The Karman Line: Defining the Edge of Space

Recently, a newspaper quiz asked the upper layer of the atmosphere. Easy answer, the exosphere. No. Karman Line. Karman line?!?

Last month, two “pioneers” of space, Richard Branson and Jeff Bezos, lifted off their respective companies’ crafts, Virgin Galactic and Blue Origin, in attempts to reach an altitude capable of allowing several minutes of weightlessness, and observations of the curvature of the Earth, before returning to solid ground. Branson traveled 86 kilometers (53.3 miles) before gliding to a runway landing, while Bezos rocketed upwards, just reaching 107 kilometers (66.4 miles) before parachuting down.

Although it wasn’t emphasized as much with Virgin Galactic, Blue Origin actually had as its goal reaching the Karman Line, before “turning around” and coming back home. But, what is this atmospheric point? Why is it suddenly such a point-on target?

The Karman Line, by definition, is an attempt to define a boundary between our atmosphere and outer space. Its name derives from Hungarian-American engineer and physicist Theodore von Karman, who, in 1957, attempted to determine an altitude limit. In the 1960s, the Federation Aeronautique Internationale (FAI), an international record keeping body, established this boundary. But, again, why, especially as it seems different countries actually define this atmosphere/space boundary differently.

Apparently, like international waters within oceans, international airspace is important for both legal and regulatory purposes. although different countries do define this airspace differently.

The Karman Line is just a few miles above the mesosphere, jutting just enough to be within the region of the thermosphere where auroras can occur. It also seems to lie right about where the atmosphere’s gases are well-mixed, and where heavier molecules tend to occupy lower parts of the atmosphere due to gravitational separation.

But, still, what makes this part of our atmosphere so relevant, especially as it appears now that commercial air travel seems to want to use it as a guide point? Actually, regular airplanes can’t travel this high, as their wings need air to move. The thinner the air, the faster it must move to generate enough lift to stay up (remember the SST?). Any craft higher, and a plane wouldn’t be able to use lift to support itself.

But, why 100 km (62 miles)? Apparently,although Karman calculated this limit to be 275,000 feet, or 84 kilometers, he decided on 100 kilometers, because he felt 100 kilometers would be an easier number to remember.

So, does this mean the private companies will utilize this Karman Line as their constant travel goal,and not the exosphere? Apparently, only Virgin Galactic and Blue Origin know for sure.