Damon Hill was zeer hard aan het denken :
=?ISO-8859-15?Q?Andr=E9,_PE1PQX?= wrote in
:

Damon: Do you have any source on that?

IFAIK The shuttle does not have an onboard ignition system build in the
SSME's.
Otherwise the crew should be able to ignite an shutdown SSME during
lift-off. If a SSME is shut down for whatever reason, it can not be
ingited wothout an external ignition source!

Absolutely not!

If a SSME shuts down it's off, period. There is no restart capability
once it's in the air because the engine requires equipment that is on
the ground. There is no ground restart for a whole bunch of safety
reasons.

The engine ignition is internal: (from Wikipedia)

quote:

The oxidizer and fuel preburners are welded to the hot-gas manifold. The
fuel and oxidizer enter the preburners and are mixed so that efficient
combustion can occur. The augmented spark igniter is a small combination
chamber located in the center of the injector of each preburner. The two
dual-redundant spark igniters, which are activated by the engine
controller, are used during the engine start sequence to initiate
combustion in each preburner. They are turned off after approximately
three seconds because the combustion process is then self-sustaining. The
preburners produce the fuel-rich hot gas that passes through the turbines
to generate the power to operate the high-pressure turbopumps. The
oxidizer preburner's outflow drives a turbine that is connected to the
HPOTP and the oxidizer preburner pump. The fuel preburner's outflow
drives a turbine that is connected to the HPFTP.

end quote

I don't know of a single rocket engine of any type that is ignited
externally, aside from fireworks.

--Damon

For what I have read on http://www.shuttlepresskit.com/scom/216.pdf:

The preburners do not actually ignite the fuel/oxidezers. It just heats
it from the super-cooled state to a higer temperature for the
main-combustion chamber.

Here a quote from page 7 of the document I mentioned:

start quote:
Preburners
The oxidizer and fuel preburners are welded to
the hot-gas manifold. Liquid hydrogen and liquid
oxygen from the high-pressure turbopumps
enter the preburners and are mixed so that efficient
combustion can occur. The preburners
produce the fuel-rich *hot* gas that passes
through the turbines to generate the power to
operate the high-pressure turbopumps. The
oxidizer preburner's outflow drives a turbine
that is connected to the high-pressure oxidizer
turbopump and the oxidizer preburner boost
pump. The fuel preburner's outflow drives a
turbine connected to the high-pressure fuel
turbopump.
end quote

André