KENNEDY SPACE CENTER, Fla. -- Before the launch of Space Shuttle Discovery with El Paso astronaut Danny Olivas inside, a lot needs to get done. Most important is filling the orange external fuel tank with more than a half a million gallons of fuel.

"That's really the real big milestone that says, 'We're really going to try launching today.' If you don't start fueling, you know it's like 'OK, you're not going to...,' but if you start feeling, you're making a real serious attempt at launching," said Allard Beutel, a seven-year veteran of NASA at the Kennedy Space Center.

It's a big deal, considering the sweltering summer Florida heat that causes a lot of thunderstorms that could stop the fueling.

"Fueling, you don't want to have lighting, makes sense you've got explosive fuels and propellants, you don't obviously want to have any lighting near," Beutel told KFOX.

Things are different for this second shuttle mission for Danny Olivas, and probably the biggest difference is the launch time -- a very late 11:36 p.m. El Paso time.

"You can blame Sir Isaac Newton on this," said Beutel.

Essentially Space Shuttle Discovery simply needs to launch at just the right time so that two days later, it can meet up with the International Space Station and successfully dock.

"We have a 10-minute window every single day where the space station passes essentially in a line over the Kennedy Space Center in Florida, over the launch pad," he said.

And while everything is a go for now, weather issues and problems with any of the millions of parts on the space shuttle could delay Monday night's launch.

"It's not routine. Space flight is not routine. There are razor thin margins of what you can and can't do and what can and cannot go wrong," said Beutel.