kaplow@crvax1.DEC (Reach for the Stars) (02/18/86)
If only one SRB ignites, you will end up with the most spectacular
pinwheel on the launch pad that man has ever created. Likewise if one
"accidentally" ignites prior to launch. Thou there is no way to
extinguish the propellant once it starts burning, the destruct system
will split them open, and cause them to burn without producing any
thrust. Either of these would result in an equipment disaster worst than
last months (orbiter plus ground support equipment being destroyed), and
most likely a larger loss of life as well (ground support personnel).
Fortunately, neither of these is likely to ever happen.
The SRB is quite difficult to ignite! It must be at the right
internal pressure to produce any thrust, and must be ignited along its
entire grain surface to burn properly. If it is not properly pressurized
at ignition, it may simply blow itself out. Ignition at the base, and
not at the top will result in a very low thrust, long burning Roman
Candle, that will likely burn thru its casing base.
Even high shock ("dropping" an SRB, banging it with a crane, a
bullet impact, and likely not even a bomb) will ignite the propellant.
The temperature necessary for ignition is so high that before the
propellant could be so ignited, the entire VAB (or whatever) would be
long gone in flames. You can safely extinguish a cigarette on a small
piece of the propellant material, although a butane lighter will usually
ignite it. I've done such demonstrations in an ashtray.
Proper ignition is not that difficult to do. The SRB simply has a
smaller rocket motor built into its top end! Fire that motor, and its
exhaust flame ignites the SRB in a fraction of a second. So how is that
motor ignited? You guessed it, a third, even smaller motor ignites the
secondary motor. That third motor is fired by redundant electrical
squibs. The entire process takes the half second from SRB ignition to
liftoff.
Bob Kaplow
Digital Equipment Corp.
Arlington Heights, IL
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