CAPE CANAVERAL, Fla. -- Shuttle Discovery's astronauts do not need to make an emergency spacewalk to fix a stuck valve at the International Space Station and can leave on time this weekend, Mission Control informed the crew Thursday.

The repairs can wait, engineers concluded following two days of analysis.

But another problem cropped up Thursday morning, this one with a latching mechanism for the cargo carrier that's parked temporarily at the space station. The removal of the compartment was delayed as flight controllers struggled to understand the trouble, apparently related to a sheared screw.

The cargo carrier, filled with trash and old equipment, needs to be placed back aboard Discovery for the trip home. It flew up full of fresh station supplies and science experiments.

Mission Control warned the problem could disrupt the rest of the astronauts' work day, and everything might need to be rearranged.

"We'll be flexible," said shuttle commander Alan Poindexter.

To NASA's relief, engineers on the ground determined that the space station can operate fine for the next few weeks with the jammed nitrogen valve, a critical part of the cooling system. That gives them more time to figure out how to resolve the problem.

If flight controllers cannot get the valve to open by remote control, the space station crew will have to perform a spacewalk to replace the entire nitrogen assembly. Nitrogen is needed to pressurize the tank full of ammonia coolant that was installed by the shuttle crew earlier this week

Mission Control said it's too soon to know when those spacewalking repairs might occur. Space shuttle Atlantis is scheduled to arrive at the space station in mid-May with more spare parts and a small Russian lab. The valve job, if required, could take place before, during or even after that mission, officials said.

The valve failed to open Tuesday after spacewalking astronauts finished hooking up the new ammonia tank.

Discovery is scheduled to undock from the space station Saturday and return to Earth on Monday.

Back at NASA's launch and landing site, meanwhile, hundreds of journalists and dignitaries gathered for an afternoon visit by President Barack Obama.

Obama will pitch his post-shuttle plans for NASA, including development of a capsule for ferrying astronauts to the space station. That spacecraft originally was canceled by the president, but revived recently following an outcry from lawmakers and space enthusiasts. Obama also wants U.S. commercial rocket builders to become involved in space station operations.

Once Discovery lands, only three shuttle flights will be left. NASA hopes to wrap up the last mission — along with space station construction — by the end of September.

Poindexter said from orbit Wednesday that he knew of no plans to beam up the president's speech, real time, to the 13 space fliers.

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On the Net:

NASA: http://www.nasa.gov/mission_pages/shuttle/main/index.html