In 1991, Helen Sharman was the first Briton in space, chosen from 13,000 hopefuls who replied to a unique advert: Astronaut wanted. No experience necessary. She tells Katie Jarvis about her eight days aboard the Mir space station – and how they changed her life

If you're prone to vertigo, then here's a helpful warning: skip the first chapter of Helen Sharman's autobiography, Seize the Moment.

If you are prone to vertigo but want the most exhilarating, exciting, sickening, terrifying, rollercoaster read of your life, then don't - whatever you do - skip the first chapter. Read it in gentle stages (as I did). It's May 1991, and Sharman is 27 years old, chosen from an astonishing 13,000 people who responded to an advert: Astronaut wanted. No experience necessary. She'd never dreamed of going into space; didn't even call up for more information until the following weekend. But here she is, nearly two years later, squeezed into an ungainly padded space-suit: one of three astronauts on launch-day of Project Juno, a private space programme run by the Soviet Union and a commercial British enterprise.

As they trundle up by bus, they see for the first time in all its glory the rocket (the unromantically named Soyuz TM-12) that will fly them to the Mir space station, orbiting at 17,500 mph, some 400km above the Earth.

Helen describes the lurch of the elevator, slowly lifting them through the white mist of water vapour, past ice-covered metal stretching dauntingly into the sky. How the small platform onto which they step sways in a stiff wind. How they struggle into their confined seats; and how she quietly, humorously, removes from her pocket a smuggled frilly pink jumpsuit a well-wisher - Cosmonaut Leonov (the first man to walk in space) - has mischievously given her. Then the checks; the countdown; the deep rumbling of the rocket engines…

And the gantries swing away.

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Wow, I say to Helen Sharman. "The description of lift-off in your book:

(The beautiful bits - I could see the curvature of the Earth! Speckly white clouds! A brilliant azure sea!;

The 'scary' bits - The second stage separated after 288 seconds: another jolt, another bang… for a brief moment our bodies felt lighter);

is one of the most mesmerising I've ever come across."

She laughs, a faint Sheffield accent still detectable in a measured, warm voice. And there's another facet of her that's instantly apparent: her unfailing honesty.

"It wasn't written by me," she says. "It was a ghost writer. Good for him!"

Since Seize the Moment was published - back in 1993 - Helen Sharman has become a writer and communicator in her own right: penning inspiring science books for children; TV and radio presenting; speaking at schools, conferences and corporate events the world over.

But it's not only her scientific expertise that makes her so in demand (she's a respected chemist, a fellow of numerous societies and on the staff of Imperial College London). It's her down-to-earth-ness (if that's not an oxymoron). The fact that she'll happily describe how un-glam her life was as a trainee astronaut in Russia (no bath plugs; hot water for one hour a day. Not even any syringes, at one point. The nurse produced a large, blunt, reusable needle and held a test-tube underneath…).

There's no ego, either.

Despite the fact that Major Tim Peake has frequently been described as Britain's first astronaut - Helen preceded him by more than two decades - she was there, cheering him on as he launched to the International Space Station in December 2015, commentating on the event for the BBC.

"For the vast majority of people in the UK, the fact that Tim is British meant we suddenly got behind space again," she says, enthusiastically. "It captured our imagination again. We're still quite nationalistic about it."

Must have been strange, though. Watching and remembering?

"It was. Particularly because I know when the different rocket stages are going to be jettisoned and where the likely problems are. So I was just willing everything to go well. Back in October last year, there was that failed launch, where the booster didn't separate properly; so you know that these things are all possible. But there's a lot of back -ups and contingency measures, so I wasn't too concerned about a complete catastrophic failure."

When she appears at Cheltenham this month, she'll be talking about her experiences in orbit. But festivals - which she loves - are also a fabulous way of bringing science back into people's lives.

"In Britain, certainly, we learn science at school; we learn it at university; and we leave it there. We don't incorporate it into our lives.

"In space, it's obvious. An astronaut would die if we didn't appreciate the science of everyday life. You would suffocate in your own breath if you thought that warm air would rise in an orbiting space station.

"What I like to do is to talk about the science of everyday life in space so that we appreciate much more the science of everyday life on Earth."

She pauses. "I'd just like us all to be able to embrace science in the same way that we include music and art in our lives."

There's a pragmatic reason, too, for why we should all be more 'scientific'. Helen has never been an unalloyed fan of the press - and with good reason. During her astronaut training, there was some appalling media behaviour. But she's particularly concerned about the ability to manipulate the public with scaremongering headlines. "Editors have to sell papers, but how do we know to question them? We're often fearful of looking stupid because we don't understand science. No scientist understands every bit of science; but, as long as we appreciate a little bit, then we start to question it. What is the problem with that vaccine, exactly? How many people were in that trial?

"It could really save lives. And what it could do is influence our political leaders to make better decisions on our behalf."

Certainly, her first-hand experiences have changed her own outlook on life. There's another wonderful chapter of her book where she describes looking out of Mir's windows. Much of Canada is white; Ireland and New Zealand's South Island look green. Forest fires belch out visible smoke in long, straight lines. France is identifiable from the way the fields are laid out; Britain's distinctive shape is often covered in cloud.

Looking at that bigger picture, she wrote, put everything into perspective.

"Yes," Helen Sharman reiterates. "All the little grizzles and annoyances became so insignificant - certainly in terms of material stuff. In space, I had everything I needed around me: I was safe, warm; I had food and water. I even had some company."

The one thing everyone missed was family and friends. "When we flew over parts of the world where we knew people, we'd talk about them."

But her view of that small green and blue planet is also of a beautiful united whole - a whole that humanity has divided. From space, you see the geographical differences. "Where the land meets the sea; mountains; rivers. What you don't see are those silly little lines down political maps.

"All of that tragedy; all of that horrendous stuff that we inflict on other people in the world. And we're fighting over these insignificant, ridiculous boundaries on a quite insignificant little planet in this vast universe."

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Can Helen Sharman envisage what we'll be doing in space in 50 years' time?

She laughs again. "Either I could say, 'Of course there's no way I can predict…' Or I could have a bit of fun," she says.

And fun wins the day.

Passenger travel is first off. "An easy one. If you want to go to Australia or San Francisco, let's say, I can see people popping into a spacecraft that will hop into a kind of low Earth orbit. You'll be able to get to Australia in half an hour."

There's manufacturing: space provides the medium for a whole range of new materials of previously unknown strength, softness and flexibility. "I can see us having space factories. I'd like to grow loads of crystals; I'd like to grow loads of metal alloys - mixtures of metals that we can bring back to Earth. Things we just couldn't grow here."

Then there's the mining of asteroids and comets. And the collecting of energy from the sun from space, to be beamed back to Earth.

"And by the mid-30s, I think we'll have gone to Mars. In 50 years' time, we may well have got Mars and moon colonies. I don't think people will be living their entire lives on different planets; but, by then, we should have created a faster form of transport that won't take quite so long."

She's completely pro the commercialisation of space. There's no reason, she says, why private missions can't include scientists, paid for in the same way as university researchers: by governments, grants, charities. "Instead of funding science to be done on Earth, it would be done in space."

And don't forget those space tourists, queuing for tickets to experience luxury weightlessness. Will she be one of them?

She shakes her head. "It's for people who are wealthier than I am!"

Three days after her return to Earth, Helen Sharman was told by a doctor that she was 150 percent fit… but with an incurable disease. "Cosmonauts never recover from it," the doctor told her. "It's a longing to go back."

Helen would beg to differ. She knew hers was a one-off experience; a pretty amazing one at that. But one she accepted shouldn't be yearned for again, but used for as much general good as she could: for inspiring schoolchildren; families at festivals; scientists at conferences.

Not that that stops her - occasionally; just occasionally - revisiting at night.

"On the odd night - when I remember a dream - sometimes I'm floating along a main module of the Mir space station, and I stop by a window that never existed. And I look out.

"And then Sergei [Konstantinovich Krikalyev, Project Juno flight engineer] floats in from the opposite direction. We don't say anything. But we just look out of the window together."

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Helen is appearing at Cheltenham Science Festival on Saturday, June 8 in Helen Sharman: Out Of This World; cheltenhamfestivals.com/science.

For more on Helen, visit helensharman.uk. You can write to her at DBA Speakers, Landmark House, Station Road, Hook, Hampshire RG27 9HA.