It may sound like science fiction, but the prototype of Foreign Office Architects' house for Mars is about to be unveiled as part of Nasa's Future Homes display in Sweden.
A spaceship descends slowly through a cloud of red dust onto the barren, rock-strewn surface of the planet Mars. As the dust begins to settle, the doors of the vessel's cargo bay open to reveal a silver cylinder cocooned in the hold. A robot crane swings into action; it reaches into the hold and lifts the cylinder high into the rarefied atmosphere before placing it gently on the planet's rocky surface.

Once on the ground, the cylinder appears to take on a life of its own - its perfectly curved wall begins to distort as it slowly swells to almost double its original diameter. A row of space-suited figures file through an airlock from the spaceship to enter the shiny, amorphous tube. It will be the space-travellers' Martian home for their sojourn, 35 million miles from planet Earth.

This is the scenario that Foreign Office Architects is working to create. Its design for an expanding cylindrical accommodation capsule has reached the final five in a competition organised by Nasa to design a house for Mars. In May this year, the first prototype of the dwelling will be unveiled at Nasa's Mars exhibition in Malmö, Sweden, as part of the Future Homes display.

The expanding cylinder is fundamental to the scheme's success. The challenge for the project's structural engineer, Adams Kara Taylor, was to develop a simple structure that would allow the cylinder's walls to expand outward, creating as much accommodation space as possible, without adding unnecessary weight to the rocket's payload.

"The cylinder's geometry is dictated by what can be transported to Mars," says Hanif Kara, a principal of the practice. A cylinder would fit snugly into a rocket's 4.2 m diameter, 11 m long cargo hold. "But this cylinder would not be spacious enough to provide the accommodation in which a group of scientists could live for months on end. We had to design a structure to allow the cylinder's walls to expand." Kara's solution involves a series of expanding structural hoops. These are spaced 1 m apart along the length of the cylinder so that, without its skin, the capsule looks like a whale's ribcage.

Each circular rib comprises three semicircular structural members: a fixed section and two movable top sections. The ribs' movable sections are pivoted from each end of the fixed section. During transportation, these movable sections are folded down on top of each other to form half of the cylinder's circular cross-section. The semicircular fixed base completes the circle. E E Once the capsule is unloaded, the top sections swing outwards to form the enlarged accommodation module (diagram, right).

In the prototype, steel will be used to form the cylinder's structural ribs. Later in the year, however, the engineers will visit Nasa to discuss the use of advanced composite materials. Likewise, although standard electric motors will be used to unfold the structure in Malmö, Kara says the robotics that Nasa has are "far more advanced and could be adapted for the real thing".

The next challenge was to find a suitable material with which to clad the capsule. Mars is an inhospitable place. Once it may have been warm and wet, but today the red planet is a frozen wasteland with temperatures as low as –120ºC. Scientists say that it is highly unlikely that any living creature, even a microbe, could survive for long on the planet's surface.

Under these conditions, the performance of the capsule's cladding is critical for the occupants' survival. Not only does this skin have to be able to withstand the Martian environment, it will also have to be flexible enough to stretch to twice its surface area as the cylinder expands. And, given the difficulties of carrying out repairs in situ, it would have to be incredibly strong. Such a material has yet to be developed, so the prototype will use silvered PVCu. But Kara is optimistic that, given Nasa's resources, a suitable material can be developed soon.

Inside the prototype, a ramp will allow visitors access to the upper levels of the accommodation capsule. However, because the top sections of the structural ribs are movable, supporting the ramp is a problem. The engineer's solution has been to gradually rotate this lower section of the structural ribs along the length of the cylinder, in effect putting a twist into the rib cage. This rotation means that at one end of the cylinder the base section forms an upright U, while at the opposite end it forms a C – a process Kara describes as similar to twisting a piece of rainwater guttering through 90º along its length.

With this twist in place, the fixed section of the ribs can be used as structural support for the ramp, which can either be cantilevered or hung from the structure. However, if the scheme does land on Mars, the ramp will not be necessary. Mars has a gravitational force about one-third that of Earth, so instead of a ramp, the architect intends the capsule's occupants to use trampolines to bounce to the upper levels.

At the moment, the design team is racing to complete the prototype in time for the Malmö exhibition. But it is the next stage of the project that Kara is really looking forward to: "We'll be visiting Nasa later in the year when we'll have access to some of their engineers," he says. In the mean time, more terrestial matters occupy Kara's time: he still has to find a steelwork fabricator in Sweden to construct the structure for the prototype.

Nasa’s Mars exploration programme

Nasa has recently stepped up its programme to explore the red planet. Six missions are planned this decade:
1 The Mars Odyssey Orbiter is scheduled to take off from Cape Canaveral on 7 April 2001
2 In 2003, two robot explorers will examine the planet’s surface
3 In 2005, the Mars Reconnaissance Orbiter mission will look for water on the surface of the planet
4 During the 2007 mission, Nasa will place a robot mobile science laboratory on the planet in the first major step toward demonstrating the technology for accurate landing
5 and 6 2007 will also see the launch of the first of two small scout missions to examine more sites on the planet. In the second decade, the first mission to collect samples from the planet’s surface will touch down in 2014, followed by a second mission in 2016. Both missions will return to earth with their cargo of samples. For the first manned mission, Nasa is developing a new propulsion system that will reduce the time taken to travel to Mars from 10 months to four. The mission will use a slow automated cargo ship, powered using conventional rockets, to place fuel and supplies on Mars. Once this has been successfully completed, a smaller, fast ship will carry the crew to Mars. As for the date of the first manned expedition, Nasa is being less specific. Its web site will only say: “Nasa’s planning for a human mission to Mars is a work in progress.” Check the site in future for further details:

Structures Special