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Wikipedia's page on escape velocity puts the escape velocity for an object travelling out of the Solar System at ~525km/s. This figure is slightly higher than the tentative velocity of Voyager-1 at ~17km/s.

Why is the vehicle spoken of as being on an interstellar course? When did the vehicle achieve Solar Escape velocity? What am I missing?

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The answers are explaining the discrepancy, but I'm hoping someone can specifically summarize the path the probe has taken and its velocities at different points, since that info is pretty hard to acquire. E.g. could it have escaped the Sun after leaving Earth with no further boosts? Was it the Saturn slingshot that did the trick? –  Chris White Feb 24 '13 at 19:39
    
@Chris: The diagram in my answer says Voyager 2 exceeded solar escape velocity in its encounter with Jupiter, and then more with Saturn. I can't find a similar diagram for Voyager 1, but it must have been similar. According to the list of escape velocities, at Earth, it takes 11.2 km/s to escape Earth, but 42.1 km/s to escape the sun. That's like 14 times as much energy. That's how much harder it would be without the slingshot effect. –  Mike Dunlavey Feb 24 '13 at 21:39

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up vote 8 down vote accepted

Escape velocity depends on what you're trying to escape from and how far away from it you are. That Wikipedia reference makes that very clear.

As Sachin Shekhar pointed out, if you're in the vicinity of the sun, and you're trying to escape the galazy, you need 525 km/s. If you're trying to escape the solar system, and you're at Neptune's distance from the sun, you only need 7.7 km/s.

When did Voyager 2 achieve escape velocity from the solar system? According to this diagram from Wikipedia, it occurred during its gravity assist from Jupiter. Voyager 1 was probably not too much different.

Trajectory of Voyager 2

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525Km/s is escape velocity w.r.t. The Milky Way's gravity at the position of solar system galactic radius. You aren't trying to escape the galaxy. Are you?

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Ah. Thank you (+: –  Everyone Feb 25 '13 at 3:41

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