There is no line where the atmosphere stops. It thins the way a beach gets wetter towards the sea, until at some point you are in the water and nobody can say exactly when that happened. So the edge of space is not something anyone discovered. It is something people chose, and they chose differently.

For decades that disagreement cost almost nobody anything. It is starting to. Tourist rockets fly into the disputed band with paying passengers and come back down. Hypersonic military vehicles pass through it. The question of which number is right has turned into a question about astronaut wings, ticket sales and, eventually, sovereign airspace.

Three numbers, one of them legal and it is blank

The familiar figure is 100 kilometres, the Kármán line. The FAI, the world air sports records body, uses it to separate aviation records from astronautics records. A 2023 FAI presentation by Nicolas Bérend says the federation set it in 1960, with a group of scientists that included Theodore von Kármán, “for separating aeronautics and astronautics records”. The name came slightly earlier: Andrew G. Haley coined “Kármán line” in a 1957 paper after discussions with Kármán. That is what the 100 kilometre figure is, a records-keeping convention with a date on it.

The American figure is 50 miles, about 80 kilometres. The US Air Force used it for its astronaut wings, and the Federal Aviation Administration used the same threshold for the commercial astronaut wings it handed out until it ended that programme after 2021. In 2005 NASA gave civilian astronaut wings to three X-15 pilots, retired NASA pilot Bill Dana and the families of the late John B. McKay and Joseph A. Walker, acknowledging “their flights above 264,000 feet altitude”. That is 50 miles. When those flights happened only the military had wings to hand out, so civilian pilots flew just as high and got no badge. Dana’s first flight into space took him 58.13 miles above the Mojave Desert on 1 November 1966.

The legal figure does not exist. The 1944 Chicago Convention gives every state complete and exclusive sovereignty over the airspace above its territory. The 1967 Outer Space Treaty says outer space is not subject to national appropriation. Neither treaty says where one ends and the other begins, a gap a 2017 briefing to the UN space committee’s legal subcommittee lays out plainly. The committee has had the item on its agenda since 1966. Inside it the USSR repeatedly proposed 100 or 110 kilometres and the United States rejected any definition at all. The subcommittee’s 2026 draft report still carries “Matters relating to the definition and delimitation of outer space”, sixty years on.

What the physics says depends on what you ask it

Kármán himself was blunt about this. In 1961 lectures quoted in the FAI presentation he said that where atmosphere ends and space begins “is a judiciary rather than a scientific problem”, and he proposed a range, 300,000 to 400,000 feet, roughly 91 to 122 kilometres, rather than a line. The 100 kilometre figure was a round number inside that range.

Bérend’s lift-based analysis for the FAI in 2023 points to about 110 kilometres. McDowell’s argument, based on satellite drag and orbital survival, points lower.

Jonathan McDowell, an astronomer who has worked at the Harvard-Smithsonian Center for Astrophysics, made the satellite case in a 2018 paper in Acta Astronautica, “The edge of space: Revisiting the Karman Line”, free to read on arXiv. He looked at the orbits of real satellites. An elliptical orbit whose lowest point sits at 100 kilometres can survive for long periods. A satellite whose lowest point drops below 80 kilometres is “highly unlikely to complete its next orbit”. That lowest point is the perigee. McDowell argues that this makes roughly 80 kilometres a useful boundary.

Two other things happen to land in the same place. Meteors, moving much faster than satellites, usually break apart somewhere in the 70 to 100 kilometre range, a sign that the atmosphere starts to bite there. The mesopause, a boundary layer in the upper atmosphere, lies in the same broad region, though its height varies with latitude and season and is not fixed at 80 kilometres. McDowell also notes that 80 kilometres falls within 500 metres of the old 50-mile astronaut wings line. Those are separate ideas that land in roughly the same place. He suggests adopting exactly 80 kilometres as a better convention, one that fits what satellites actually do.

He is also clear about how arbitrary the field has been. Citing an earlier survey by Goedhart, he counts almost 30 different proposals between 1951 and 1962, ranging from 20 kilometres to 400. A spread of twenty to one, inside a single decade, tells you how little the physics forced anyone’s hand before McDowell checked the orbits.

The FAI took the argument seriously. In a statement on 30 November 2018 it said recently published analyses presented “a compelling scientific case” for lowering the line from 100 to 80 kilometres, and it proposed a joint workshop with the International Astronautical Federation for 2019. The workshop did not move the line. The 2023 presentation’s own conclusion is that the boundary of space “is, in any case, a matter of convention”, and the commission’s March 2025 plenary minutes record “the decision to retain the 100 km value”. The FAI has looked at 80, and has chosen 100.

Why the 20 kilometres now matter

On 11 July 2021 Richard Branson flew on Virgin Galactic’s Unity 22 to an apogee of about 86 kilometres. Nine days later Jeff Bezos flew on Blue Origin’s New Shepard past 100. Two days before Branson’s flight, Blue Origin posted that New Shepard was designed to fly above the Kármán line “so none of our astronauts have an asterisk next to their name”. By McDowell’s number, and by the US number, Branson’s passengers went to space. By the FAI’s, they did not. Virgin Galactic has kept selling tickets in that gap ever since, even through its current pause in flights while it builds its next ships. The dispute is no longer about an X-15 pilot’s badge. It is about what a company can truthfully print on a brochure.

The military version is less visible and more serious. Some hypersonic boost-glide weapons pass through the band on the way up and down; a 2023 Congressional Budget Office analysis models one US design reaching about 120 kilometres before spending most of its flight at 30 to 40 kilometres. For a vehicle passing over another country at 90 kilometres, an agreed boundary could help determine whether it had entered sovereign airspace. Neither an astronaut-wings rule nor an air sports convention settles that question. Nor would being in space put a weapon beyond the law: the Outer Space Treaty says activities there are carried out in accordance with international law, including the UN Charter. An agreed boundary could clarify the sovereignty question, although it would not by itself settle the legality of a weapon’s passage or use. It is the piece that is missing.

We put that to McDowell by email. “I think indeed the choice of a boundary does start to matter more as there is more activity in that liminal region,” he wrote, “both tourist suborbital flights and hypersonic military tests.”

So why has the world not switched to 80? “These things take a long time, decades,” he said. “I think my view is slowly gaining ground but I don’t know if it will ever win out!”

What to make of it

The honest reading is this. Physics does not hand you one number. Different physical criteria produce different answers: about 110 kilometres in Bérend’s analysis, about 80 in McDowell’s, and Kármán’s own answer was a range. Every line anyone has drawn is a convention. McDowell’s case is that 80 is a better convention than 100 because it matches what satellites actually do, and that is a fair case. But physics can inform the choice without settling what the boundary should mean in law.

What has changed is not that vehicles reached the band. X-15 pilots were there in the 1960s. What has changed is that the band now has customers, competitors and weapons in it, and each of them is in space according to one authority and not according to another. The edge of space was always going to be a decision. For decades, states managed without agreeing on it. Commercial flights and military vehicles now give that unresolved question practical consequences, without making agreement inevitable. McDowell’s own estimate is decades, if ever.

The post Nobody can agree where space starts, and the 20 kilometres in dispute now matter to astronaut wings, space tourism and hypersonic weapons appeared first on Space Daily.

On 28 November 1967, at the Woomera rocket range in outback South Australia, a six-hour countdown started on time and ticked all the way down to 30 seconds before launch. Then it stopped. A heating-cooler unit attached to the rocket had failed to eject, and everyone had to come back the next day.

I’m not a space engineer. I came across this story the way most people probably would, through a passing mention of Australia’s first satellite, and the more I read the more amazing it got. The rocket on that pad was a spare, left over from an American weapons test and given to Australia. The 45-kilogram satellite on top of it had been designed and built in Australia in about eleven months. And when it finally flew, at 2:19 the following afternoon, Australia had launched its first satellite, from its own soil, on an American rocket.

It was called WRESAT, short for Weapons Research Establishment Satellite. Here’s how it happened.

A spare rocket nobody wanted to ship home

The opportunity came out of a weapons program. During 1966 and 1967, Woomera hosted SPARTA, a joint US, UK and Australian project to gather data on the conditions nuclear warheads would face as they plunged back into the atmosphere. Ten American Redstone rockets were brought to Woomera for it, along with re-entry vehicles and an American team to fly them. If the name Redstone sounds familiar, it should. Modified Redstones launched America’s first satellite in 1958 and its first two astronauts, Alan Shepard and Gus Grissom, in 1961.

Only nine of them were needed, as Kerrie Dougherty OAM, space historian at the Australian Space Agency, notes in a paper on Australia’s early satellites. That left one spare. By then the Redstone was an obsolete rocket, and as Dougherty explained to me by email, the Americans “weren’t particularly interested in taking the spare back to the US”. Shipping it home wasn’t cheap either. As the Honeysuckle Creek history site puts it, “To send them back to the US would be a considerable expense.”

Project manager Des Barnsley, whose account is reproduced on that site, wrote that by late 1966 it was clear at least one of the ten vehicles would be surplus, and the idea of using it to launch an Australian satellite “was unofficially raised”. Who suggested it first has never been completely clear, Dougherty says. The Americans may have made the offer on their own, or WRE staff may have hinted that a rocket nobody wanted to take home would make a nice gift. Either way, the US decided it would be “a nice gesture of support to Australia” to donate it.

The catch: it had to fly before the end of 1967

The gift came with a deadline. The experienced American launch team would prepare and fire the rocket for the WRE, but only before they packed up and went home. That meant the launch had to happen as soon as possible after SPARTA wrapped up, and “definitely before the end of 1967”.

Everyone brought something to the table. The US supplied the rocket and a launch team from the aerospace company TRW “at no cost”. NASA agreed to track the satellite and collect its signals through STADAN, its worldwide network of tracking stations, “also at no cost”. The UK supported the launch operations through its long involvement with Woomera. Australia’s job was the satellite itself.

In other words, three countries lined up a rocket, a launch crew and a global tracking network, and Australia had less than a year to build something worth putting on top.

Eleven months, start to finish

Defence Science and Technology, the Weapons Research Establishment’s successor, records that design work began in early 1967 as a joint venture between the WRE and the University of Adelaide, and that the satellite was designed, developed, built and launched in eleven months. Barnsley’s own figure, written later, was “just less than twelve months”.

Whichever figure you use, the whole thing fitted inside a single year, with the team working towards a launch deadline that couldn’t move.

Not everyone thought it could be done. “There was plenty of scepticism from the US,” Dougherty told me. When I asked her what made it possible to build WRESAT so quickly, her answer was one word: “necessity!” If the satellite wasn’t ready before the US team left, the launch wouldn’t have gone ahead, or would have had to wait until a WRE team could be trained to prepare and fire the rocket themselves.

It also helped that the Australians weren’t starting cold. Barnsley put the speed down to work that had started long before the offer arrived. The WRE and the University of Adelaide’s physics department had spent years working together on upper atmosphere research using sounding rockets, small locally built rockets that carry instruments high into the sky and then fall back to Earth rather than going into orbit. WRESAT’s scientific payload, developed by the University of Adelaide, grew directly out of the instruments they had been flying on sounding rockets since 1962. The team already knew how to build the instruments. What they had never done was put them into orbit.

“With a lot of ingenuity, innovation and pragmatic decisions, they were able to have WRESAT ready to fly by November 1967,” Dougherty said.

The key people named on the history site are Barnsley as project manager, Professor J H Carver of the University of Adelaide, Bryan Rofe as officer in scientific charge, and Dr Don Woods. By Barnsley’s account, the outside contracts cost “a few hundred thousand dollars”.

Who deserves the credit?

I also asked Dougherty how she would split the credit between the two countries. She started with the Americans. The project “simply would not have occurred if the rocket had not been offered by the US”, the launch was handled by the experienced US team, and NASA provided the global tracking.

“But the rapid design and construction of the satellite itself, and its scientific payload, was an all-Australian project, albeit with advice and guidance from the US.”

Weighing it all up, this is where she landed.

“So I guess that I would have to put it at 50/50, or maybe even 60/40 in favour of the US, since their offer made the whole project happen. Australia gained entry to the ‘Space Club’ at a greatly discounted price!”

The tight schedule did come at a cost. The biggest drawback of working to the US timetable, Dougherty said, was that there was no time to design and build solar panels, so WRESAT had to run on batteries, “which severely limited its operational lifespan”.

Bumping around in the back of a truck

The satellite stayed attached to the rocket’s spent third stage in orbit, so there are two weights for it. The satellite on its own was a cone about 1.6 metres long, weighing 45 kilograms. Together with the burned-out stage it rode on, the whole package that reached orbit weighed about 72.5 kilograms and was a little over two metres long.

My favourite detail comes from the curator’s notes on Australian Screen Online. The American team was reportedly horrified to see WRESAT bumping around in the back of an open truck. The Australians’ response was that if it couldn’t survive the short ride, it was unlikely to survive lift-off.

The same notes record that very few dignitaries turned up to watch when it finally launched on the 29th.

What it did up there

WRESAT went into a near-polar orbit, so each lap carried it high over the far north and far south of the planet, without passing directly over either pole. Its path was a stretched oval, ranging from a couple of hundred kilometres above the Earth to more than 1,200 kilometres.

Its instruments measured ultraviolet light and X-rays coming from the Sun, along with a faint ultraviolet glow, called Lyman alpha, made when sunlight is scattered by the thin cloud of hydrogen surrounding the Earth. In plain terms, it was measuring kinds of sunlight that the upper atmosphere soaks up before they can reach the ground, which you can only properly study from above. Defence’s history describes the aim as improving understanding of how the upper atmosphere affects climate and weather, and helping US research programs gather physical data. The readings came back by radio on 136.350 MHz.

That was the big step up from the sounding rockets the team had flown before. A sounding rocket only spends a few minutes high enough to take these readings before it falls back to Earth. WRESAT could take them orbit after orbit, for days. Short as its working life was, Dougherty says it “obtained valuable data for comparison with the sounding rocket data already obtained at Woomera”.

With no solar panels, WRESAT simply transmitted until its batteries ran flat. According to DST, it completed 642 orbits and sent back scientific information during 73 of them, roughly its first five days. It then kept circling silently for weeks until it re-entered the atmosphere and burned up on 10 January 1968, over the Atlantic Ocean west of Ireland.

There’s one more neat footnote. As space writer Andrew LePage notes at Drew Ex Machina, the rocket that carried Australia’s first satellite was also the last known Redstone ever flown.

A donated rocket and a lot of goodwill

The successful launch brought congratulations from the US, including a message from the US Vice-President. Among them was a note from Gilbert Ousley at NASA in Maryland: “There were many sceptics here concerning the time scale, but you proved them wrong.”

Barnsley was blunt about where the whole thing came from. He wrote that “without the outstanding relationship between Australia and the US DoD and NASA the project could never have been contemplated, let alone undertaken.”

That seems fair to me. The rocket, the launch crew and the tracking network all belonged to someone else, and the window was a matter of months. What Australia brought was a group of people who already knew how to build the instruments, and who finished them inside a deadline that was set before the work began.

Dougherty summed it up better than I can. “WRESAT was a fine example of Australian technical and scientific skills, innovation and our inventive ‘make do’ tradition, made possible by the generous donation of the launch vehicle by the US.”

That’s what amazes me most. It wasn’t one country going it alone. It was three countries deciding a leftover rocket was too good to waste, and a small team in Adelaide and Woomera making sure it wasn’t.

The post In 1967 the Americans had a spare rocket at Woomera, and Australia built a 45-kilogram satellite to fly on it in eleven months appeared first on Space Daily.