Escape timelines for my interstellar ark

Leafing through uk.sci.astronomy, I read Abdul Ahad's message of Mon, 17
Apr 2006:

The next part is where the possibility of gravity-assisted swing by's
of bodies like Venus, Mars, or the Earth becomes feasible to propel it
out of the *inner* solar system toward the *outer* solar system. The
timescale for this is going to be into several *decades* I reckon,
since we're using a myriad of low thrust, multiple impulses.

I've had time to have a good look at this now.

Using gravity assists to get out of the inner solar system to Jupiter is
a well-known procedure. I'd recommend researching how the Voyagers did
it, because that is more similar to your requirement. (In contrast,
Galileo needed to arrive at Jupiter as slowly as practical, because it
needed to stop there, and Cassini similarly needed to arrive at Saturn
as slowly as possible).

You are also correct to assert that you should be able to engineer your
ark not to be torn apart by such gravity assists - solid rock bodies of
20km diameter may have problems, but rock lacks tensile strength, and
presumably you will be using materials with high tensile strength.

The more novel requirement is leaving the solar system with the velocity
your scenario requires, and for that you will need a velocity of 25
km/sec after getting out of Jupiter's gravity well. As Jupiter moves
around its orbit at 13 km/sec, this equates to a velocity of 12km/sec
relative to Jupiter. (Fortunately for you, I believe Alpha Centauri
will be comparatively near the ecliptic in 50,000 years' time, otherwise
this figure would be significantly larger and your task more difficult
still.)

To leave at a relative velocity of 12km/sec, you need to approach at 12
km/sec, and that is not trivial - I don't believe there is a way using
gravity assists from Earth, Venus and Mercury for you to achieve this
(and Mars will hardly help at all).

I think the best bet is a gravity assist from Jupiter, sending your ark
hurtling towards Saturn faster than either Voyager did. Saturn is then
used to tip your ark's orbit out of the ecliptic, but back inward
towards Jupiter. (This style of manoeuvre has been used before, when
Jupiter was used to send the Ulysses probe out of the ecliptic to study
the Sun from far above its poles.)

I haven't done the detailed calculations for this, but it may be
possible to achieve another rendezvous with Jupiter one and a half
orbits later (if not, then two and a half orbits, or half a century,
later). This time your ark will be approaching Jupiter's orbit from the
North or South and you will have the 12km/sec relative approach speed
that you need.

This final assist will need to occur when Jupiter is in the part of its
orbit where its velocity is directed in the general direction of where
Alpha Centauri will be in 50,000 years' time. (George is correct to
point out you will lack the energy resource to make more than trivial
changes of course afterwards.) This needs a more thorough analysis, but
I would be very surprised if an appropriate alignment of Jupiter and
Saturn occurs every century.

HTH

Peter
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Peter Munn wrote:

I haven't done the detailed calculations for this, but it may be
possible to achieve another rendezvous with Jupiter one and a half
orbits later (if not, then two and a half orbits, or half a century,
later). This time your ark will be approaching Jupiter's orbit from the
North or South and you will have the 12km/sec relative approach speed
that you need.

This final assist will need to occur when Jupiter is in the part of its
orbit where its velocity is directed in the general direction of where
Alpha Centauri will be in 50,000 years' time.

Hi Peter,
Thanks very much for these pointers, really appreciated.
They should come in handy if someone actually decides to build this
thing (for real!) one day... who knows!?

Abdul

Leafing through uk.sci.astronomy, I read Abdul Ahad's message of Tue, 25
Apr 2006:
Peter Munn wrote:
[...]
This final assist will need to occur when Jupiter is in the part of its
orbit where its velocity is directed in the general direction of where
Alpha Centauri will be in 50,000 years' time.

Thanks very much for these pointers, really appreciated.
They should come in handy if someone actually decides to build this
thing (for real!) one day... who knows!?

Thankyou, but I doubt the world needs my help to calculate gravity
assists - there are plenty of others more capable. And, my own best bet
is we will get to nearby star-systems by sending nano-robots to do the
colonising (and their journey velocity will be perhaps 5% light speed),
and our descendants will follow on somewhat later, but at the speed of
light, as codified DNA sequences.

However, I am prepared to offer help with your story-line for the heck
of it. For instance, the orbits you show on
http://www.astroscience.org/abdul-ah...ntauri/escape-
sequence.htm would take over 300 years to complete. (So "several
decades", as you put it, could be read as a significant underestimate.)
The final orbit which loops out beyond Neptune, to nearly 50 AU it
seems, would take about 125 years.
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Hello,

Get a better starship engine, like mine! Go faster, get their sooner, go
further.

Chris.

"Peter Munn" wrote in message
news
Leafing through uk.sci.astronomy, I read Abdul Ahad's message of Tue, 25
Apr 2006:
Peter Munn wrote:
[...]
This final assist will need to occur when Jupiter is in the part of its
orbit where its velocity is directed in the general direction of where
Alpha Centauri will be in 50,000 years' time.

Thanks very much for these pointers, really appreciated.
They should come in handy if someone actually decides to build this
thing (for real!) one day... who knows!?

Thankyou, but I doubt the world needs my help to calculate gravity
assists - there are plenty of others more capable. And, my own best bet
is we will get to nearby star-systems by sending nano-robots to do the
colonising (and their journey velocity will be perhaps 5% light speed),
and our descendants will follow on somewhat later, but at the speed of
light, as codified DNA sequences.

However, I am prepared to offer help with your story-line for the heck
of it. For instance, the orbits you show on
http://www.astroscience.org/abdul-ah...ntauri/escape-
sequence.htm would take over 300 years to complete. (So "several
decades", as you put it, could be read as a significant underestimate.)
The final orbit which loops out beyond Neptune, to nearly 50 AU it
seems, would take about 125 years.
--
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_./ \_.' without altering the subject line.
'..l.--''7 If this newsgroup message is over
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| Peter Munn problems, please mail to newsreply
| Staffordshire UK @pearce-neptune... instead.