tl;dr: for a rocket it is waaaay more important to go fast than to go high. and earth rotates very slowly, so going higher doesn't make you much faster.
iirc correctly it should still be less costly of you start way northern and still start eastwards. you'd get a high inclination and changing inclination is definitly cheaper in space.
I might be wrong and starting directly into 90 degrees is actually the cheaper way, but I can imagine that at least using some momentum from the earth's rotation should be better than actively working against it
Inclination changes are extremely expensive until you get to a very high orbit. An inclination change is changing your direction, so the faster the spacecraft is moving the more expensive it is. Low orbits work by having extremely high speed, so it is consequently extremely expensive to change their inclination once they're launched.
To throw some numbers at it, the delta V for a circular orbit inclination change is 2*v*sin(delta inclination / 2). If you launched East from Kodiak Alaska you'd get into an orbit with a 58 degree inclination, so you'd need to plane change 32 degrees. At a LEO velocity of 7.8 km/s that works out to 4300 m/s of delta V.
By launching due east you'd get a boost to get into LEO of 2*pi*(1/day)*(radius of earth)*cos(58 degrees) = 250 m/s (plus you don't have to spend the few dozen m/s of extra delta V to burn off that eastern motion for a direct polar launch).
There are theoretically some launch points and destination orbits where launching East and doing a plane change makes sense, but they're pretty edge case. For example, from Kodiak if your target orbit was polar and had a radius of about 2 * 109 meters (about 5x the distance to the moon) then the plane change would be so cheap that you may as well launch East. That isn't a particularly popular altitude to launch a satellite to, though. There may be a less extreme scenario where the plane change makes sense--I didn't do the math to find the best case scenario since a more equatorial launch needs a bigger plane change but gets more delta V at launch--but they should all be pretty high orbits like this.
4.7k dV is really extreme and yeah, I didn't think about the LEO speeds needed.
So what's the actual use case here? Launch directly to 90° or rather something like 80° due to the fight against the rotation and then either say "good enough" or correct the last bit of inclination? Or just don't plan with 90° in the first place?
Yes, ideally you launch straight into an orbit that's as close to your end goal as possible, then do some fine tuning when you get there.
The more accurate your launch vehicle is the less fine tuning you have to do. When JWST was launched one of the news stories was that the launch was more accurate than planned so the vehicle would have more fuel left over for station keeping. That was a big deal since that's what will likely determine the lifespan of that telescope.
The desired orbit is generally determined by the mission that the satellite is setting out to do, then from there a launch site is chosen to make that orbit the easiest. Modestly inclined orbits will tend to launch from close to the equator for the free delta V from Earth's rotation, while polar (or nearly polar, e.g. the slightly retrograde sun synchronous orbit) tend to launch more or less due south from sites like Vandenburg or Kodiak.
Where you do have to just launch east and perform a plane change is for uninclined orbits, most notably geostationary orbits. Any orbit you launch into will be inclined by at least as much as your launch latitude, so unless you're launching from exactly the equator you're going to wind up with some inclination to deal with. Fortunately this mostly only matters for GEO and that's a relatively high orbit--orbital speed of "only" 3.1 km/s. If you launched there from Canaveral then you're looking at "only" 1.5 km/s of delta V to come into plane. There also might be a bi-elliptic shenanigan you could pull here (raise apogee far beyond the target, perform the plane change at apogee where speed is virtually zero and plane changes are virtually free while raising perigee to target, then circularize at perigee); I haven't done that math in a long time.
The other big exception to launching straight to your target orbit is when the target orbit is something like a trans-lunar injection or an interplanetary transfer. Here it's technically a tiny bit more efficient to burn straight to the follow-up orbit, but it's lower overall mission risk to launch into a temporary orbit, check that everything still works after launch, then proceed on to the subsequent maneuvers. This can give much wider launch windows than a direct launch to the transfer orbit, lowering risk of bad weather or a launch hiccup derailing the entire mission.
You gotta protect yourself legally. That's why I always send home permission slips before I take my students on a dangerous field trip into someone's body or into space or something. I like to trick the parents into thinking it's a normal field trip.
We are outside the bus, doing a space walk. Next thing we knew a god damn Tesla roadster blaring fucking David Bowie came out of nowhere and hit Arnold and launched him into deep space. We couldn't catch him in time.
In orbit around the equator you are always over the equator. In polar orbit the earth is rotating under your orbit. If the orbital velocity/period is timed right, then over time you fly directly over every part of the world.
There's also not much land south of the Kodiak Spaceport other than Hawaii and Antarctica to have rocket bits fall on. That's also why most of the US polar launches are from Vandenberg SFB. Polar launches from Cape Canaveral are doable but difficult and restricted. You have to thread needles between islands. Starbase Texas has too much land north and south of it. Starbase Louisiana might be able to do it, but Mexico won't be too happy about it.
No one in their sane mind does any significant plane change maneuvers in low earth orbit. It's ridiculously expensive. If you want to launch to a polar orbit, you launch directly into a polar orbit.
Holy hell. I learn things on Reddit that I never knew I was interested in until I read it on Reddit. Now I have been furiously researching this stuff. Awesome comments.
Not all satellites desire an Equatorial orbit (An orbit that follows the equator). There are many other orbital inclinations that may be desired, to reach them it would be more efficient to launch from a more advantageous location on earth. Its more fuel efficient to launch from a location that is slower but closer along your desired orbit rather than to launch from the equator and then perform an extremely expensive correction burn.
The only advantage of launching from a higher latitude is if the desired orbit is retrograde (opposite to the Earth's rotation) where the extra rotational speed at the equator has to be counteracted. Prograde orbits are more common simply because they're cheaper (you get some free delta-V from the Earth's rotation).
But in practice, the ability to use a single launch pad for every orbit invariably outweighs the cost of the extra delta-V for retrograde orbits. A launch pad at high latitudes can't directly put something in an equatorial orbit; it would have to start with an orbit which peaks at the launch latitude then apply a correction at the equator. Whereas an equatorial launch pad can directly launch to any orbit.
It would be more efficient to launch closer to equator, as long at the target orbit has more velocity in the direction of Earth's spin, than the launch site has. Which means pretty much every orbit except near polar and retrograde orbits, because with those you need to cancel out the 465m/s velocity given by earth.
Because having it quickly wind up over water rather than populated land is a common requirement, and the convenient places you can do this with enough fairly-flat space for a pad, near the equator, are rapidly running out...
So you make a smaller pad for lower orbits that require less speed, farther north/south.
Some rockets need to go into higher inclination orbits, where you'd need to cancel out the launch pad's starting velocity if you launched from the equator.
For certain orbits it can be beneficial. It depends on the inclination, which is the angle of orbit. Some orbits are equatorial, most are angled 40-60° (such that they see different parts of the earth with each orbit), some are polar (such that they get comprehensive coverage over multiple orbits). There are lots of different orbits for different reasons.
I'm pretty sure the Alaskan launch site is better for a polar launch, whereas Florida mainly allows for launches over the Atlantic ocean.
However you can always do a launch and then change inclination on orbit. This is more expensive on fuel, but not all that uncommon, particularly for military missions.
Polar orbits. They're more expensive (in energy terms primarily, but energy costs money) because they don't get the ~1600km "boost" from the Earth's rotation.
However, there is another consideration in here; most of the rocket doesn't make it to space. SpaceX may be able to land their boosters (well, the first stage) Rocketlab does not. This means that there are boosters falling back down to Earth. If they launch over the ocean, it's a lot easier to implement large "no go" areas for the duration of the launch where boosters are predicted to crash back down.
Similar reasons to why Russia has some of the northernmost spaceports in the world. Satellites and payloads of the sort don’t need as much speed, making it better for them to get into polar orbits. Granted, Russia also has some of the northernmost cosmodromes because they in general aren’t very southern, so much so that their southernmost one, Baikonur Cosmodrome isn’t even in Russia, but in Kazakhstan, since it’s decently flat and was in the Soviet Union, which means now they pay millions upon millions to rent it from Kazakhstan, in addition to maintenance and managing the city that houses the staff.
From an AI overview, so take from it what you want:
Rocket Lab uses high-latitude locations like the Pacific Spaceport Complex in Alaska rather than the equator because the destination orbit matters more than equatorial rotational boost. [1, 2]
While launching near the equator gives a free eastward velocity boost (about 1,000 mph) ideal for equatorial or geostationary orbits, it creates a major disadvantage for other paths. [1, 2, 3]
Polar and Sun-Synchronous Orbits
The Inclination Match: A rocket's lowest possible initial orbital inclination matches the latitude of its launch pad. Launching into a polar or near-polar orbit from the equator requires a massive, fuel-heavy plane-change maneuver. [1, 2]
The High-Latitude Advantage: Launching from a high-latitude site like Alaska or New Zealand allows rockets to fly directly into polar or sun-synchronous orbits without wasting fuel fighting Earth's equatorial bulge. [1, 2]
Geography and Trajectory
Safe Flight Paths: High-latitude and coastal pads offer clear trajectories over open ocean waters. This minimizes risk to populated landmasses during initial ascent. [1, 2, 3, 4]
Specific Customer Needs: Many Earth-observation and weather satellites require polar orbits to scan the entire globe as the Earth rotates underneath them. For these missions, high-latitude spaceports provide the most direct and efficient route. [1]
Not just because of that. It's because there's a coastline there - rockets want to launch over water - and because it's the only reasonable way to get to lower inclination orbits. Low inclination orbits are better to go to things like geostationary , to the moon, to the plane of the ecliptic in the solar system.
probably not. based on a different reddit post (great source i know), ground wind and direction are important because it might blow the rocket into the launch structure or affect flight stability. once the rocket reaches a certain height there's not much wind left to affect it. interestingly, rain is usually not too big of an issue because rockets clear clouds so quickly anyways (and rain doesn't affect the rocket which is sitting in the rain before launch)
i wasn't able to get as much info on this. it seems like a desert would be ideal because they have less wind? however a more practical aspect is it needs to be a coastal region because no one wants to launch rockets over a populated area. so regardless of biome, the location would need to have a large body of water to the east and ideally have low winds.
Wait to the east? Isnt that the direction the earth is spinning towards?
I ask because sun rises in the east. And, if the rocket leaves the surface the land would be spinning eastward faster than the rocket. So rocket would be going in a more westward direction if shot straight up, right?
Or do they "aim" the rocket eastward to begin with, to assist in velocity?
Edit; or is this a centripetal/inertia kindof thing?
because the earth rotates towards the east, everything has some momentum in that same direction. at the equator the earth's rotational speed is the highest so you get the biggest bosot. so if you launch a rocket at the equator, the earth is effectively flinging you. the only thing that really matters is going fast enough.
Low Earth orbit is around 400km up (90min orbital period or so). The edge of space is considered to be around 100km up. The atmosphere is pretty thin. If you are sending up a geostationary satellite though, you are comparing, say, Everest (9km) to the orbital distance of 70 000km, that's indeed nothing. The difference in velocity you need to get is very small.
He wasn't talking about the launch having to cover less distance if it was released higher, but how you are technically moving faster with the Earth rotation if you are farther to the center.
So the number is +- 6700 km against the height of the mountain.
maybe the first person didn't fully understand the question but they still provided the answer, intentionally or not. being further away from sea level gives a few km/h in terms of speed...which is really nothing compared to the escape velocity required. good question though.
Also the radius of the earth is 6400km. Another 9km is about 0.1%. So technically you get a little more, but practically the juice ain't worth the squeeze.
(atmospheric density might matter a little more, but I'm pretty sure the rocket scientists of the world would already be doing it if the payoff were 'enough')
You mixed up Earth's atmosphere and Earth's size as a whole, the atmosphere is much thinner. Moreover, at the altitude of Mt. Everest, the atmosphere is around 1/3rd as dense as at the sea level already (hence the breathing problems). This would've made a large difference to the possible nozzle designs/engine efficiency if they were designed for that. So, ignoring logistics(!), it would be more efficient, but it's just not worth the hassle currently. There are more easily accessible mountains in South America that lie on the equator that would be a more realistic site for a spaceport, I think.
The atmosphere is "thinner" when talking about a specific layer of it, to get to space you have to go through every layer of the atmosphere, which is in fact 10,000km.
The atmosphere is 100km, but it's not equally thick everywhere. At the top of Everest, the air density (and pressure) is only one third of the sea-level. Because pressure is directly related to the weight of the air column above you, this means that a rocket launching from Everest only needs to go through one third of the air that a rocket launching from sea level would. Less air to go through, less energy lost to air resistance, less fuel consumed.
Further, because the air is less dense, the dynamic pressure acting on the rocket would be much lower, which means the rocket doesn't have to be as strong to withstand it, so it can be even lighter, resulting in more fuel savings.
However, even with taking all this into account, it's nowhere near worth it.
And if you are a company or a country who cares about people, you need to have a see or a desert on the east of your launching pad (in case of failure it can rain fire on thr people just like when it happened in China)
The earth’s radius is almost 4000 miles. Even if you had a 40 mile tall mountain (fyi, Everest is less than 6 miles) that would only be 1% further out than a launch at sea level. The rotational speed difference from an actual mountain near the equator would be a rounding error.
The thing that most humans have trouble grasping (this is no shade on you, yourself, it's a whole human society sort of thing) is that Mountains are not all that tall, on the scale of the solar system.
The amount of height you gain from launching at the top of a mountain is relatively negligible compared to what you've got to attain.
In the very most literal technical sense, and ignoring all set-up costs, yes a Mountain near the equator would be better than sea level. Similarly, an air-based launch (i.e. a plane carrying a launchpad that the space rocket takes off from) achieves about the same benefits.
Mt Everest, tallest we can find, is around 9km tall (over sea level).
Low Earth Orbit, the target of most space journeys, is at about 1,000km.
In nearly every situation, it just isn't worth the hassle to do anything other than build a robust base near to the equator on flat land (for ground logistics/transportation reasons).
The increase in speed from rotation would be effectively none. What you would gain, and i haven't seen anyonemention this, is that you would avoid the thickest parts of the atmosphere, reducing loss from air resistance, and, depending on your rocket engine design, could gain more velocity from the same amount of fuel because of the lower atmospheric pressure.
The mountain has well maintained roads to get up to the launch point
The launch point has the space to build out all the various support equipment for a launch--hangars, bunkers, fuel tanks, water tanks, support towers, etc.
The mountain is somewhere politically friendly to the launching country
The weather on the mountain is consistently conducive to launching rockets
The mountain is located West of an area that won't complain if you sometimes drop boosters on them
Those extra caveats are more important than a bit of bonus altitude at launch, so they tend to be satisfied and "mountain" gets cut. Even "equatorial" is often cut in favor of convenience of access and political friendliness.
However, even better than a mountain would be to launch from above the mountain, and with a running start. That's the idea behind the Pegasus launch system, a relatively small payload rocket that is launched from a L-1011 during flight (or previously from a B-52). This concept can only handle payloads that a plane can carry, which leads to the development of some true monsters like the Scaled Composites 351 Stratolaunch, a plane that is by various metrics the largest in the world.
If you ignore the difficulty and safety factors, yes, mountains near the equator would be the best spot on Earth. The highest equator peaks also stick out "into space" more than Mt. Everest because of the way the Earth bulges at the equator.
It is possibly marginally better on paper but then you have to deal with the practicalities of hauling your rocket up a mountain, getting it staged up there, and then all of the energy requirements to power the thing, maintenance, etc.
At the end of the day, the equations and science tells you that you need your rocket to fly at a delta v of around 9.4 km/s or 21000 mph to get to the ISS, about 400km up in space.
For reference, Everest is like around 9 km in height compared to sea level. So the difference is not very much when we are talking about these velocities.
They pretty much just launch sounding rockets. Nothing to orbit. Although they could, depending on the orbit they are trying to use and the fuel they have available.
This and it being a beautiful tropical destination led to the mafia using that area as a preferred place to hide from the law. Fast forward to today and the area is full of Italians on beach vacations.
I always thought it was to be closer to the water landings and for rockets to possibly land in the ocean if the launch goes bad. This also makes sense cool
3.5k
u/Icy_Concern_9804 4d ago
tl;dr: for a rocket it is waaaay more important to go fast than to go high. and earth rotates very slowly, so going higher doesn't make you much faster.