Nasa starts countdown for shuttle launch tomorrow

Countdown clocks at the Kennedy Space Centre blinked to life for the first time in two-and-the-half-years as Nasa made final preparations for shuttle Discovery's tomorrow's planned liftoff.

"Countdown for launch of Discovery is now underway," Nasa spokesman George Diller said as the clocks began ticking at 6 p.m. EDT (2200 GMT) at the Florida spaceport.

The launch, set for 3:51 p.m. EDT (1951 GMT) tomorrow, will be Nasa's first since the 2003 Columbia disaster.

"Discovery is in excellent shape as we prepare for tomorrow's launch," said Nasa test director Jeff Spaulding.

The seven members of the Discovery crew arrived at the Kennedy Space Centre in Florida over the weekend.

"It sure does feel good to be back in the saddle again. It's been too long," Discovery's payload manager, Scott Higginbotham, said at a news briefing.

The shuttle Columbia disintegrated over Texas during a landing attempt on February 1, 2003, killing all seven astronauts aboard. The accident was blamed on technical problems - a piece of foam debris had hit Columbia and damaged its wing during launch - and poor management practices.

The US space agency immediately grounded its three remaining shuttles and pledged to find the problems, fix the shuttle and return to flight.

Even the weather appears to be cooperating for an on-time liftoff. Forecasters predicted a 70-per cent chance the weather will be acceptable for launch tomorrow. The odds dip to 60 per cent on Thursday and on Friday, said shuttle weather officer Kathy Winters.

In addition to good weather in Florida, Nasa will need clear skies at one of its three US landing sites - Florida, California and New Mexico - as well as at a transatlantic emergency landing site in case the craft fails to reach orbit.

The weather in Florida will be a key factor if Discovery's modified external fuel tank is to pass preflight ice inspections early tomorrow. After the tank is filled with the 535,000 gallons of cryogenic propellants need to get Discovery in orbit, a special team will scrutinise the tank for ice buildups.

Engineers say ice particles, which can form on the outside of the full tank as the shuttle sits on the launch pad, pose as great a risk as foam pieces breaking off the tank during launch and striking the shuttle, as happened during Columbia's launch.

The inspection team will have an extra hour to check the shuttle's tank for ice. Nasa also has toughened its flight rules to prohibit launch if ice buildup is found in critical areas.

Nasa has replaced the foam chunks that triggered the Columbia disaster with electric heaters and redesigned how hand-sprayed areas of foam were applied. Managers then delayed Discovery's launch from May to July to add another heater to help prevent ice formations around a pipe that feeds the supercold liquid oxygen to the shuttle's main engines.

The launch would be called off if inspectors find ice buildups on the tank. "We have mitigation tools to prevent ice from forming. We don't have anything to remove ice," said Mr Spaulding.

Factbox

Deadly accidents in space exploration

Space travel, tests and launches have killed more than 200 people through the years. Here are some of the deadly accidents:

October 24, 1960 - USSR - R-16 rocket explodes on Baikonur launchpad, killing more than 90 people.

January 27, 1967 - US - Fire sweeps Apollo 1 on Cape Canaveral launchpad, killing astronauts Virgil "Gus" Grissom, Edward White and Roger Chaffee.

April 24, 1967 - USSR - Soyuz 1 crashes on re-entry, killing cosmonaut Vladimir Komarov.

June 30, 1971 - USSR - Soyuz 11 loses pressurisation during re-entry, killing cosmonauts Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsayev.

March 18, 1980 - USSR - Vostok rocket explodes on launch pad at Plesetsk space center, killing 50 people.

January 28, 1986 - US - Shuttle Challenger explodes 73 seconds after liftoff, killing astronauts Francis "Dick" Scobee, Michael Smith, Judith Resnik, Ellison Onizuka, Ronald McNair, Gregory Jarvis and Christa McAuliffe.

February 1, 2003 - US - Shuttle Columbia breaks apart during re-entry, killing astronauts Rick Husband, William McCool, Michael Anderson, Ilan Ramon, Laurel Blair Clark, David Brown and Kalpana Chawla.

August 22, 2003 - Brazil - Rocket explodes on the ground a few days before scheduled launch, killing 21 people.