The only thing remarkable about the building I am standing outside is that it doesn't have any windows. Other than that, it's the same nondescript beige concrete as all the others. It looks like it was built in the 1960s.
We are led up a flight of 250 stairs through what looks like a fire escape, and it isn't until we've gone through the door on the third floor and down a corridor that we see it: in the room below, taking up an entire wall, is a bank of screens, with on the left a digital read-out: "Crew time left to sleep: 8 hrs 41 mins".
We are inside Nasa's Mission Control in Houston, and the crew referred to is on the International Space Station 200 miles or so above our heads. A few minutes before, on the tram that took the tour group here from the Johnson Space Center's visitor hub, the disembodied voice of Eugene Cernan, the astronaut who commanded Apollo 17 in 1972, told us over the public address system: "I was the last human ever to set foot on the moon. But not for long. This is an exhilarating time to be here. "
He's not wrong. It's Nasa's 50th birthday on Tuesday. On 29 July 1958, President Dwight D Eisenhower signed Public Law 85-568, which established the National Aeronautics and Space Administration (Nasa). In October this year, the unmanned Lunar Reconnaissance Orbiter will take off for the moon to map its surface and identify future landing sites. Nasa's ambitious $104bn (£55bn) plan to replace the Shuttle programme involves putting man on the moon no later than 2020, and they would like to put man on Mars not too far after that. In addition, the Hubble telescope – which can see nine galaxies in detail – will be decommissioned in 2014 and replaced by the James Webb telescope. This will be able to see 900 galaxies. There hasn't been this much interest in space since the Shuttle began in the early 1980s.
To the right of the digital read-out is a computerised map of the world showing what look very much like shuttle flightpaths. Next to that is a live image of the International Space Station which, we're told, is orbiting the Earth at 17,500 mph, or five miles per second. Its crew is experiencing 16 sunrises and sunsets a day. Signs above the various desks below the giant screens indicate where the Capcom (or Capsule Commander), Booster Team and Flight Director sit. During space-shuttle flights, not even the President of the United States can override a command from the Flight Director. The Capcom is the only person allowed to speak to the crew during a mission and the chair is always occupied by an astronaut.
"It takes one to talk to one," our guide tells us. "They speak the same language. We tell the crew when to wake up, when to sleep, when to install new equipment or work on an experiment, when to eat, when to exercise and to rest."
You could invent a game spotting how many businesses have capitalised on Houston's intergalactic fame: I noticed Space Center Automotive, Nasa Bone and Joint Specialist, Nasa Liquor Store, Nasa Casino and the Nasa Nail Spa. There are also roads with names like Moon Rock Drive and Saturn Lane.
Nasa itself is right next to Skywalker Drive. I'm not kidding.
Houston is not the prettiest city in America, but has a saving grace 15 miles to the south east. Two graces, in fact, in the shape of the Johnson Space Center and Space Center Houston. The former is the original; 15 years ago it was augmented by a theme park that trades on the space story. Both occupy a surprising pleasant location just across from the bay.
All the staff at Space Center Houston sport matching blue jumpsuits with Nasa and Constellation badges sewn on – and they look faintly ridiculous. In fact it's all a bit disappointing when you first arrive, like something out of Disneyland. There's a huge "Kids' Space Place" where little ones can "explore and experiment commanding the space shuttle or living on the space station". But it's really just a huge climbing frame. And there are far too many, well, kids. But don't let that put you off.
Just across the vast room there's a series of tram tours. I chose the "blue" tour. The tours are narrated by the recorded voices of various former Nasa employees. The first is Gene Kranz, a retired flight director best known for his role in the successful Mission Control team's efforts to save the crew of Apollo 13. "This isn't a theme park," he says, "this is real."
While on the tram, you're basically travelling round Nasa's parking lot. You're only allowed in certain buildings, and the ones you can't see inside are just that – buildings – but it's what could be going on behind the concrete and glass that's so exciting. We pass Building 17, where teams of boffins are designing a new generation of spacecraft. Next door are the kitchens where the astronauts' food is prepared (fresh fruit and bread and freeze-dried spaghetti with meatballs is typical). Building 31, we're told, houses the world's largest collection of moon rock, and Building 9 is the astronaut training centre.
A pretty little stone building, surrounded by trees, which looks newer than the other buildings, is the astronaut quarantine, where they're sent for a week before their trips into space, to prevent them from getting infections.
The tour doesn't shy away from disasters that have befallen Nasa either: the tram stops next to a field, in the centre of which is a small circle of oak trees – each planted in memory of a lost astronaut from the Challenger and Columbia disasters. Over the loudspeakers they play a surprisingly touching eulogy that was given by George W Bush. We are taken to a large hanger and drive through a security gate. Inside is the immense Saturn V, known as the moon rocket, which remains the most powerful launch vehicle ever brought to operational status. It is lying on its side, but if it was upright it would be taller than the Statue of Liberty. It's the largest rocket in the world. Between 1977 and 2000 it lay outside the Johnson Space Center; since then it has been in a climate-controlled building to combat corrosion.
It's truly monstrous. Five enormous engines at the back were powered for just two and a half minutes and managed to lift the rocket to an altitude of 41 miles and a speed of 6,000 mph. Each engine weighted 15,650lbs and developed a thrust of 1,500,000lbs.
Back outside in the baking Texas heat (it has already topped 100F this year and it's not even August) we jump onto the tram and head back to Space Center Houston. Looking past the Kids' Space Place and other attractions I notice a number of spacesuits behind glass. Some are copies of originals worn by both astronauts and cosmonauts over the years. Some, including the biological isolation suit worn by Michael Collins as a precaution against catching "moon germs" after the first moon landing, are the real thing.
For a little more money (currently $80/£42), you can sign up for Nasa's Level Nine tour, which includes a trip to the Neutral Buoyancy Lab, Space Vehicle Mock-Up Facility, and Astronaut Cafeteria (where, presumably, you can see real astronauts tucking into burger and fries before it's freeze-dried spaghetti for weeks on end). They let only 12 people do this each weekday, so book in advance.
State lines: Texas
Population: 21 million
Area: 33.5 times the size of Wales
Date in Union: 29 December 1845
Flower: Blue bonnet
Nickname: Lone Star State
Space Traveller's Guide
Houston is served by British Airways (0844 493 0787; www.ba.com) from Heathrow, and Continental (0845 607 6760; www.continental.com) from Heathrow and Gatwick.
You can buy an "offset" through Abta's Reduce my Footprint initiative (020-7637 2444; www.reducemyfootprint.travel).
Alden Houston, 1117 Prairie Street, Houston, (001 832 200 8800; www.aldenhotels.com). Doubles start at $233 (£123), room only.
The Lancaster, 701 Texas Avenue, Houston (001 713 228 9500; www.thelancaster.com). Doubles start at $151 (£79), room only.
Space Center Houston, 1601 Nasa Parkway, Houston (001 281 244 2100; www.spacecenter.org). Open 10am-5pm daily, weekends to 6pm; $18.95 (£10).
Eating and drinking there
Cullen's Restaurant, 11500 Space Center Boulevard, Houston (001 281 991 2000; www.cullenshouston.com).
Greater Houston Convention and Visitors Bureau: 001 713 437 5200; www.visithoustontexas.com; Texas Tourism: 001 800 888 8839; www.traveltex.com