The scrap-hull vs. the ET-salvage dream (was The scrap-hull vs. the

I guess I should explain what I mean. The idea is the same whether it is a Sea Dragon being reused in orbit or a shuttle external tank being reused: in either case, you have an airtight (by definition) volume in orbit that would otherwise be wasted, instead being reused as an orbiting propellant depot or living quarters or some other use. It makes so much sense to get a second use out of something that is already going to orbit anyhow. Ed

Received: Wednesday, October 22, 2008, 9:42 PM

> This is the same idea that Space Island Group had,
> reusing these pressure vessels in orbit, except Gene
> Meyers was talking about reusing STS external tanks.
>
> http://www.spaceisl andgroup. com

I don't think the two ideas have much in common:

1) ET's are aerospace-grade, and not marine-shipyard- grade (or
lower), so they are not cheap per pound to obtain.

2) No one talking about ET salvage has ever (to my knowledge)
proposed salvaging them for scrap-metal (and it is difficult to
recycle aluminum-lithium alloy (Al 2195) anyway).

3) ET's only launch with the Space Shuttle, which causes myriad
problems.

By the way, thanks for your informative ET-Why post from January 2004:
http://tech. groups.yahoo. com/group/ ssi_list/ message/5131

Your belly-to-belly ET's-by-themselves launch idea is interesting,
except that launching aerospace-grade $5 million ($100/lb, if no
insulating-foam is included (and no foam is needed if we don't need
to worry about Shuttle-tile- damaging ice-chunks forming on the
tanks)) artworks simply to be used as as scrap-metal doesn't make
sense. If we are comparing launch cost to the cost of shipping steel
to Hawaii, or to the cost of shipping rock from the moon to Earth-
orbit, then we should be considering single-stage- to-orbit scrap-
hulls made out of heavy-gauge steel (or heavy-gauge aluminum, or
heavy-gauge fiber-reinforced concrete, etc.).

Materials-costs for a fiber-reinforced- concrete scrap-hull should be
on the order of 10 cents/lb. if the concrete costs $270/yard^3 =
$10/foot^3, and masses 100 lbs/foot^3 (so a yard would weigh 2,700
lbs). This compares favorably to the $100/lb costs of the Space
Shuttle External Tanks. If high-volume fly-ash is employed to replace
Portland cement, the cost can potentially drop below 3 cents/lb. Two
recent published papers on high-volume fly-ash "concrete" (PVA-ECC,
actually) are here:
http://ace-mrl. engin.umich. edu/NewFiles/ journals(07-08).html

"Engineered Cementitious Composites with High-volume Fly Ash"

"Use of High Volumes of Fly Ash to Improve ECC Mechanical Properties
and Material Greenness"

Here is a fiber-supplier:
http://www.kuraray- am.com/pvaf/ pva-ecc.php

$3/lb for the fiber. (If a lot of fiber is needed, perhaps the cost
can be negotiated downward.) Nominally, 2% by volume is used. That
usually works out to 44 lbs/yard. More fiber can be used for more
tensile strength and ductility -- and I assume a lot more would be
used for a scrap-rocket application, hence the $270/yard price guess
(ordinary gravelly, brittle concrete tends to be around $100/yard).
If the tensile strength is high enough, the need for steel rebar can
be avoided, and a structure can then simply be spray-formed or slip-
formed by climbing slip-forming robots (this has been demonstrated in
commercial practice). A slip-formed concrete tower/rocket might be
hundreds of feet high -- just like a Sea Dragon, except that the
latter is designed to made from heavy-gauge steel.