NASA managers today cleared the shuttle Discovery's external fuel tank for flight based on wind tunnel data and computer modeling that show the huge tank can stand up to the aerodynamic rigors of launch despite the recent removal of long foam wind deflectors. Launch currently is targeted for July 1, at 3:48 p.m., but the long-awaited flight could slip another day or so to ensure better lighting for critical photography of the tank after Discovery reaches orbit. NASA managers are expected to discuss the lighting issue during a weekly review Thursday.

Discovery's launch window is defined, in part, by a requirement to launch in daylight and to have the external tank separate from the orbiter in daylight, half a world away. The goal is to obtain good photos of the tank's redesigned foam insulation as well as the shuttle's heat-shield tiles and wing leading edge panels to spot any potential impact damage.

As it turns out, a new analysis of orbital lighting conditions shows a camera mounted in the belly of the shuttle will not have enough light for good photography if Discovery takes off July 1. Conditions improve on July 2 and subsequent days.

Even then, lighting is not expected to be acceptable for crew handheld still and video photography until around July 5. But the critical driver is the umbilical camera, which is positioned to provide good views of foam ramps around external fittings on the tank that carry pressurization lines.

Those so-called ice/frost ramps have not been modified. But long protuberance air-load - PAL - ramps that provided some aerodynamic shielding for the pressurization lines and a critical cable tray, were removed in the wake of major foam shedding during Discovery's launch last July on the first post-Columbia mission.

Shuttle program manager Wayne Hale approved removal of the PAL ramps on the assumption wind tunnel data and computer modeling would show the pressurization lines, cable tray and other fittings will stand up to increased aerodynamic buffeting during the climb out of the lower atmosphere.

During a meeting at Lockheed Martin's external tank assembly facility near New Orleans today, shuttle managers concluded the PAL ramp-free tank has enough of a margin of safety to endure even worst-case aerodynamic loads.

The results of the certification meeting, which focused on the removal of the PAL ramps and modifications to prevent foam shedding near the bipod that attaches the shuttle's nose to the tank, will be presented at a formal flight readiness review June 16-17 at the Kennedy Space Center.

Discovery's crew, meanwhile, flies to the Florida spaceport June 12 for launch site emergency drills and a dress-rehearsal countdown June 15.