Commercial Space Vehicle Emissions Modeling (2021) / Chapter Skim
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From page 56... ...
Commercial Space Vehicle Emissions Modeling 45 5 Model Validation The commercial space vehicle emissions model is based on the best available data in the literature. Nevertheless, the model must be validated before it can be applied to analyze the environmental impacts of commercial space operations.
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Commercial Space Vehicle Emissions Modeling 46 governed by the accuracy of the user-specified operational data. If the user does not provide the time-varying mass flow rate, the nominal mass flow rate and burn time from the fleet database are used to calculate the propellant mass burned.
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From page 58... ...
Commercial Space Vehicle Emissions Modeling 47 The uncertainty in the propellant mass flow rates in the fleet database can be partially quantified by comparing the initial and average mass flow rates listed in Table 2. The initial mass flow rate is estimated from the sea level thrust and specific impulse, and the average mass flow rate is estimated from the total propellant mass and burn time.
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Commercial Space Vehicle Emissions Modeling 48 CEA predicts a somewhat higher amount of H2O and lower amount of H2 compared to the EIS, which suggests that the chemical reaction may not achieve equilibrium in the rocket engine. The ratio of CO2 to CO is approximately 1 to 4 for the CEA predictions, whereas the ratio is approximately 1 to 7 for the EIS results.
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Commercial Space Vehicle Emissions Modeling 49 Furthermore, most of the results that are reported were used to develop the first-order estimates, so these sources do not provide independent validation results for the final emissions indices. The remaining literature sources investigated the effects of alumina, chlorine, or NOx emissions from solid rocket motors on stratospheric ozone, but the rockets involved in those studies have since been retired.
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Commercial Space Vehicle Emissions Modeling 50 Results of the Emissions Inventory Validation Figure 26 shows the comparison between the emissions inventory calculated by the commercial space vehicle emissions model and the emissions inventory published in the Space Shuttle EIS [14]
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Commercial Space Vehicle Emissions Modeling 51 Figure 26. Comparison between the emissions inventory calculated by the commercial space vehicle emissions model and the emissions inventory published in the Space Shuttle EIS [14]
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Commercial Space Vehicle Emissions Modeling 52 5.2 Future Model Validation Plan As discussed in the previous section, no high-quality emissions inventories that include all secondary emissions species for current commercial space vehicles are available in the literature. Thus, additional work is needed to fully validate the commercial space vehicle emissions model.
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From page 64... ...
Commercial Space Vehicle Emissions Modeling 53 5.2.2 High-Fidelity Modeling High-fidelity computational models should be leveraged as the first step to validate the final emissions estimates for commercial space vehicles across a range of altitudes. The following highfidelity codes may be useful for future model validation: The Rocket Exhaust Effluent Diffusion Model (REEDM)
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From page 65... ...
Commercial Space Vehicle Emissions Modeling 54 5.2.3 Field Measurements Although high-fidelity modeling is recommended as the first step for future model validation, even advanced computational models must be validated based on measurements. Unfortunately, only a limited number of rocket emissions measurements have been conducted to date.
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Commercial Space Vehicle Emissions Modeling 55 Figure 28. Conceptual roadmap for future model validation.
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Commercial Space Vehicle Emissions Modeling 56 In addition to emissions measurements at engine test stands, ground-based emissions measurements should be conducted at rocket launch sites. The emissions produced by a rocket during launch may differ from the emissions produced by a rocket engine on a test stand due to the following factors: Orientation of the rocket engine, Plume impingement on the ground, Plume interactions between multiple engines, Rocket engine power settings, Reactions with local chemical compounds, Deluge water at the launch pad, Dispersion time, and Initial ascent.
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Commercial Space Vehicle Emissions Modeling 57 The ground-based measurements of commercial space vehicle emissions described above will provide the expected emissions species and concentration levels for commercial rocket engines. The RISO rocket encounters [41, 42]
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Commercial Space Vehicle Emissions Modeling 58 The chase planes that are instrumented for aviation emissions measurements, such as NASA's DC-8 and DLR's Halo aircraft, are capable of flying in the troposphere and lower stratosphere. NASA's WB-57 aircraft is the highest-altitude airborne emissions platform, with a ceiling of roughly 60,000 ft (20 km)
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