4 ms·
Almost all the energy/velocity needed for orbiting is "sideways" to the earth. Imagine needed to throw a baseball fast enough that it goes fast enough that the
by danielvf 5y ago
Almost all the energy/velocity needed for orbiting is "sideways" to the earth. Imagine needed to throw a baseball fast enough that it goes fast enough that the barely visible curve of earth falling away the same as the dropping of the baseball from gravity.
The ISS moves around the Earth at approximatle 28,800 kilometers per hour (17,900 mph).
For comparison, a bullet fired in a vacuum at only 2,000 kilometers per hour will reach about 15km up, or a reasonable ballon launch height.
- NortySpock 5y agoI have started phrasing Earth's orbital velocity as "Mach 25" to give people a sense of scale. For some reference, "hypersonic" is defined as "greater than Mach 5", and Google says the fastest rifle muzzle velocity is under Mach 4.
- SiempreViernes 5y agoYeah, hypersonic has really gotten the buzzword treatment these last few years.
- SonicScrub 5y agoJust to be clear, space vehicles are not "hypersonic". They travel these speeds outside of substantial atmosphere, where the speed of sound is undefined. Mach number is relative to local air conditions, ergo their Mach number isn't 25. It's undefined. Mach Number is a meaningless quantity. It's not accurate to say that a space vehicle travels Mach 25, only that it's speed is 25 times higher than the speed of sound at sea-level conditions. Saying this can be a useful reference to give context to the insane speed of orbital vehicles (as was done by the commenter above you). I say all this to give context about the surge in hypersonic research in recent years as being something distinctly different than achievements made in space-vehicles. It's not really accurate to say it's been given the "buzzword" treatment simply because things in space already move so fast. There's a distinct advantage (particularly for military objectives) to flying above Mach 5 in the atmosphere.