The International Space Station is about to get an inflatable extension

Bigelow Expandable Activity Module via NASA

Space travel: Pump it up, Scotty

AT 73 metres long and 420 tonnes, the International Space Station is the biggest artificial object in space. And it is growing: its 15 existing modules are due to be joined by five more before the decade is out. On April 8th, if all goes according to plan, a rocket will lift off from Cape Canaveral in Florida carrying the first of these new additions. But it is no ordinary module.

The Bigelow Expandable Activity Module (BEAM—illustrated above) is the first bit of the ISS created entirely at the initiative of a private company. Bigelow Aerospace, its manufacturer, is an American space firm set up in 1999 by Robert Bigelow, a businessman who made his money in the hotel trade. And unlike the rest of the ISS, which is essentially a series of space-going aluminium cans, the BEAM is made from cloth. It is folded up and stowed for the journey into orbit, much like a tent, and then inflated to its full size after being attached to the station.

An inflatable space station might sound a bit mad (perhaps for that reason, Bigelow Aerospace prefers the word “expandable”). But many space cadets are fans of the idea. In the 1950s Wernher von Braun, a Nazi rocket prodigy poached by the Americans after the second world war, described a space station 75 metres across with room for 80 people, made of reinforced, inflatable rubber tubes. In the 1960s, with the space race in full swing, NASA built a full-sized test model of a smaller, 7.3 metre model. And in the 1990s the agency returned to the idea with a design called the TransHab, an inflatable spaceship designed to take a crew of humans all the way to Mars. But that mission never happened. In 1999, in a neat bit of symmetry, Bigelow Aerospace bought the relevant patents from NASA and began working on the technology itself.

Inflatable spaceships offer several advantages, but the main one is mass. An inflatable module is much lighter than its metal counterpart, and mass is the rocket scientist’s worst enemy. Lugging mass into orbit requires a lot of energy. Adding extra mass requires more fuel. That fuel, in turn, has mass of its own, requiring yet more fuel to lift, meaning that even a small increase in mass can end up requiring a dramatically bigger rocket. Bigelow Aerospace reckons that its inflatable designs offer more than twice as much internal volume per kilo as a traditional, metal design.

Space is another advantage. The size of a rigid spacecraft is limited by the size of the rocket that launches it.

Learn more: Space travel: Pump it up, Scotty