In one of the major reversals -- literally -- in the history of the U. S. space program, Kennedy Space Center launch managers, based on an improved Ernesto storm forecast, reversed an early Aug. 29 decision to roll the space shuttle Atlantis back to the Vehicle Assembly building and headed the vehicle back to Pad 39B after it was already halfway to the VAB.

The change preserves an option to launch the STS-115 mission to re-initiate station assembly by the end of the shuttle launch window with a liftoff about Sept. 6-7, or possibly Sept. 8. It will still be a challenge to make those dates, however, given some disruption at Kennedy is expected from the storm, and technicians will not be able to work on the vehicle in earnest until Aug. 31.

Normally re-hooking the vehicle, replenishing fuel cell oxygen/hydrogen cryogenics, and doing basic checkout can take up to eight days, but Kennedy will be able to streamline that process. Then there are the normal potential pitfalls with weather and hardware that can befall any launch attempt. So while the decision will give NASA a shot at launching by end of the formal window Sept. 7, it will be a limited shot.

The decision by Kennedy managers is based on new weather forecasts that show tropical storm Ernesto is weakening and will pass somewhat further from Kennedy, creating sustained winds no greater than 45 kt. with gusts to 65 kt. at the launch site.

The pad is considered safe for shuttles as long as gusts do not approach 70 kt. Forecasters earlier Aug. 29 were calling for gusts to 65 kt., but managers did not want to leave the vehicle at the pad with only a 5 kt. forecast margin. The shuttle can only be moved when the winds are under 40 kts. So rollback was begun with the hope the forecast would change before Atlantis was buttoned up back inside the VAB -- it did.

The 2 million-lb. crawler transporter had begun to move the 12 million-lb. combined load of the Atlantis vehicle and its Mobile Launcher Platform at about 10 a.m. EDT. The decision to reverse course was made at about 2:45 p.m. when the crawler was only about a mile from the VAB and about 2.5 miles from the pad. It was to be back at the pad by 8 p.m. EDT surrounded by its rotating service structure.