If you drive east over the Indian River Bridge on State Road 528 to Merritt Island, FL and look to your left at the top of the span, you'll see a small shape out there on the horizon. It's square and stands alone in a sea of scrubby pines and sand. If you're curious, you might turn left onto State Road 3 and follow that for six or seven miles. If you do, you'll come to a security-manned gate which reads KENNEDY SPACE CENTER - EMPLOYEE ENTRANCE (GATE 2). If you're fortunate enough to be one of those employees, or to have a pass to enter this gate, you can continue driving north for another several miles while you watch that shape grow larger in front of you.

By the time you reach the Saturn Causeway and turn right, it dominates the landscape.

The Vehicle Assembly Building, or VAB, does exactly what it says on the tin. It is an enormous building built specifically to house the delicate processes of putting together the fragile, precise, and sometimes highly explosive components that make up space launch systems right before their flight. It was built in the early 1960s for use by the Apollo Program, when Kennedy Space Center was being hacked out of the Merritt Island wilderness with machetes and determination. Today, it dominates the small collection of low buildings around it which have sprung up to further NASA's activities.

It is 525 feet high at its highest point. This is not that tall, for a building, some will claim; and they'll be absolutely correct. In a world where even the 80 year old Empire State Building reaches over a thousand feet into the sky, what is 525 feet? Well, that's not what makes it special. What makes it special is apparent when you first walk into it, likely through one of the enormous doors that open onto The Aisle - a clear path that runs directly through the VAB.

Once you're in, look up.

See, the VAB is remarkable because the entire 525-foot high structure is one room. At the moment, I think it's still the third or fourth largest building in the world as measured by interior volume - only the Sears Tower, the Petronas Towers and the Burj Kalifa have more interior space than its 130 million cubic feet. When it was built, the American flag painted on its exterior was the largest in the world.

Inside, the Aisle is clear all the way to the ceiling of both the low and high segments There is a smaller block on the south side as you enter, which houses the Low Bays on either side of the Aisle, and then the main building which houses the High Bays is the northern half. The Low Bays were last used to assemble the Saturn V stages for the Apollo launches, and contain folding work platforms that when dropped down level obviously would fit around a Saturn V booster. The High Bays have been used for the past 30 years to assemble the Space Transportation System (the Space Shuttle) before launch.

There are two High Bays on each side of the Aisle. Their bases are open to the Aisle, and there are large 'windows' in their surrounding catwalks and platforms - windows some hundreds of feet high and dozens of feet wide, starting a hundred or two feet up.

To assemble a shuttle stack (and the VAB, as I write this, is assembling the last STS stack that will ever be - the STS-135 stack which will include the orbiter Atlantis on its last flight and the last flight of the Space Shuttle) you first roll up the outside door which each High Bay has on its outside wall.

That can take up to 45 minutes. Those doors are hundreds of feet high.

Then have one of the NASA Crawler/Transporters slowly bring a Mobile Launch Platform into the High Bay and set it gently down on its pedestals - a 6 million lb. vehicle, carrying a roughly 8.2 million lb. structure some 160 feet by 135 feet, with its top 47 feet up.

When you've finished and it's in place, wheel two Solid Rocket Boosters into the VAB and use the enormous crane which lurks at the top of the building to lift them to a vertical position. Lift them up one at a time and and slide them through the window of the High Bay, bringing each into position atop the Launcher Platform. When that's done, do the same with an External Tank - bolting the SRBs onto the Tank with breakaway links and mounting them all securely to the platform itself.

Finally, carefully tow a Space Shuttle Orbiter into the Aisle. Lift a gigantic metal sling onto its back and bolt it to the orbiter securely, then use the crane to lift the 200,000 pound spacecraft up into the air, tail down. Gently move it into position in the High Bay and connect it to the External Tank so that the iconic Space Transportation System is complete.

At last, open the external doors again, and have the Crawler/Transporter (either Hans or Franz, depending on which is available) return to the High Bay and lift the MLP and the now-attached Shuttle, ET and SRBS up off the ground - an additional six million pounds of equipment atop the platform. Watch as it slowly (at around 0.5 mph) moves out of the VAB. Close the door.

That's what the VAB is for.

It's an amazing place. If the cloud cover is low (under a few hundred feet) then, naturally, there will be cloud cover inside the building since it's mostly open air and when the doors are open its enormous volume is just part of the atmosphere. When the temperature outside changes rapidly, condensate gathers on the miles of steel and aluminum girders inside the VAB, and it 'rains' down onto the concrete floor of the Aisle.

It's not clear, at this point in time, what the VAB will be used for next. But if NASA plans come to fruition, commercial space launch providers such as SpaceX will one day use Kennedy Space Center to launch payloads both manned and unmanned into Low Earth Orbit. To do that, they'll need to assemble their vehicles if they want to use KSC's facilities - and the VAB will be waiting. Perhaps NASA will develop a heavy-lift system of its own - and that, too, will use the VAB to stand itself up vertical before flight.

The VAB itself hasn't changed much since 1965. The gray paint marks on the Aisle floor used to align Saturn V boosters for the Moon missions are still there, looking almost unscuffed. Banners from the various STS missions decorate the catwalks and walls. Standing there, you can almost feel the building contemplating its future, wondering what it will be asked to shelter as it takes shape within.

I hope that it has a job for years to come, and that whatever comes to life inside its walls is something wonderful, icon of science and engineering made metal and plastic, waiting to cradle fragile humans on their way up into the universe.