"Ground control, it's all looking good," says the astronaut. "I'm finally inside the International Space StationA joint project between the US, Russia, Japan, Canada and the European Space Agency.. I'm removing my helmet now and... good grief! What's that fearful pongA bad smell or a two-dimensional table tennis arcade game. Created in 1972, it is one of the earliest video games.?"

"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."

The smell is metallic. It comes from anything that has been in space, because of the radiationEnergy given off when radioactive material decays. It can be extremely harmful and sometimes fatal, causing vomiting, skin damage, hair loss and cancer. it is exposed to.

This is one of the things Suni Williams and Butch Wilmore have to cope with. The two travelled to the International Space Station (ISS) in June. But problems with their spacecraft meant it was not safe for them to go back on it.

Instead, they have to wait for another one to take them home. So their mission will take eight months, not the eight days it was supposed to.

The whole of each day on the space station is arranged for them. They get up at 6.30am GMTShort for Greenwich Mean Time after sleeping in cubicles the size of phone booths.

Most of the day is spent on 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. is bad for your bones and muscles. 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 atmosphereThe layer of gases surrounding a planet or moon, held in place by that planet's gravity. Small planets and moons have weak gravitational fields, and therefore only a very thin 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. 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.