5 ms·

A little off topic.. I've always wondered why NASA lunched rockets from Cape Canaveral (only 3 meters above sea level). Granted, it's a little tricky to transp

A little off topic.. I've always wondered why NASA lunched rockets from Cape Canaveral (only 3 meters above sea level). Granted, it's a little tricky to transport rockets, but surely it would have made more sense to move the operations to a mountain near the equator? How much fuel would be saved by lunching 3000 meters above sea level instead?

karkisuni 10y ago
Not much at all. Low earth orbit is ~200km so the mountain is only helping by 1.5% of the needed altitude. Altitude is not even the most difficult part of getting to orbit. Getting to the necessary horizontal speed to stay in space takes a hell of a lot more fuel than going straight up.
- velox_io 10y ago
  So say a 4000m launchpad is feasible, that's 2% of the needed altitude. While gravity will be roughly the same (yeah it's higher altitute, but there's the mass from the mountain). There is much less atmosphere* (~50% less pressure & 1/3 less of it to get through). Given that payload to fuel ratio is roughly 1:10, this does seem to add up to a significant saving. *Air pressure numbers http://www.mide.com/pages/air-pressure-at-altitude-calculator http://www.mide.com/pages/air-pressure-at-altitude-calculato...
  - karkisuni 10y ago
    you're missing the point. altitude and drag losses are nothing compared to horizontal velocity. you need to be going 7.8km/s. Per second! That takes a lot more energy than gaining any kind of altitude or overcoming atmospheric drag. It's not significant savings.
Merad 10y ago
Obligatory xkcd: https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/ In short, gaining altitude, even 3000m, isn't that hard for a rocket. The problem is that they have to go fast.
gozur88 10y ago
The short answer is being as close as possible to the equator and able to launch over an unpopulated area (like an ocean) is more important than altitude. There might be some benefit to launching off of a really tall mountain, since it would make your first stage engine more efficient, but not enough to justify the extra logistics.

karkisuni 10y ago

Not much at all. Low earth orbit is ~200km so the mountain is only helping by 1.5% of the needed altitude. Altitude is not even the most difficult part of getting to orbit. Getting to the necessary horizontal speed to stay in space takes a hell of a lot more fuel than going straight up.

velox_io 10y ago
So say a 4000m launchpad is feasible, that's 2% of the needed altitude. While gravity will be roughly the same (yeah it's higher altitute, but there's the mass from the mountain). There is much less atmosphere* (~50% less pressure & 1/3 less of it to get through). Given that payload to fuel ratio is roughly 1:10, this does seem to add up to a significant saving. *Air pressure numbers http://www.mide.com/pages/air-pressure-at-altitude-calculator http://www.mide.com/pages/air-pressure-at-altitude-calculato...
- karkisuni 10y ago
  you're missing the point. altitude and drag losses are nothing compared to horizontal velocity. you need to be going 7.8km/s. Per second! That takes a lot more energy than gaining any kind of altitude or overcoming atmospheric drag. It's not significant savings.

Merad 10y ago

Obligatory xkcd: https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/ In short, gaining altitude, even 3000m, isn't that hard for a rocket. The problem is that they have to go fast.

gozur88 10y ago

The short answer is being as close as possible to the equator and able to launch over an unpopulated area (like an ocean) is more important than altitude. There might be some benefit to launching off of a really tall mountain, since it would make your first stage engine more efficient, but not enough to justify the extra logistics.