Could robots really replace human astronauts?

On Christmas Eve, an autonomous spacecraft flew past the Sun, closer than any human-made object before it. Swooping through the atmosphere, Nasa’s Parker Solar Probe was on a mission to discover more about the Sun, including how it affects space weather on Earth.

This was a landmark moment for humanity – but one without any human directly involved, as the spacecraft carried out its pre-programmed tasks by itself as it flew past the sun, with no communication with Earth at all.

Robotic probes have been sent across the solar system for the last six decades, reaching destinations impossible for humans. During its 10-day flyby, the Parker Solar Probe experienced temperatures of 1000C.

But the success of these autonomous spacecraft – coupled with the rise of new advanced artificial intelligence – raises the question of what role humans might play in future space exploration.

Some scientists question whether human astronauts are going to be needed at all.

“Robots are developing fast, and the case for sending humans is getting weaker all the time,” says Lord Martin Rees, the UK’s Astronomer Royal. “I don’t think any taxpayer’s money should be used to send humans into space.”

He also points to the risk to humans.

“The only case for sending humans [there] is as an adventure, an experience for wealthy people, and that should be funded privately,” he argues.

Andrew Coates, a physicist from University College London, agrees. “For serious space exploration, I much prefer robotics,” he says. “[They] go much further and do more things.”

They are also cheaper than humans, he argues. “And as AI progresses, the robots can be cleverer and cleverer.”

But what does that mean for future generations of budding astronauts – and surely there are certain functions that humans can do in space but which robots, however advanced, never could?

Robotic spacecraft have visited every planet in the solar system, as well as many asteroids and comets, but humans have only gone to two destinations: Earth’s orbit and the Moon.

In all, about 700 people have been to space, since the earliest in 1961, when Yuri Gagarin from the then-Soviet Union became the first cosmic explorer. Most of those have been into orbit (circling the Earth) or suborbit (short vertical hops into space lasting minutes, on vehicles like the US company Blue Origin’s New Shepard rocket).

“Prestige will always be a reason that we have humans in space,” says Dr Kelly Weinersmith, a biologist at Rice University, Texas and co-author of A City on Mars. “It seems to have been agreed upon as a great way to show that your political system is effective and your people are brilliant.”

But aside from an innate desire to explore, or a sense of prestige, humans also carry out research and experiments in Earth’s orbit, such as on the International Space Station, and use these to advance science.

Robots can contribute to that scientific research, with the ability to travel to locations inhospitable to humans, where they can use instruments to study and probe the atmospheres and surfaces.

“Humans are more versatile and we get stuff done faster than a robot, but we’re really hard and expensive to keep alive in space,” says Dr Weinersmith.

In her 2024 Booker Prize-winning novel Orbital, author Samantha Harvey puts it more lyrically: “A robot has no need for hydration, nutrients, excretion, sleep… It wants and asks for nothing.”

But there are downsides. Many robots are slow and methodical – for example on Mars, the rovers (remote-controlled motor vehicles) trundle along at barely 0.1mph.

“AI can beat human beings at chess, but does that mean they’ll be able to beat human beings in exploring environments?” asks Dr Ian Crawford, a planetary scientist at the University of London. “I just don’t think we know.”

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