The Vienna, Va.-based firm that arranges private trips to the international space station (ISS) now is offering a bonus spacewalk for clients willing to pay for more than a standard $20 million trip.

Space Adventures announced July 21 that future paying visitors to the space station can take a 90-minute spacewalk, or extravehicular activity (EVA), and extend their orbital trip by up to eight days for an additional $15 million.

“It’s a logical extension,” Eric Anderson, Space Adventures’ president and chief executive, said of the spacewalk availability in a July 21 telephone interview. “It’s one of the perhaps premier experiences of spaceflight.”

Paying spacewalkers would don a Russian-built Orlan spacesuit, exit a Russian-built airlock and be accompanied by a Federal Space Agency cosmonaut during the spacewalk, Space Adventures spokeswoman Stacey Tearne said. At all times the spacewalker would be tethered to the ISS, she added.

Space Adventures has brokered deals with Russia’s space agency to launch three space tourists to the ISS : U.S. entrepreneur Dennis Tito in 2001; South African businessman Mark Shuttleworth in 2002; and American scientist-turned-entrepreneur Gregory Olsen in 2005.

The fourth space tourist, Japanese businessman Daisuke Enomoto will launch toward the ISS with Expedition 14 astronauts Michael Lopez-Alegria and Mikhail Tyurin in September.

Like his predecessors, Enomoto is set to spend 10 days in space, eight of them aboard the ISS, as part of his $20 million deal with Space Adventures and the Federal Space Agency. U.S. entrepreneur and spaceflight supporter Anousheh Ansari of Texas is Enomoto’s backup.

But Enomoto will not walk in space during his flight because of the additional training needed, Tearne said. An extra month — or about 190 hours — on top of the typical six-month training would be required for spacewalking clients, she added.

Meanwhile, NASA officials said they had yet to be notified about any plan by its international partners to sell spacewalk experiences. NASA spokesperson Melissa Mathews said in a July 21 interview that the agency does have processes in place to review ISS crew assignments and spacewalk safety.

Anderson said Space Adventures has spent between one and two years studying the feasibility of a spaceflight participant spacewalk.

“They would just go right out the airlock and they would stay pretty close,” Anderson said of prospective paying spacewalkers. “They would just look around and enjoy it; it’s not something that involves an incredible amount of risk. They’re going out and they’re coming back in after an hour an a half.”

Russian space officials said they also have completed an in-depth study of the risks involved with a space tourist-staged spacewalk.

“At the conclusion of our internal feasibility assessments and after careful consideration, we have come to the conclusion that subject to the personal physical and psychological capabilities and with the completion of additional specific cosmonaut training, spaceflight participants could potentially perform an EVA,” Russia’s Alexei Krasnov, director of manned spaceflight for the Federal Space Agency, said in a statement.

Accomplished professional spacewalkers said there is no major obstacle between a space tourist and a 90-minute jaunt outside the ISS.

“There is risk involved in going outside, but if you’re going to sign up for that and accept the risk that’s fine,” said Tom Jones, former NASA astronaut and three-time spacewalker . “I think it is an incomparable personal experience.”

Jones, who serves as an adviser for Space Adventures, added that as long as space tourists have the finances, training and physical fitness to stage a spacewalk, few hurdles remain to marvel at the Earth and space from inside a spacesuit.

During a 90-minute EVA, which is the time it takes the ISS to make one complete orbit around Earth, a spacewalker would experience orbital sunrise and sunset, Jones said.

“That 90 minutes is like gold to a real spacewalker,” Jones said.