The 67-year-old Virgin boss has set his sights on turning commercial space travel into a reality since he founded Virgin Galactic and hopes to be among the first space tourists.
“We’re talking about months not years – so it’s close. There are exciting times ahead,” he told BBC Radio 4’s You And Yours, to be broadcast on Monday.
“I’m going for astronaut training, I’m going for fitness training, centrifuge and other training so that my body will hopefully cope well when I go to space.”
He said he has increased his fitness training by playing tennis four times a day.
“Instead of doing one set of tennis every morning and every evening I’m doing two sets. I’m going kiting and biking – doing whatever it takes to make me as fit as possible.”
Sir Richard is also taking part in gruelling centrifuge training which recreates the pressures the human body experiences during space flight.
All astronauts endure G-force training which simulates the experience of take-off and travel through the earth’s atmosphere.
Earlier this year Virgin Galactic completed a supersonic test flight of its SpaceShipTwo passenger rocket ship.
It was the first return to the air for the company since a crash in the Californian desert in 2014 in which one pilot was killed and another was injured.
Sir Richard, tech entrepreneur Elon Musk and Amazon founder Jeff Bezos are in a race to get tourists into space.
While Sir Richard believes Mr Musk is “doing fantastically well” in getting cargo into space and building bigger and bigger rockets, the real tussle is between the Virgin boss and Mr Bezos.
“I think we’re both (Sir Richard and Mr Bezos) neck and neck as to who will put people into space first,” he said.
“Ultimately we have to do it safely. It’s more a race with ourselves to make sure we have the craft that are safe to put people up there.”