BAIKONUR, Kazakhstan?- The mothballing of the space shuttle will be mourned by many astronauts, but Russia is relishing the prospect of serving as the only carrier to the International Space Station.

That honor will earn Russia hundreds of millions of dollars in fees for ferrying US and other astronauts to the orbiting laboratory in its Soviet-vintage Soyuz spacecraft.

Some experts have noted, however, that Russia has done little to design a replacement to the Soyuz, which is more than 40 years old, and risks falling behind the US soon when NASA launches a new generation spacecraft.

Some, like veteran US astronaut John Glenn, are wary of the United States relying too much on the Soyuz and point to some technical problems with the craft in the past few years.

"What if something goes wrong with the Soyuz?" Glenn asked in a phone interview with The Associated Press. "If we have a hiccup on the Soyuz right now, we don't have a m a permanent human presence in space.

The final flight of the Apollo spacecraft, which took man on the first voyage to the moon in 1969, saw the completion of a groundbreaking scientific and diplomatic mission in 1975 to dock in space with a Soyuz.

Six years later, the shuttle made its first manned flight. Now, even the shuttle is almost gone, while the hardy Russian craft is still around.

A space shuttle left the International Space Station for the last time Tuesday, heading home in what marks the historic closure of a program that has become synonymous to many with space travel. The Atlantis was targeting a pre-dawn landing Thursday at Cape Canaveral, Florida.

Sergei Krikalyov, chief of the Russian cosmonaut training center, praised the shuttle program as a "grandiose achievement."

"It has been a big, complex and interesting program that has achieved a lot," said Krikalyov, who holds the world record for cial opportunity, Russia has regularly raised its prices for berths in what is described derisively by some as a "space cab." The Soyuz's imminent monopoly status has given Russia even more bargaining leverage.

The $56 million price that the Russian Space Agency charges NASA to send up astronauts is set to go up to $63 million per passenger from 2014. A recent contract extension totals $753 million and covers trips for a dozen NASA astronauts from 2014 through 2016.

If NASA is annoyed, then it is trying not to show it.

"When you look at inflation, when you look at what they are providing with the service and the capability, I look at it as a good investment. It's necessary," said Patrick Buzzard, NASA's representative to Russia.

James Oberg, a NASA veteran and currently a space consultant who has closely followed the Russian space program, played down concerns about excessive dependence on the Soyuz, saying the Rrtant, then funding priorities need to change. If we think we can accept some average results, then we will eventually get them."

Igor Marinin, editor of leading Russian space magazine Novosti Kosmonavtiki, is less worried. He argues that the Soyuz meets all current requirements and will only need replacing once more ambitious missions are devised.

"If Russia sets itself broader tasks, such as flights to Mars or to the Moon, flying around the Moon, or the intensive construction of a new space station, then maybe we will need a new craft," Marinin said. "But to create new technology, you need a purpose for it."