Nasa should leave human spaceflight to billionaire adventurers such as Jeff Bezos and Elon Musk, a top astronomer said.
Martin Rees, the UK’s Astronomer Royal, said AI technology made human beings increasingly redundant for scientific missions.
But, he said, the world should be celebrating the “crazy adventurers” who fund their own missions.
Recent flights into orbit by Mr Bezos and Britain’s Richard Branson signalled the dawn of a privately funded space race.
It rivals efforts by Nasa and other government-funded space programmes, which once held a monopoly on space travel.
“I’m not an American taxpayer, but if I were, I would be against spending any Nasa funds on human spaceflight,” Mr Rees told the Aspen Security Forum.
“I don’t think it’s got any practical use for mining, for assembling structures or indeed for exploration. That can all be done by robots and not by people.
“I think we should leave that to the private companies ... we should cheer on the crazy adventurers who want to go into space.”
Nasa has a stated aim of returning US astronauts to the Moon by 2024, more than half a century after the last Apollo mission.
Mr Bezos chose the 52nd anniversary of Apollo 11 to make his 10-minute flight to the edge of space last month, launched by a rocket known as New Shepard.
He was beaten by a week by Virgin boss Richard Branson, who hopes to start taking paying customers to space next year.
Meanwhile, SpaceX founder Elon Musk wants to go to Mars and has spoken of 2024 as the earliest possible date for a human flight.
Experts at the Aspen Institute event raised concerns about a space collision that could knock out satellites and affect critical infrastructure on Earth.
Defence experts fear that rogue states or other groups could cause worldwide chaos by exploiting such a scenario to bring down hundreds of satellites.
The so-called Kessler Effect predicts that collisions caused by space junk would trigger a chain reaction of further collisions, making it virtually impossible for spacecraft to navigate.
Ankit Panda, a fellow at the Carnegie Endowment for International Peace, said efforts to regulate space lagged behind the pace of commercial activity.
“As large as space is, Earth orbits are getting more crowded,” he said. “We don’t really have a good international framework to ensure the sustainability of space.
“Dealing with this as we have other domains on Earth, including the maritime domain … that is going to be the first step to effective international governance.”
Kerry Buckley, an air and space specialist at the Mitre corporation, compared the management of space with the way that air traffic is controlled on Earth.
“We’re going to have strong indications that the early stages of this crowding is going to have a real impact on launch windows,” she said.
Mr Rees said preventing collisions in space was an urgent concern and predicted that the military threat would become serious over time.
“Of course we depend on GPS and the rest of it, and I think the vulnerability of those is really scary,” he said.