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New Horizons Trajectory
Greg Hullender
post Jun 28 2008, 05:55 AM
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dmuller: Yikes! I'm repeating myself and doing more work the second time! :-) Getting old sucks . . . :-)

Note that the hyperbolic excess doesn't actually depend on which direction NH is going; any small body with the same speed but ANY vector would end up with the same excess (unless it hit something first). That means you can compute hyperbolic excess without knowing the semimajor axis of the hyperbola, as follows:

sqrt(v^2 - 2*mu/r)

So if you know a thing's speed and its distance from the Sun, you can compute the hyperbolic excess with no other info. Of course, if the object isn't in a hyperbolic orbit, then this'll give you an imaginary result, so you should test that v^2 > 2*mu/r -- which is the same as testing that v^2/2 > mu/r which is the same as kinetic energy > -(potential energy).

Cool stuff! :-)

--Greg
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dmuller
post Jun 28 2008, 07:59 AM
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QUOTE (Greg Hullender @ Jun 28 2008, 03:55 PM) *
Getting old sucks . . . :-)

Well, at least you're not on the record for calling the mission "New Messenger" like I am unsure.gif


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Juramike
post Jun 28 2008, 05:09 PM
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QUOTE (dmuller @ Jun 27 2008, 11:47 PM) *
16.6 km/s - Voyager 1
14.9 km/s - Voyager 2
12.5 km/s - New Horizons
11.3 km/s - Pioneer 10
10.4 km/s - Pioneer 11


Tougher question: Are any of these going fast enough (in the right vector) to eventually escape the Milky Way?


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Greg Hullender
post Jun 28 2008, 09:48 PM
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QUOTE (Juramike @ Jun 28 2008, 09:09 AM) *
Tougher question: Are any of these going fast enough (in the right vector) to eventually escape the Milky Way?


I figure local escape velocity from the Milky Way at about 800 kps, assuming none of the mass of the galaxy is outside the Sun's orbit. Wikipedia says ~1000.

http://en.wikipedia.org/wiki/Escape_veloci...cape_velocities

The Sun's orbital velocity is 220 kps, so just adding 10 to 20 kps isn't anywhere near enough.

--Greg
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