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NASA NTRS2017

The Profile Envision and Splice Tool (PRESTO): Developing an Atmospheric Wind Analysis Tool for Space Launch Vehicles Using Python

Tropospheric winds are an important driver of the design and operation of space launch vehicles. Multiple types of weather balloons and Doppler Radar Wind Profiler (DRWP) systems exist at NASA's Kennedy Space Center (KSC), co-located on the United States Air Force's (USAF) Eastern Range (ER) at the Cape Canaveral Air Force Station (CCAFS), that are capable of measuring atmospheric winds. Meteorological data gathered by these instruments are being used in the design of NASA's Space Launch System (SLS) and other space launch vehicles, and will be used during the day-of-launch (DOL) of SLS to aid in loads and trajectory analyses. For the purpose of SLS day-of-launch needs, the balloons have the altitude coverage needed, but take over an hour to reach the maximum altitude and can drift far from the vehicle's path. The DRWPs have the spatial and temporal resolutions needed, but do not provide complete altitude coverage. Therefore, the Natural Environments Branch (EV44) at Marshall Space Flight Center (MSFC) developed the Profile Envision and Splice Tool (PRESTO) to combine balloon profiles and profiles from multiple DRWPs, filter the spliced profile to a common wavelength, and allow the operator to generate output files as well as to visualize the inputs and the spliced profile for SLS DOL operations. PRESTO was developed in Python taking advantage of NumPy and SciPy for the splicing procedure, matplotlib for the visualization, and Tkinter for the execution of the graphical user interface (GUI). This paper describes in detail the Python coding implementation for the splicing, filtering, and visualization methodology used in PRESTO.

Orcutt, John M.↗

NASA NTRS2017

NASA's Space Launch System: Deep-Space Delivery for SmallSats

Designed for human exploration missions into deep space, NASA's Space Launch System (SLS) represents a new spaceflight infrastructure asset, enabling a wide variety of unique utilization opportunities. While primarily focused on launching the large systems needed for crewed spaceflight beyond Earth orbit, SLS also offers a game-changing capability for the deployment of small satellites to deep-space destinations, beginning with its first flight. Currently, SLS is making rapid progress toward readiness for its first launch in two years, using the initial configuration of the vehicle, which is capable of delivering more than 70 metric tons (t) to Low Earth Orbit (LEO). Planning is underway for smallsat accomodations on future configurations of the vehicle, which will present additional opportunities. This paper will include an overview of the SLS vehicle and its capabilities, including the current status of progress toward first launch. It will also explain the current and future opportunities the vehicle offers for small satellites, including an overview of the CubeSat manifest for Exploration Mission-1 in 2018 and a discussion of future capabilities.

Robinson, Kimberly F.↗

NASA NTRS2017

Update on Risk Reduction Activities for a Liquid Advanced Booster for NASA's Space Launch System

The stated goals of NASA's Research Announcement for the Space Launch System (SLS) Advanced Booster Engineering Demonstration and/or Risk Reduction (ABEDRR) are to reduce risks leading to an affordable Advanced Booster that meets the evolved capabilities of SLS and enable competition by mitigating targeted Advanced Booster risks to enhance SLS affordability. Dynetics, Inc. and Aerojet Rocketdyne (AR) formed a team to offer a wide-ranging set of risk reduction activities and full-scale, system-level demonstrations that support NASA's ABEDRR goals. During the ABEDRR effort, the Dynetics Team has modified flight-proven Apollo-Saturn F-1 engine components and subsystems to improve affordability and reliability (e.g., reduce parts counts, touch labor, or use lower cost manufacturing processes and materials). The team has built hardware to validate production costs and completed tests to demonstrate it can meet performance requirements. State-of-the-art manufacturing and processing techniques have been applied to the heritage F-1, resulting in a low recurring cost engine while retaining the benefits of Apollo-era experience. NASA test facilities have been used to perform low-cost risk-reduction engine testing. In early 2014, NASA and the Dynetics Team agreed to move additional large liquid oxygen/kerosene engine work under Dynetics' ABEDRR contract. Also led by AR, the objectives of this work are to demonstrate combustion stability and measure performance of a 500,000 lbf class Oxidizer-Rich Staged Combustion (ORSC) cycle main injector. A trade study was completed to investigate the feasibility, cost effectiveness, and technical maturity of a domestically-produced engine that could potentially both replace the RD-180 on Atlas V and satisfy NASA SLS payload-to-orbit requirements via an advanced booster application. Engine physical dimensions and performance parameters resulting from this study provide the system level requirements for the ORSC risk reduction test article. The test article is scheduled to complete fabrication and assembly soon and continue testing through late 2019. Dynetics has also designed, developed, and built innovative tank and structure assemblies using friction stir welding to leverage recent NASA investments in manufacturing tools, facilities, and processes, significantly reducing development and recurring costs. The full-scale cryotank assembly was used to verify the structural design and prove affordable processes. Dynetics performed hydrostatic and cryothermal proof tests on the assembly to verify the assembly meets performance requirements..

Crocker, Andrew M.↗

NASA NTRS2017

NASA's Space Launch System: Progress Report

After more than four decades exploring the space environment from low Earth orbit and developing long-duration spaceflight operational experience with the International Space Station (ISS), NASA is once again preparing to send explorers into deep space. Development, test and manufacturing is now underway on the launch vehicle, the crew spacecraft and the ground processing and launch facilities to support human and robotic missions to the moon, Mars and the outer solar system. The enabling launch vehicle for these ambitious new missions is the Space Launch System (SLS), managed by NASA's Marshall Space Flight Center (MSFC). Since the program began in 2011, the design has passed Critical Design Review, and extensive development, test and flight hardware has been produced by every major element of the SLS vehicle. Testing continues on engines, boosters, tanks and avionics. While the program has experienced engineering challenges typical of a new development, it continues to make steady progress toward the first SLS mission in roughly two years and a sustained cadence of missions thereafter. This paper will discuss these and other technical and SLS programmatic successes and challenges over the past year and provide a preview of work ahead before first flight.

Cook, Jerry↗

NASA NTRS2017

NASA's Space Launch System: SmallSat Deployment to Deep Space

Leveraging the significant capability it offers for human exploration and flagship science missions, NASA's Space Launch System (SLS) also provides a unique opportunity for lower-cost deep-space science in the form of small-satellite secondary payloads. Current plans call for such opportunities to begin with the rocket's first flight; a launch of the vehicle's Block 1 configuration, capable of delivering 70 metric tons (t) to Low Earth Orbit (LEO), which will send the Orion crew vehicle around the moon and return it to Earth. On that flight, SLS will also deploy 13 CubeSat-class payloads to deep-space destinations. These secondary payloads will include not only NASA research, but also spacecraft from industry and international partners and academia. The payloads also represent a variety of disciplines including, but not limited to, studies of the moon, Earth, sun, and asteroids. While the SLS Program is making significant progress toward that first launch, preparations are already under way for the second, which will see the booster evolve to its more-capable Block 1B configuration, able to deliver 105t to LEO. That configuration will have the capability to carry large payloads co-manifested with the Orion spacecraft, or to utilize an 8.4-meter (m) fairing to carry payloads several times larger than are currently possible. The Block 1B vehicle will be the workhorse of the Proving Ground phase of NASA's deep-space exploration plans, developing and testing the systems and capabilities necessary for human missions into deep space and ultimately to Mars. Ultimately, the vehicle will evolve to its full Block 2 configuration, with a LEO capability of 130 metric tons. Both the Block 1B and Block 2 versions of the vehicle will be able to carry larger secondary payloads than the Block 1 configuration, creating even more opportunities for affordable scientific exploration of deep space. This paper will outline the progress being made toward flying smallsats on the first flight of SLS, and discuss future opportunities for smallsats on subsequent flights.

Robinson, Kimberly F.↗

NASA NTRS2017

NASA's Space Launch System: SmallSat Deployment to Deep Space

Robinson, Kimberly F.↗

NASA NTRS2017

Human Factors Virtual Analysis Techniques for NASA's Space Launch System Ground Support using MSFC's Virtual Environments Lab (VEL)

Using virtual environments to assess complex large scale human tasks provides timely and cost effective results to evaluate designs and to reduce operational risks during assembly and integration of the Space Launch System (SLS). NASA's Marshall Space Flight Center (MSFC) uses a suite of tools to conduct integrated virtual analysis during the design phase of the SLS Program. Siemens Jack is a simulation tool that allows engineers to analyze human interaction with CAD designs by placing a digital human model into the environment to test different scenarios and assess the design's compliance to human factors requirements. Engineers at MSFC are using Jack in conjunction with motion capture and virtual reality systems in MSFC's Virtual Environments Lab (VEL). The VEL provides additional capability beyond standalone Jack to record and analyze a person performing a planned task to assemble the SLS at Kennedy Space Center (KSC). The VEL integrates Vicon Blade motion capture system, Siemens Jack, Oculus Rift, and other virtual tools to perform human factors assessments. By using motion capture and virtual reality, a more accurate breakdown and understanding of how an operator will perform a task can be gained. By virtual analysis, engineers are able to determine if a specific task is capable of being safely performed by both a 5% (approx. 5ft) female and a 95% (approx. 6'1) male. In addition, the analysis will help identify any tools or other accommodations that may to help complete the task. These assessments are critical for the safety of ground support engineers and keeping launch operations on schedule. Motion capture allows engineers to save and examine human movements on a frame by frame basis, while virtual reality gives the actor (person performing a task in the VEL) an immersive view of the task environment. This presentation will discuss the need of human factors for SLS and the benefits of analyzing tasks in NASA MSFC's VEL.

Searcy, Brittani↗

NASA NTRS2018

Powered Explicit Guidance Modifications and Enhancements for Space Launch System Block-1 and Block-1B Vehicles

NASA is currently building the Space Launch System (SLS) Block-1 launch vehicle for the Exploration Mission 1 (EM-1) test flight. NASA is also currently designing the next evolution of SLS, the Block-1B. The Block-1 and Block-1B vehicles will use the Powered Explicit Guidance (PEG) algorithm (of Space Shuttle heritage) for closed loop guidance. To accommodate vehicle capabilities and design for future evolutions of SLS, modifications were made to PEG for Block-1 to handle multi-phase burns, provide PEG updated propulsion information, and react to a core stage engine out. In addition, due to the relatively low thrust-to-weight ratio of the Exploration Upper Stage (EUS) and EUS carrying out Lunar Vicinity and Earth Escape missions, certain enhancements to the Block-1 PEG algorithm are needed to perform Block-1B missions to account for long burn arcs and target translunar and hyperbolic orbits. This paper describes the design and implementation of modifications to the Block-1 PEG algorithm as compared to Space Shuttle. Furthermore, this paper illustrates challenges posed by the Block-1B vehicle and the required PEG enhancements. These improvements make PEG capable for use on the SLS Block-1B vehicle as part of the Guidance, Navigation, and Control (GN&C) System.

Von der Porten, Paul↗

NASA NTRS2018

NASA's Space Launch System: Deep-Space Opportunities for Smallsats

Designed to provide the significant capability required for human deep-space exploration, NASA’s Space Launch System (SLS) also provides a unique opportunity for lower-cost deep-space science in the form of small-satellite secondary payloads. This opportunity will be leveraged beginning with the rocket’s first flight; a launch of the vehicle’s Block 1 configuration, capable of delivering 70 metric tons (70t - tonnes) to Low Earth Orbit (LEO), which will see the Orion crew vehicle travel around the moon and return to Earth. On that flight, SLS will also deploy 13 6U (6 Unit) CubeSat-class payloads to multiple destinations including deep space. These secondary payloads will include not only NASA research, but also spacecraft from international partners, industry and academia. The payloads represent a variety of disciplines including, but not limited to, studies of the moon, Earth, sun, and asteroids, along with technology demonstrations that could pave the way for even more ambitious smallsat missions in the future. As the SLS Program is making significant progress toward that first launch, preparations are already under way for future missions, which will see the booster evolve to its more-capable Block 1B configuration, able to deliver 105t to LEO. That configuration will have the capability to carry large payloads co-manifested with the Orion spacecraft, or to utilize an 8.4-meter (m) fairing to carry payloads several times larger than are currently possible. The Block 1B vehicle will be the workhorse of the Proving Ground phase of NASA’s deep-space exploration plans, developing and testing the systems and capabilities necessary for human missions into deep space and ultimately to Mars. Ultimately, the vehicle will evolve to its full Block 2 configuration, with a LEO capability of 130 metric tons. Both the Block 1B and Block 2 versions of the vehicle will be able to carry larger secondary payloads than the Block 1 configuration, creating even more opportunities for affordable scientific exploration of deep space. This paper will outline the progress being made toward flying smallsats on the first flight of SLS, and discuss future opportunities for smallsats on subsequent flights.

Robinson, Kimberly F.↗

NASA NTRS2018

NASA's Space Launch System Gains Momentum Toward Integration and Testing

NASA’s Space Launch System (SLS) (Fig. 1) entered a new phase in 2017, completing major structural manufacturing on the core stage and delivering for launch the first flight hardware of the world’s most capable launch vehicle. The program is now in a stage of hardware assembly, integration and testing in preparation for the first integrated flight of SLS and the Orion crew vehicle. SLS is critical to U.S. leadership in future human and robotic space exploration, including a presence on the Moon in preparation for missions deeper into space. This paper will elaborate on SLS accomplishments in 2017 and plans for progress in 2018.

Askins, Bruce R.↗

NASA NTRS2018

Risk-Based Explosion Assessment Internal Explosion of Exploration Upper Stage in Vehicle Assembly Building

This paper presents risk-based explosion analyses used to determine if an explosion of NASA's Space Launch System (SLS) Exploration Upper Stage (EUS) during fueling in Vehicle Assembly Building (VAB) High Bay 4 can hazard the Space Launch System (SLS) being processed in Bay 3. This paper focuses on blast fragmentation as it was the controlling hazard. An estimate of the amount of Net Explosion Weight (NEW) was used to develop a fragment list (mass, shape, takeoff velocity/angle) given an explosion occurs at ground level in Bay 4. Intervening superstructure that exists between Bay 4 and Bay 3 (that could potentially block EUS fragments) was modeled based on detailed visual images (VISSIM) and AUTOCAD/structural drawings. The fragment list was input to a 3D trajectory application that performs multiple random explosion simulations; each simulation varying fragment ballistic coefficient and takeoff angle/velocity. Individual fragments are tracked until stopped by the intervening superstructure or reach Bay 3, potentially impacting the SLS. The probability of impacting the SLS is then determined from the random simulations; the results are used to help decision-makers determine the efficacy of co-processing within the VAB and decide what mitigations may be appropriate.

Explosion Assessment↗

NASA NTRS2018

NASA's Space Launch System: Secondary Payload Accommodations in Block 1 and Beyond

Launching from pad 39B at Kennedy Space Center no earlier than December 2019, NASA's Space Launch System (SLS) will send the Orion crew vehicle to a distant retrograde lunar orbit in order to test and validate the new systems developed for SLS, Orion and Kennedy Space Center's Exploration Ground Systems (EGS). In addition to these primary mission objectives, the first integrated fight of NASA's new deep space exploration system, Exploration Mission-1 (EM-1), offers accommodations for 13 6U CubeSats, which will be deployed in deep space after Orion separates from the SLS Interim Cryogenic Propulsion Stage (ICPS). In 2017, the SLS Program, managed by NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, completed the ICPS and delivered it to the EGS Program, which has responsibility for stacking and launch operations. The 13 EM-1 secondary payloads will reside in the Orion Stage Adapter (OSA), which connects the ICPS to Orion's spacecraft adapter. The OSA is essentially complete with preparations being made for transporting the hardware to Kennedy Space Center with accommodations for secondary payload dispensers and with the secondary payload avionics unit installed.

Robinson, Kimberly F.↗

NASA NTRS2018

NASA's Space Launch System: Opportunities for Small Satellites to Deep Space Destinations

The first flight of NASA's new exploration-class launch vehicle, the Space Launch System (SLS), will test a myriad of systems designed to enable the next generation of deep space human spaceflight, while also providing the rare opportunity for 13 6U CubeSat-class payloads to be deployed in several locations along the flight path. The first mission of SLS and NASA's new Orion crew vehicle, Exploration Mission-1 (EM-1), will launch from upgraded facilities at Kennedy Space Center no earlier than fiscal year 2020. The initial Block 1 configuration for EM-1 will be capable of lofting at least 26 metric tons (t) of payload to the moon, with propulsion supplied by twin five-segment solid rocket boosters, four RS-25 engines and an Interim Cryogenic Propulsion Stage (ICPS). SLS will send Orion into a distant retrograde lunar orbit, paving the way for future missions to cislunar space and eventually Mars. The multidisciplinary small satellites for EM-1 derive from NASA research, as well as from international partners, industry and academia. Research subjects for the various smallsats include the moon, sun and an asteroid. Science objectives vary from characterizing the effects of radiation on living organisms (yeast) to landing the smallest spacecraft yet on the moon to supporting space weather research. Some of the payloads are technology demonstrations that will pave the way for more ambitious future missions that will be deployed by the more powerful SLS Block 1B configuration.

Robinson, Kimberly F.↗

NASA NTRS2018

Nasa's Space Launch System: Exceptional Opportunities for Secondary Payloads to Deep Space

When NASA’s Space Launch System (SLS) launches for the first time from Kennedy Space Center, it will send the Orion crew vehicle farther into space than a human-rated spacecraft has ever traveled. The primary objectives of this first uncrewed mission, Exploration Mission-1 (EM-1), focus on verifying and validating the new technologies and integrated systems developed for SLS, Orion and Exploration Ground Systems (EGS), which together comprise NASA’s new deep space exploration system. EM-1 also provides the opportunity for 13 6U CubeSat secondary payloads to be deployed in deep space. As progress is being made toward that first launch, planning is also taking place for secondary payload opportunities on future missions. This paper will provide an overview of the status of the SLS Block 1 launch vehicle and an overview of the 6U payloads selected for EM-1. In addition, an overview of the EM-1 mission trajectories and the “bus stops” along the trajectory where the payloads will be deployed will be noted. Challenges and new workflows required in identifying and certifying potential payloads will be discussed. The paper will also discuss opportunities that will be presented by future evolutions of SLS.

Robinson, Kimberly F.↗

NASA NTRS2018

NASA's Space Launch System Moves into Testing and Integration

NASA's Space Launch System (SLS) has moved from design and manufacturing into testing and integration for its first flight as early as December 2019. In 2017, the NASA/industry team completed manufacturing of all major structural elements for the launch vehicle for Exploration Mission-I (EM-1 ). That work included shipping the first major flight hardware element to the launch site. The team processed all four RS-25 engines for stage integration, cast all 10 booster flight motor segments, and manufactured all five major sections of the core stage. The program also completed major structural work on the B-2 test stand at Stennis Space Center, which will be used for the core stage "green run" test; delivered the core stage and engine simulators used for training; and much of the transportation equipment for the core stage. Engineers completed structural testing on the upper stage/payload section of the vehicle as well as the engine section test article. In 2018, the program will deliver the Orion Stage Adapter (OSA) to Exploration Ground Systems (EGS) at KSC and send the test articles for the core stage liquid hydrogen tank, liquid oxygen tank, and intertank to NASA's Marshall Space Flight center for structural testing. Additionally, workers will begin the challenging process of integrating the major sections of the 212-foot EM-1 core stage. This work is focused on the initial Block 1 variant of SLS, capable of launching more than 70 metric tons (t) to low Earth orbit (LEO). However, work concurrently is underway on the Block lB variant, which will enable 105 t to LEO and more than 37t to trans-lunar injection (TLI). Block lB will be the workhorse vehicle of NASA's lunar exploration plans. As the needs of the nation's deep space exploration program grow, SLS performance is designed to evolve to a payload mass of 130 t to LEO and up to 45t to TLI. The advantages of this mass - as well as volume- are critical to the entire exploration architecture for deep space exploration. They translate to greater capability, greater infrastructure and operational simplicity, less overall mission risk, and opportunities to accomplish unprecedented exploration and discovery. This paper will discuss SLS progress to date and planned future work.

Honeycutt, John↗

NASA NTRS2018

Accommodations for Secondary Payloads in NASA's Space Launch System

NASA's new heavy-lift launch vehicle, the Space Launch System (SLS), is moving closer to its planned 2019 launch, with the in-space stage and spacecraft adapters complete and all other major elements of the rocket manufactured and currently being outfitted for flight. Exploration Mission-1 (EM-1), the first flight of SLS and the new Orion crew vehicle, will verify and validate new systems and provide an unparalleled opportunity for 13 6U CubeSat-class payloads to be released into deep space. Payloads are being developed by NASA, industry, international and academic partners and were selected for the EM-1 flight to address strategic knowledge gaps in the agency's plans for human deep space exploration. Destinations range from the lunar surface to an asteroid to an orbit around the Earth-moon L2 libration point. Missions include studying the effects of space radiation on a living organism (yeast), landing the smallest lander to date on the moon, and searching for water in permanently shaded lunar craters. Propulsion technology demonstrations include solar sails, use of inert water to carry out lunar gravity assist maneuvers, and use of new "green" chemical propellants. SLS employs an evolutionary design approach, with an initial capability of at least 26 metric tons (t) to trans-lunar injection (TLI). The later Block 1B configuration, which will become the Agency's workhorse launch vehicle into the 2020s, will lift at least 34 t to TLI in its crew configuration and at least 37 t in the cargo configuration. In addition to greater lift capability, Block 1B will also offer larger payload volume than Block 1 for both co-manifested and secondary payloads. In Block 1B, various combinations of 6U, 12U and 27U payloads may be accommodated in the vehicle's stage adapter. Opportunities for deep space research once out of reach for small science payloads will be within reach, opening many possibilities for exciting new technology demonstrations and scientific missions. This paper will provide an overview of the capabilities and the status of the Block 1 vehicle, with particular emphasis on the secondary payload accommodations and the deployment system. Brief descriptions of the 13 6U EM-1 payloads will be included. In addition, a discussion of the payload developers' responsibilities and the Space Launch System Program's roles and responsibilities in accommodating these and future payloads will be included. Finally, the author will look ahead to SLS Block 1B and missions beyond EM-1 and the opportunities for 6U, 12U and 27U CubeSats.

Robinson, Kimberly F.↗

NASA NTRS2018

Payload Utilization in NASA's Space Launch System

With Space Policy Directive 1, the United States administration has directed the National Aeronautics and Space Administration’s (NASA’s) Human Exploration & Operations Mission Directorate (HEOMD) to return to the Moon with missions and infrastructure designed to support a sustained presence in cislunar space, with robotic and human lunar surface operations. NASA’s new deep space exploration system — the super heavy-lift Space Launch System (SLS), the Orion crew spacecraft and revamped launch facilities at Kennedy Space Center (KSC) — will enable NASA and its commercial and international partners to meet this goal for human exploration of deep space. SLS is the most capable launch vehicle for these efforts, as well as for sending robotic missions deep into the solar system, or even to interstellar space. The vehicle will be available in crew and cargo configurations in progressively more powerful block variants. The initial Block 1 lift capability of at least 26 metric tons (t) to trans-lunar injection (TLI) will be followed by a more powerful Block 1B with the power to loft more than 37 t to TLI. The ultimate Block 2 variant will lift more than 45 t to TLI. For payload accommodation, the Block 1 vehicle can utilize a 5 meter (m) fairing in its cargo configuration with the crew version also able to provide berths for 6U and 12U CubeSats as secondary payloads. The Block 1B crew vehicle will provide as much volume as the space shuttle payload bay in a Universal Stage Adapter (USA) for co-manifested payloads (CPLs). Block 1B cargo vehicles will offer 8.4 m-diameter fairings in 19.1 m and possibly longer lengths, with enough volume to accommodate lunar-orbiting habitat modules and other elements of NASA’s Gateway science outpost. For Mars-class payloads, larger fairings for the Block 2 cargo launcher are under consideration. For missions beyond the Earth-Moon system, SLS offers greater characteristic energy (C3) than any other launch vehicle, enabling shorter transit times or heavier payloads with more robust science packages for missions to the outer solar system. Indeed, the unmatched combination of thrust, payload volume and departure energy that SLS provides opens new opportunities for human and robotic exploration of deep space. This paper will provide an overview of the various vehicle block configurations, their capabilities and payload accommodations for sending primary, co-manifested and secondary payloads to deep space

Creech, Stephen D.↗

NASA NTRS2019

CHANGO: A Software Tool for Boost Stage Guidance of the Space Launch System Exploration Mission 1

The Day of Launch Initiation Load Update (DOLILU) System is the means by which the Space Launch System (SLS) Vehicle trajectory is designed, verified, and uploaded on the Day of Launch (DOL) in order to ensure a safe flight. Launch vehicles are designed to fly down a narrow angle of attack and sideslip angle corridor in order to keep them within structural load limits. The angle of attack and sideslip angle response to the launch vehicle experiences can vary significantly based upon the winds experienced on the DOL. SLS Boost Stage flight employs an open-loop guidance scheme through Solid Rocket Booster (SRB) separation. In the SLS open-loop scheme, the vehicle will fly a prescribed set of attitudes as a function of the change in altitude since launch. This set of reference attitude values and corresponding altitude reference independent values are designed with ground software using winds measured on the DOL with the goal of minimizing angle of attack and sideslip angle, thereby minimizing related ascent integrated vehicle structural loads. The table of Boost Stage attitude commands as a function of altitude gained since launch is called the chi table. A software tool called CHANGO (Chi Angle Optimizer) designs the Boost Stage chi table which is uploaded to the vehicle’s flight computer and used during ascent by the flight software (FSW). The wind and atmospheric conditions are measured prior to launch and pre-processed to become input to the CHANGO software along with a set of parameters developed in advance of the DOL. CHANGO’s target set consists of the heading and altitude rate at SRB separation determined well before launch by the Program to Optimize Simulated Trajectories (POST). CHANGO consists of a simplified three degree-of-freedom (3-DOF) simulation representing the SLS launch configuration. In general, the launch azimuth is strongly correlated with the heading at SRB separation, and the initial pitchover rate is strongly correlated with the altitude rate at SRB separation. CHANGO uses an adaptation of Powell’s method to vary the initial pitchover rate and launch azimuth to solve a 2-dimentional minimization problem. CHANGO’s trajectory simulation is phase-based, with flight events separating the phases. Each flight phase has different attitude alignment logic. CHANGO’s 3-DOF simulation starts when the vehicle’s thrust-to-weight ratio equals one, and ends at a pre-calculated SRB separation time.

Ahmad, Naeem↗