Escape timelines for my interstellar ark

On 2006-04-15, wrote:

Do you know the escape velocity for the solar system? How much
propellant you'd have to burn to attain it with chemical rockets? How
long it would take to reach it with ion engines? There's a *reason*
that this is strictly fiction.

My understanding of escape velocity is that it assumes that it is
reached (relatively) quickly) and once the "burn phase" is over there
is no more significant force applied in direction of travel.
If you are able to _sustain_ your velocity (not your acceleration)
by powering your engines to overcome the effects of the sun's gravity
you could escape the solar system at any speed.
Obviously, the slower you go the longer it takes.

The reason escape velocity is loved by 1960s genre sci-fi (and therefore
most films) is that when you have to carry your chemical propellant, there
are huge advantages to high acceleration for a short time.

If the mass of your propellant is only a small proportion of your
total mass, the balance changes and it's not necessary to reach
escape velocity to escape from the sun's gravity well.

Pete

p.s. since this is fiction, I'd suggest dreaming up some form of
warp-drive or jump-gate. Failing that, you may be able to form an
argument that newtonian mechanics only applies inside a gravity
well.

--
.................................................. .........................
.. never trust a man who, when left alone ...... Pete Lynch .
.. in a room with a tea cosy ...... Marlow, England .
.. doesn't try it on (Billy Connolly) .....................................

On Sun, 16 Apr 2006 09:23:22 GMT, in uk.sci.astronomy , Peter Lynch
wrote:

On 2006-04-15, wrote:

Do you know the escape velocity for the solar system? How much
propellant you'd have to burn to attain it with chemical rockets? How
long it would take to reach it with ion engines? There's a *reason*
that this is strictly fiction.

My understanding of escape velocity is that it assumes that it is
reached (relatively) quickly) and once the "burn phase" is over there
is no more significant force applied in direction of travel.

Indeed. Escape velocity is the velocitry an _unpowered_ object needs
to be travelling at to escape the gravitational field it is in.
Provided you pick the right course /and/ have power to maintain it,
you can escape at any speed you like.

The reason escape velocity is loved by 1960s genre sci-fi (and therefore
most films) is that when you have to carry your chemical propellant, there
are huge advantages to high acceleration for a short time.

Well, the reason sci-fi films love it is because it makes for good
spectacle... :-)

The point is that you don't need any particular velocity to escape,
just to provide enough extra energy. EV as a concept assumes you need
to provide that energy in short order at lift-off, you can just as
easily supply it in tiny amounts.

Mark McIntyre
--

JRS: In article , dated Sun, 16 Apr
2006 09:23:22 remote, seen in news:uk.sci.astronomy, Peter Lynch
posted :
On 2006-04-15, wrote:

Do you know the escape velocity for the solar system?

If the OP had not cross-posted to so many newsgroups, his article would
have been auto-killed by fewer people.

The escape velocity for the Solar System is as low as one likes,
provided that one starts from far enough out and is not significantly
influenced by outside bodies.

The escape velocity from any point within the Solar System (outside Sol,
and ignoring nearby planets, moons, etc.) is Root2 times the circular
orbit speed at that point; and, for Earth, that speed is two pi AU per
year which I think is nearly 30 km/s. But if escaping from circular
orbit, one only needs to add (Root2-1) * circular speed.

Orbit calculators in gravity2.htm; travel calculators in astron-3.htm;
enter via URL:http://www.merlyn.demon.co.uk/astron-1.htm.

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