16.512, Rocket Propulsion
Prof. Manuel MartinezSanchez
Lecture 30: Dynamics of Turbopump Systems: The Shuttle Engine
Dynamics of the Space Shuttle Main Engine Oxidizer Pressurization Subsystems
Selected SubModel
In the complete SSME engine, all variables affect each other in complex ways.
In order to test our fault detection algorithms, a dynamic subsystem is desired, with
reduced order, but with the unmodelled states interacting as weakly as possible with
those modelled. Attention was focused on the liquid oxygen subsystem for two main
reasons:
(a)
The O/F ratio at rated power is 6, so that the LOX dynamics should dominate
over the LH effects wherever they interact, and
(b)
The turbopump preburners are run very fuelrich in order to limit the turbine
inlet temperatures below the metallurgical limits of the uncooled blades;
small excursions of the LOX flow to the preburners are then immediately
translated into large and potentially critical turbine temperature excursions.
In our submodel we therefore focus attention on the LOX turbopump, which
feeds both, the main LOX injectors, and (after the boost stage) the two turbine pre
burners. Also modeled are the dynamics of the LOX feeding line to the preburners,
as well as to the main LOX valve and main injector, plus the LOX preburner itself
and the main chamber pressure. Variations of the LHrelated states should indeed
couple weakly to the LOX system, mainly through LH flow variations onto the pre
burners (insensitive, since they are fuelrich), and into the main chamber (choked
flow, no feedback).
The Dynamic Equations
There are three types of dynamic equations to be considered:
(1)
Rotational dynamics of the LOX turbopumps.
(2)
Equations expressing the liquid inertia under pressure difference variations
(analogous to inductance in electric circuits).
(3)
Equations expressing the ability of cavities to store fluid due to its
compressibility under pressure fluctuations (analogous to capacitive effects).
(1) Rotational Dynamics
If I
OTP
is the moment of the inertia of the Oxidizer Turbo Pump (OTP) rotor,
its
angular velocity,
02
Ω
2
OT
τ
the torque delivered by the OTP turbine,
2
OP
the torque
absorbed by the main oxidizer pump stage, and
3
OP
the torque absorbed by the
oxidizer booster pump, then
16.512, Rocket Propulsion
Lecture 30
Prof. Manuel MartinezSanchez
Page 1 of 11
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02
Ω
=−−
OTP
OT
OP
OP
d
I
dt
τ
(
1
)
In a hybrid system where
02
Ω
is in rad/sec, t in seconds, and the torque in lb
in, the constant I
OTP
has a value
1
0.916
(which implies I
OTP
= 422 lb
m
in
2
).
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 Fall '05
 ManuelMartinezSanchez
 Dynamics, Fluid Dynamics, Propulsion, Rocket Propulsion, Space Shuttle main engine, Prof. Manuel MartinezSanchez

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