiles and reinforced carbon-carbon panels (RCC) around the nose and wings. Damage to the RCC panels on the left wing led to Columbia's destruction.

The space agency has spent two years developing what it calls "the most comprehensive understanding of the overall Space Shuttle in the history of the Program," according to a March 18 Return to Flight update.

Since its last launch in 2001, Discovery has undergone 286 modifications, including 41 recommended by the Columbia Accident Investigation Board, or CAIB, the independent panel that examined the disaster.

"We have done the things required to make sure this vehicle is the safest vehicle ever," said space shuttle program manager Bill Parsons at a press briefing in Houston, Texas. "The time ... to make this vehicle any safer goes into years, not months, so I think we're on the right timeline."

NASA planned to launch Discovery in May but concerns about ice falling off the shuttle's external tank during liftoff postponed the launch to July. On July 13, the launch was scrubbed after a faulty fuel tank sensor was found.

Discovery, the fleet's oldest vehicle with 30 flights since 1984, is scheduled to rendezvous with the ISS on the third day of the mission. (Flight calendar)

The first four days are devoted to docking with the space station, transferring tons of fresh water and food and installing new additions to the station.

Inspecting the shuttle's skin

The seven-member crew will also perform the first in-orbit inspection of the shuttle's protective thermal skin.

"We not only eliminated to the best of our ability sources of debris, but we want to make sure we have a thorough inspection of the heat shield before re-entry," Hale said.

A newly built appendage to the robotic arm, the Orbiter Boom and Sensor System, will scan the shuttle exterior with lasers and high-resolution cameras to illuminate faults in the skin. The 50-foot-long boom will take about seven hours to examine all of Discovery, scanning about 2 1/2 inches per second.

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Along with testing safety measures, the crew will also deliver supplies to the international space station.

The crew also has scheduled three spacewalks, the first and most important to inspect the RCC segments that cover the shuttle's wing and nose and download impact data from sensors in the wings. Newly developed fabric blankets, chemical washes and mechanical braces to repair damage to the thermal protection system also will be tested. The other two spacewalks will install the gyroscope and storage platform on the ISS.

"We've done more than we've ever done to minimize the risk going uphill," said Paul Hill, flight director for the Discovery shuttle mission. "There are still some uncertainties (about repairing the shuttle), but we are still a lot farther down the road than we were two years ago. And that is 20 years after we declared (the repairs) to be technically impossible."

One technique employs a silicon-based resin to fill cavities or missing tiles on the shuttle's underbelly. The other uses a "chemical wash," layering cured glass over silicon, to insulate the vehicle from re-entry temperatures that can exceed 3,000 degrees F as the shuttle cuts through the atmosphere at 25 times the speed of sound. The third technique tested will drill holes in the tiles to anchor insulating blankets to the shuttle.

The new techniques can fix cracks up to four inches long or holes up to six inches in diameter. The hole in Columbia's left wing in 2003 was believed to have been 6 to 10 inches long.

As a result, NASA says prevention is the shuttle's first line of defense.

Engineers have focused their efforts on redesigning the orange External Fuel Tank, which carries tons of frigid liquid hydrogen and oxygen and detaches during ascent, to reduce the "debris environment." The tank has lost foam that damaged tiles during other launches, but was not thought to pose a serious threat until the loss of Columbia.

Engineers have dissected the 15-story tank's foam insulation "millimeter by millimeter" and identified weak areas that could shake loose during flight. They also replaced the foam ramp that struck Columbia.

"Thousands of man hours [were spent] in developing new techniques so that foam in part and other components of the flight vehicle do not come loose during supersonic flight in the atmosphere as the orbiter climbs to orbit," Hale said.

NASA engineers say they don't expect foam larger than .03 ounces (.002 pounds) to come off the tank, although debris weighing up to .3 ounces (.02 pounds) would be considered safe. The briefcase-size chunk that hit Columbia may have weighed as much as 2 pounds.

Watched closely

It's safe to say that Discovery's will be the best-observed launch ever.

A major element of the mission will be ground controllers' ability to view the shuttle and track damage. At least 107 cameras will be trained on Discovery, along with a battery of high-resolution radar arrays and reconnaissance aircraft helping spot damage to the shuttle's thermal protection system.

Each wing also has 88 sensors embedded behind its reinforced carbon-carbon panels. Data from those instruments will download to mission control to identify potential impacts.

A digital camera on Discovery's underbelly will replace the standard 35 mm model to snap images of the external fuel tank and send instant images to Earth after reaching orbit. The astronauts will snap photos once they are in space. As it approaches the space station, Discovery will perform a pirouette to allow station astronauts to inspect its underbelly.

As a last resort, a second shuttle will stand by in case a rescue mission is needed. Astronauts could evacuate to the safety of the international space station if the shuttle is damaged. This "safe haven" option is far down the list of options to rescue a crew. (Emergency scenarios)

"It's something you don't want to do, but in a survival sense, it's executable," said Bill Gerstemaier, program manager for the international space station.

The space station is designed for three to six crew members, but NASA estimates that a shuttle crew could live on the station for up to 45 days before exhausting food, water and life-support. That may give enough time for NASA to prepare a second shuttle, Atlantis in this case, for launch.

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