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Commercial Space Vehicle Emissions Modeling 1 Summary Motivation: Commercial space transportation is a rapidly evolving industry with a growing number of launch vehicles and spaceports currently under development. The Federal Aviation Administration (FAA) requires all new launch vehicles and spaceports to acquire operator licenses. This licensing process involves an environmental review to assess the potential impacts of rocket emissions. However, no standard procedure for estimating rocket emissions currently exists. Objective: The objective of this research project was to develop a user-friendly tool for practitioners to estimate the emissions from commercial space vehicles. Key Results: Our team developed a commercial space vehicle emissions model and integrated it into RUMBLE, the launch vehicle acoustic simulation model created by Blue Ridge Research and Consulting, LLC (BRRC) under ACRP project 02-66. The integrated tool, RUMBLE 3.0, is the first software tool that enables practitioners to accurately model the noise and emissions produced by commercial space vehicles. RUMBLE 3.0 implements the rocket noise and emissions models via a user-friendly interface, as shown in Figure 1. The user interface adopts a similar workflow as the Aviation Environmental Design Tool (AEDT), which is the standard tool for modeling the noise and emissions from commercial aviation in the United States. Our team also developed a comprehensive, more than 100-page user guide that provides instructions for using the tool. RUMBLE 3.0 and its accompanying user guide are freely available to the public through the Airport Cooperative Research Program (ACRP). RUMBLE 3.0 is currently the first publically available tool for estimating the noise and emissions from commercial space vehicles. Figure 1. Preview of the RUMBLE 3.0 user interface.
Commercial Space Vehicle Emissions Modeling 2 Methodology: The commercial space vehicle emissions model calculates the mass of each pollutant emitted into each atmospheric layer. The calculations depend on the following parameters: ï Engine performance data to estimate the propellant mass flow rate and burn time, ï Emissions indices to relate the amount of propellant burned to the amount of each pollutant emitted, and ï Trajectory data to determine the amount of time spent in each atmospheric layer. The emissions index for a pollutant reports the outcome of a complex series of chemical reactions as a single number. Unfortunately, high-quality emissions data are not publicly available for most commercial space vehicles. Instead, our team generated a database of emissions indices using NASA- developed software and estimates based on prior results from the literature. Figure 2 shows the estimates of the emissions indices for selected first-stage rocket engines at sea level. RUMBLE 3.0 stores the emissions indices and engine performance data in an internal fleet database. The fleet database includes every orbital-class launch vehicle built or launched in the United States in 2019 as well as several launch vehicles of historical interest. Users can also add new vehicles to the database. Unlike the vehicles in the fleet database, the trajectory is typically unique to each operation. RUMBLE 3.0 enables users to provide custom trajectory data or select a built-in example trajectory. Figure 2. Estimates of the final emissions indices, in grams of pollutant emitted per kilogram of propellant consumed, for selected first-stage rocket engines at sea level.
Commercial Space Vehicle Emissions Modeling 3 Validation: The commercial space vehicle emissions model is based on the best publicly available data in the literature. However, it contains uncertainty due to the scarcity of high-quality emissions data. Our team validated the emissions model using the Space Shuttle, which has the most complete and well-documented emissions data in the literature. The validation results demonstrate that the emissions indices and modeling methodology are accurate within an acceptably low margin of error. Additional work is needed to fully validate the emissions model for current commercial space vehicles. Our team proposed a future model validation plan consisting of high-fidelity modeling, ground-based measurements, and measurements at altitude. The plan targets the pollutants with the greatest environmental impacts and highest uncertainty in the emissions model. RUMBLE 3.0 enables users to incorporate future emissions measurements into the fleet database so that the emissions model always contains the best available data for commercial space vehicles. AEDT Integration: AEDT is the standard tool for modeling emissions from commercial aviation in the United States. Integrating the commercial space vehicle emissions model with AEDT is a logical step toward achieving a comprehensive suite of software tools for assessing the environmental impacts of both aircraft and spacecraft. Our team developed conceptual AEDT user interface modifications, pseudocode, and a spreadsheet emissions estimator tool to assist future programmers with AEDT integration. In the interim, RUMBLE 3.0 enables practitioners to accurately model the noise and emissions produced by commercial space vehicles. Future Research: RUMBLE 3.0 provides new capabilities to practitioners, researchers, and decision makers. Practitioners can use RUMBLE 3.0 to prepare environmental documents for launch vehicle and spaceport operator licenses. Researchers can apply RUMBLE 3.0 to develop more reliable emissions inventories for future growth scenarios of commercial space operations to analyze their global environmental impacts.