The term astronaut was only rarely disputed until the first "celebrity" suborbital flight in 2021. In the 1960s, pilots flying the experimental, rocket-powered X-15 jet were awarded astronaut status by the US Air Force if they flew above 50 miles (80km).

Sir Richard Branson's 2021 flight aboard his Virgin Galactic vehicle reached 53 miles (85km) - an altitude recognised by some experts as being within outer space. Bezos followed a few days later, travelling on his Blue Origin New Shepard vehicle. This flight reached about 68 miles (106km) in altitude.

Bezos has focused on reaching an altitude of about 62.1 miles (100km), one proposed boundary of space known as the Karman line, named after the early 20th-century polymath Theodore von Karman.

A 2021 post on social media by Bezos's Blue Origin capitalised on the fact that his New Shepard vehicle reached the higher boundary. The suggestion from the post was that those who travelled to the lower boundary on rival Virgin Galactic flights could have their "space traveller" status questioned, whereas those who travelled with Blue Origin could not.

This particular post did not mention the question of who is an "astronaut". However, this is how Blue Origin currently describes those who travel on New Shepard.

Indeed, some definitions of "astronaut" simply state that it is a person who has been to space. Therefore, another implication of the post - intentional or not - might be that those who travel with Bezos's company are more eligible for such a designation than those who have been to lower altitudes.

While Blue Origin calls the Karman line an "internationally recognised boundary" of space, it is far from universally accepted. Theodore von Karman wanted to separate out aeronautics (the science of flying aircraft) and astronautics (the science of space travel).

As a byproduct, he calculated the maximum altitude that an aircraft could go without reaching orbital velocity (where it would start orbiting the Earth) to be around 52 miles (84km).

A researcher and associate of von Karman called Andrew Haley was interested in space law. He established von Karman's calculation as the boundary of space. This was later raised to 62.1 miles (100km) by the world governing body for air sports, the Federation Aeronautique Internationale.

The Karman line has very little scientific rationale, however. If you ask a geologist, an atmospheric scientist and a space physics expert where the definition of space is, you will get vastly different answers.

For example, as somebody who specialises in magnetospheric physics and solar influence, I would say space properly starts at the plasmapause. This is a boundary around the Earth that's based on differences in the charged particles that exist on either side of the division. The plasmapause sits at an altitude of around 35,000 miles (57,000km).

Who is an astronaut?

The effusive reactions from the passengers, along with King's and Blue Origin's use of the term "astronaut" to describe the team members prompted a backlash online. King noted that men on similar flights hadn't been subjected to such criticism, and Katy Perry says she felt "battered and bruised" by the reaction.

Among the critics was the US transport secretary, Sean Duffy, who stated that the participants could not be astronauts as they failed to meet the Federal Aviation Administration (FAA) astronaut criteria. The FAA requirements for an astronaut are for them to be a member of crew, to contribute to spaceflight safety and to demonstrate activities essential to public safety. Their minimum altitude for "space" is the 50 mile (80km) limit.

As New Shepard is fully automated, none of the passengers could really be considered "crew members". Similarly, if you buy a ticket on a plane, you are not crew unless employed by the airline to do a job.

Would it be different if private space travellers were able to carry out scientific research during their journey? This might make them more than just passengers and potentially qualify them for the "crew" designation. Blue Origin and Virgin Galactic are actually not suited for any sort of weightlessness research. Passengers experience around 3-4 minutes of weightlessness.

By contrast, a flight on the Airbus A310 zero-G plane gives 25-30 seconds of weightlessness. When this is repeated 25-30 times, you get between 10 and 15 minutes of weightlessness in total. This avenue for carrying out research in microgravity is also open to anybody with a sensible scientific idea to test rather than just members of the rich elite.

Why it matters

But let's consider the legal dimension. Star Trek actor William Shatner flew with Blue Origin on a New Shepard vehicle in 2021. If Shatner had experienced a health-related incident during the flight, who would have been at fault?

If Shatner was an "astronaut", could it be argued that he held a greater level of responsibility for any adverse effects from the flight? If he was simply a passenger, might the company share more responsibility?

Thankfully, such a situation has not yet occurred, which means that any associated legal arguments remain hypothetical. But as more paying passengers travel on flights to space, the chances of adverse incidents increase.

Ultimately, everyone can have an opinion about whether just going into space - wherever the boundary may lie - makes you an astronaut. But there may be more to consider than a nice title.

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