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What’s a suborbital flight? An aerospace engineer explains

“Suborbital” is a term you’ll be hearing a lot as Sir Richard Branson flies aboard Virgin Galactic’s VSS Unity winged spaceship and Jeff Bezos flies aboard Blue Origin’s New Shepard vehicle to touch the boundary of space and experience a few minutes of weightlessness.

But what exactly is “suborbital”? Simply put, it means that while these vehicles will cross the ill-defined boundary of space, they will not be going fast enough to stay in space once they get there.

If a spacecraft – or anything else, for that matter – reaches a speed of 17,500 mph (28,000 km/h) or more, instead of falling back to the ground, it will continuously fall around the Earth. That continuous falling is what it means to be in orbit and is how satellites and the Moon stay above Earth.

Anything that launches to space but does not have sufficient horizontal velocity to stay in space – like these rockets – comes back to Earth and therefore flies a suborbital trajectory.

Why these suborbital flights matter

Although the two spacecraft launched in July 2021 will not reach orbit, the accomplishment of reaching space in private spacecraft is a major milestone in the history of humanity. Those aboard these and all future private-sector, suborbital flights will for a few minutes be in space, experience a few minutes of exhilarating weightlessness, and absolutely earn their astronaut wings.