A company that blasted the first space tourists into orbit is offering future clients the chance to do a space walk. Space Adventures say the optional excursion will cost $15m (£8m) on top of the $20m cost for the flight. For that, private space explorers will get a 1.5 hour accompanied extra-vehicular-activity (EVA) outside the International Space Station (ISS). The EVA would lengthen a stay on the ISS from 10 days to between 16 and 18 and would require additional training. Eric Anderson, president of and CEO of Space Adventures said they already had "potential clients" for the spacewalks. Those with enough money would get to "hang out" outside the space station with a trained cosmonaut as a guide, he said. "One and a half hours is about one orbit of the earth so they'd see the entire planet," said Mr Anderson. "They'd experience complete day-time and night-time and watch the planet in its beauty and splendour." Space Adventures has previously sent three private explorers to space. In 2001, American Dennis Tito was the first space tourist. He was followed by South African Mark Shuttleworth the year after and American Greg Olsen last year. Japanese entrepreneur Daisuke Enomoto is currently training for his spaceflight scheduled for September. All flights to the ISS are on board Russian Soyuz spacecraft. Training for the flight takes six months at the Yuri Gagarin Cosmonaut Training Centre in Star City, Russia.