"Michael S. Lorrey" wrote:
>
> Doug Jones wrote:
>
> > Nanopowdered aluminum is not all that remarkable- there's a product
> > called AlEx or some such which is nanoscale aluminum powder made by
> > exploding a wire with a capacitor discharge in a helium atmosphere. It
> > has a slightly positive heat of formation relative to bulk Al, but solid
> > fuels are inherently a poor match for orbital launch- you get better Isp
> > and effective bulk density out of liquid fuels, and for SSTO or even a
> > cheap TSTO, delta-V is most important. Solids are great for tactical
> > propulsion (ie missiles) but just can't compete with liquids for system
> > bulk density, mass fraction, and Isp.
>
> This is something I've wondered. If liquid fuel is so much better, why
> does the shuttle, the Delta, the Araine, the Titan, etc all need solid
> boosters to get decent enough mass fractions to put decent payloads in
> orbit? I was wondering if people were biased toward hydrogen merely for
> purists sake. Sure you get great Isp, but you get great Isp from an ion
> engine too, and you wouldn't want to power a launch system with an ion
> engine.
>
> Mike Lorrey
Large solid fuel rockets were developed for strategic missile
propulsion- were it not for that subsidy, they would not be in use
today. Disregarding political and operational issues, solids do provide
good thrust/weight ratios, which are the important feature for
boosters. Lower stages are not as sensitive to Isp and mass fraction as
upper stages, so solids are acceptable there. Note that upper stages on
commercial launch vehicles do emphasize Isp, and most are hydrogen
fueled.
For better Space Shuttle operations safety and performance, pressure-fed
LOX-kerosene boosters would have been a better choice- but important
congressional committee member was from Utah, so SRBs were speced and
Thiokol got the job even though another company had a better SRB design
and more experience.
Politics as usual.
-- Doug Jones Rocket Plumber, XCOR Aerospace http://www.xcor-aerospace.com
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