"Ground control, it's all looking good," says the astronaut. "That was a tricky docking, but we got there in the end. Hard to believe that I'm finally inside the International Space StationA joint project between the US, Russia, Japan, Canada and the European Space Agency.: I can't wait to say hello to the rest of the crew. I'm removing my helmet now and... good grief! What's that fearful pong?"

"On Earth we have lots of different smells, like washing machine laundry or fresh air," says Helen Sharman, Britain's first astronaut.¹ "But in space there's just one smell, and we get used to it quickly."

She explains that anything which goes out into space, from equipment to a spacesuit, is exposed to strong radiation. "Radiation forms free radicalsA type of unstable molecule. on the surface, and they react with oxygen inside the space station, creating a metallic smell."

This is one of the things Suni Williams and Butch Wilmore have had to cope with. The two travelled to the International Space Station (ISS) in June to test the new Starliner capsule made by BoeingAn American multinational corporation that designs, makes and sells aircraft, rockets, satellites and missiles.. But because of problems with its thrusters and a heliumA very light gas used in balloons to make them float. Old airships used hydrogen, but it burnt easily. Helium does not burn. leak, engineers decided it was not safe for them to return on it.

Instead, they have to wait for a SpaceXFounded in 2002 by South African entrepreneur Elon Musk, SpaceX's mission is to reduce the cost of space transportation to make possible the colonisation of Mars. craft to take them home - so their mission will take eight months instead of the expected eight days.

The whole of the astronauts' day on the space station is mapped out by mission control. They get up at 6.30am GMTShort for Greenwich Mean Time after eight hours sleeping in cubicles the size of phone booths.

Most of the day is spent on scientific experiments or maintenance. But exercise is vital, because living in zero gravityAn invisible force that pulls objects towards each other. Earth's gravity keeps us on the ground and makes things fall. It is less strong on Mars. reduces bone density. The astronauts spend at least two hours a day on a treadmill or an exercise bike.

But they get far more sweaty than they would on Earth, because there is no gravity to pull sweat from the body. Their exercise clothes become so disgusting that they have to be thrown out in a cargo craft which burns up in Earth's atmosphere.

But their ordinary clothes are fine: "Clothes float on the body," says American astronaut Nicole Stott, "so oils and everything else don't affect them. I had one pair of trousers for three months."²

Food comes in packets, supplied by the different countries involved, "like camping food... good, but it could be healthier".

The loo is a small cubicle where everything that comes out is sucked away. Urine is recycled as drinking water.

Will humans ever live on other planets?

Yes: The main challenges are to get people there with enough resources to create the habitats, grow the food and generate the energy needed to sustain them. Scientists are well on the way to meeting these.

No: Space travel takes too heavy a toll. The lack of gravity and exposure to radiation would wreck our bodies. Not being able to feel the sun on our skin or wind on our faces would drive us mad.

Or... Even if we could, we should not. We have done so much damage to our own planet that we are morally obliged to leave others alone. Instead, we should focus on putting things right on Earth.