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Comment by Haugsevje | Hacker News Reader

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Haugsevje·

Are they as high up that it could start orbiting?

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> Are they as high up that it could start orbiting?

1. No

2. Orbit is more about speed than height. You have to get high enough that the atmosphere doesn't aggressively degrade your velocity, but the key is to hit ~8km/s, although that number changes depending on your altitude.

edit: 30km/s -> 8km/s

30 km/s is ~the speed at which Earth orbits the Sun. For orbiting Earth you just need a mere <8 km/s.

Thanks for the correction.

Orbiting has more to do with velocity than altitude.

Specifically, you need to be moving approx 10 km/s which 22,000 mph or mach 30.

You only need to be moving ~7.5-8km/s, but getting to orbit tends to take 9.5-10km/s of total delta-v due to needing to ascend, aerodynamic drag, and other losses.

Ahh yes, of course! I guess they are not high enough for geo stationary orbit?

Even if they were high enough they would just fall back to earth. There are lots of videos explaining orbit, this one looks good: https://www.youtube.com/watch?v=bcvnfQlz1x4

That's a very clarifying video! Suddenly i remembered my pre-college physics:)

Geo stationary orbit is 36000 km give or take.

Orbiting however is more about radial velocity. You are sort of constantly falling towards Earth, but you are moving so fast that you always miss it and so you end up orbiting it. A great animation on the subject: https://www.reddit.com/r/Damnthatsinteresting/comments/1btbn...

Even for geostationary you still need to gain a ton of horizontal velocity, more than LEO. You are staying over the same spot on the earth, but the earth is rotating and you need to match that same angular velocity. Being at a higher altitude you need a faster linear velocity to match that angular velocity, since you have a larger circle to travel in the same amount of time.

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