Russia has so far sent four commercial space tourists to the orbital station on board Soyuz spacecraft.
Nikolai Sevastyanov, the head of the Energia rocket and space corporation, said the price rise was caused by growth in the cost of materials and components used in the construction of the Soyuz spacecraft.
"Roskosmos [the Federal Space Agency] has fixed the tariffs at around $21 million, due to an increase in the prices of materials and components," Sevastyanov said.
The official said two of the three astronauts carried in Soyuz spacecraft on trips to the ISS pay for their flights. "The first one, as a rule, is a NASA astronaut, and NASA pays Roskosmos for his flight; the second is a commercial astronaut whose flight is paid for from private funds," Sevastyanov said.
He said a Russian cosmonaut commands the team, and his flight is paid for under Russia's federal space program.
Dennis Tito, an American businessman and former NASA scientist, became the first space tourist when he visited the ISS in 2001. He was followed by South African computer millionaire Mark Shuttleworth in 2002 and Gregory Olsen, a U.S. entrepreneur and scientist, in 2005.
Anousheh Ansari, 40, a U.S. citizen of Iranian origin and a telecommunications businesswoman, became the first female space tourist this year. Charles Simonyi, 58, a U.S. citizen of Hungarian descent and a key figure in developing Microsoft's Word and Excel applications, recently began training in the Moscow region's Zvyozdny Gorodok space training center for a flight in 2007.
