Billionaire entrepreneur Elon Musk has fuelled hopes for manned missions to Mars but the head of the European Space Agency says it could be decades before humans walk on the red planet.
Both men were in Australia on Friday, with Mr Musk addressing the International Astronautical Congress in Adelaide as ESA director-general Jan Woerner visited WA for the first time.
In New Norcia, where one of only three ESA deep space ground stations has played an important role in communications for the Rosetta and Mars Express missions, Mr Woerner told reporters the fourth planet from the sun was an enormous challenge.
"I am quite sure humans will go back to the moon in the next 50 years and maybe also to Mars but Mars is a very special challenge. It's really hard," he said.
"The trip to Mars takes about two years and we do not have the technology right now to do so.
"Radiation is heavy - after one month or two months, you are developing some health issues - and cannot return with today's technology.
"You have to go on for two years.
"Humans will go there and I hope humans go even beyond but not in the next 20 years, let's say 15 years. There is no real concrete project for that."
Mr Musk spoke of new space rockets he hopes will be able to service the International Space Station as well as establish human colonies on the moon and Mars, and said the program could be funded by the money his SpaceX company receives for launching satellites.
He believes he could send the first two cargo ships to the red planet by 2022 with the first two crewed craft touching down just two years later.
The re-usable rockets will lift a payload of more than 4000 tons and feature 40 cabins, each capable of carrying three people, he says.
Australian National University College of Science associate professor Charley Lineweaver said the science behind Mr Musk's plan was realistic.
"The unrealistic part - the thing holding us back - has always been finding the political will to invest in space," Dr Lineweaver said.
But Mr Musk was "not a committee", he said.
"He shows what intelligence and money can do when they are combined."
Mr Woerner also welcomed Australia's plan to create its own space agency but advised against agonising over where it will be headquartered.
"Rather than going into a competition in Australia, I would say join forces and do something great out of it," he said.
"Australia, this is the land of pioneers and dreamers, and so you are the best basis for space."
