Sea dragon and Big Dumb Booster.

>
> In the Early 1960's, Aerojet designed a BDB (sea dragon) capable of putting
> 550 tonnes into LEO
> http://www.friends-partners.org/mwade/lvs/searagon.htm
>
> I have been looking at various designs and BDB concepts. If we were to
> design a BDB today, how would we design for minimum cost? I suppose that we
> could use fibre-glass for much of the upper stage design. With a 550 tonne
> to LEO booster, we could assemble something like the ISS on the ground and
> fire it into orbit in one piece. This would surely be much cheaper than
> carting 30 different pieces up on the ultra-expensive shuttle and trying to
> assemble them in a vacuum.
> The BDB that I had in mind would have a lift capacity closer to 1000
> tonnes to LEO. Something like this, would be capable of putting 200 tonnes
> of men and materials on the lunar surface or alternatively, 500 tonnes in
> HEO or 450 tonnes on a NEA.

As far as minimizing costs, it depends whether you plan to launch 1 of
these, or many. If many, developing something new from scratch (or based
on reasonably good existing designs) is definitely the way to go - the
operational cost of using a design based on the shuttle, and using its
facilities, is going to be ridiculously high.

One problem with BDB's or any large rocket is transport and assembly
from the manufacturing facility to the launch pad. Transport over land
for any significant distance is vastly more expensive for objects larger
than a typical shipping container. Transport over water makes things
easier, and if you launch from the water as SeaLaunch does, and as
SeaDragon was supposed to, and manufacture at some coastal facility,
you'll be cutting transport costs quite a bit.

Non-cryogenic fuels simplify fuel transport, transfer, and storage, so
they are worth looking at even with the lower specific impulse. Since
BDB's are generally expendable, you'll save costs using cheaper
materials; fiberglass, or steel say. Probably more important is ease of
manufacture: what is the lowest precision in parts that's acceptable?

Having lots of comfortable margins is a good way to reduce operational
costs - you don't have to so precisely monitor everything if you have
20% extra fuel as if you have only 5% extra for the mission; but of
course there's a balance there with the loss of cargo capacity. Other
redundant systems similarly can reduce operational costs by limiting the
things you have to worry about, but also reduce cargo capacity and
increase the sunk costs in expendable systems.

I'd be interested to know who is actively working on any such thing? The
real problem seems to be the lack of a market, the usual chicken and egg
problem.

Arthur Smith (apsmith@...