Subject: Re: shuttle landings

From: [email-masked] (Michael R. Grabois)
Date: Wed, 28 Feb 1996 05:37:48 GMT

On Tue, 27 Feb 1996 15:49:23 GMT, [email-masked]
(Jeramie Hicks) wrote:

>>>Does the shuttle land under power?  I read somewhere that the shuttle has
>>>to dump its fuel before re-entry.

>>As to whether or not it dumps its fuel before re-entry, I don't really
>>know, but it would make sense if it is a safety issue, since the fuel
>>really isn't doing any good.  The entire descent is unpowered after
>>the deorbit burn anyway.  Most of the shuttle's fuel is gone by then
>>anyway, from the launch, the main reason for fuel afterward is for
>>maneuvering thrusters.

>Right before entry, the shuttle does kinda "dump" its extra fuel: it
>floods the engine compartments with stored helium to remove any trace
>of explosive hydrogen or corrosive oxygen from the engines.  This
>prevents the possibility of an explosion or corrosive engine damage.

A portion of the propellant (forward RCS) is dumped while on orbit to
control the center of gravity of the vehicle. Most of the rest of the
prop in the aft end (OMS) is burned out of plane during the deorbit
burn.

The forward and aft compartments you mention don't actually hold the
propellant; they hold the propellant tanks, among other stuff.

>The maneuvering thrusters are not used during the atmospheric portion
>of landing, only the airflow control surfaces (ie normal airplane
>control). In fact, I think the GPCs totally shut down the RCS during
>atmospheric re-entry.

Actually, the RCS jets are used almost all the way to the ground.
Until the dynamic pressure gets up to 10 psi, all jets (roll, pitch,
and yaw) are used since the air is too thin to use the aerosurfaces. 

At 10 psi, the roll surfaces become useful; at this point, a large
enough moment is possible due to the distance from the CG to the
aerosurfaces (moment arm) and moments of inertia. So now the roll jets
are deselected.

At 40 psi, the pitch surfaces are able to control the vehicle. This
comes in later due to the smaller moments of inertia than roll. Now
the pitch jets are deselected.

Since the vertical stabilizer is much less surface area than the
ailerons and elevons, yaw is the last of the three to come in. Because
the shuttle is pitched so high, the airflow doesn't travel around the
tail very well, and it only gets picked up at Mach 1. 

NOW all the RCS jets are shut down.

>NASA has the 1988 News Tech Reference online at their web site. It's
>effectively the Owner's Manual of the entire STS system, from plumbing
>to administration.  Technical answers can be found there.

>BTW, I'm just remembering from the TechRef. I may be wrong...
>- Hicks

Not too bad, if you're remembering from memory. Just got a few things
mixed up....

 Michael R. Grabois  | http://ourworld.compuserve.com/homepages/mgrabois
 Houston, TX         | [email-masked]    CI$: 74737,2600
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"Some people call me Maurice, 'cause I speak of the Pompatus of Love."