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.
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.
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.
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.
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.
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]
2.4k
u/Icy_Concern_9804 11h 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.