Space Shuttle Endeavour STS-134 launch: BB liveblog on-site, SpaceFlightNow webcast with Miles O'Brien

[ 1:53pm ET: ]
President Obama is en route despite launch scrub, scheduled to arrive Kennedy Space Center at 2:10pm ET. We may see Air Force One overhead shortly. The president is reportedly en route to say hello to astronauts and Gabrielle Giffords.

[ 1:03pm ET: ]
Mike Leinbach, Shuttle Launch Director with NASA, is speaking about why the launch was called off. NASA now says Endeavour won't launch before Monday at 2:33pm EDT. My notes:

A thermostat on one of the fuel lines, one of the heater units, failed. We tried to get the line to cool down, to see if thermostat would kick in, and tried other methods to activate — but failed. We have a hard failure. There was another heater also exhibiting funny behavior. We believe we have a problem in the LCA, load control assemblies, switch box. Maybe a problem in the box, or in the line leading in to the box, or out of the box. But we didn't want to commit to flight with only one of the heaters functioning. Need to be able to heat the fuel [Ed. note: fuel can become very cold in space, you don't want your fuel freezing]. Probably tomorrow afternoon they'll get hands on the assembly. Once we can get in to the avionics bay where the LCA exists, we can do troubleshooting, see if we need to change out that box. We've declared a minimum of 72 hours. Today the orbiter's not ready to fly. We will not fly before we're ready.

[12:52pm ET]
NASA: launch may be scrubbed for at least 72 hours.

[12:30pm ET]
Steven Young from SpaceFlightNow explains what we know about why Endeavour's launch today was scrubbed. Short version: Not the weather, but reportedly because of a problem with one of the orbiter's Auxillary Power Units. Steven explains that there are three of these on the shuttle, to provide power for hydraulic system: during launch, they are a crucial element. They're started up about 5 minutes before launch, and they sound like giant steam engines; they're run until the shuttle reaches orbit, then they shut down. The day before launch, they fire up one of them to see if it's still working, and right before launch, they fire up one again. The rules, Steven explains, are that you want all three to be working. Two are enough to fly the shuttle normally. We don't know exactly what the problem was yet, but whatever it is, it's serious enough to cause the launch to be called off. NASA is telling us that the delay will be more than 48 hours.

[ 12:18pm ET ]
: Space shuttle Endeavour's launch has been scrubbed due to a problem with one of the orbiter's Auxillary Power Units. The launch will not take place at 3:47pm ET today as planned. Will post an update when we know the next launch window, but at best, odds are at least 48 hours we are now told the next window will be longer than 48 hours.

[12:17pm ET]

Something unusual just happened. The crew normally heads to the launch pad, but this time they stopped at Launch Control Center (LCC) to drop off officials who were with them but aren't going to the launchpad. They pulled into the LCC entrance, went into parking lot (normally they just stop on the road outside), then made a U-turn. This may mean the launch is scrubbed.

[11:52am ET]
We're seeing a cavalcade of tweeters walking out of the NASA Tweetup tent, heading off to greet the STS-134 astronauts. Pretty cool to see NASA exploring new ways to connect with people through Twitter and the like. Follow the Tweetup with the hashtag #nasatweetup.

[11:41am ET]
I asked this last night over Twitter, and I'll ask you good folk here: What do atheists say when they want to wish someone (or someshuttle) a good flight? "Sciencespeed"? Your thoughts in the comments, please.

[11:34am ET]
Today's scheduled launch is the penultimate launch for NASA's shuttle program; walking around KSC today, I'm hearing much nostalgia in snippets of conversations among journalists and NASA folk. As you drive around the towns surrounding Cape Canaveral, signs on local businesses—pizza parlors, strip clubs, churches—are all wishing "Godspeed Endeavour." What will happen to these communities, the countless mom and pop enterprises that depend on space industry and concomitant tourism? What happens to these thousands of space workers when the shuttle program ends? Some will be swooped up by private space industry, but how many will, say, SpaceX employ? Much talk of 15% or greater unemployment, property values plummeting, and an ambient sense of the rug being pulled out from under a place that calls itself the Space Coast, a place with a glamorous history during the Apollo years. Those years here are over.

[11:30am ET]
Thanks for tuning in to Boing Boing's royal wedding coverage: the marriage of a spacecraft with her sky.

[11:26am ET]
The continuing gusts (whoosh, there's another one!) we're feeling here at Kennedy Space Center in Florida are but one challenge. Meteorologists also keeping an eye on the iffy conditions at emergency runways in Europe, where the shuttle would make an emergency landing if there were problems. SpaceFlightNow:

The outlook is a chance of showers at the Zaragoza and Moron runways in Spain. The Istres landing site France had been promising, but the most recent update from meteorologists calls for a "slight chance" of showers there today.

[11:06am ET]
The weather is the story out here today, and specifically: they'll be watching the wind. Gusts are so forceful out here that my Mac Air just blew right off the table and hit the ground when I stepped away for a moment. More importantly: will the wind affect the launch? Miles just spoke to the chief weather officer for NASA. 15 knots is the maximum threshold NASA will be allow, and some forecasts are calling for 18 knots. Last night, there were dramatic lightning storms and menacing clouds around KSC; the last of the storm bands from the powerful series of fronts that spawned devastating tornadoes throughout the south.

[10:56am ET]
Greetings from a spot on the grass just 3 miles away from the launchpad where Space Shuttle Endeavour is set to lift off today. Blast-off is scheduled for 3:47pm ET, and I'll be here liveblogging all day from the Kennedy Space Center (KSC) with the SpaceFlightNow team. Miles O'Brien is hosting their live webcast, tune in here. Notable guests expected at the launch today include President Barack Obama and the first family (we're told they'll land nearby around 2:20pm ET), and Arizona congresswoman Gabrielle Giffords, whose husband Mark Kelly is the commander of the STS-134 mission.

Image (Robert Pearlman): The shuttle Endeavour, bathed in blue light, April 29, 2011.