CAPE CANAVERAL, Fla. -- NASA's top spaceflight managers Tuesday officially approved an April 4 launch of shuttle Atlantis on an 11-day mission to begin the next phase of construction at the International Space Station.
"This flight is every bit as complex and challenging as the Hubble maintenance flight completed a few weeks ago. It starts an ambitious year of station missions, delivering more than 50 tons of components by year's end," said shuttle program manager Ron Dittemore.
Liftoff from the Kennedy Space Center of NASA's 109th shuttle voyage is expected between 2 and 6 p.m. EST (1900 and 2300 GMT). Citing security concerns, space agency officials said they will not announce a more precise time until 24 hours before launch.
Publicly available information from government sources, however, indicate the launch is expected somewhere around the 5:10 to 5:15 p.m. EST (2210 to 2215 GMT) time period.
But if computer software tests planned for next Monday at the frontier outpost don't go well, Atlantis and its seven-member crew could remain grounded for at least a few extra days while officials troubleshoot the problem.
"Those tests are out there and we will eagerly await the results," said NASA spokesman Bruce Buckingham.The software was written to overcome a recently discovered hardware problem with the station's Canadian robot arm, which is critical to the installation of Atlantis' main cargo on the outside of the outpost's Destiny science laboratory.
Known as Canadarm2, the 57.7-foot (17.5-meter) robot arm can operate in either a primary or backup mode. The trouble comes when an operator tries to release a brake on one of the arm's seven joints while using the primary mode. The backup mode is working fine.
Mission managers want both modes to be reliable before allowing Atlantis to lift off.
As a result, Canadian engineers wrote new software to work around the problem and Atlantis' astronauts trained to handle the resulting new procedures for installing the cargo -- a 44-foot-long (13.4-meter-long) truss segment that, when other pieces are added, will stretch to 356 feet (109 meters) and hold the outpost's solar wings and radiators.
The software is scheduled to be delivered to Mission Control in Houston by the end of this week, uplinked to the space station during the weekend and tested by the Expedition Four crewmembers on Monday, officials said.
Mission managers have expressed confidence in their plan and remain hopeful Atlantis' mission will not be delayed because of this problem.
NASA delayed shuttle Endeavour's next mission nearly four weeks to May 31 to include a replacement part for the Canadarm2 on the manifest, as well as add an extra spacewalk to the flight plan so the new joint can be installed.
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