So far, the company has sent five tourists to the space station, but it has also been dreaming about other destinations, including a swing around the far side of the moon.
Brin didn't appear at the company's news conference at the Explorer's Club in Manhattan, but he said in a statement that he considered his $5 million deposit an investment in the company, as well as an option to participate in a future space flight.
"I am a big believer in the exploration and commercial development of the space frontier, and am looking forward to the possibility of going into space," the statement said. Google Inc. chief executive Eric Schmidt declined to comment Wednesday, calling it a personal matter.
On each of its five previous missions, the Virginia-based company has essentially been tagging along aboard flights already scheduled by the Russians.
The sixth customer, computer game designer Richard Garriott, is scheduled to go up in October after paying $35 million for his seat. He is a vice chairman of Space Adventures and the son of NASA astronaut Owen Garriott, who sits on the company's advisory board.
For the 2011 mission, however, Space Adventures would charter an entire Soyuz space flight, with space for two clients plus a Russian cosmonaut. Russia's Federal Space Agency would still run the mission, but Space Adventures would pay for the trip and buy its own Soyuz spacecraft.
"The Soyuz to be used for this mission shall be a specially manufactured craft, separate from the other Soyuz vehicles designated for the transportation of the ISS crews," Alexey B. Krasnov, who heads Russia's manned space program, said in a statement released by the company.
Top Russian space officials had expressed doubt recently that they could continue to offer seats to tourists after 2009, citing increased demand for trips to the space station, due in part to NASA's reitrement of the space shuttle in 2010.
Krasnov said the private mission wouldn't interfere with the Russian space program or other missions to the space station. "On the contrary, it shall add flexibility and redundancy to our transportation capabilities," he said.
Kenny Todd, a NASA space station manager, said he didn't know anything about the private flight and wasn't involved in any consultations with the Russians.
Since NASA is the primary operator of the space station, "it certainly wants to have an understanding of how that's going to happen and what all would be involved," he said about the private flight.
Space Adventures President Eric Anderson wouldn't disclose how much the mission will cost, or how much a passenger might pay for a ticket. He also wouldn't say how much Brin might eventually pay for his ride into space.
As for the possibility that the company might travel as far as the moon someday, the company's managing director and co-founder, Peter Diamandis, expressed optimism.
Space Adventures has been planning for a trip in which one of its craft would circle - but not land on - the moon. Diamandis said he expects to have a customer take the first such flight within five years.
It has been advertising tickets on that flight at $100 million per seat.