Countdown and launch of the space shuttle

As Columbia left the ground at 0031 EST (0431 GMT), Mission Control said: "We have lift-off - reaching new heights for women and X-ray astronomy."

Cathy Killick reports: "It was a case of third time lucky"

Within eight minutes of launch, the craft had reached a speed of 17,500 kph (10,900 mph).

Referring to two last-minute postponements, Nasa said shortly before the successful launch: "A few days delay, but the same enthusiastic launch team wishes you luck on your mission."

Booster rockets separate

The Nasa mission is the first to be commanded by a woman, Colonel Eileen Collins.

The deployment of the shuttle's cargo, the Chandra X-ray observatory, is almost one year behind schedule.

Thunderstorms near the launch site prompted Nasa officials to cancel Wednesday's scheduled launch.

'Flight no-go'

Mission Control explained to the crew that lightning strikes were reported within 10 miles of the launch site.

Colonel Collins is a former Air Force test pilot

A 20-mile clearance is required for a safe launch, as a lightning strike could in theory ignite the hydrogen fuel in the shuttle's main tank.

"It's a flight no-go," the launch controller, Ralph Roe, told Commander Eileen Collins. "We'll give it another try on another day."

The countdown was stopped five minutes from ignition as controllers waited for the storm to abate - and the launch "window" was extended by 10 minutes - but to no avail.

Try and try again

The mission had already suffered at least 10 delays since its original lift-off date of November 1998. These were caused by problems with both the shuttle engines and its cargo, the Chandra X-ray observatory.

The Chandra telescope just squeezes into Columbia's cargo hold

The observatory is the world's biggest and most powerful X-ray telescope and cost $1.5bn. Columbia is the only shuttle powerful enough to carry it and even then had to be stripped down to accommodate the 25-tonne weight.

The Chandra Observatory will study X-ray emissions from distant stars and galaxies that are largely undetectable from Earth because of atmospheric absorption.

Scientists hope the telescope will, for example, help them estimate the so-called "dark matter" that scientists know exists but cannot be seen.

False alarm

The first launch attempt was dramatically aborted on Tuesday just six seconds before blast off, when sensors reported a possible hydrogen gas leak in an engine compartment. It turned out to be a false alarm.

"The call came less than half a second before we would have started the engines," shuttle launch director Ralph Roe said.

The shuttle's three main engines fire several seconds before lift-off as they build up power. If they had fired, Columbia would have had to be refitted with new engines, delaying the mission by up to a year.

The launch had been scheduled to coincide with the 30th anniversary of the first moonwalk on 20 July.

First woman commander

Colonel Collins - who piloted the shuttle in February 1995 - admits being the first woman commander does add extra pressure but says: "The extra pressure doesn't bother me - I find that I can still do my job effectively."

She does not see it as a "giant leap for womankind".

"It's an honour for me to be chosen, but I also see it as an evolutionary process. Eventually, having women in these roles won't be news anymore," she says.

Nasa's head, Dan Goldin, obviously agrees: "Eileen Collins is the commander. So what's the news?" he said.