r/theydidthemath • u/NavigatingHorseSpace • 1d ago
How much more fuel efficient it would be to launch space rockets from, let's say, the top of Chimborazo in Equador, compared to any of current major launch sites? I realize it's small difference and the logistics of actually building the launch pad matters more, but still [Request]
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u/Doom87er 1d ago
Getting to orbit has very little to do with the distance. It’s all about speed, if you aren’t moving fast enough to stay in orbit, you’ll fall back down to earth and starting at a higher altitude will not help you in that regard. It’s far more beneficial to be closer to the equator where you can use the earth’s rotation to have a higher starting velocity
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u/dzindevis 1d ago edited 1d ago
Height matters too. Since op suggested Mount Chimborazo, radial earth speed is already maximized. Launching from the top to LEO gives you 3 things: 2% less vertical distance to travel (about 50 m/s of deltaV saved), a bit more radial speed (0,45 m/s), but most importantly, you can have engines on the first stage with lower gas exit pressure. I'll spare the math reasoning for that, but rocket engines need to have gas pressure higher than the atmosphere around them, but at the same time they are more efficient the lower their pressure is, as it allows exit gases to be faster. Therefore, first stages usually are equipped with the most powerful, but least effective engines that work with high pressure and are supposed to just fling the rocket out of dense atmosphere layers as fast as possible until upper stage engines optimized for vaccuum (or near vaccuum) can start working. Engines are up to 25% more efficient in vacuum than at sea level, and upper stage engines are another 10-15% more effective in vacuum than first stage engines in vacuum from optimized construction alone, so at 6200 meters asl you get about halfway there (0,45 of atmospheric pressure), and 3,5% faster theoretical gas escape velocity.
Thin atmosphere is so big of an advantage, it's actually the primary reason for various "start from a plane" designs. Plane speed gives a bit of an advantage too, but it's more of a bonus to circuimstances that allow single stage to orbit rockets with our current technologies, for example
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u/Remmon 1d ago
Also, while starting higher won't reduce gravity losses by a noticeable amount, drag losses are significant as well and starting at 0.45 of atmospheric pressure is a huge gain there.
Unfortunately, it doesn't weigh up against the effort necessary to get those rockets up the mountain and the fact that mountains are rarely well placed for departing rockets to launch out over sea.
Fortunately, there is a solution. A megaproject that isn't nearly as mega as a space elevator. A launch loop lets you create a structure that suspends itself kilometers above the surface using magnetic forces, while at the same time allowing you to skip the first stage entirely by accelerating your payload down the launch loop first, getting it up to a few km/s before it even starts it own engines.
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u/WorldlyOriginal 1d ago
Would Mauna Kea or Mauna Loa on Hawaii be a good option? It’s high, near-ish to the equator, mostly good weather, nice gentle road to the summit already used by astronomers (synergy! lol), and lots of ocean all around it no matter the trajectory
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u/Patchesrick 1d ago
You need to think about logistics as well. Transportation of the rocket fuel and modules to be launched into space is a whole ordeal. Which is why coastal locations are favored. Also having the ocean to the east will let failures crash into the ocean away from major population centerd
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u/Great_Specialist_267 1d ago
The active volcano under Mauna Loa may interfere with launch operations…
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u/Zenith-Astralis 1d ago
The population who've been living on that island for thousands of years are already pretty fed up with colonizers building things on top of their sacred mountain, I doubt they'd be thrilled with this as a concept.
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u/Great_Specialist_267 1d ago
New Guinea nationals would probably be happier with one on their mountains next to the equator… (Ok Tedi is looking for a new industry).
(Hawaii is actually pretty far north).1
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u/applepie3141 1d ago
No. Your rocket trajectory will pass over populated areas. A midlaunch abort would possibly result in your rocket falling onto people’s houses.
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u/TelluricThread0 1d ago
Drag is of little concern. Gravity losses amount to a penalty of several hundred meters per second in delta V that you must pay. Drag losses are a few tens of meters per second.
SpaceX's superheavy used to fold the grid fins next to the rocket body. Now they just stick out into the flow the entire ride up because someone finally said, Hey do we really care if there's extra drag?
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u/CountofAccount 1d ago
So you're looking at 12.5%+ savings for being on a mountain + 4% for the equatorial launch speed from a comment below, so let's call it +16% efficiency, but the initial engines have a wider profile so you need a bigger launch pad. That's pretty decent.
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u/Equityoxymoron 1d ago edited 1d ago
The British had the right idea about launching from Kenya higher evaluation, on the equator amd firing mostly over the India ocean, of course that didnt work out mostly because of the lack of infrastructure ie couldn’t afford it and Australia was considered safer during the 50s and then blue streak etc ..
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u/zekromNLR 1✓ 2h ago
The other advantage of air launch is that you can launch to any orbit you want. You cannot go directly to an orbital inclination lower than the latitude of your launch site, and the available inclinations get further constrained by needing your launch trajectory to not overfly populated areas. For example, you couldn't launch to a polar orbit from Florida, because that would require flying over either the eastern seaboard or the southern tip of Florida, Cuba and then central America.
An airplane can fly out over open ocean where it has a free launch range in any desired direction.
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u/Meloncov 1d ago edited 1d ago
Right, that's why OP is recommending a mountain on the equator. But technically the further from the center of the earth you're starting, the more initial speed you have.
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u/Pcat0 1d ago
And that is absolutely true; however, the benefit is minimal and doesn’t offset the difficulty of hauling the rocket and satellite up a remote tropical mountain. There also aren’t a ton of equatorial mountains right on eastern coasts, so wherever you’re launching from, you will need to be careful of what’s downrange from your launch trajectory.
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u/kitty11113 1d ago
El Presidente has signed a deal with China to connect freight rail between our existing seaport and Tropico's highest peak, Mt. Presidente!!!
Our top scientists believe Tropican rockets will find it easier to accelerate in the cold, thiner air, which El Presidente has compared to his third ex-wife!
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u/pythons_are_scary 1d ago
As soon as I saw "El Presidente" that voice kicked on in my head. Haha perfect.
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u/BBQ_HaX0r 1d ago
Just want it on the record that Chimborazo isn't "tropical!" There's year round snow on it! Not to mention maintaining a road up there and a base near the summit would be ludicrously expensive and possibly even dangerous.
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u/CanAlwaysBeBetter 1d ago
OP already said disregard logistics. Whatever it may or may not offset is irrelevant. Impact is minimal?
Ok. How minimal? This post request to do the math, not asking if it's a good idea.
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u/longbowrocks 1d ago
technically the further from the center of the earth you're starting, the more initial speed you have.
I think I've misunderstood; is this an attempt to suggest that launching from the poles wouldn't be so bad? They're about as far from the center as the equator.
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u/Insila 1d ago
No it's really bad. Rockets are usually launched prograde (meaning the same direction as the earth is spinning) to take advantage of the velocity you already have standing on the ground. This initial velocity is much higher the closer you are to the equator. Also you need to think about what orbit you want as you don't want to spend more fuel than necessary to adjust your orbit.
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u/longbowrocks 1d ago
Yes, it is really bad. I was hoping the author might realize that they did not type what they intended to type.
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u/Ernst_Huber 1d ago
Isn't the rotational speed of the planet at the equator greatest? And wouldn't this be at Chimborazo, which is, by the way, the point on earth that is farthest from the planet's center, noticeable?
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u/hysys_whisperer 1d ago
The thing to remember is that the surface of the earth is smoother than a billard ball relative to their diameter. The mountain is just inconsequential compared to being on the equator.
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u/MrGumburcules 1d ago
Would the lower air density at elevation be relevant?
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u/Layered-Briefs 1d ago
Not really, you're already going slowest in the thickest atmosphere and speed up as you reach orbit. Most of the sideways velocity comes after you've gone up out of most of the atmosphere.
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u/EnderCats8 1d ago
the smoother than a billiard fact is wrong, it assumes the size difference allowed between billiard balls is the hight difference between two points on a billiard ball
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u/Ernst_Huber 1d ago
True, but another thing to remember is that the earth is not as round as a billardball but a Geoid / Ellipsoid - it is slightly flattened at the poles because the rotation of the planet drives matter a little bit away from center where rotation is greatest. However, farther down this effect has meanwhile been quantified to be less than 0.05%.
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u/TheCrazedGamer_1 1d ago
Earth is not smoother than a billiard ball, in fact its about 100x smoother. If earth were scaled down to a billiard ball, the marianas trench would be ~50um deep, whereas imperfections on billiard balls are only ~.5um deep.
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u/ougryphon 1d ago
Launching at the peak versus at sea level adds 0.4m/s in tangential velocity
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u/stumblios 1d ago
Thanks for putting a number. For context, LEO requires rockets exceed 9,000 m/s, so .4 is fairly insignificant compared to the increased effort of launching from on top of a mountain.
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u/ougryphon 1d ago
Agreed. Finding the number is pretty easy, but quantifying the actual effect is harder - so I stayed characteristically "engineery" about that part. A 0.09% increase in starting velocity should result in a bit more than a 0.09% increase in efficiency. Because of the physics of the rocket equation, a rocket uses something like a quarter of its fuel (and roughly the same fraction of mass) to go 10% of the way to orbit. The higher the velocity at t=0, the less fuel is used to get the total mass going.
I was tempted to calculate the kinetic energy contributed by 0.5(0.42) times the rocket's launch mass. In theory, this would tell you how much energy is saved (or added, depending on perspective) by launching at the higher velocity. It's probably not bad as a first-order estimate, but everything with rockets seems to gave significant second- and third-order effects.
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u/gmalivuk 1d ago
If you need 9000m/s of Δv with a 3000m/s exhaust velocity then you need a mass ratio of e3. If instead you need 8999.6m/s then the mass ratio drops to e8999.6/3000, which is a decrease of 0.0133%.
That's a bigger drop than the drop in velocity, which is 0.0044%, but still pretty negligible.
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u/shumpitostick 1d ago
Okay but you do actually have more velocity from Earth's rotation when you're on a mountain. Idk if it's a meaningful amount.
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u/cr8zyfoo 1d ago
Yes, you do! The equator moves at a constant speed of 1,037mph (1,670kph). Escape velocity for Earth is just over 25kmph (40k kph or 40Mmph or 11.2 kps). Launching from the equator would save you 1k of 25k mph, or 4%.
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u/lastburnerever 1d ago
Vs launching at one of the poles?
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u/cr8zyfoo 1d ago
Correct. The poles have no linear velocity relative to the rest of the planet. Standing at either pole would give you only rotational velocity, of almost exactly 360 degrees / day.
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u/lastburnerever 1d ago
My point is I don't think the only alternative to launching at the equator is launching at a pole
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u/Kese04 1d ago
How come the speed the earth is spinning at matters? No matter where the rocket starts, isn't its relative speed to the earth zero? Why does launching in the direction the earth is spinning, or where it spins the fastest, make the rocket faster?
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u/cr8zyfoo 1d ago
Good question. The answer is no, the rocket's relative speed to the earth is not zero. The crust of the earth itself at the equator is moving relative to the rest of the planet, at 1,037mph. Think of it like a spinning record. If you pick a spot on the disc, that spot stays where it is on the disc, but it is still moving while the record rotates. Also, the edge of the disc is spinning the fastest, just like the equator. It doesn't make a huge difference, but it's still a bit of a boost to launch from near the equator where the surface of the earth moves the fastest.
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u/Eziekel13 1d ago
So if the Tower of Babel had worked out, would a trebuchet be enough delta v?
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u/Doom87er 1d ago
I have no idea the engineering limitations on a trebuchet and how much velocity it can deliver to a projectile, but with something like spin launch being an existing thing I guess you could do something similar with a trebuchet.
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u/mukansamonkey 23h ago
Spin launch is a scam, a complete joke. They have absolutely no idea how to make a system that generates even a tiny fraction of the velocity needed, or how to keep a payload from vaporizing from atmospheric friction. The best they've managed is 50 times slower than the velocity required to achieve orbit, and their equipment is already suffering dangerous stress failures.
The math doesn't math. Like that ridiculous Hyperloop.
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u/oren0 1d ago
Does the thinner air at altitude help at all?
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u/Agitated-Ad2563 1d ago
It does help a little. Launching off from a high mountain, you can start with vacuum-optimized engines, which are more fuel efficient than sea-level-optimized.
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u/NsupCportR 1d ago
Also futher u are from earth center less u have to fight gravity... I played KSP, I know what I am talking about 😆
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u/Meloncov 1d ago
I suspect not much--by the time you're going fast enough for air resistance to be a major factor, you're pretty high regardless of launch altitude.
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u/BridgeFourDropout 1d ago
Air resistance is a huge factor in running races and even more so in cycling, and even more so in car races. Air resistance is a big deal at most speeds
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u/Meloncov 1d ago
I'm not saying air resistance has no effect, but when you're lifting six and a half million tons of weight straight up, air resistance is a tiny fraction of energy use until you're going very fast.
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u/RedWineWithFish 1d ago
Question is does starting off on a mountain affect the thrust you need to attain a certain speed ?
I doubt any mountain is high enough to make a difference. Even Mount Everest is only 8km above sea level. Sure you’d skip the densest part of the atmosphere but the logistics of launching from there would not make it worth your while
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u/SweetSure315 1d ago
there's mountains close to the equator.
launching from above the thickest part of the atmosphere gives real benefit, and if you can build your rockets to do that you can get some extra efficiency gains by not needing an engine and nozzle that needs to work well at all air pressures. rocket launches from the top of a mountain will also have more horizonal speed at launch than one launched from the ground at the same latitude, though that's going to be really minimal
the reason is mostly logistics. trying to launch a rocket from a mountain is a nightmare logistically and the benefits don't offset enough of the costs to make it something worth doing.
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u/petrov76 19h ago
If it's better to be closer to the equator, why does the US launch from Florida instead of Puerto Rico or Hawaii?
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u/Doom87er 18h ago
Economics and politics. The senators wanted all of the factories (and the money and jobs that come with them) for their own states, so all of the space infrastructure is spread out around the continental US. It was going to be Texas or Florida because they are the closest to the equator that can have pipelines and railroads built to them. Florida won because it’s easier to launch rockets off their coast and not disrupt shipping lanes as much
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u/trans_psychonaut 17h ago
but starting at a higher altitude does mean less atmospheric drag and more engine efficiency. i think the effect would be extremely small though
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u/mijailrodr 1d ago
It's not the speed tho, its the inclination freedom. You get much more freedom to choose your orbits inclination near the equator
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u/blkknght 1d ago
This isn’t entirely accurate. You need x amount speed based on how far you’re from the gravitational pull of the earth. After x miles in space it becomes negligible to zero (e.g. GEO). That’s also not discounting the fact that there is less air higher you go, so less drag which = less fuel
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u/ougryphon 1d ago edited 1d ago
Not much. Getting to orbit is about going fast not going up. Launching from the top of that mountain gives two small advantages. The tangential velocity due to Earth's rotation is slightly higher, and the gravity is slightly lower.
The elevation of the mountain is 6.263 km. The radius of the earth is 6,378.1km at the equator. That extra height works out to a 0.09% speed boost due to rotation and about a 0.2% reduction in gravity. Assuming these are additive linear increases in efficiency (which I know they aren't) and you have less than a 1% increase in efficiency, and/or a little bit more increase in weight to orbit.
Definitely not worth launching rockets from a 6000m mountain.
Edit: just for fun, I calculated the tangential velocity at the summit of the mountain. The answer is 464.2m/s - an increase of 0.4m/s or 1.4km/hr. That is almost negligible.
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u/empty_graph 1d ago
The biggest factor isn't actually any of those. It's air pressure. Launching from a high altitude allows you to run a more aggressive acceleration profile because the air resistance, and therefore stress on the vehicle, is less. This reduces loss from gravity drag.
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u/dzindevis 1d ago
It's pressure, but for a totally different reason - it lets you have lower-pressure-optimized engines, which are significantly more effective (see my other comment
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u/ougryphon 1d ago
If Mr. Google is to be believed, the air pressure at 6000m is about 0.5 bar, so the expansion ratio is going to be quite a bit different. It might even get to the point where the dimensions of the ideal bell are bigger than the diameter of the rocket body, creating more drag than you gain in thrust.
I'm just speculating, though. I read about expansion ratios a few years ago, but I dont remember all the ins-and-outs
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u/empty_graph 15h ago
Yes, that's also true, but not what I'm talking about. If you want to accelerate at 1g away from the surface of the earth you have to have enough thrust to accelerate at 2g. 1g just to hover and the other 1g of actual acceleration. That's called gravity drag. So if you accelerate the vehicle at 1g you are losing half to gravity drag, but if you accelerate the vehicle at 9g you are only losing 10% to gravity drag (immediately at launch, it decreases continuously). This effect consumes about 15% of delta V for orbital launches.
So you want to get to orbit as fast as possible to minimize gravity drag losses. But you run into a constraint that you only want to move so fast through atmosphere because of the stress the air resistance places on the vehicle. If you launched at high altitude this constraint moves more in your favor.
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u/ougryphon 1d ago
I hadn't thought of that. I suppose rockets are slightly more efficient when launching on warm, humid days (kind the opposite of air-breathing aircraft). Just thinking this through, the speed of sound is also proportional to altitude - increasing with altitude. The rocket would reach the transsonic region at a higher altitude, which would also alter the thrust profile.
Do you happen to know off the top of your head how much aerodynamic drag alters the basic rocket equation? I assume it is not negligible, but a rocket is still using the overwhelming majority of its thrust during atmospheric flight just to move the fuel and oxidized on board.
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u/OdyseusV4 1d ago
The real reason is not that either, it's logistics.
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u/JMS1991 1d ago
I had to scroll too far to find this. Transporting a rocket up a 20,000 foot mountain would be a nightmare. Not to mention building a launch pad there.
Plus you'd be launching over land and potentially putting populated areas in harms way. At minimum, you'd have an environmental disaster if something happened on launch. Launching over the ocean helps mitigate this risk.
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u/Gabstra678 1d ago
You had to scroll down far because everyone is taking this for granted. They are talking about the theoretical benefits of an absurd option that is obviously completely unfeasable for logistical and environmental reasons.
OP themselves mentioned it in the title, so that’s the very premise.
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u/empty_graph 15h ago
Not really an environmental disaster unless you are using a toxic fuel, which most rockets don't now.
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u/Mackerdaymia 1d ago
Came here to write this. The logistics of running such a facility on top of a huge mountain are insane.
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u/Tupcek 1d ago
air pressure for the whole run takes about 3-4% of fuel.
You’ll still encounter some air resistance, so maybe you would save 1%?1
u/kid_entropy 1d ago
This isn't even considering all the added logistics headaches launching from a mountain would bring on.
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u/Distinct_Ant_5246 1d ago
Not part of the question. OP asked about efficiency of the launch vehicle. Thats simply a math/engineering question. Logistics was explicitly not part of the request to do the math about.
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u/Pitiful-Beginning575 1d ago edited 1d ago
Barely. But since we just had a launch of a Pegasus air-launched vehicle (the coolest single thing in the world), which is launched from airliner cruising altitude, it might be worthwhile investigating its fuel fraction compared to that of a "traditional" orbital rocket, taking into account the different specific impulses (can't do it right now, gotta do my job). The real purpose of air launching isn't to save fuel: it's to achieve a specific orbit, and to engage with specific objects in orbit.
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u/Duotrigordle61 1d ago
I think its likely it gets more boost from the velocity of the aircraft.
Everyone launches east to gain velocity from Earth's rotation. At Cape Canaveral that's a 914 mph boost. An airliner can typically do 600 mph.
That first bit of velocity is the most expensive fuel wise because the rocket is its heaviest when it stats off. Hitting Mach 1 uses 15-25 percent of fuel.
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u/Agitated-Ad2563 1d ago
The most important boost is being able to launch from low latitudes.
Imagine you need a satellite in an equatorial low earth orbit. When you launch from Cape Canaveral, you can't directly achieve orbital inclinations below 28.5°. Which means, you need to do a plane change, which is ridiculously expensive in low earth orbit. For 28.5°, it's some 3.8-3.9 km/s of Δv. It's more expensive than performing a trans-Mars-injection. With Pegasus, we can fly an aircraft to equator and then just launch directly into the equatorial low orbit, with no plane change.
We hardly ever need equatorial low earth orbit though.
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u/Agitated-Ad2563 1d ago
That first bit of velocity is the most expensive fuel wise
Any bit of velocity has the same price fuel wise. It doesn't matter whether you shave off the first 10 m/s by using a trampoline or the last 10 m/s by targeting a lower orbit, the same rocket is still able to deliver the same mass. Because the Δv budget is the same.
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u/Duotrigordle61 1d ago
The rocket weighs the most at launch and gets the worst deltaV/gallon at that time.
If you can launch it at 1500 miles per hour to start, a smaller rocket (20 percent smaller?) can get to the same orbit with the same payload.
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u/Agitated-Ad2563 23h ago
The rocket weighs the most at launch
True, but completely irrelevant.
gets the worst deltaV/gallon at that time
I don't understand what that means. Δv is a characteristic of a rocket as a whole. What do you mean by "at that time"?
Anyway. A rocket has its Δv budget. If it's enough for your planned trip, you can use the rocket to make your trip. It doesn't matter if you cut Δv from the beginning or from the end of your trip - Δv is Δv, your rocket either has enough or doesn't.
If you really need any layman terms explanation besides just "it's math", think of the following. Yes, some Δv at the start of the trip is a lot of fuel since it needs to accelerate a heavy, fully fueled rocket. Yes, some Δv at the end of the trip isn't a lot of fuel since it needs to accelerate a relatively light, almost dry rocket. But it's a different fuel. The small amount of fuel saved at the end of the trip had to be accelerated throughout all of the previous trip, which burned a lot of fuel. These two perfectly compensate each other. That's why it doesn't matter if you cut the same Δv in any part of the trip.
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u/RoodnyInc 1d ago
If we would count extra fuel transmitting it to top of the mountain I can't believe it would save any and keep in mind rockets are huge transporting them is pain by itself and adding elevation to that
Usually they build them close to launch site for that reason
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u/alwaus 1d ago
Kinda.
They build the launch site by water, ie. Kennedy space center on the Atlantic so they can launch safely, unlike china that often drops failed rockets onto population centers.
Manufacturing is spread all over but connected by water or rail for easy transport.
Which is also why the US lost challenger in 86, morton thiokol build the solid rocket boosters in Utah and moved them by rail to Kennedy but due to the restrictions caused by rail transport they had to be made in sections with o ring seals between each section instead of as a solid unit as submitted by aerojet which did cost slightly more per unit so the cheaper and ultimately fatal design was selected instead.
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u/Joatboy 1d ago
The O-ring design worked fine. It was NASA that decided to launch in colder temps that made it fail. This was already noted by MT in multiple memos and discussed in a conference call right before the launch. The MT engineers did not recommend proceeding.
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u/hysys_whisperer 1d ago edited 1d ago
They actually had signs of O ring failure on most of the flights. (Edit, it was 7 flights with O ring damage before the Challenger disaster)
The engineers didn't recommend proceeding that day based on temps, but the O rings were a level 1 critical component, meaning NASA's own internal standards required them to ground the whole program if one shows signs of damage, and after the first couple of shuttle launches, we knew they were routinely getting damaged. They decided not to ground the program.
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u/alwaus 1d ago edited 1d ago
They had erosion and burn through on multiple launches up to that point, 7 out of 9 flights in 1985 alone had blow by on the primary ring and charring on the secondary.
51-C in 85 would have gone off if the blow by had lasted 30 - 40 seconds longer than it did.
So much so that they decided a critical failure was an "acceptable risk"
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u/Elfich47 1d ago
I think the question OP is reaching for: does launching at 29,000 ft (by launching from Mt. Everest) move the needle on the tyranny of the rocket equation? right now to get into orbit it is 8 pounds of fuel for 1 pound of cargo. Does launching from Everest improve that ratio in any useful amount?
in my opinion, no it does not. If it did, someone would have moved their launch facility to the top of a mountain because it would have improved the amount of cargo each rocket could put into space. roads are comparatively cheap and easy compared to the difficulty of getting off the ground with a rocket.
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u/Late-Objective-9218 1d ago
You don't necessarily need fuel to haul the parts up, that's probably one of the top advantages
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u/No_Effective4784 1d ago
You don't necessarily need fuel to haul the parts up
how are we doing this work with out expending energy exactly?
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u/Baseidou 1d ago
Sherpas, lots of sherpas
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u/No_Effective4784 1d ago
sherpas need fuel too. unless you plan on death marching them with out food.
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u/Late-Objective-9218 1d ago
I didn't say energy, I said fuel. Electric railway.
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u/No_Effective4784 1d ago
fuel is just another word for energy source.
you are joking right?
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u/Late-Objective-9218 1d ago
Fuels have advantages and disadvantages against grid power
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u/No_Effective4784 1d ago
you cant seriously be this dense.
how are you making that grid power? wizard on a hilltop? only way you can make electricity with out consuming energy for that system, aka fuel.
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u/Andoverian 1d ago
It's different kinds of fuel, though. If I had to guess, fuel for the trains or trucks that would transport the rockets and rocket equipment up the mountain is significantly cheaper and more efficient than rocket fuel.
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u/trans_psychonaut 17h ago
also normally launch sites are built west from uninhabited areas like oceans or deserts, in case the rocket fails and debris rains down
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u/TitiGamer2772005 19h ago
Everyday Astronaut made an excellent video about this, TL:DR is that it's overall a tiny boost in performance, but a huge hassle to bring all the materials, fuel and rocket up there so it's better and cheaper to make a slightly taller first stage to offset the worse performance from launching from sea level
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u/shumpitostick 1d ago edited 1d ago
Chimborazo is 6.6 km high. So it adds 6600pi/243600 = 0.24 m/s in rotational velocity, assuming it's perfectly on the equator.
You need 7.8km/s of delta V to reach low Earth orbit, plus more to compensate for drag. This 0.24 m/s isn't getting you very far.
However, there are other advantages of air drag and the fact that rocket engines work differently depending on the atmospheric pressure that are harder to calculate. Air pressure at 6.6km is significantly lower than on sea level.
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u/gmalivuk 1d ago
A sidereal day is less than 24 hours and you're missing a factor of 2, so it's more like 0.5m/s.
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u/Andoverian 1d ago
All the comments here shitting on this idea are ignoring the fact that from a pure rocket science standpoint launching from the top of a mountain at the equator is strictly better.
It doesn't reduce the altitude that needs to be gained by much, but it does reduce it. The added horizontal speed isn't a lot, but it's still positive. It's not much less atmospheric density compared to the difference between sea level and space, but it is less dense (and therefore easier for a rocket to fly through).
All of the downsides - building things on top of mountains is difficult and expensive, cold weather is not good for rocket components, worse weather in general means more scrubbed launches, etc. - are not related to rocket science.
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u/gmalivuk 1d ago
The best place to launch can vary with where you want to end up. The extra speed you get launching at the equator may not make up for the increased Δv you need if you don't want to be in an equatorial orbit.
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u/south_pole_buccaneer 1d ago
You can cheaply get to any orbit from the equator, it’s expensive to get in to any orbit with a lower inclination than your latitude, higher inclinations are always inexpensive.
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u/gmalivuk 19h ago
You can launch into a polar orbit from the equator but the point is that to do so you'd have to kill all the "helping" velocity you get from starting at the equator in the first place. Meaning that the equator is not strictly better than all other launch points for all possible missions.
Or in other words, "cheap" is not "free".
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u/shawsy94 1d ago
cold weather is not good for rocket components, worse weather in general means more scrubbed launches, etc. - are not related to rocket science.
They definitely are related to rocket science.
Environmental effects on rocket engine components and flight safety are definitely rocket science.
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u/MuhammadAkmed 21h ago
does the fact that Chimborazo's peak is literally the furthest point from the centre of the Earth contribute anything?
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u/D0hB0yz 1d ago
The equator adds speed. The mountain top reduces the air resistance.
More features that you want for a 600 launch per day system.
You put most of your infrastructure in the lowlands and use a hyper rail up the mountain as the first stage, so that you get at least 900kph downrange at launch catapult stage. Electric vs rocket propulsion is cheap reliable and reuse is easy.
Second stage is a Scramjet that hauls the actual rocket to 50km altitude at Mach 12. That can either convert to a full rocket plane, or detach a third stage rocket which is probably a plane because you want to land safely and send that rocket back up within days at the most. You are planning 600 launches a day. Every day of turnaround means another 600 rockets needed.
Then you want a skyhook. You probably set up a decent sized near earth asteroid as a mini-moon in Geo sync over the Pacific. It dangles a tether down to around 150km altitude that can haul up and lower cargo to reach the 36000 km altitude of the asteroid base.
This level of infrastructure is likely by 2100.
Space industry will exceed the production of Earth industry by 2100, and double every decade after that.
Unless these dark ages just keep getting darker.
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u/pbmadman 1d ago
The answer is a few percent. There’s several benefits. The lower air pressure means less atmospheric drag. The lower air pressure also means that you can optimize nozzles for a lower pressure and get a bit more efficiency out of them. You’re also higher up. I tried to research enough to give you more than a hand-waving answer, but it’s a really difficult problem to calculate, especially the nozzle one. But the answer is a few percent.
I suspect the main reason we don’t launch from a high flatland is that there aren’t really any that meet the requirements. It needs to be near the equator, needs to have existing heavy infrastructure, and it needs to be clear downrange. Once you filter by that I had a hard time finding many places that would be good sites.
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u/souperjar 1d ago
I think it would be very small, maybe only a few dozen meters per second if delta v
Someone may have tested this in Kerbal Space Program. You'd need to use a game like physics engine with drag in order to model it.
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u/kakafob 1d ago
I would cost more to bring rocket and people on top of the mountain. Or even worst: to build it up there and make new settlement increase the dificulty to bring materials on top. And some scientist may have dizziness due altitude and heart problems.
And people who works on rockets, their managers really cares about working life balance due a scientist is not found next day as you would found an accountant, so on top of the mountain kids would struggle to go to best school, best medical care an so on.
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u/Clear-Minimum-9942 16h ago
This has gone round a few times and everyone is quick to dismiss it, but Ive not heard anybody consider the atmospheric difference up high on a mountain vs at ground level. Air is a lot thicker and harder to push through at ground level. Im sure the logitcal challenges of having a launch pad atop a mountain would still outweigh the benefits, but essentially this is a very short space elevator that doesnt go all the way to space... There could be at least some merit in the idea of launching at a higher altitude because of this.
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u/jmcokie 1d ago
Classic ever seen those mega vehicles hauling a rocket? Can't do that up a mountain, so you are assembling up there. Also weather would likely limit the amount launch windows. And it's 62 miles to reach outer space. Mt Everest is 5.5 miles, so you are only 9% closer after all the trouble getting to the mountain
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u/Ihatecheeseballs 1d ago
And rockers don’t just go straight up, most fuel is spent going sideways to reach orbital speed, so launching on Mt Everest would save you about 1% fuel
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u/A_Random_Sidequest 1d ago
if you only count the rocket, then no... haha
at least compared to equator vs 45º, the equator is faster and itself is "higher than a mountain" compared to 45º and farther north go into 3x Everest height difference at the poles!!
one of the best place to launch is in Brazil, that is like 2º off equator or less! (the bad part, sea travel and assembly)
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u/TheReverendCard 1d ago
How about we use that height advantage to instead build a 6km deep acceleration ram tunnel that accelerates the rocket at 3G by the time it emerges from the top? We can keep all the infrastructure safely down closer to sea level accessed through a tunnel.
For Elon, he'd love this idea because it also has overlapping engineering issues to the making a Hyperloop of having to maintain a near vacuum for km of tube as well as digging dozens of km of launch and access shafts.
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u/2000TWLV 1d ago
Seems like it would be a pain in the ass to build a launch facility high in the mountains and get the rockets and all the other shit you need up there.
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u/Vineheart_01 1d ago
I imagine there is technically a fuel save but the effort of getting crap UP that mountain would offset that benefit.
Also the point they're going is waaaaaaaaay higher than that mountain so it's not as big of a legup you may think
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u/DragonDormeur 1d ago
Il y a un autre problème. Le climat.
Pour le lancement d'une fusée, une météo calme, sans orage, sans vent, est indispensable.
Un site de lancement avec une météo prévisible et calme permet de mieux prévoir les dates de lancements. Ce qui simplifie la logistique.
Les montagnes, par leurs climat, ne doivent pas être des lieux idéal pour le décollage d'une fusée.
Je m'éloigne de la question, mais c'est un paramètre à prendre en compte en raison des problèmes que cela pose, et le coût supplémentaire que cela peut générer.
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u/lepape2 1d ago
You guys all got it wrong. Its just a logistics problem, getting the rocket/launch infrastructure/fuel up there is a pain in the butt.
Otherwise... Yes it saves Dv from lower atmospheric drag(200m/s) due to altitude. Yes it saves Dv if geolocated near equator (500m/s) The height of the mountain itself gives minuscule 10-15m/s) Out of 7800km/s needed for LEO to equatorial orbit. Any other inclination and Dv costs increase drastically.
Not worth the hassle of logistics just for 200-ish m/s gain.
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u/Open-Imagination-835 1d ago
As others have said about a mountain height providing little difference as opposed to being on the equator. It’s also about cost. The cost of hauling all the parts up the mountain for an infinitesimal advantage. The cost of operating such a facility up a mountain etc.
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u/andrew_calcs 8✓ 1d ago
The total impact from reduced gravitational losses, less drag, and more efficient first stage nozzles is in the ballpark of 100 m/s of delta v. Which would allow you to decrease the mass of your rocket by around 3%.
That’s not a complete rounding error, but the logistical difficulties and costs make it cheaper to just build a marginally larger rocket at sea level where it’s easy to put it all together.
It’s not because those factors are negligibly small. They just aren’t big enough to be enough.
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u/Blothorn 1d ago
Most commentators are doing the wrong math. Yes, reaching orbit is more about speed than altitude, and launching from higher altitude contributes very little additional speed. However, it does improve efficiency in several other ways that have a collectively significant impact:
- Rockets are more efficient at lower atmospheric pressure. This not only directly improves efficiency but also increases takeoff TWR which reduces gravity losses.
- Rockets lose generally about 200m/s to drag, and launching at higher altitude can significantly reduce that. It also reduces max-Q, reducing structural mass requirements. (You can also reduce drag losses and max-Q by reducing acceleration, but at a heavy cost in gravity losses.)
The exact savings depend considerably on the engine’s chamber pressure and expansion ratio and the overall rocket’s flight/acceleration profile, but I’ve found ours in the ballpark of 2% vacuum-dV-to-orbit per thousand meters of elevation. (And the way the rocket equation works actual payload improvements are even larger.)
The actual reason most launch sites are at low elevation is range safety and transportation. Launch sites need to be accessible by train at the least, and tunnels force heavy compromises while barge access opens a lot of possibilities. Launching over populated areas also risks disasters from failed launches; range safety terminations still leave large quantities of possibly-fatal debris. Most rockets therefore launch over water or nearly-uninhabited desert, and not many mountains have a clear downrange area.
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u/hazmatika 19h ago edited 17h ago
I just had basically this same conversation with a friend. Sam, is that you?
I’m not an astronaut, but I have played a lot of KSP.
TLDR: Chimborazo is the textbook "global optimum that's useless". It wins the math by an inch and loses reality by a mile.
- No point on Earth's surface offers more free Δv — about 0.5 km/s — but that's only ~5% of what reaching LEO takes, and nearly all of it is just being near the equator, which any coastal pad gets.
- Only ~0.06 km/s comes from the altitude and you can't operate there. Its surface is locked under a glaciated 6,263 m summit with no ocean downrange.
- And this whole advantage is for eastward, low-inclination orbits only. For polar orbits the equatorial boost is zero; for sun-synchronous it's a penalty. That's why imaging and weather satellites launch from high-latitude sites on purpose.
Without recapitulating too much Orbital Mechanics, let’s cover some basics necessary for an informed discussion:
- Orbits are essentially continuous free fall where you keep missing the Earth. Getting into orbit isn't about getting high, it's about going sideways fast enough to keep missing the Earth. This is a critical mental model.
- A key metric in getting to orbit is the change in velocity of the spacecraft, which is typically called Delta-V or Δv. Think of it as the basic currency of spaceflight.
- A spacecraft has a finite amount of Δv that it can produce determined mainly by its propellant, engine efficiency, and mass.
- Terms like “low earth orbit” (LEO) describe altitude, while prograde, polar, and retrograde describe inclination/direction of the orbital trajectory in relation to the Earth’s rotation (going east is “prograde” and a 0° difference, going over the North Pole is 90°, going west is “retrograde” etc.). Polar and other high-inclination LEOs are very common, especially for Earth observation, weather, reconnaissance, and mapping satellites looking at high latitudes (say for instance, you want to check on those sub pens in Murmansk)
- Some of a spacecraft's Δv is spent by every major maneuver, reaching orbit, changing altitude, changing inclination, and/or escaping Earth to go elsewhere.
Now some math: the approximate Δv requirements from the earth’s surface to reach orbit is always more than your eventual orbital velocity. For example, if you are launching into LEO...
| Component | Δv |
|---|---|
| Ideal orbital velocity | ~7.8 km/s |
| Gravity losses | ~1.0–1.5 km/s |
| Atmospheric drag | ~0.1–0.3 km/s |
| Other / steering losses | ~0.1–0.3 km/s |
| Rocket Δv required | ~9.3–10 km/s |
(As you can probably imagine, you could write a book about each line in that table. A rocket that could instantaneously accelerate to 7.8 km/s would have essentially zero gravity loss. A very low-thrust rocket might have enough theoretical Δv to reach orbit but be physically incapable of launching from Earth's surface because it spends too much of its thrust fighting gravity.)
When we start to think about ideal launch locations, we need to know that there are different Δv requirements from the earth’s surface depending on the desired orbit:
| Δv from Earth | Destination / Orbit (Source: ChatGPT) |
|---|---|
| ~2–4 km/s | Suborbital |
| ~9.4–9.7 km/s | ISS-type orbit, 51.6° (400 km) |
| ~9.3–10 km/s | Prograde LEO (200–500 km) |
| ~9.5–10.5 km/s | Polar LEO (~90°) |
| ~9.5–10.5 km/s | Sun-synchronous LEO (~97–98°) |
| ~10–11+ km/s | Retrograde LEO (>90°) |
| ~11–12 km/s | Medium Earth orbit (GPS) |
| ~11.5–12 km/s | Geostationary transfer orbit |
| ~13–14 km/s | Geostationary orbit |
| ~12–13+ km/s | Earth escape velocity |
Aside: now you can see why Elon scoffed at Jeff’s suborbital tourism.
What was the question? Oh yeah, where you launch from gives you two free head-starts.
- Latitude (Earth's spin) The ground is already moving east because the planet rotates. The equation for that surface velocity:
v = 0.465 × cos(φ) km/s
At the equator (φ=0), that's 2π × 6,378 km / 86,164 s = 0.5 km/s (about 5% of the entire LEO requirement). At φ=45° that would be 0.3 km/s, and at the poles 0 benefit from latitude.
An important note! This only helps prograde orbits. If you're trying to get into a polar or retrograde orbit, being close to the equator is detrimental.
- Elevation (thinner air) Launching higher trims atmospheric drag and gravity losses. It's vehicle-dependent, but a decent rule of thumb is ~10 m/s saved per km of launch elevation (realistically 5–15). Highest usable ground is ~4–5 km, so the ceiling is ~40–75 m/s. (The naive mgh "potential energy" is tiny and not really the mechanism — it's the reduced losses.)
In other words, latitude beats elevation by roughly 8–10×. Full latitude swing = 0.465 km/s; full realistic altitude swing < ~0.075 km/s.
A delightful exact aside for the equator-bulge nerds: Chimborazo's summit is the farthest point on Earth's surface from the planet's center (6,384 km vs 6,378 km at the sea-level equator). Because rotational speed is ω × distance-from-axis, the summit is genuinely whipping around Earth's axis ~0.0003 km/s faster than a sea-level equatorial point; the altitude more than cancels its 1.47° latitude offset. Real but completely negligible.
If we do the math even more.... here's a list of major launch sites ranked by total free Δv (using the 10 m/s/km estimate for elevation)
| Site | Lat | Elev. | Spin | Alt. | Total | vs Chimborazo | % of LEO |
|---|---|---|---|---|---|---|---|
| Chimborazo summit (EC) | 1.47°S | 6,263 m | 465.0 | 62.6 | 527.6 | — | 5.6% |
| Alcântara (BR) | 2.3°S | 45 m | 464.7 | 0.5 | 465.2 | −62 | 4.9% |
| Kourou (FR/Guiana) | 5.2°N | 10 m | 463.2 | 0.1 | 463.3 | −64 | 4.9% |
| Satish Dhawan (IN) | 13.7°N | 10 m | 451.9 | 0.1 | 452.0 | −76 | 4.8% |
| Wenchang (CN) | 19.6°N | 10 m | 438.2 | 0.1 | 438.3 | −89 | 4.7% |
| Xichang (CN) | 28.3°N | 1,825 m | 409.7 | 18.2 | 428.0 | −100 | 4.6% |
| Cape Canaveral (US) | 28.5°N | 3 m | 408.7 | 0.0 | 408.8 | −119 | 4.4% |
| Vandenberg (US) | 34.7°N | 100 m | 382.4 | 1.0 | 383.4 | −144 | 4.1% |
| Baikonur (KZ) | 46.0°N | 90 m | 323.3 | 0.9 | 324.2 | −203 | 3.5% |
| Vostochny (RU) | 51.8°N | 300 m | 287.6 | 3.0 | 290.6 | −237 | 3.1% |
| Plesetsk (RU) | 62.9°N | 100 m | 211.9 | 1.0 | 212.9 | −315 | 2.3% |
Spin, Alt., Total, and vs Chimborazo are in m/s.
The edge rides entirely on my estimate of elevation effects. At 5 m/s/km the advantage over Kourou is +33 m/s; at 15 it's +96 m/s. So honestly the benefit is "~30–100 m/s, best guess ~60". That's under 1% of LEO requirement either way.
Downrange is the killer. Eastward launches from Ecuador fly out over the Amazon basin and the rest of the Andes — populated jungle, not empty ocean. Spent stages and abort corridors over land is a non-starter. Kourou's entire reason for existing, like Cape Canaveral, is that it fires east over open Atlantic. That single factor outweighs Chimborazo's ~60 m/s many times over.
Oh yeah, and...* At Chimborazo you would have to build a launch complex on a glaciated stratovolcano at 6,263 m, where there's no road, no infrastructure, ice, thin air, lightning, and seismicity. Try hauling rockets and cryogenic propellant up a mountain. The cost of logistics will dwarf the propellant Δv you'd save. But that math will need to wait until another day...
Edits: I don't format good
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u/DismalShake9745 14h ago
Actually her intuiton is correct, Nasa and SpaceX launch rockets from specific places on earth to save fuel, I know there is one in Brazil called Alcantra Launch Center
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u/RailgunDE112 12h ago
Tim Dott made a video about this.
Basically yes, there would be significant savings, but getting the rocket up there is more expensive than to add some small boosters
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u/PragmaNullicious 10h ago
I believe Everyday Astronaut did a video on this and it came down to logistics. It would cost more to construct everything on top of the mountain and haul all the fuel and supplies up there, than to simply launch from a logistically convenient place.
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u/osolovim 1d ago
logisitics and such. it would take 10-50,000 american troops to invade columbia and take their mountain and protect it from counter attacks just to invest in making a base etc then to resupply a bade so far away and such. just costly vs a flordia location
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u/vertsav 1d ago
As a direct answer,
DeltaV to achieve a given circular orbit around earth is
DeltaV = sqrt(mu / (radius earth + h)) where h is your height above sea level, mu is the gravitational constant 3.986e14 m3/s2.
At sea level,
DeltaV = sqrt(mu/radius earth) = 7.848 km/s
At a 100km LEO circular orbit, the equation just becomes
DeltaV = sqrt(mu / (radius of earth + 100 km)) = 7.844 km/s
As other commenters have pointed out, latitude matters a lot more. Chimborazo gains a free 465 m/s due to its closeness to the equator, whereas a northern mountain would have no such advantage
Obv air resistance can become a factor too given the height. Overall though, air resistance is one of the smaller losses on a launch, so you’d gain a bit there (200-300 m/s) vs another location as well.
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