NASA's next space shuttle flight may have to wait until fall 2006, as the agency grapples with the effects of Hurricane Katrina and external tank concerns, according to an internal memo by a top shuttle official.

Damage sustained to NASA's shuttle external tank factory, in New Orleans, and main engine test site in Mississippi have left many employees homeless and left the facilities inoperable. But the memo states that, even without the hurricane, meeting a March 2006 launch target could have been a challenge.

"A best case estimate pre-hurricane...would have made the March launch date infeasible, May unlikely," according to the Sept. 1 memo written by Wayne Hale, NASA's acting shuttle program manager, and obtained by SPACE.com.

According to the memo, which was first reported by MSNBC.com, post-hurricane estimates on shuttle external tank modification work to reduce the insulation foam shedding like that seen in Discovery's July 26 launch - and that which doomed the space shuttle Columbia - are underway.

Hale described the assessment as "extremely preliminary," but concluded the memo citing that "launch dates before fall of '06 may not be credible." A better understanding of the external tank work and hurricane's impact will be available by next week.

"It is pre-decisional and is part of the ongoing assessment," NASA spokesperson Katherine Trinidad said of the memo.

Meanwhile, an update on Hurricane Katrina's impact to NASA facilities and the shuttle program will be presented during teleconference with reporters at 3:00 p.m. EDT (1900 GMT) today, she added.

NASA made reducing foam debris shedding from external tanks at launch a priority after the 2003 Columbia disaster, which led to the loss of one orbiter and the deaths of seven astronauts. During launch, a piece of foam fell from Columbia's tank and pierced the orbiter's heat shield. The damage allowed hot gases to enter the wing during atmospheric reentry on Feb. 1, 2003 and rip the vehicle apart.

The space shuttle Discovery's STS-114 flight in July-August marked NASA's first orbiter launch since the Columbia accident. Despite more than two years of work, unacceptably large pieces of foam fell from Discovery's tank during launch - one large piece swinging past the orbiter's wing without hitting it.

According to the memo, Hurricane Katrina damaged the roof of NASA's Michoud Assembly Facility in New Orleans, where external tanks are built, and led to debris damage to one of the fuel tanks there. The only access to the facility is by helicopter due to road and bridge damage, and at least 50 percent of the surrounding homes are destroyed or suffered significant damage.