GUADALAJARA, Mexico - Though often talked about, mass space travel remains a distant possibility, US and Russian astronauts said here on Friday.

Addressing the 67th International Astronautical Congress, held in Mexico's western city of Guadalajara from Sept 26 to 30, Russian cosmonauts Sergei Krikalev and Oleg Kotov, and their US counterpart Sandra Magnus, said there are unlikely to be space shuttles for average citizens anytime soon.

"There's still a long way to go," said Krikalev, a seasoned cosmonaut who has flown 11 missions and spent more than 800 days in space.

Accessible space travel has been in the headlines as recently as Tuesday, when Elon Musk, CEO of SpaceX and car company Tesla, unveiled an ambitious plan to colonize Mars.

The fact that entrepreneurs such as Musk are getting involved in space travel, one of the exclusive realms of governments, does mean the industry is evolving, said Krikalev.

However, for space travel to become available on a large scale, scientists need to develop rockets that are more user-friendly than those we have now, he said.

"Not everyone can fly a plane, much less a spacecraft, so to be able to send thousands of people into space we need to continue to develop the technology," said Krikalev.

Extended stays in space present another challenge, said Kotov, because "our bodies are not designed to live in space."

Those planning to stay up there any length of time would have to undergo physical training, said Kotov, who has made three trips, in 2007, 2010 and 2013, and spent 526 days in total in space.