Totally crazy idea: Space launch site on Mt Kilimanjaro?

[hkultala]

Not sure why this thread is zombified, but since it is:

Why bother with existing mountains? Build your own.

Open frame towers can be built taller than the tallest buildings for orders of magnitude lower costs. For a long time, antenna masts had to be excluded from "tallest building in the world" records, because of they always won. (We don't really need tall antennas any more, so buildings are back in front.)

For the price of Burj Khalifa, and with no exotic materials, you could go many, many times taller with a simple open frame tower. Above the bulk of the atmosphere, taller than any mountain. String many such towers in a row near the equator and hang a long platform from the top like a suspension bridge, but upwardly sloping towards the east. Run a rail up the length. Launch a rocket on a sled on the rail.

Perhaps the "first stage" would be permanently mounted to the sled, braking before the end, fully and immediately reusable. "Second" stage would ignite during the loft towards apogee after it leaves the end of the platform.

Sure it would cost billions. And billions. But how much has SLS cost so far?

An antenna mast has to hold an antenna and basestation that weight maybe some tens of kilograms.
And the weight of a 100kg maintainance person.

A heavy lift rocket weighs over million kilograms.

Bulding a super-high tower for launch use MUCH more expensive than you think.

[IRobot]

For the price of Burj Khalifa, and with no exotic materials, you could go many, many times taller with a simple open frame tower.

For the price of Burj Khalifa you can launch 21 Falcon 9 disposable rockets.
What about maintenance and operational costs? Forget it, the improvement is marginal compared to the costs.

Sure it would cost billions. And billions. But how much has SLS cost so far?

Compare with commercial launch providers, not with SLS.

[gin455res]

If we consider reusable rockets, the F9 uses the thick atmosphere to slow down. What’s the fuel penalty for F9 to land at 19,000 feet?

And I always thought the point of Kilimanjaro was to rocket sled up the slope and launch already at some speed.

I'm interested if an upper-stage with perhaps 3 or 5 engines would gain any useful ISP improvement (on the way up) with a higher expansion-ratio* central landing engine, and/or any engine mass reduction** that might end up in an improvement in mass fraction.

*enabled by a high altitude landing pad
**enabled by better T/W after staging. i.e. all engines thrusting for longer after staging, instead of just the vacuum engines. Might this allow the engine to be slightly downsized?
And what constrains landing engine expansion ratio, landing air pressure or 'effective air pressure' during supersonic retro-propulsion?

[RobLynn]

19000 feet engine Isp would only be something like 5% higher than at sea level.  with air density about half of sea level terminal velocity will be approximately 40% higher, so would need something like 40% more landing fuel.