The Edge of Space
A story has been going around about a group of students that managed to send a balloon “to the edge of space” on a shoestring budget. While there, it snapped pictures of the Earth, the atmosphere, and space.
This story is factually incorrect and misleading. This balloon did not make it to the edge of space.
First, balloons rely on buoyancy. You can’t be buoyant if there’s no atmosphere in which to be buoyant.
Second, as the atmosphere gets thinner, so too does the pressure exerted on objects grow lighter. This is why, for example, boiling water requires different temperatures at varying altitudes. A balloon is inherently reliant on the gas pressure contained within its membrane. If the pressure inside is too great in comparison to the equilibrating pressure outside, such as one finds when one gets very high in the atmosphere, the membrane will break. In layman’s terms, the balloon pops.
Third, the “edge of space” has a (somewhat arbitrary) definition in the form of the Kármán Line. This line is 100 kilometers (about 62 miles) above sea level, and was the threshold for the Ansari X prize. The student balloon made it to an altitude of 17 miles, 45 miles short of the Kármán Line.
As a corollary to the above, though, the “edge of space” is a somewhat arbitrary notion. The atmosphere does not simply “end” at any point. It grows thinner and thinner until it is infinitesimal and indistinguishable from the general particulate density of “empty” space. There’s no true number for this. This misconception is similar to the idea that astronauts are in “zero G.” In fact, the gravitational pull from Earth on orbiting astronauts is not greatly reduced from that pulling on you right now. The difference is that they are in a continuous state of free fall (the accurate and preferred term) due to their orbital pattern and a handful of other factors. Earth’s gravity doesn’t attenuate to near-0 (for an average human of 70 kg / 150 lbs.) until you get three million kilometers away (0.05% normal gravity). By comparison, the moon is a scant 380 thousand kilometers away.
I don’t in any way want to belittle the accomplishment of the students in question. They did a great and admirable thing. My issue is with how it’s being reported. Scientific achievements are almost universally treated incorrectly and inaccurately by media outlets and it sucks.
Mirrored from Blog-at-McC3D.