On 31 Aug 2004 03:05:11 -0700, Abdul Ahad
wrote:

I was toying with this idea for a *possible* futuristic voyage to
Alpha Centauri, with a big emphasis on water and life support resource
mining from comets and planetoids encountered along the journey:-

http://uk.geocities.com/aa_spaceagen...ropulsion.html


Specifically, I would like to know if anyone has thoughts on whether
an inter-vessel, ship-to-comet robotic attachment of some kind could
be built (with technology easy to visualise in the current era), which
scoops up and proceses the frozen material from comets into water and
hydrogen/oxygen for power and life support. The robotic arm would dig
into the exterior ice of the comet upon a gentle, speed-matched
docking rendezvous in-flight.

My starship concept demands a large scale structure extending perhaps
a few kilometres in length. Is our current materials science
technology adequate to build and operate something on that scale that
would be robust enough for the job to take the stresses involved where
the asteroid has a spin as well?

A further complexity is to rotate my asteroid to create artificial
gravity. As the robotic mining "arms" are going to be erected to
either side of the cylindrical asteroid body, upon contact with comets
the spin rate would slow down due to the added mass of the comet. If
the asteroid is say 10km long and 5km wide (and highly dense e.g. 2.9
grams/cm^3), and the cometary nucleus captured by the arms is say just
2 or 3km in diameter (with a density equivalent to that of water,
since its "icy"), would the spin rate of the asteroid slow very
drastically in such an encounter?

My last point is if my asteroid is rotating along a spin axis which
runs through the *length* of its body (through the core), what are my
options of "pitching" the asteroid from side to side without
disrupting the spin rate (and the artificial gravity that it
generates)? Would it be feasible to use *pulse* thrust at favourable
intervals if I wanted to turn the body around?

Thanks for all thoughts.
Abdul Ahad

Indeed you get a lot of fuel that way. But not in a very manageble form.
Breaking up the water into hydrogen and oxygen will require
you to use as much energy breaking the binding as you get when recombining
the elements. Altso the sheer mass of the comet is huge meaning
you would need a huge thrust.

The key to interstellar travel is to maximize the mass to energy ratio.
(the infamous antimatter motor perhaps)

Or you could get your energy as you go.

Robert Forward suggest not bringing it allong but focusing huge
lasers on a sun sail. (probaly the most plausible suggestion I
have seen so far)

Larry Niven prefers the Buzzard ramscoop, a fusion jet that uses a
huge magnetic field in front of the ship to scoop up interstellar hydrogen.
(Probaly won't work..)

From what I can see we are nowhere near solving the problem.
Even when fusing hydrogen, say, the energy to weight ratio is not
favorable.

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