Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Launch Escape Tower/Rocket
Date: Tue, 2 Jan 2001 17:00:19 GMT

In article <92r9cn$r2l$1@nnrp1.deja.com>,
Seagull_k  <seagull_k@my-deja.com> wrote:
>So instead of disconnecting the BPC and having the LET system take
>itself out of the way, they had a seperate system for jetison?

Correct.  In fact, there were three solid rocket motors in the tower:  the
big escape motor, a smaller motor used for tower jettison (although the
escape motor could be used as a backup), and the pitch-control motor.

There had to be a separate jettison motor so that the tower could be
jettisoned after an escape.

The escape motor was built with slightly off-center thrust, so that it
would take the CM off to one side, but low-altitude escapes needed a
larger sideways component (to ensure landing clear of the fireball) than
high-altitude escapes could tolerate.  Hence the pitch-control motor, used
only at low altitudes.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Launch Escape Tower/Rocket
Date: Tue, 2 Jan 2001 17:05:07 GMT

In article <3uj46.49$t6.6198@news.corpcomm.net>,
Patrick Flannery <flanner@daktel.com> wrote:
> Wouldn't there be a danger of the booster/space craft stack running into
>the tower after separation? After all they are still under thrust-I wonder
>if they fired the side thrust motor just to get it out of the vehicles
>flight path?

No, the pitch-control motor was used only at low altitudes.  Both the big
escape motor and the smaller jettison motor were built with their thrust
lines slightly off-center, so they headed off to one side automatically.
But this wasn't quite enough for worst-case low-altitude escapes.

(In the case of the escape motor, the thrust skewing was done by making
two of the four nozzle throats slightly different sizes.  I believe the
same technique was used for the two nozzles of the jettison motor, but I
don't have confirmation of that.)
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)