Re: The Five-Billion-Star Hotel / propulsion

[Mark Reiff <markreiff@xxxxxxxxxxxxx>]

Ellen,

Ellen Hughes wrote:
> What would you say is a "safe" fuel for space flight?

Kerosene/Jet fuel is probably one of the safer liquid fuels used in spaceflight.
 That is why it is used so much in early manned spaceflight.
But your question is the wrong question.  A fuel itself isn't inherently safe or
hazardous, but when it is in close proximity to an oxidizer and a heat source,
then the same thing that makes it an energetic propellant also makes it an
energetic explosive.  Just like with any other engine control and isolation of
fuel and oxidizer make for better safety and reliability.

A hybrid solid engine, where the oxidizer in pumped through the fuel core, can
be throttled up or down or turned off, nearly instantainiously, like a liquid
propellant engine.  You can ship a fuel only hybrid core without concern that it
might blow up (not so with an SRB.)  A hybrid core fuel might be nothing more
than a type of rubber or asphalt.  Sure it could be caught on fire, but it would
take an effort to do so and then it would burn rather slowly and not very hot.
If you ever get the chance to visit Thikol's manufacturing facility in Utah, you
would see how careful they are to ensure no ignition source comes anywhere near
the facility.

Cryogenic fuels and oxidizers have the additional hazard of instantly freezing
anything they come in contact with, making most materials very brittle.

And then there are the mono-propellants, which don't require an oxidizer to
ignite, just a heat source.  They tend to be highly toxic as well.  They are
usually only used for in-space propulsion only.

Then there are oxidizers that act like fuels.  Hydrogen Peroxide in high
concentrations is one of these.  Some claim that by using a catalyst can make
Hydrogen Peroxide safe to use as a propellant, but handling the stuff on the
ground is still quite dangerous.

Not much in traditional rocketry tends to lend itself inherently to safety, as 
performance is always at a premium.  The aircraft and automotive industries 
spend a lot of money trying to optimize performance and safety in their fuels, 
so it isn't any easier in space propulsion.

--
Mark Reiff <markreiff@xxxxxxxxxxxxx>

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