So one of our readers asked us this question the other day: When rockets launch they must have tonnes of momentum from the earth spin and orbit. Is this used to their advantage when plotting a course?
ANSWER
Short answer: Yes. By launching near the equator rather than the poles, you can get up to a 1,000 mph boost just from the earth’s rotation. Additionally, you should launch to the east to get this benefit.
Long answer: In low earth orbit you need to be going 17,000 mph – it doesn’t matter which direction. But at the equator the earth is rotating 1,000 mph counterclockwise, so if you launch east into a counterclockwise orbit you only need to gain 16,000 mph. If you launch to the west into a clockwise orbit you need to gain 18,000 mph.
By launching west, you’re basically starting out with a 1,000 mph deficit that you have to overcome, like running the wrong way on a moving floor.
In the US, this is why we launch missions from Florida – because it’s pretty far south, and if you’re launching to the east you’re over ocean and not populated areas.
On the other hand, Israel, doesn’t have this advantage. They have to launch their Shavit rockets (Hebrew for ‘comet’) to the west so that they pass over the Mediterranean, rather than potentially hostile neighbor states. This puts their satellites on “retrograde orbits,” meaning they orbit the earth opposite the direction of pretty much every other man-made satellite. While that may seem cool it comes at the expense of more fuel, limiting them to payloads 30% smaller than if they were launched eastward.
To add to this, when it was first proposed, the ISS was originally sold as a station that could be built up as a sort of staging station for Moon or Mars missions, among other things. However, in order to make it international (and get something like 20% of the funding from the Russians) we had to place the ISS in an inclined orbit that made it useless for this task.
It needed to have the inclination, because Russian rockets launched from Russia, and they lacked the power to reach an equatorial orbit after starting out at such a high latitude. That deficit being the energy lost from not being at the equator to start with, and from having to correct their inclination once in orbit. So the ISS is where it is right now precisely because the Earth gives you momentum, but the Russians couldn’t take advantage of that.
The above answers the earth’s rotation benefit. Adding to that concerning your earth’s orbit benefit question, the answer is yes also. When we launch a mission to someplace like another planet, the satellite also has the initial prograde orbit velocity the earth has while orbiting the sun. We accelerate the satellite from it’s earth’s orbit in a direction close to the same prograde direction as the earth’s orbit around the sun, requiring less fuel for it to reach escape velocity from the earth, and also causing the satellite to start increasing it’s orbital distance from the sun. This is the usual initial method used for missions to the outer planets (Mars and beyond). For missions to Venus or Mercury which are in orbits closer to the sun, we would make the acceleration retrograde the the earth’s orbit around the sun. We need to slow down the satellite’s orbital speed around the sun so it will “fall” into a lower orbit around the sun to intercept the Venus or Mercury orbits. Various combinations of the two methods can be used for missions that need to leave an orbit around the earth and escape earth’s gravity to go to other celestial destinations.
“So the ISS is where it is right now precisely because the Earth gives you momentum, but the Russians /couldn’t/ take advantage of that.”
Ok this is what I hate the most: Saying America’s #1 and the coolest kid when it comes to space travel. It’s bull, and shows a fundamental misunderstanding between political boundaries and scientific ones.
First, it’s not “Oh the Russians are so stupid they can’t even use earth’s momentum like us!” If you know what a globe is or have a prefrontal cortex in your head you know that Russia is darn far north. Russia does its launching from Kazakhstan, which is as far south as they could go even when it was the cold war and they had half of Asia. Here’s where it gets interesting: Both America and Russia are on the northern hemisphere. Orbits have to be complete circles, and can’t bend. So if there were to be a space station merely accessible by the other guys on the other side of the world to both them and us, we’d have to cut our differences and play fair. Besides, Russia started the station and without cooperation there’d be less stuff to allow us to get to mars via station. Not only that, but even now it’s easier doing it stationless. A rocket just gets up and goes, no need to dock or refuel, and even if it did we might as well use new almost-warp drives which soon won’t need gas.
Second part: Russia is and has been cooler than us at keeping its rockets up. A bigger rocket is nothing if you can’t fund it. Guess who doesn’t have a space shuttle? Us. Guess who doesn’t even need one? The Russians. And the world rotates, you know. It’s not like it’s forever stuck in one place. Station may be over Hawaii one day and Arizona 6 hours later. It’s a matter of getting it to sync just right.
Also, propositions for space stations never stay the same. Back when america first was about to get a space station they had a bunch of guys make all kinds of proposals but none satisfied the admins so they were all canned. Then in the 80’s there was this thing like the ISS but just american, called Space station Freedom. It turns out it’s hard to fund a football field of metal in space by yourself, which is why it’s called the “Paper station,” having never existed past blueprints.