Machine Learned Atmospheric Force Model Trained With Two Line Elements
Thousands of objects orbiting in Low Earth Orbit (LEO) are catalogued and tracked by US Space Force (USSF) in a database of Two-Line Elements (TLEs) that is available online. A time series of TLE states for a particular object will show its orbital decay over time due to atmospheric drag. The decay data across multiple objects can form a training set to create a Machine Learning (ML) model for the atmospheric drag force. This paper investigates a demonstration of this process by training a an ML atmosphere model with decay data from a historical object.
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Stationkeeping, Orbit Determination, and Attitude Control for Spacecraft in Near Rectilinear Halo Orbits (NRHOs)
From a Near Rectilinear Halo Orbit (NRHO), NASA’s Gateway at the Moon is planned to serve as a proving ground and a staging location for human missions beyond Earth. Stationkeeping, Orbit Determination (OD), and attitude control are examined for uncrewed and crewed Gateway configurations. Orbit maintenance costs are investigated using finite maneuvers, considering skipped maneuvers and perturbations. OD analysis assesses DSN tracking and identifies OD challenges associated with the NRHO and crewed operations. The Gateway attitude profile is simulated to determine an effective equilibrium attitude. Attitude control propellant use and sizing of the required passive attitude control system are assessed.
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Earth-Moon Near Rectilinear Halo and Butterfly Orbits for Lunar Surface Exploration
NASA is planning the next phase of crewed spaceflight with a set of missions designed to establish a human-tended presence beyond low Earth orbit. The current investigation focuses on the staging post potential of cislunar infrastructure by seeking to maximize performance capabilities by optimizing transits in the lunar vicinity for both crewed and robotic spacecraft. In this paper, the current reference orbit for the cislunar architecture, known as a Near Rectilinear Halo Orbit (NRHO), is examined alongside the bifurcated L2 butterfly family for their use as a staging location to the lunar surface.
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Ballistic Lunar Transfer Design using the Deep Space Trajectory Explorer
In the coming years, numerous commerical companies and government agencies plan to expand their presence in cislunar space. Subsequently, an understanding of the cislunar gravitational environment is crucial to the success of these programs. Development of tools to effectively leverage natural dynamical structures helps streamline the trajectory design process. In this investigation, the functionality of the JavaFX-based Deep Space Trajectory Explorer (DSTE) is extended to construct ballistic lunar transfers to libration point orbits in the vicinity of the Moon.
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Change of Inertia Tensor Due to a Severed Radial Boom for Spinning Spacecraft
The spin-stabilized spacecraft is a convenient platform for the measurement of magnetic and electric fields, plasma properties, and other physical phenomena best observed over a wide baseline. Many spinning spacecraft have radial booms that are constructed from very thin and flexible multi-stranded wire. These radial booms can be quite long, with examples ranging from 25 to 250 m, and are kept under tension by centrifugal force. This paper explores the risks and benefits of using radial booms on spin-stabilized spacecraft.
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Disposal, Deployment, and Debris in Near Rectilinear Halo Orbits
The Lunar Orbital Platform-Gateway is proposed as an outpost in deep space: a proving ground for deep space technologies and a staging location for missions beyond Earth orbit. Envisioned as a crew-tended spacecraft, the Gateway will be constructed over time as various components are delivered either as co-manifested payloads with Orion or independently without crew presence. Naturally, spacecraft and objects with a wide range of shapes and masses will also depart the Gateway for other destinations. Read this white paper to learn about the Lunar Orbital Platform-Gateway and Disposal, Deployment, and Debris in Near Rectilinear Halo Orbits.
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Assessing Performance Characteristics of the SGP4-XP Propagation Algorithm
In 2020 the United States Space Force (USSF) released an implementation of the SGP4-XP propagator, an advanced version of the existing SGP4 propagator stated to deliver accuracy roughly equivalent to that of the USSF’s Special Perturbations Ephemeris propagator (SPEPH) with runtimes only 50% to 100% longer than SGP4. This paper presents an analysis of the performance characteristics of the SGP4-XP propagation algorithm and considers new and existing practical applications where it can be used more effectively than SGP4.
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Flight Dynamics Planning and Operations Support for the JWST Mission
The James Webb Space Telescope (JWST) was launched from Kourou Spaceport on December 25, 2021, at 12:20 UTC on an Ariane 5 launch vehicle. The launch vehicle inserted JWST into a 30-day transfer trajectory to the Sun-Earth-Moon (SEM) Lagrange point L2 region. JWST executed three mid-course correction maneuvers (MCCs) to insert the spacecraft into a quasi-halo orbit about SEM L2; JWST will maintain its trajectory about L2 for at least 5.5 years, with a goal of at least 10.5 years. This paper summarizes the flight dynamics support for JWST, including the prelaunch nominal trajectory design, the launch window analysis, contingency planning for trajectory-related anomalies, mission operations support for the first 6 months, and a comparison of the planned and achieved actual JWST trajectory results. The orbit determination strategy, both planned and executed, will be summarized, and the method of addressing the anomalies as they occurred will be included.
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Implementation of the Solar Exclusion Zone Burn Through Maneuvers for DSCOVR to Preserved Fuel for the Gyro-less Spacecraft in a Sun-Earth L1 Lissajous Orbit
DSCOVR (Deep Space Climate Observatory) is a National Oceanic and Atmospheric Administration (NOAA) space weather, space climate, and Earth observation satellite operating in a Sun-Earth L1 Lissajous orbit. This report summarizes the two-burn maneuver campaign performed in Summer 2021 to transfer DSCOVR from the collapsing phase into the expansion phase of the Lissajous orbit to avoid the Solar Exclusion Zone (SEZ). The two-maneuver campaign per- formed in July and August 2021 was successful and resulted in saving the mission 31 kilograms of fuel and 100 m/s of delta-v reserved for SEZ maneuvers which are no longer required until 2026 or 2027.
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JWST Real-Time Mid-Course Correction Maneuver Monitoring Contingency Preparation
The NASA James Webb Space Telescope (JWST) mission successfully launched on Dec 25, 2021 , at 12:20 Coordinated Universal Time (UTC). During the 30-day transfer to the second Sun-Earth-Moon (SEM) libration point (L2), JWST executed three mid-course correction (MCC) maneuvers to insert into a quasi-halo orbit about L2. This paper covers the design and modeling for these three maneuvers with a focus on the timeline around the execution of each MCC maneuver. It will summarize the actual on-board events as well as the contingency preparation done for maneuver planning, monitoring, and final post-burn reconstruction of all three MCC maneuvers.
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Orbit Determination for the James Webb Space Telescope During Launch and Early Orbit
The NASA James Webb Space Telescope (JWST) mission successfully launched on December 25, 2021, at 12:20 UTC. This paper details several novel challenges encountered in the orbit determination (OD) of JWST during the launch and early orbit. The first OD solution used only 6.5 hours of tracking data, much less than the 24 hours of data usually required for libration orbiters on an outbound trajectory. In addition, the observatory area exposed to solar radiation pressure changed through a series of sunshield deployments while concurrent momentum unloads and attitude telemetry outages occurred. This paper covers how the Flight Dynamics Team (FDT) prepared for these challenges, how these challenges were handled on-orbit, and the performance of the resulting OD solutions.
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Planning and Execution of the Three Mid-Course Correction Maneuvers for the James Webb Space Telescope
The James Webb Space Telescope (JWST) was successfully launched on December 25, 2021 12:20 UTC on an Ariane 5 rocket out of Kourou, French Guiana on a direct, lower energy manifold transfer out to the Sun-Earth-Moon (SEM) L2 point. Three mid-course correction (MCC) maneuvers, designated MCC-1, MCC-1b, and MCC-2, were required to provide the energy necessary to reach L2 due to a purposeful biasing down of the launch vehicle. This paper will document the prelaunch preparation, nominal planning, contingency preparation, and successful execution of the three mid-course correction maneuvers.
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Examining the Feasibility of Relative-Only Navigation for Crewed Missions to Near Rectilinear Halo Orbits
Recently, lunar Near Rectilinear Halo Orbits (NRHO) have been the focus of much study, and they have been selected as the target orbit for the Gateway mission, formerly the Deep Space Gateway. Also, the Deep Space Network (DSN) is increasingly congested and over-subscribed. In this work, the performance of relative-only navigation between a spacecraft in an NRHO and a relay in a Distant Retrograde Orbit is examined and compared to simulated DSN tracking using a Square Root Information Filter. Various tracking scenarios are examined using a closed-loop simulation where navigation errors inform maneuver planning and maneuver execution errors affect navigation performance. Results indicate that relative-only navigation can provide comparable levels of orbit determination error and orbit maintenance costs.
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Distant Retrograde Orbit Constellations for Relative-Only Navigation in Near Rectilinear Halo Orbits
NASA is currently working on the spacecraft and trajectory design for the Gateway mission that will reside in a Near Rectilinear Halo Orbit (NRHO). In the NRHO, Gateway will nominally require orbital maintenance maneuvers once per revolution. Separately, NASA is also working to develop technologies and techniques for relative navigation in cis-lunar space. Together, these concepts represent an opportunity for interesting research in cis-lunar navigation performance.
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Survey of Ballistic Lunar Transfers to Near Rectilinear Halo Orbit
This paper provides a thorough review of how ballistic lunar transfers (BLTs) can be used to transfer from Earth to near rectilinear halo orbits (NRHOs) in an efficient manner.
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Heliocentric Escape and Lunar Impact from Near Rectilinear Halo Orbits
Spacecraft departing from the Gateway in a Near Rectilinear Halo Orbit (NRHO) experience gravitational forces from the Moon, the Earth, and the Sun, all of which can be simultaneously significant. How do these celestial objects influence the trajectory of spacecraft? Find out more by reading this white paper.
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NASA Conjunction Assessment Risk Analysis Updated Requirements
The NASA Conjunction Assessment Risk Analysis (CARA) program has been performing routine on-orbit satellite conjunction risk analysis for unmanned NASA spacecraft since 2005, and has developed a robust operations procedure and set of recommended best practices for operational conjunction assessment. Read this article to learn more about the CARA program's updated requirments.
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L2 Station Keeping Maneuver Strategy for the James Webb Space Telescope
The L2 station keeping plan for the James Webb Space Telescope achieves zero velocity in the x-component at the fourth successive crossing of the XZ plane of the rotating libration point frame. The techniques developed to determine the minimum maneuver direction in a full ephemeris model, along with strategies to cope with the attitude constraints imposed by the sunshield that prevents the ability to maneuver along the stable eigenvector, are examined in this study.
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