Using Concrete to build space ships...

>>
>How is this different from Aldrin's Cycler?

When the discussion was started, I had forgotten about Aldrin's cycler. This
was later pointed out by Mike Combs, I believe, and I refreshed my memory at
his suggestion. So, essentially it is the same basic principle.

>
>How will you give this hollow asteroid the delta-v to get it into
>the cycler orbit?

First, this idea would entail something with much less mass than an
asteroid, and said delta-v would therefore be far less, as well. I imagine
that the initial boost into orbit would be accomplished with somesort of
motor that could provide the necessary delta-v. Conventional or nuclear come
to mind, but other options could be used, I'm sure.

>
>Why not just follow Aldrin's plan and just capture an asteroid that
>is *almost* following a cycler orbit and apply less delta-v than
>would be needed compared to one that starts from a standstill.

This is, of course, an option. However, the mass would be far greater and
thus more difficult to move. Also, building a cycler cheaply allows for many
to be put on the orbital path, therefore allowing much more flexibilty in
the transit schedule of any cargo. They also become more disposable, which
may be an issue as far as damage from misc events and general wear and tear.

>
>Also, Aldrin's cycler had a very high mass:cargo ratio so when there
>was no cargo in it on legs of its cycler orbit, the orbit wouldn't
>be perturbed too much.

>
>A much lighter concept like I think you're describing would have its
>orbit perturbed by cargo being present on on leg and not another.
>How would you rectify this?
>

A good point that I hadn't considered... However, with the mass levels much
less than an asteroid, the energy required for course adjustments is much
less as well. These types of cyclers would certainly be capable of carrying
fairly substantial loads before this would become an to great an issue. At
that time, perhaps the asteroid could be employed as well for truly huge
loads.

> > I had thought of this idea before, and it seems a very good idea.
>However,
> > the shell idea takes it a step further, offering much more
>protection. This
> > is most useful when Earth-Mars transits become more routine. If
>practicle,
> > it would certainly be far better than an H20 shield.
>
>Why? The concrete mass is only there for shielding. The water is
>mroe efficient shielding and serves a life support function and
>could also be a working fluid within the vessel to assist in heat
>collection and radiation. The water isn't a dead mass that has to be
>propelled. Why is the concrete a better solution?

Actually, I think that using concrete would be to problematic for a variety
of reasons, and am therefore advocating a twin thin-skin frame work with
lunar regolith (or asteroid stuff) sandwiched between. The thickness could
be increased to any level of desired protection, would offer superior
ballistic protection, and be easy and cheap to repair. As far as H20, well,
how much would you need, and its going to be repeatedly melting and thawing
as the shell turns, which introduces fairly large expansion-contraction
issues. Using regolith avoids this to a large extent. In addition, the
cargo/crew carrying insert could (and should) be constructed in such a way
as to make use of H20 shielding, as well.

For a visualization of this idea, imagine a toilet paper tube with the
inside coated with sand/dirt, which is pressed by another, slightly less
diameter tube inside. Set this rotating and you now have artificial gravity
as well. The insert would, of course, insert into this and ride to
Mars/Earth, whereupon extracting and entering an orbit at the destination.

Again, remember that this is designed to be very reusable, relaible, easily
maintained. I also feel that if such transits are to become routine,
exposure to cosmic hazards in the form of radiation and micrometeors will
become a much greater issue. This method conceivably offers a much greater
deal of protection from these things than could be reasonably afforded to
launch every time (in terms of mass).

Of course, this is all speculation, and what the actual hazards will be in
terms of identity and frequency are only educated guesses at best :-)

Val