Commercial Space Operations Noise and Sonic Boom Modeling and Analysis (2018)

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1-2 TABLE 1-1 Active Launch Licenses. Company Vehicle Orbital ATK Minotaur IV Lockheed Martin Commercial Launch Services Atlas V Orbital ATK Minotaur-C Orbital ATK Pegasus Orbital ATK Antares Configuration 230 Space Exploration Technologies Corporation Falcon 9 Version 1.2 United Launch Alliance Atlas V-401 Virgin Galactic SpaceShipTwo Launch vehicles are grouped into four basic types: (1) those that take-off horizontally using jet engines with a rocket igniting after the vehicle is launched, (2) those that take-off horizontally under rocket power, (3) those that are attached to an aircraft that take-off and are later released with a rocket igniting after release, and (4) those that take-off vertically. Each of these types of launch vehicles generates different noise and sonic boom impacts. Two examples are provided to illustrate the complexity of the noise and sonic boom exposure generated by these space operations: Example #1: Vehicles in the third category above, which can be represented by Virgin Galactic’s WhiteKnightTwo (WK2) and SpaceShipTwo (SS2), generate noise from both the aircraft take-off part of the mission (WK2) and the subsequent rocket powered suborbital flight (SS2). SS2 is a reusable, winged spacecraft designed to carry as many as eight people into space [Virgin Galactic, 2017]. Sonic boom from this type of suborbital flight may occur on ascent as the rocket powered vehicle reaches a high enough Mach number and pitches over; on descent sonic boom always occurs but overpressures are lower than on ascent, although small focal zones may develop and may be the dominant impact if they occur over populated areas. SS2 rocket engine noise occurs primarily during the ascent part of the suborbital flight which starts at approximately 50,000 feet MSL. Example #2: Another unique example of a commercial space operation that generates noise and sonic boom at multiple times during the operation is SpaceX’s launch of the Falcon 9 and recovery landing of its first stage. Figure 1-2 shows a graphic of the entire operation (launch, stage separation, and guided powered landing of the first stage.) The Falcon 9 is a vertically launched rocket that generates engine noise during the launch and ascent phase (for example from Kennedy Space Center); a sonic boom is then generated during the ascent phase, typically during and after the vehicle pitches over, and the resulting boom exposure occurs off coast in uninhabited areas; if SpaceX plans to recover the Falcon 9 first stage for reuse, then the first stage will generate a sonic boom during its reentry phase and the boom exposure will occur partly over land, with the highest boom levels occurring near the landing site; this is followed by the engine noise generated by the first stage during the landing phase of this operation. A time-lapse photo of the historic, first Falcon 9 launch and landing at Cape Canaveral on December 21, 2015 is shown in Figure 1-3. The above two examples illustrate several different components of acoustic impact that occur during a single launch mission. They underscore the need to use rocket noise and sonic boom models during different phases of spaceflight and to predict the overall acoustic impact of a launch mission.

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1-4 The FAA has not yet designated an approved method for rocket noise analysis of commercial space operations. Although there is an approved modeling method for sonic boom analysis of commercial space operations [FAA, 2015], it is practiced by few and, until recently, did not include many of the current spacecraft as standard inputs. Developing rocket noise and sonic boom models that are considered standard for commercial space operations assessments will require that these models: have approved modeling methodologies, include all current spacecraft and operation types, and have been validated in comparisons with field- measured acoustic data for spacecraft operations. These models should also have support for further development and eventually be commonly used by the environmental planning community. 1.2. Objectives The objectives of this research are the following: 1. Develop a set of noise and sonic boom models suitable for environmental analysis of commercial space operations and airport/space launch site facilities that are compatible with, or can be integrated into the FAA’s Aviation Environmental Design Tool (AEDT) software. 2. Develop a database of existing rocket/engine/motor data for commercial space launch operations. 3. Describe the approval process for the noise and sonic boom evaluations from airport/space launch operations. While AEDT [Zubrow et al., 2016] is the standard tool used to evaluate aircraft noise around airports, currently there are no standard tools for evaluating noise and sonic boom from commercial space operations at airports and spaceports. A further objective of this research, as mentioned above, is to develop noise and sonic boom modeling tools that are considered industry standard for assessing commercial space operations. 1.3. Research Overview To meet the objectives of this research, a review was conducted of the rocket noise model (RUMBLE) and sonic boom model (PCBoom) to assess the current state of their databases, modeling capabilities, and functionality/usability in order to identify changes required to model current spacecraft operations and for the possible future integration into AEDT. A summary of the improvements that have been made to the rocket noise and sonic boom models are provided in Sections 1.3.1 and 1.3.2, respectively. Additionally, recommended guidance for an official approval process to conduct reviews of modeling methodology and input data used have been developed. 1.3.1. Rocket Noise Model RUMBLE 2.0, the rocket noise model developed by Blue Ridge Research and Consulting, LLC (BRRC) under this ACRP project, will be the first publicly available software tool to predict noise of commercial space operations. All aspects of the software development process were considered to provide users with an accurate, efficient, and well-designed tool. The RUMBLE methodology has been approved for numerous environmental analyses of commercial space operations and it was the starting point for development efforts on this project. Efforts on this project have been focused on the development of a

1-5 Graphic User Interface (GUI) and accompanying User Guide, improving the program’s efficiency, strengthening the model’s compatibility with AEDT, and developing a database of spacecraft parameters. RUMBLE Graphic User Interface and User Guide RUMBLE’s graphical user interface was designed to improve user experience by allowing users to define all the necessary components of a commercial space noise study within an intuitive interface. The design of the RUMBLE GUI leverages the design concepts implemented in AEDT’s modeling environment. The accompanying RUMBLE user guide provides detailed instructions on how to install, run, and interact with the RUMBLE application. Additionally, the user guide provides examples and exercises to learn how to create study elements, guidance on the FAA approval process when using RUMBLE to conduct environmental studies, and a description of the RUMBLE Standard Input File (RSIF) format and its usage. RUMBLE Program Efficiency RUMBLE implements industry standard modeling practices, available noise source data sets, and fully geo-referenced source/receiver definitions and calculations. RUMBLE is a fully featured time-simulation based model, which is computationally intensive. Detailed modeling of the propulsion noise of a single spacecraft operation often includes hundreds of time-steps in which rocket noise source parameters are generated and propagated to thousands of receiver locations. Code optimization techniques were implemented throughout the RUMBLE program, including the time intensive ground interference component, and a significant reduction in run-time has been achieved. RUMBLE Integration with AEDT Tool development efforts have focused on strengthening the model’s compatibility with AEDT so that users familiar with performing environmental analyses within the AEDT modeling environment will have the skills to easily navigate the RUMBLE tool. AEDT compatibility issues have been carefully examined in every aspect of RUMBLE including program workflow, model input/output, database management, and user-interface design. The input file for RUMBLE uses xml file format, which is an open source text file format used by AEDT. Additionally, RUMBLE has adopted the same Noise Model ASCII Grid Format (NMAGF) files used by AEDT to ensure that users can load and combine RUMBLE and AEDT metric results within the AEDT user interface. RUMBLE Spacecraft Database A database of spacecraft airframe and engine/motor characteristics has been compiled and is accessible in the RUMBLE GUI. The organization of the database was adopted from AEDT to simplify future integration into the existing AEDT databases. The database contains data collected from publicly available sources. Use of standardized spacecraft parameters will ensure uniformity across studies, simplify the data collection process, and alleviate the current demands of FAA’s approval process. 1.3.2. Sonic Boom Model PCBoom, the sonic boom model developed under this project, is a single event, arbitrary maneuver, full ray tracing model that has been developed by Wyle for more than twenty years. The latest version of this model is PCBoom6 [Plotkin et al., 2010] although this version is primarily a research tool

1-6 and its release is restricted making it unsuitable for use on this project. PCBoom4 [Plotkin et al., 2002], also referred to in this report as PCBoom and the sonic boom model, is the version that has been used most often for sonic boom prediction of space vehicle operations and was recommended as the basis for the current project. A primary objective of this project is to develop a sonic boom model that is suitable for environmental assessment of commercial space operations and useable by the AEDT practitioner. Towards this objective, a review of PCBoom4 modeling methodology and functionality was conducted. Although PCBoom4 is a mature program, several modeling gaps related to analysis of commercial space operations were identified along with some usability issues as described following. Sonic Boom Source (F-function) Database One of the primary inputs to PCBoom is the sonic boom source or F-function. There are a number of ways that users can input F-functions into the model. However, when a new F-function is required, it is expected that model users will primarily use Carlson’s method [Carlson, 1978] to calculate a simplified N-wave F-function using area-rule methods. Although, for complicated vehicle geometries, it has been found that this process can be difficult to implement correctly. To improve usability of this method, the PCBoom user guide includes a discussion of Carlson’s method, simplified where possible. A modeling gap related to space vehicle F-functions, identified at the start of the project, was that PCBoom4 did not include many of the current spacecraft in its database. For this project, the database of vehicle inputs (sonic boom sources) was expanded to include all of the current FAA licensed spacecraft. Launch Vehicle Mode A new launch vehicle operation mode was developed that provides users with better control of spacecraft staging events and, accordingly, which vehicle inputs (sonic boom sources) are used at different points in the trajectory. This permits easy transitioning of the vehicle inputs at user defined times when staging occurs or when engine thrust has changed. For example, the vehicle input for a two-stage launch vehicle is initially the entire vehicle as it is after launch, but after stage separation the vehicle input transitions to the second stage only. The new launch vehicle mode also provides easy control over rocket engine thrust and plume effects. PCBoom Noise Metrics PCBoom was also limited in the number of noise metrics the user could output. Internal to the program, data were available to compute these metrics, however peak overpressure (psf) was primarily reported for sonic boom exposure. To improve compatibility with AEDT, PCBoom can now output additional noise metrics including A-weighted sound exposure level (ASEL), C-weighted sound exposure level (CSEL), loudness (PL), and other metrics. PCBoom-AEDT Interface and User Guide As mentioned in Section 1.2, one of the main objectives of this project is to make PCBoom compatible with or able to be integrated with AEDT. An integration plan that describes how the sonic boom model could be integrated with AEDT is presented in Section 3.2. This AEDT Integration Plan describes how the sonic boom model would fit into the structure of AEDT and identifies possible

1-7 upgrades to AEDT to aid the integration of both models. The accompanying user guide for PCBoom provides detailed instructions on how to install the program, run sample cases and generate noise grids that are compatible with AEDT. The user guide also includes a section with guidance on FAA’s noise modeling review and approval process which should aid practitioners in the preparation of commercial space environmental studies. 1.4. Document Organization This final report for ACRP Project 02-66 is organized into the following sections:  Section 1 Introduction. This section provides background information and a research overview related to the ACRP Project 02-66 objectives to develop a set of noise and sonic boom models for commercial space operations.  Section 2 describes the rocket noise and sonic boom modeling methodologies. These methodologies were developed to produce accurate acoustic predictions relevant to environmental analysis of commercial space operations. This section describes the core components of each model, which provides the knowledge necessary for users to prepare accurate model inputs and interpret the results generated by the models.  Section 3 presents the AEDT integration plans for the rocket noise and sonic boom models. Two integration plans are presented: a low-level integration plan to import RUMBLE and PCBoom results into AEDT and a full integration plan to incorporate the RUMBLE and PCBoom models into AEDT. The low-level integration plan represents the current status of integration capabilities between RUMBLE (OR PCBOOM) and AEDT, whereas the full integration plan considers future development efforts for the complete integration of both models into AEDT.  Section 4 describes a plan for model validation of the rocket noise and sonic boom models. Model validation requires checking the accuracy of the models’ acoustic predictions compared to field-measured acoustic data for commercial spacecraft operations. A validation plan is outlined in this section to address computer model validation procedures, modeling requirements, and the data collection and validation test requirements needed to validate the rocket noise and sonic boom models.  Section 5 discusses development of a modeling review and approval process for commercial space noise studies. This section discussed development of an official approval process to conduct reviews of modeling methodology and input data used in the RUMBLE and PCBoom models.  Section 6 provides a list of possible research that could enhance the models’ databases/inputs/outputs, noise modeling methodology, user experience and move towards validated and standardized models within AEDT. A separate document is also provided that includes the user guides for the rocket noise and sonic boom models.