A Mountain of Myths about Space Launch
Altitude |
Density |
Year |
Record |
|
km |
atmos. |
|
|
|
0.0 |
1.00 |
|
Standard density 1.225 kg/m³, varies |
|
8.848 |
4.07e-1 |
1953 |
Everest, Highest Mountain |
|
37.65 |
4.62e-3 |
1977 |
Highest Airbreathing Manned Aircraft |
|
41.4 |
2.66e-3 |
2014 |
Highest Altitude Manned Balloon |
|
53.0 |
5.86e-4 |
2002 |
Highest Altitude Unmanned Balloon |
|
99.0 |
5.49e-7 |
|
"in" the atmosphere, national airspace |
|
100.0 |
4.58e-7 |
|
Legal Boundary of Space |
|
101.0 |
3.83e-7 |
|
"out of" the atmosphere, international |
|
160.0 |
1.01e-9 |
|
rapidly decaying single orbit |
|
200.0 |
2.1e-10 |
|
practical short term orbit |
|
400.0 |
2.3e-12 |
|
International Space Station |
orbit decays 2 kilometers per month |
Space is high vacuum. Zero lift for wings or balloons. The legal boundary of 100 km is convenient but entirely arbitrary; it is twice as high as any atmospheric vehicle can fly or float, and half as high as any practical satellite can orbit. Tourist suborbitals to 100 km (like SpaceShipOne ) are not practical spacecraft, merely dangerous and ostentatious displays of wealth, like climbing Mount Everest without the exercise.
Real space is orbit, and the lowest practical orbit is 200 km. Even that is far too low for a large, high-drag object like ISS, which requires frequent reboost to compensate for air drag, even though the air is 2 parts per trillion of the density at sea level. That is a difficult number to grasp - a volume of "ISS vacuum" as big as AT&T Stadium in Texas (104 million cubic feet, 3 million cubic meters) would fit in 7 cubic centimeters, half a tablespoon, if compressed to sea level density.
If you were suddenly transported to 400 km altitude and dropped from there, you would not orbit the Earth, you would fall down, your vertical speed increasing rapidly.