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NASA on track for July launch of space shuttle Discovery
 The space shuttle Discovery is on course for a July launch, NASA says. YOUR E-MAIL ALERTS(CNN) -- NASA is a step closer to a July launch of space shuttle Discovery on the agency's maiden return-to-flight mission -- the first since Columbia broke up upon re-entry in 2003, shuttle program managers said Friday. The possible launch edged closer after NASA engineers met at the Kennedy Space Center in Florida to discuss the risk to an orbiter posed by ice falling off the shuttle's external tank during liftoff. "At the end of the day, the recommendation from the board was the that we were in an acceptable risk posture," said Shuttle Program Manager Bill Parsons in a post-meeting teleconference with reporters. "They recommended to me ... that we proceed on with the launch. I accepted that recommendation. And that's where we are headed now." Successful resolution of the ice issue is regarded as the last big hurdle the shuttle program needs to clear before NASA Administrator Michael Griffin gives the go-ahead for the return of the space shuttle fleet to service. In late April, Griffin cited concerns about the ice when he postponed Discovery's launch from May to July. No date has been set for the possible launch. NASA has an opportunity from July 13 to July 31 to conduct a daytime launch on a rendezvous trajectory with the space station. If Discovery does not launch during that window, shuttle managers would have to wait until September 9 for acceptable lighting conditions to return. NASA engineers in recent weeks have been conducting tests to refine the risk analysis related to ice that builds up on a shuttle's external tank just before launch, when it is filled with super-cold liquid oxygen and hydrogen fuel. Program managers have expressed concern that sizable pieces of that ice could break off during liftoff and damage a shuttle orbiter. The shuttle fleet has been grounded since February 1, 2003, when Columbia broke apart over Texas while on landing approach to Florida's Kennedy Space Center, killing all seven astronauts on board. Seven months later, the Columbia Accident Investigation Board (CAIB) concluded that foam insulation broke off during liftoff from the shuttle's external fuel tank, striking and cracking a panel on the orbiter's wing. When the shuttle re-entered the Earth's atmosphere, searing hot gases seeped into the wing and incinerated the spacecraft. NASA engineers believe foam and ice debris have fallen off the external tank on every shuttle launch since the first one in 1981. Prior to the Columbia accident, no one at the space agency believed the debris was dense enough to do any serious damage to an orbiter. But since the accident, engineers have conducted an extensive analysis of the risks associated with foam strikes. They turned their attention fully to the risks associated with ice debris in the past few months. Crucial meetingsThe positive outcome of Friday's so-called "Debris Verification Review" sets the table for two crucial meetings next week: -- On Monday, the Stafford-Covey Return to Flight Task Group will hold its final meeting in Washington. The task group is the independent oversight panel chartered by NASA to certify that the agency has completed a 15-point "do list" drawn up by the CAIB. Shortly afterward, the task group intends to issue a final report to Administrator Griffin, who will make the ultimate call as to whether or not the agency is ready to return to flight. -- On Wednesday and Thursday, senior NASA officials and shuttle program managers will meet at the Kennedy Space Center for a "Flight Readiness Review," and any lingering issues related to the Discovery launch will be aired and an official launch date will be set. To date, the Stafford-Covey group has indicated NASA has met 12 of 15 of the CAIB recommendations for return to flight. Friday's apparent resolution of the ice issue should result in the close out of two more. The only other unmet CAIB recommendation has to do with NASA's ability to repair an orbiter's "thermal protection system" (TPS) during orbit. But members of the task group have already indicated they don't see failure to meet that mandate as a show-stopper for return to flight. The underside of a space shuttle is covered with insulating tiles, and the edges of the wings are clad with reinforced carbon-carbon panels. Together, they make up the TPS, which is designed to ensure the shuttle can withstand the intense heat of re-entry. Prior to the Columbia accident, astronauts had no way to inspect for and repair any damage to the TPS that they might find. But since the Columbia accident, NASA engineers have designed an Orbital Boom Sensor System, which is a second robotic arm that is tipped with cameras and other instruments and mounted in the shuttle's payload bay. Once in orbit, shuttle astronauts will use the boom to inspect the panels on an orbiter's wings and nose cone for any damage that might have occurred during launch. But repairing damage to the TPS -- should they find any -- has turned out to be a tough nut to crack. Engineers have been developing and testing plugs and crack-repair procedures for the reinforced carbon-carbon panels, as well as tile-repair techniques, for use in the event of damage. Limited testingTwo such methods will undergo limited testing in orbit by Discovery astronauts, but mission managers acknowledge that their techniques will likely need to be modified before they can be certified. And most NASA engineers agree that astronauts would never be able to repair a hole the size of the one that doomed Columbia. Nevertheless, members of the the Stafford-Covey group have indicated that, in their estimation, NASA has adequately compensated for the lack of an effective TPS repair capability by redesigning the external tank to minimize the size of any foam or ice that might come off and hit the shuttle during liftoff. The Stafford-Covey group also has endorsed NASA's "safe haven" plan, which calls for the International Space Station to be equipped to provide shelter to a shuttle crew in the event an orbiter is irreparably damaged upon liftoff and cannot safely re-enter Earth's atmosphere. In such an emergency scenario, a shuttle crew would live aboard the station for six to eight weeks while another orbiter is prepared to undertake a rescue mission. NASA has committed to daytime launches for the next two shuttle missions in order to ensure ideal lighting conditions for the cameras that will scrutinize the shuttle's ascent into orbit. 
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