STS-121 at the Pad: NASA's Discovery Shuttle Reaches Launch Site
Amid the glow of lights from the fixed and rotating service structures, Space Shuttle Discovery rests on the hardstand of Launch Pad 39B at NASA's Kennedy Space Center after completing the 4.2-mile journey from the Vehicle Assembly Building.
Credit: NASA/Ken Thornsley.

This story was updated at 9:30 p.m. EDT.

CAPE CANAVERAL, Fla. – The space shuttle Discovery is back at the launch pad as workers prepare the spaceplane for NASA’s second orbiter mission since the 2003 Columbia accident.

A massive crawler carrier hauled Discovery and its mobile launch platform up to Pad 39B at the Kennedy Space Center (KSC) here more than seven hours after leaving the shelter of NASA’s Vehicle Assembly Building (VAB) at about 12:45 p.m. EDT (1645 GMT).

“It’s a fabulous feeling to see that we’re rolling Discovery back to the launch pad for our next launch attempt,” NASA’s shuttle program manager Wayne Hale told reporters after riding with the orbiter as it left the VAB. “I think we’re on a really good path to make that July 1 window opening day.”

The orbiter's move marked a major milestone for NASA's STS-121 mission – the agency's second shuttle test flight since the 2003 Columbia accident. Discovery is currently slated to launch its astronaut crew, commanded by shuttle veteran Steven Lindsey, on a mission to test shuttle fuel tank modifications, orbiter repair techniques and resupply the International Space Station (ISS) between July 1 and July 19.

Hale said that preliminary results of wind tunnel tests to check changes to Discovery’s external fuel tank – primarily the removal of a foam ramp that guarded pressure lines – are positive, but won’t be final for about three weeks. While wind tunnel tests have concluded, a detailed analysis of their data is still underway, he added.

“We have to wait until we get to the bottom line,” Hale said. “We could be smarter tomorrow and somebody could find out something we need to deal with.”

Today’s rollout allowed Discovery to join its payload – a cargo pod dubbed Leonardo, spare space station parts and other items – at Pad 39B. The Leonardo module and equipment palettes will be loaded into Discovery’s cargo bay after engineers shroud the spacecraft with its protective Rotating Service Structure, an activity currently slated to occur Sunday, NASA officials said.

Meanwhile, Hale said he is confident that Discovery’s planned July launch will be the first of three shuttle flights this year. Additional launch opportunities arise on Aug. 28 and Dec. 14, he added.

“Now it will be tight…it depends a lot on the tank,” Hale said of the third shuttle flight’s external tank – External Tank 123 – which engineers are working to complete early to support a possible rescue flight should anything go awry during the planned August space shot.  “Given that, we have a good shot at making three shuttle flights this year.”

Preparing Discovery

Engineers at KSC spent the last week mating Discovery to the external tank and solid rocket boosters – known as the launch stack – that will push the 100-ton spaceplane into orbit. During that time, shuttle workers also took detailed photographs of the orbiter's heat shield to be compared to images from in-orbit inspections during the STS-121 mission, integration engineers told SPACE.com, adding that they took similar photos while preparing Discovery for NASA's first post-Columbia mission STS-114.

"Everyone was excited for STS-114 and they're doubly so for STS-121 because it's our opportunity to get into regular launch mode again," said Tim Riley, the shuttle's integrated operations chief for NASA contractor United Space Alliance, in a recent interview. "Hopefully, we'll get a couple more [shuttle flights] in this year.

Discovery's STS-121 mission is the last of two post-Columbia accident test flights to shakedown new shuttle safety and repair methods before NASA can resume construction of the ISS later this year. While NASA is currently targeting July 1 to launch Discovery's STS-121 mission, the orbiter has a flight window that extends through July 19. Additional shuttle launch opportunities open in late August and mid-December.

NASA's 5.5 million-pound (2.5 million-kilogram) crawler vehicles have transported NASA spacecraft to and from their launch pads since they first became operations in 1966. The entire assembly – including Discovery, its fuel tank and boosters, mobile launch platform and crawler vehicle – weight about 17.5 million pounds (7.9 million kilograms) and move at a top speed of about one mile per hour (1.6 kilometers per hour).

 “It was great,” said Hale, who rode the immense crawler as hefted Discovery toward the launch pad. “It’s better than going on a cruise ship.”