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Lynx ilustration
The Mark 1 version of XCOR’s Lynx suborbital spaceplane will fly to an altitude of 60 kilometers: is that high enough for it to have been considered to be in space? (credit: XCOR)

How high is space?

It seems, at first, like a simple question. After all, space is, well, high. Really high. You know, higher than airplanes fly, up where satellites orbit. For most of the Space Age, that Potter Stewartesque definition—we know something is in space when we see it—has been satisfactory. Indeed, not making a precise definition of the “boundary” of space was a deliberate step by some spacefaring powers to avoid debates and disputes about airspace and overflights.

However, the emerging commercial suborbital spaceflight industry might press the issue in the next several years. Part of the emphasis will be on marketing: how high does a suborbital vehicle have to go to for its operator to claim that its occupants flew in space? Another push could come from a regulatory standpoint, as countries determine how to regulate such vehicles—or if they should even be considered spacecraft at all.

While those who fly on the Lynx will get to experience the key attributes associated with suborbital spaceflight, can they say that they’ve been in space if they’ve “only” flown to an altitude of 60 km?

Those tensions were evident during some of the presentations at the “Space Tourism: A New Industry in the Making” forum hosted by the Royal Aeronautical Society in London on June 30. They first emerged after a presentation by Andrew Nelson, chief operating officer of XCOR Aerospace, about his company’s Lynx suborbital spaceplane. One of the distinguishing characteristics about the Lynx is that—at least in its Mark 1 iteration—its peak altitude is only 60 kilometers. That’s well short of the 100-kilometer mark commonly called the Kármán Line (after legendary aerospace engineer Theodore von Kármán) used by the Ansari X PRIZE as the minimum altitude competing vehicles had to fly to. It also falls short of the 50-mile (80-kilometer) altitude used by US government agencies, including the FAA, for awarding astronaut wings.

While those who fly on the Lynx will get to experience the key attributes associated with suborbital spaceflight, including weightlessness, seeing black sky, and looking down on the Earth from an extreme (from a conventional viewpoint) altitude, can they say that they’ve been in space? That was the question raised after Nelson’s presentation by Carolyn Wincer of Virgin Galactic, who, after confirming that the customer reservations XCOR and its partner, RocketShip Tours, said, “So it’s not actually a suborbital flight?”

“No, it is a suborbital flight,” Nelson responded. “You can talk to George Nield about what a suborbital flight is,” he added, referring to the associate administrator for commercial space transportation at the FAA, who was in the audience at the event. The Commercial Space Launch Amendments Act of 2004 provided definitions of a suborbital vehicle and suborbital trajectory in the US, neither of which makes any reference to altitude.

“I’m interested in hearing what your definition is of a space flight,” Wincer said.

“Well, it’s what everyone else’s definition is. It’s getting into space,” he said, then he paused for a beat. “Well, it depends on who you talk to. It’s 50 miles for the United States Air Force, it’s 60 miles for most people, and just recently I saw they wanted to move it up to 75 or 80 miles. There’s some new body that wants to move it up even higher so that none of us will be flying into space if they get their way.”

It wasn’t clear what Nelson was referring to, but it may have been a reference to the proceedings of the meeting of legal subcommittee of the Committee on Peaceful Uses of Outer Space (COPUOS) earlier this year. The subcommittee addressed the issue of the “definition and delimitation of outer space”, as it has for many years without significant progress. One section of that report, though, does suggest what at least some members of that subcommittee have in mind:

The view was expressed that current and foreseeable civil aviation operations would not exceed altitudes of 100-130 km, where there was a potential danger of collision with numerous spacecraft. In this connection, that delegation proposed that the boundary between airspace and outer space be established in that range.

A boundary at the lower end of that range—should any agreement on the issue ever be reached—would be compatible with most of the suborbital vehicles currently under development or in the planning stages. The upper end, though, might well be beyond the reach of most, if not all, of those vehicles without significant modifications or even complete redesigns.

“Personally, I believe that this activity today is basically an aeronautic activity,” said Farand of suborbital spaceflight.

Similarly, a paper by several representatives of the European Aviation Safety Agency (EASA) presented at a conference last year discusses using 110 kilometers as the boundary for space, noting its heritage dating back to old Soviet proposals at COPUOS and its use by “many” space law practitioners. That boundary could end up affecting the design of vehicles intended to just pass 100 kilometers altitude: SpaceShipOne crossed that boundary only once, on its final, prize-winning flight, when it flew to 112 kilometers.

The paper adds that what it calls “sub-orbital aeroplanes”—defined as winged vehicles, and thus excluding expendable or reusable vertical take-off vehicles—that derive support from the atmosphere “for the largest part of their flight” are considered aircraft by EASA, and thus regulated as such, with only additional complications if such vehicles fly into space—however that is defined.

Some European officials have even questioned if suborbital spaceflight is really, well, spaceflight, at least from a regulatory standpoint. “We’re still wondering from the agency’s point of view if this is truly a space activity,” said André Farand, head of the Launchers and Exploration Legal Matters Office of ESA, at the London conference. ESA has, despite that question, developed a policy on commercial suborbital spaceflight last year, whose theme is one of “cautious interest and informed support”, including contributing to the development of regulations governing such flights in Europe.

“Personally, I believe that this activity today is basically an aeronautic activity,” he continued. “It’s taking place in the airspace of a given country. The fact that it may go for a few minutes above 100 kilometers is altitude is accessory to a larger activity taking place in airspace. I believe that this would not justify the application of space law, at least as we know the activity today.”

Even if regulators never select an arbitrary altitude at which space “begins”, altitude won’t immediately go away as an issue that suborbital vehicle operators will have to deal with, at least in terms of the perceptions of potential customers and the broader public of what constitutes flying into space. Will people consider vehicles that fall short of some altitude boundary—de facto or de jure—as not providing a “real” spaceflight experience?

“In international law, if you want to be called an astronaut, you have to go, at least for a certain period of time, into outer space,” Farand said. “Obviously, people will be interested in buying space tourism services if they can be assured that they will become truly an astronaut.” Operators, he added, need to ensure that they “go to the right place for the right amount of time” so that their customers qualify.

As the saying goes, “size isn’t everything”, and in the case of commercial human suborbital spaceflight, altitude isn’t everything. Companies offering such flights may do well to emphasize other aspects of the experience—weightlessness, the view, etc.—than an altitude, as some already have. Perhaps the philosophy of that late Supreme Court justice was right, and we’ll know a spaceflight when we see—and experience—one.


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