(CNN) -- More than two years after losing the space shuttle Columbia and its seven crew, NASA said Friday it has set May 15 as its target date for once again launching shuttles into space.
NASA said Discovery's launch is to be followed by a July 12 Atlantis launch.
Discovery's crew of seven is to be led by Commander Eileen Collins.
The shuttle fleet has been grounded since Columbia broke apart over Texas while on landing approach to Florida's Kennedy Space Center on February 1, 2003.
In August 2003, the Columbia Accident Investigation Board officially concluded that insulating foam flew off the shuttle's external fuel tank during liftoff, striking and cracking a panel on the orbiter's wing.
When the shuttle re-entered the atmosphere, searing hot gases seeped into the wing and incinerated the spacecraft.
The CAIB made 15 recommendations to NASA on ways to improve the shuttle program.
In addition, NASA imposed its own restrictions, including limiting launches to daylight hours -- at least for the first two test flights -- so that any falling debris from the external tank could be seen and investigated before the shuttle tried to re-enter Earth's atmosphere. NASA will also require the first two shuttles to go to the international space station so that if there were irreparable damage, the astronauts could wait there for another shuttle to get them.
Because of these restrictions there are only a limited number of opportunities to launch the space shuttle. The first starts May 15 and runs through June 3, when NASA hopes to launch Discovery. The second window opens July 12, when NASA hopes to launch Atlantis.
Discovery and Atlantis will be so-called rescue shuttles for each other should something go wrong. NASA has been readying both shuttles side by side.
The daylight launch restriction may be lifted if both Discovery and Atlantis go up without any critical debris falling off the external tank during liftoff. NASA has been testing a new radar which it claims day or night has a better eye than optical cameras for debris shedding from the external tank.
"I'd be very surprised if we had any damage as a result of debris shedding. ... We will be flying much more safely than we've ever flown before," Bill Readdy, NASA associate administrator, told reporters Friday.
According to Readdy, engineers at the Kennedy Space Center have been working hard to upgrade the space shuttles, including hardening the vehicle and preparing them for returning to space, "The vehicles look like they are brand new cars," he said.
NASA has been developing repair techniques for the space shuttle's thermal protection system for the past two years. Not all of the techniques have panned out and the Discovery crew will be testing only three potential fixes for tile instead of the five originally planned. There will be no tests on repair techniques for the reinforced carbon used on the shuttle's wings, where the hole was created in Columbia.
Also, NASA has stated there will be no repair technique for a hole the size of the one that caused Columbia's demise. Instead, the agency has focused on stopping foam from shedding from the external tank so no hole will be created in the first place.
Readdy admitted he hoped the techniques would be further along, but said that two years ago repairing the shuttle's thermal protection system while in flight was thought impossible.
Both the Discovery and Atlantis missions will be test flights to the international space station to demonstrate the shuttle is once again safe to fly.
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