The space shuttle Discovery is set to launch April 5 on one of NASA’s few remaining shuttle flights to the International Space Station, mission managers announced Friday after settling concerns over potential valve leaks.

Discovery is slated to blast off from a seaside launch pad at the Kennedy Space Center in Florida at 6:21 a.m. EDT (1021 GMT) on Easter Monday. It is one of NASA’s final four shuttle missions before the fleet is retired later this year.

“We are ready to fly,” said NASA’s space operations chief Bill Gerstenmaier in a briefing late Friday.

Discovery will launch seven astronauts on a 13-day mission to deliver a cargo module packed with supplies, new science experiments and other vital gear to the International Space Station. The shuttle is also hauling large spare parts for the station, pieces so big that they will take three spacewalks to install.

Shuttle valves pass test

Earlier this month, engineers found what appeared to be a leak or stuck valve in the helium lines that pressurize the aft-mounted thrusters on Discovery’s right rear engine pod. Since then, they performed more tests of other hardware associated with the system, and found it in good working order.

Mission managers discussed the tests and decided the system was working fine enough to press ahead with Discovery’s mission, even though they still aren’t sure what caused the initial glitch.

“After looking at all the testing on it, we’re very confident that the system will work as designed,” NASA’s shuttle program manager John Shannon told reporters.

Some shuttle experts did express concern that more tests might be needed, but eventually agreed that Discovery was safe to fly. The decision to press forward toward launch was unanimous, Shannon said.

The risk of damage from loose ceramic inserts wedged between the protective heat shield tiles around Discovery’s flight deck windows was also found to be low, NASA officials added. Engineers tested the ceramic inserts after one shook slightly loose during the space agency’s last shuttle flight in February.

Discovery’s STS-131 mission is the second of five final shuttle missions planned for this year before the aging three-orbiter fleet is retired in the fall. One mission, aboard the shuttle Endeavour, successfully flew to the station in February to add a new room and a seven-window observation deck that gives astronauts stunning views of Earth from space.

All four of the remaining missions are also aimed at completing construction of the $100 billion International Space Station. The station, a cooperative effort by 16 different countries, is 98 percent complete, with several new modules and other parts to be added this year.

Discovery is also slated to fly the final shuttle mission, which is due to launch Sept. 16 on NASA’s current schedule.

Few flights remain

Space shuttle managers have repeatedly said that they are confident they will be able to complete the remaining four shuttle flights in 2010 as planned. However, a report issued Thursday by NASA’s Inspector General office found that given the history of shuttle flight challenges and delays, a shuttle retirement date in January or February of 2011 is more likely.

But Shannon stressed that barring any unforeseen and lengthy delays, the shuttle fleet is on track to retire on Sept. 31 as planned.

“We take each flight one at a time,” Shannon said, adding that it is the fuel tanks and other hardware for each mission which drives the schedule. “The tanks are showing up on time to support a last launch in September.”

NASA is retiring its orbiter fleet without a clear-cut successor. In February, U.S. President Barack Obama ordered the agency to cancel its Constellation program developing the new Orion spacecraft and Ares rockets slated to replace the shuttle fleet.

Instead, the president proposed setting aside $6 billion over the next five years to spur new commercially built spaceships to fly Americans into orbit. The goal is to free up NASA to tackle more ambitious missions beyond low-Earth orbit, such as manned flights to the moon, asteroids or Mars.

President Obama is expected to discuss his new space plan in more detail during a space summit in Florida scheduled for April 15. That meeting, if all goes according to plan, would occur a few days before the planned landing of Discovery at the Kennedy Space Center.

Gerstenmaier said that President Obama’s presence in Florida should not disrupt the focus of shuttle personnel during Discovery’s flight.

“The teams are pretty focused … folks really know what they need to go do,” Gerstenmaier said. “I don’t see any impact there at all.”

Discovery’s seven-astronaut crew will travel from Houston to the shuttle’s Florida launch site next week to begin preparing the upcoming mission.

• Images – Shuttle Discovery’s Midnight Launch
• Final Countdown: A Guide to NASA’s Last Space Shuttle Missions
• Video Show – Riding the Space Shuttle

By Tariq Malik
SPACE.com Managing Editor

Tags: discovery, linkedin, nasa, shuttle, space, space shuttle, space station