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Imaginary scenario: The US, Russia, China, Europe, India, and all the private space companies in between combine resources for a sustained space exploration program beyond Earth. They can choose any location on Earth for their new program's launch site.

Question: Energy-wise, what is the most optimal location on Earth for launching rockets?

Would a launch pad on Mt. Chimborazo ( 1° 28′ 9″ S, 78° 49′ 3″ W), be the most efficient launch pad on Earth in terms of delta-V? Or does distance from the center of the Earth not contribute much to the energy required to launch a payload into space?

Note: I realize building a launch pad on a mountain and sending rockets up to the mountain isn't very efficient itself, but I'm just curious.

techSultan
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    Reopening as per reopen votes (since aged away) and comments (since deleted as obsolete) that this question is more than just about altitude and atmospheric drag discussed in Effect of atmospheric drag on rocket launches and benefits of high altitude launch sites. It's closely related, but this one isn't a duplicate of the one suggested. I would suggest an [edit] of the question to clarify these points to avoid it being closed again in the future. Thanks! – TildalWave Apr 03 '15 at 02:06
  • Cayambe would be better than Chimborazo - Chimborazo's summit is slightly further from the Earth's center, but Cayambe's summit is further from the Earth's axis (due to its closer proximity to the equator - in fact, the equator runs across Cayambe's southern flank) than Chimborazo's, and, hence, moves faster as the Earth rotates. – Vikki May 03 '20 at 22:59

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The equator enjoys an advantage as it's moving about .47 km/second. Other points on earth's surface are moving this speed * cos(latitude). So for example Kennedy Space Center at 28º degrees latitude moves .47 km/s * cos(28º) which is .42 km/s. So the equatorial French Guiana Space Centre enjoys a .05 km/s advantage over KSC.

As for mountain tops like Chimborazo:

6.4 kilometers is about 1/1000 of earth's radius. So if we choose earth radius as our unit of length, it's 1 vs 1.001.

Gravity acceleration is $GM/r^2$. $1/1.001^2 = .998$. So gravity advantage is about .2%.

So called centrifugal force is $\omega^2r$. $\omega^2*1.001$ gives a .1% advantage over $\omega^2*1$.

These are negligible advantages for a huge price tag.

A little more interesting is the rarefied mountain top atmosphere -- about half that of sea level. Still doesn't justify the expense of building a launch pad atop a high mountain. You need to get up to around 100 km before the air's thin enough to do the major burn to achieve orbital velocity.

It is also good to have a launch pad on an eastern seaboard so the booster stage doesn't fall on a populated area. Unfortuneately there are people living downrange from Chimborazo.

Somalia is on the equator and has an eastern seaboard. I've often thought this would be an excellent location for a space center. But I believe political instability is the show stopper in this case.

SE - stop firing the good guys
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HopDavid
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  • "A little more interesting is the rarefied mountain top atmosphere.." Don't forget that engines are tuned (typically) for a particular pressure. I doubt tuning them to the more rarefied conditions on top of a mountain would make any more difference to the minimal gains you quoted, but it is worth noting. – Andrew Thompson Mar 19 '15 at 05:13
  • @AndrewThompson but you need to overcome less drag because you are already above half the atmosphere – kim holder Mar 19 '15 at 16:44
  • @AndrewThompson The Merlin exhaust velocity is 3 km/s in a vacuum and 2.73 km/s at sea level. I believe the exhaust velocity would be somewhere between those numbers for half an atmosphere. – HopDavid Mar 19 '15 at 23:31
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    @brillig the ship still needs to climb about 90 kilometers to do the main burn. Most of the ascent loss is gravity loss during the ascent, not from atmospheric drag. – HopDavid Mar 19 '15 at 23:32
  • Just curious, does the ascent loss due to gravity loss during the ascent happen because one is going slow to a) avoid the drag loss, or b) avoid high mechanical stress induced by drag? – uhoh Nov 05 '16 at 01:07
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    @uhoh I'm no expert but I think slow ascent is mostly due to thrust to weight ratio. We could boost T/W by adding more rocket engines but that would consume more of the very slim dry mass fraction available. – HopDavid Nov 07 '16 at 01:00
  • @Hohmannfan Thank you for the correction! I feel like a dunce making boneheaded arithmetic errors. – HopDavid Nov 07 '16 at 01:02
  • @HopDavid If you are up for a challenge, there is a bounty on that bi-tangential transfer question again. I hope it can finally be solved. – SE - stop firing the good guys Nov 07 '16 at 01:19
  • If the global powers were really, really, really, really, really interested in this type of program and equally interested in cost efficiency, then I'm sure they would band together to "invest" in a "solution" for Somalia's political instability. – Ellesedil Feb 16 '18 at 22:21
  • Gravity loss during ascent is a function of how quickly you ascend. It's not that rockets can't have a higher T/W ratio, it's that they're designed not to because the drag and mechanical stress due to drag would be too much. Maybe Elon Musk's Boring Company could make a convenient train tunnel to the top of a large mountain near the equator. Lifting mass via train will be be orders of magnitude cheaper per kg*m than lifting it via rocket. – Jonathan Ray Sep 13 '18 at 02:13
  • but it would probably be cheaper and more convenient to do air launch to orbit, like SpaceShipOne. – Jonathan Ray Sep 13 '18 at 02:38
  • When I added nozzle backpressure (atmospheric ISP effects) to my trajectory optimizer, it immediately started to try to move Kennedy up to height of 10,000m to try to get above the bulk of the atmosphere before I nailed it down to sea level and stopped giving it any choice in the matter. Based on that I would hazard a guess that Everest would beat out Chimborazo because cutting out the bottom 10,000m of atmospheric soup vs only 6,000m of it, will beat the incredibly slim advantage Chimborazo has gravitationally. – lamont Feb 02 '20 at 07:27
  • @lamont (checking it out...) About 9 km for Everest. That is a substantially thinner atmosphere. Also latitude is 28º, fairly close to the equator. So it's moving .9 the speed of Chimborazo. I believe you're right. Everest is better than Chimborazo. – HopDavid Feb 02 '20 at 17:45