To simplify it for my mind, I envision the Earth being a car, and the space craft being something like a bullet. If the car (Earth) is orbiting at 30,000 m/s, and the bullet (spacecraft) is traveling at 17,000 m/s (Voyager 1 speed), the bullet is then traveling at 47km/s, but only at 17km/s relative to the car. But, if the car’s direction changes and goes the opposite way at the same speed (as with orbit), it is actually then going 77km/s. This is confusing me 😩.
In: Physics
You’ve kind of got it. For a near-equatorial satellite, there is a huge advantage to launching near the equator and towards sunrise.
Like the car, the path of the satellite is completely independent of the Earth’s rotation after launch. Unlike the car, both the orbit and the rotation are periodic (repeating) functions. This means that you can pick orbits that have certain relationships to the Earth’s surface. For example at an orbital height of about 36,000 km, the orbital period is about 24 hours. A satellite placed at that height over the equator will seem to be stationary from the perspective of the Earth’s surface. This is a geostationary or geosynchronous orbit. In the case of polar orbits (that go around the earth from top to bottom) the Earth rotates under the satellite. If the orbit is tilted just very slightly so that the orbital plane precesses around the earth once per year, the satellite will always pass overhead at the same times of the solar day (eg: sunrise and sunset). This is called a “sun synchronous orbit” and is really useful for many studies involving imagine.
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