When launching a deep-space craft, how do the rotation and orbit speeds of the Earth and direction (relative to the prior) impact the travel time and actual velocity of the space craft?

Question

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

Answer 1

You have the general idea correct, it is beneficial to launch the probe in the direction of both the rotation and orbit of Earth to use that existing velocity. Keep in mind though that there is no absolute frame of reference for the probe’s “true velocity”.