Figure 4.3.1: SSME Oxidixer System Schematic ^[1]

Low Pressure Oxidizer Turbopump

We begin our analysis with the Low Pressure Oxidizer Turbopump. Liquid oxygen from the external tank enters the pump at Station 17 with a known temperature, pressure, and mass flow rate. The desired pressure at the pump exit is known, along with the pump efficiency. The task is to determine the amount of power required to drive the pump and the thermodynamic properties of the liquid oxygen at the pump’s exit.

There is one key difference between this pump and the Low Pressure Fuel Pump. The output from the from the Low Pressure Oxidizer Turbopump is mixed with the output from the Low Pressure Oxidizer Turbine. Both of these flows combine at Station 18. The Low Pressure Fuel Turbopump uses separate lines for the flow traveling through the pump (Stations 1 and 2) and the turbine (Stations 10 and 11). In this analysis, Station 23 represents the Low Pressure Oxidizer Turbine exit, prior to mixing at Station 18. Station 18p will be used to represent the Low Pressure Oxidizer turbopump exit prior to mixing at Station 18. The calculations are performed with an analogous procedure to that described in Section 4.1 to solve for the output conditions at Station 18p. Results are shown below.

Figure 4.3.2

We can then use Equation 4.3.1 to solve for the power required to run the pump:

The results of the calculation are tabulated below. The model predicts the pump power requirement to within 1% of the actual value utilized in the SSME.

Low Pressure Oxidizer Turbine

This turbine powers the Low Pressure Oxidizer Turbopump. From the preceding analysis, we know that 1614 HP must be generated. The task is to solve for the mass flow rate through the turbine that will generate this much power. We assume the flow inlet conditions at Station 22 are known. We also know the maximum allowable pressure drop between Stations 22 and 23 (flow leaving the turbine merges with the output flow from low pressure pump). Output conditions are solved for using a similar procedure to that described for the Low Pressure Fuel Turbine in Section 4.1. Input and output conditions are shown below on Figure 4.3.3. Once again, the model performs well, predicting the required mass flow rate within one percent of actual value measured in the SSME.

Figure 4.3.3

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