After almost five years rooted on Earth, NASA's shuttle Endeavour is again being primed for launch after a major overhaul to upgrade and refit the 100-ton space plane.

The shuttle and its STS-118 astronaut crew are slated to launch Aug. 7 on a construction mission to the International Space Station (ISS).

The upcoming spaceflight will mark Endeavour's first flight since late 2002 following several years' worth of maintenance and modifications.

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"It's like a new space shuttle," Wayne Hale, NASA's shuttle program manager, said of Endeavour, adding that the orbiter has been inspected from stem to stern. "It's like driving a new car off the showroom floor."

During Endeavour's downtime, engineers inspected some 150 miles (241 kilometers) of wiring, enhanced its avionics interface and added new power-transfer and engine-monitoring systems, among other upgrades.

About the only current hitch with the orbiter is an apparent cabin leak somewhere inside Endeavour's crew module, its attached payload bay-mounted SPACEHAB cargo module or their connecting tunnels and hatches.

As of Thursday, engineers were still working to fix the leak, thought to be somewhere in the vicinity of the toilets.

Endeavour, also known as Orbiter Vehicle-105 (OV-105), is NASA's youngest space shuttle and was commissioned in 1987 as a replacement for its sister ship Challenger following the loss of that older orbiter, its six-astronaut crew and Teacher in Space Christa McAuliffe in January 1986.

The shuttle rolled out of its then-Rockwell International (now Boeing) hangar in Palmdale, Calif., in 1991 to join NASA's orbiter fleet.

Endeavour is now poised to make its 20th launch into space on NASA's STS-118 mission to deliver cargo, spare parts and a new piece of starboard-side framework to the ISS.

Commanded by veteran astronaut Scott Kelly, the mission also features the first flight of teacher-turned-spaceflyer Barbara Morgan, who served as McAuliffe's backup in 1986.

Endeavour's new tech

Standing out among Endeavour's nearly 200 modifications is a trio of systems making their first operational appearance on a NASA shuttle flight.

The shuttle is NASA's first to carry a Station-Shuttle Power Transfer System (SSPTS), which is designed to allow Endeavour to siphon electrical power from the station's 120-volt grid via a docking port connection.

The system then converts that power to feed the orbiter's 28-volt system.

If successful, the new power transfer system will allow the STS-118 astronauts to conserve Endeavour's own fuel cell supplies.

"[A]ssuming that it works, we'll be able to fly a 14-day mission so we can add three extra days to our flight," Kelly said in a NASA interview.

Endeavour also sports the first fully activated Advanced Health Management System to watch over the shuttle's three main engines during launch, as well as a three-string global positioning system (GPS) for pinpoint navigation during landings, NASA said.

The health management system is designed to monitor vibrations in each of the high-pressure fuel and oxidizer turbopumps — which rotate 34,000 times and 23,000 times per minute, respectively — that feed Endeavour's three main engines with the 526,000 gallons (1,991,126 liters) of propellant required for the 8.5-minute launch into space.

If an engine's turbopumps vibrate too much, the new system is designed to shut it down.

"An engine would be shut down before it could progress to any catastrophic situation," Hale said of the monitoring system.

The three-string GPS system, which was tested in part on a shuttle flight last year, replaces Endeavour's 1950s-era TACAN system that is gradually being phased out worldwide, he added.

"We've got a far superior system, far safer, far more accurate to fly our big glider back home with," Hale said.

Other major upgrades

In addition to testing new shuttle technology, Endeavour is now also equipped with hardware already installed aboard its sister ships Discovery and Atlantis.

Perhaps the biggest bit of shuttle catch-up for Endeavour is the addition of its "glass cockpit," a series of flat screen, full-color multi-functional electronic displays that present flight data to the orbiter's astronaut crew.

"Endeavour was the last orbiter to get that modification," Tassos Abadiotakis, NASA's vehicle flow manager for Endeavour, told SPACE.com.

Atlantis first flew with the upgrade during its STS-101 mission in 2000, followed by Discovery in 2005 during NASA's STS-114 flight.

Like Discovery and Atlantis, Endeavour is also now equipped to carry a 50-foot (15-meter) sensor boom, a vital extension of the orbiter's robotic arm which allows astronauts to scan the orbiter's heat shield in flight to seek out signs of damage, Abadiotakis said.

The sensor boom was added as a safety measure following the 2003 loss of seven astronauts aboard Columbia during its landing approach after the orbiter's heat shield had been damaged by fuel tank debris.

The orbiter's wing leading-edge sensors, also a post-Columbia safety measure designed to record any impacts from debris or micrometeorites, sport a new voltage booster to extend their in-flight operations, NASA said.

A team of up to 200 shuttle workers helped upgrade Endeavour, as well as perform vital wiring and structural inspections to once more prepare the spacecraft for flight.

"I would say that it's better than when it first rolled out of the barn in Palmdale," Abadiotakis said of Endeavour. "We basically reset the vehicle, the clock, back to zero."

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