Remember this thing?

It's a floating x-band radar system that has come to Seattle for maintenance. (It cost nearly a billion dollars to make, but spends a lot of time in shipyards getting maintenance—according to Wikipedia, it spent 170 days in Pearl Harbor in 2006, 63 days in in 2007, 63 days in 2008, 177 days in 2009, and 51 days in 2010.) An old family friend is involved with the SBX radar and yesterday he let me and some retired military guys spend four hours climbing up, around, and inside this military-engineering colossus. We went from the top of the dome to the bottom of its underwater pontoons.

I was there as a family friend, not a reporter, so I didn't take photos or notes. But I can tell you that the thing is huge—it's 280 feet from top to bottom, nearly 28 stories tall. The dome is made of kevlar-like fabric and inflated by an extensive fan system. The radar inside the bulb looms above people like a massive alien monolith, a staggeringly large cube studded with shiny metal plates and hundreds of sensors that look like small, rectangular spyglasses. (There's a video below the jump that has a glimpse of the radar cube at the 20-second mark. But it doesn't do justice to the scale of the thing.)

SBX is designed to sit at a secret spot in the Pacific Ocean and wait around for someone to tell it to look for a missile. When SBX gets the word, the cube swivels around on two axes (azimuth and elevation) and looks. The cube is so heavy, they say you can sometimes feel the platform—a thoroughly stable platform bigger than a 20-story building—move a little when it goes into action. To enter the dome, visitors must pass through airlocks and relinquish anything that might fall off of their bodies and get lost among the moving parts.

A few other facts from the long tour—including SBX t-shirt logos—below the jump.

There were two t-shirts for sale up in the bridge (the command-and-driving room, for you non-nautical types). One had a silhouette of SBX against the Seattle skyline. The other had an eagle with a missile in its claws and a logo that said: "America—you're welcome."

Overheard in the bridge. Engineer: "Now let me take you to the most important part of the vessel." Bored-looking crew member: "The gangway?"

The SBX floats on top of two giant pontoons and can travel under its own power, be pushed and pulled around by tugs, or carried by a heavy-lift ship that partially sinks, lets the SBX position itself above the deck, then rises up to lift the thing above water and cart it around.

The platform sits fairly high in the water when moving, but when it finds where it wants to be, it partially floods itself and sinks 30 or so feet in the water. The platform was designed by Norwegians (and built by Russians) for ocean oil drilling. The radar was designed and built by Raytheon, a defense contractor.

One of the engineers on my small tour had worked for classified, Star Wars-type projects during the Reagan administration. "We all had security clearances," he said as he huffed and puffed up some stairs. "But I worked on one project that nobody ever talked about. I didn't know what it was or what it did. All I know is that it had a launch date. I don't know whether it's still in orbit or not."

After the tour, as we returned our hardhats and VIP badges there was some light chuckling about people who get paranoid that the SBX radar—which is never used when it's in port—has interfered with civilian life: pacemakers malfunctioning, garage doors going up and down, even the weather. I quietly remarked to one of the retired military guys that if defense engineers were working on high-tech projects that even they didn't know anything about, us poor, benighted civilians might have a right to a little paranoia. He quietly agreed.

This was not mentioned on the tour, but SBX failed a test last February.

Here's the video, starring Don Draper from Mad Men: