The tube is out back, 11 feet in diameter, 60 feet long, the unfinished end spiraling into wide ribbons of steel--like a gigantic Pillsbury dough container with its seams gaping open. Behind the tube is a big blue tent known as the robot school, where autonomous welders wheel or crawl along, making the tubes airtight. The goal is to put tracks and electromagnets inside the tube and vacuum the air out. Ultimately, capsules will scream through the center of such a tube at 700 miles per hour on a cushion of air--a way to get from A to B faster and more efficiently than planes or trains. The first public tests of this concept, albeit on an open-air track, will take place in North Las Vegas this week.