NASA's search for a simple answer to the problem that has grounded space shuttle Discovery "did not provide any resolution," deputy program manager Wayne Hale said at a news conference Friday afternoon.

He said that rather than give a possible launch date, he could only say that the launch team was operating on a day-by-day basis.

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But since the simple solutions won't work, engineering teams are "going into a more exensive set of tests."

Once the problem is fixed, it would be four days before the orbiter could lift off.

The mission management team isn't giving up on the launch window that stays open until July 31, Hale said.

"We're not, in any sense of the word, pessimistic," he said.

Earlier Friday, NASA said it would launch the space shuttle Discovery no earlier than the end of next week.

If the flight does not go up in July, the next opportunity for a daylight launch, with the space station in close alignment, would be in September. Hale said that a team is checking into the implications of extending the opening into August.

NASA backed out of the posture for a 48-hour countdown Friday and secured the shuttle for rest on the pad. Hale said that allowed a large number of people to be sent home for the weekend.

There are 12 teams around the country working to diagnose the problem.

Hale said that despite problems, administrators have decided to have shuttle Atlantis mated with its booster rockets and external tank as it prepares for a later mission.

Faulty Sensor

A sensor in the craft's external fuel tank to send back faulty readings just over two hours before a planned return to flight Wednesday.

The sensor gave an improper indication, after the astronauts had already suited up and climbed aboard.

It continued to malfunction after the tank was drained, reading "wet" for three hours more, NASA said Thursday. After various test commands, the device worked properly for a time.

Hale said Wednesday if there's a quick, easy and safe fix, it would be possible to launch Discovery on Saturday. That has now been ruled out.

Mission Plan

The planned mission is to take a crew of seven to the international space station, where it will install a new gyroscope, among other tasks. They will also test methods for inspecting and repairing damage in flight.

There are three spacewalks planned during the mission.

Discovery is outfitted with a redesigned fuel tank and has dozens of motion and temperature sensors embedded in the wings to detect any blows from fuel-tank foam or other debris.