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Re: Propellant fluid dynamics at zero-g



Speaking of ullage,  why do we think it is a good
idea to spin down when we are trying to get
the remaining mass loss to apply acceleration
along the velocity vector at apogee?   Since
the He valves are closed, isn't the ullage
applying  the pressure?    Maybe we should do an
He pressure profile for the last week.  I will look at
it.

Maybe we are spinning down so that it will be
easier to change the rotational vector.  But
if we want to dump, and spinning is the
pressurization technique, we will have to spin
back up won't we (especially since mass loss
has already somewhat depleted the tanks).

Bob

----- Original Message -----
From: "Phil Karn" <karn@ka9q.net>
To: <gmemory@compuserve.com>
Cc: <ulf@symek.de>; <amsat-bb@AMSAT.Org>
Sent: Thursday, January 11, 2001 11:03 AM
Subject: Re: [amsat-bb] Propellant fluid dynamics at zero-g


> >I once read somewhere (cobwebs tearing apart here) that on manned (or
maybe
> >it was unmanned) missions, just prior to engine firing, either the
thrusters
> >or the main engine was ramped up with an initial low energy burst in the
> >direction of flight.  Maybe this happened a split second before a burn at
>
> Yes, this has been common practice with many launchers for many years.
> Small solid-fuel rockets are typically attached to the outer surface
> of each stage, some pointing forward and others aft. They are fired in
> sequence when staging.
>
> The forward-pointing rockets are called "separation motors" and are
> fired when the stage is depleted to back it away from the next
> stage. The rearward-pointing rockets are called "ullage motors" and
> they act primarily to settle the fuel in the tanks so the engines in
> that stage can be ignited. They also help move the upper stages away
> from the just-jettisoned lower stage.
>
> On the shuttle, the separation motors are at the top of the SRB cones
> and fire mostly sideways. They act to rotate the top of the SRBs away
> from the orbiter and external tank.
>
> The separation and ullage motor firings are easily seen during a
> launch.  They generate the big puffs of smoke that often seem to
> envelop a launcher at staging. They were especially visible on the old
> Saturn V launches.
>
> Phil
> ----
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>

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