So after months of waiting, we just knew that Thursday would be the day. The countdown went off without a hitch, and things finally looked to be going in Discovery's favor.  That was until the countdown clock reached the 5 minute mark and was held.  The rumor mill started circulating and there was a very real fear we'd have yet another mission scrub.  None of us at the time realized how close things were to be called off again.

The hold was due to a problem with a range safety display.  Range safety is responsible for the very difficult decision of destroying the Space Shuttle if it veers off course and poses a threat to people on the ground.  Apparently the officer's visual display wasn't working properly, requiring him to rely on just raw data (and not a video picture) of the Shuttle's trajectory to orbit.   Read more about the range safety officer and his self destruct switch at Popular Mechanics.    

With the clock ticking towards the end of the window but the launch clock still on hold, somebody called the Range Safety Officer's superior and had his hold overruled.  You can hear at the end of this video one of the mission managers instructing the range officer to flip their swtich from the hold to go position.  If he waited another two seconds the mission would have been scrubbed.  Again.

It must have been a very frantic couple of minutes in the firing room at Kennedy Space Center.  

There have been 133 Space Shuttle launches over the last thirty-one years.  I've watched many of them on television and it never gets old.  But there's something about experiencing a launch that just can't be appreciated by a television broadcast or a YouTube video.  It starts with seeing the Shuttle, three miles away, lifting off silently from the pad with its exhaust plume brighter than the sun as it streaks towards orbit.  And, perhaps most unforgettable, the thundering roar and shockwave that slowly approaches and hits like an earthquake - shaking even the air in a way that's unmatched by any fireworks demonstration.

You're also struck by how sad it is that something so uniquely American is being phased out with no clear replacement on the horizon. Bittersweet indeed.

Take a look at the video to see what the experience was like for me and about a hundred lucky NASA Tweetup participants yesterday afternoon.  None of us will ever forget this day, that's for sure.

We're sitting here enjoying a beautiful view of Space Shuttle Discovery full fueled and crewed approximately three miles from our location at the press site. There is a lot of confidence of a launch today and there's a ton of excitement in the air.  The internet connection is a little sluggish here so videos and photos might be a little slow in coming.  I have opened up my Facebook album to the world, so click here to see some shots from my iPhone. 

NASA Tweetup is back at the Kennedy Space Center!   More than a hundred of the original crew from November is back to hopefully witness the launch of Space Shuttle Discovery tomorrow at 4:50 p.m. eastern time.  There were many happy faces all around as Tweetup participants reconnected with each other after months of correspondence via Twitter.  

NASA once relied on big networks and even bigger names like Walter Cronkite to help carry its message. But now NASA is broadening its reach to social media.

The agency recently invited 150 of its Twitter followers to a space shuttle launch “tweetup” event, giving people like math professor Joel Glickman - and his live streaming iPhone - access that was once reserved only for the media's elite.  

But this is more than a fan appreciation day. NASA officials estimate that the videos, photos, blog posts and tweets will reach more than 1.8 million people, an audience size that rivals most cable networks in primetime.

NASA knows all too well what happens when the public's interest goes elsewhere. A Saturn V Rocket, once destined for the moon, now sits in a museum at the Kennedy Space Center - the result of budget cuts in the 70's. With the Space Shuttle program set to conclude in 2011 and no immediate replacement vehicle ready, NASA hopes reaching the public through its most enthusiastic supporters will keep interest in the program strong during this critical transition.

The rockets we send to space are big and heavy, but it isn't until you actually see it up close to get a sense for how enormous they really are.  From top to bottom the Shuttle stack measures 184 feet in height and weighs approximately 4.5 million pounds at launch.  The above photo I shot at the launch pad puts that scale into perspective.

See more photos from my evening visit on my Flickr!

Dane Golden interviewed me for his show on Hey.com this afternoon.  I give an overview of the press site and some of the activities we experienced this week as part of the NASA Tweetup program.