By Paul Rincon
BBC News science reporter
The British-born astronaut who will fly aboard the next US space agency shuttle mission says the UK government should fund human spaceflight.
Dr Sellers flies aboard the shuttle as a US citizen
Piers Sellers comes from Crowborough in East Sussex, but had to become a US citizen to achieve his goal.
He told the BBC News website: "The UK is one of a few countries that does not participate. I think it would be great if some time in future it would join."
Dr Sellers will fly aboard shuttle Discovery, due to blast off in July.
He was speaking from Nasa's Johnson Space Center in Houston, Texas.
When I came back from space last time, I felt very sad. I wondered whether I would see that place again
The UK does not support a manned space programme, even through the European Space Agency (Esa), of which it is a member.
Asked whether he would like to see Britain fund its own astronauts, he replied: "Yes I would.
"Most of the European member states participate in a manned programme and have astronauts in the programme. They are either working in Russia, Europe or the United States."
Some supporters of the idea believe a UK government-backed astronaut would be an ambassador for spaceflight and would act as an inspiration to the young.
But the UK has traditionally been against costly human spaceflight, instead directing money towards space science and the satellite industry.
Last year, the Royal Astronomical Society (RAS) urged the UK to rethink its policy ban on astronauts.
In a report, the RAS warned that Britain risked missing out on scientific, educational and economic benefits if it continued its longstanding refusal to fund the human exploration of space.
Piers Sellers is a mission specialist on STS-121, the second shuttle flight since Columbia broke up over Texas in 2003, killing its seven crew.
A hole in one of Columbia's wing panels, caused by the impact of foam debris during launch, triggered the break-up of the orbiter and the deaths of seven astronauts.
The shuttle Discovery will carry Dr Sellers into space
Dr Sellers will be one of the spacewalkers onboard the shuttle. With fellow crew member Michael Fossum, he will demonstrate repair techniques designed to prevent another disaster like Columbia, and fix broken equipment on the outside of the International Space Station (ISS).
The latter task will enable subsequent shuttle missions to resume construction of the space station.
"They can't do that while some of this equipment is broken," Dr Sellers explained.
"It's basically a kind of railroad car and a crane that people need to continue putting new pieces on the station."
In addition, Dr Sellers will help transfer tonnes of cargo, including food, water and other consumables, from the shuttle to the space station.
Commenting on the efforts to return the shuttle to flight after the Columbia tragedy, he said: "It has taken a while to get all the problems straightened out so we are back on track."
He added: "Columbia was very tough on everybody in the programme."
Dr Sellers has already flown aboard space shuttle Atlantis on a mission in 2002.
"I feel more comfortable going into this mission than the last time around, obviously.
"When I came back from space last time, I felt very sad. I wondered whether I would see that place again."
Prior mission experience will stand Dr Sellers in good stead
He said he had learnt two principal lessons from his previous mission: "Don't get out of my seat too fast, I banged my head on the ceiling. Second of all, I'm going to take up some bungee straps to tie myself into my sleeping sack so I sleep better.
"It's very difficult to sleep when you're floating around - the trick is to tie yourself to the wall. You can trick your body into thinking it's back home in bed."
He explained he had held out hope of becoming an astronaut since hearing about Yuri Gagarin's pioneering space flight as a six-year-old.
"It was a field that fascinated me as a kid... I spent many years thinking it wouldn't be realised and I was delighted when it was."
It's not quite the job I thought it was when I was nine years old
He described passing the selection process as "a great moment". He added: "I was surprised, my wife was shocked.
"As one gets older and you participate in a programme like this, you realise how big it is. As an astronaut you only fly 1% of your career. The other 99% of your job is spent helping other people to fly, helping the programme go smoothly.
"So it's not quite the job I thought it was when I was nine years old."
Dr Sellers is the third Briton in space after Helen Sharman, who stayed aboard Russia's Mir space station for a week in 1991, and Michael Foale, who went into orbit the following year.
A veteran of the US space programme, Foale is Nasa's record holder for spending the most cumulative time in space (374 days, 11 hours and 19 minutes).
Another British-born astronaut, Nicholas Patrick, is assigned to the crew of STS-116, a future US mission currently under review.