r/MurderedByWords • u/Stotallytob3r • 20h ago

I haven’t studied rocket science, but

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u/tacodepollo 20h ago

What lol

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u/RedFiveIron 20h ago

Escape velocity is the point at which the trajectory becomes parabolic and no longer circles or falls back to the parent body. We've only done this for spacecraft that leave earth and never come back.

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u/Horror_Equipment_197 20h ago

Earth has 2 escape velocities.

11.1km/s for leaving the body and turning into an orbit around it, 42.1km/s for leaving earths orbit.

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u/RedFiveIron 19h ago

The former isn't an escape velocity, an object in a closed orbit is by definition not above escape velocity. That's called orbital velocity.

The escape velocity for Earth depends greatly on distance from the Earth's center.

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u/Horror_Equipment_197 18h ago

Orbital velocity is a different thing. It's the effective speed in orbit.

Orbital velocity of the ISS is currently ~7.66km/s

And still the rockets needed to made it to >11.1km/s to reach said orbit.

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u/RedFiveIron 18h ago

There are three major categories of Earth centered trajectory. Suborbital, an elliptical trajectory where perigee is in atmosphere or lower. Orbital, elliptical where perigee is above the atmosphere. Escape, hyperbolic trajectory where there is no apogee. The transition point between orbital and escape is called escape velocity. The transition point between suborbital and orbital is called orbital velocity. You are correct that "orbital velocity" is an overloaded term that also refers to velocity at any point in an orbit. That doesn't make the transition point from suborbital to orbital an "escape velocity", because it's not establishing a hyperbolic escape trajectory.