Results for “THRUST” — Page 46

NASA NTRS2018

Parallel Monotonic Basin Hopping for Low Thrust Trajectory Optimization

Monotonic Basin Hopping has been shown to be an effective method of solving low thrust trajectory optimization problems. This paper outlines an extension to the common serial implementation by parallelizing it over any number of available compute cores. The Parallel Monotonic Basin Hopping algorithm described herein is shown to be an effective way to more quickly locate feasible solutions, and improve locally optimal solutions in an automated way without requiring a feasible initial guess. The increased speed achieved through parallelization enables the algorithm to be applied to more complex problems that would otherwise be impractical for a serial implementation. Low thrust cislunar transfers and a hybrid Mars example case demonstrate the effectiveness of the algorithm. Finally, a preliminary scaling study quantifies the expected decrease in solve time compared to a serial implementation.

McCarty, Steven L.↗

NASA NTRS2018

Aero-Propulsion Control Research in Support of NASA Aeronautics Research Strategic Thrusts

In the past few years, NASA (National Aeronautics and Space Administration) Aeronautics Research Mission Directorate (ARMD) has introduced and updated a â€œNew Blueprint for Transforming Global Aviationâ€ . This blueprint consists of six NASA Aeronautics Research Strategic Thrusts â€" â€œThe updated vision is designed to ensure that through NASA's aeronautical research the United States will maintain its leadership in the sky and sustain aviation so that it remains a key economic driver and cultural touchstone for the nation.â€ In mid-2016, technology development roadmaps were developed by ARMD for each of the strategic research thrusts and these roadmaps are continually being updated based on feedback from the broader aeronautics research community. The NASA Aeronautics research vision is implemented through a set of 4 programs â€" Advanced Air Vehicles Program (AAVP), Airspace Operations and Safety Program (AOSP), Integrated Aviation Systems Program (IASP), and Transformative Aeronautics Concepts Program (TACP). The Intelligent Control and Autonomy Branch (ICAB) at NASA Glenn Research Center (GRC) in Cleveland, Ohio, is leading and participating in various projects in partnership with other organizations within GRC and across NASA, the U.S. aerospace industry, and academia to develop advanced controls and health management technologies for aero-propulsion systems that will help meet the goals of the ARMD programs. These efforts are primarily under the various projects under AAVP, AOSP, and TACP. The ICAB current research tasks in support of ARMD program are described in this paper. The paper provides motivation, background, technical approach and recent accomplishments for these tasks, as well as a couple of tasks completed in the previous fiscal year.

Propulsion Control↗

NASA NTRS2018

A Monte Carlo Approach to Measuring Trajectory Performance Subject to Missed Thrust

A spacecraft using solar electric propulsion (SEP) to reach its destination must operate its thrusters for very long periods of time compared to one using chemical propulsion. Some spacecraft may be required to thrust almost the entire duration of the transfer to reach their target. A side-effect of this characteristic of SEP missions is that a spacecraft could be subject to an anomaly or fault that forces it to stop thrusting when it should be, causing it to drift away from its nominal trajectory. A diagram of this situation is shownin Figure 1. Because these shut-down events (commonly referred to as safe mode or safing events), are not uncommon and can be caused by uncontrollable external factors (such as a cosmic ray striking an electronic component), the spacecraft and trajectory should be designed such that the spacecraft can continue on to its destination in a reasonable time and propellant expenditure once operations resume.

Laipert, Frank E.↗

NASA NTRS2019

Low-Thrust Trajectory Design for a Cislunar CubeSat Leveraging Structures from the Bicircular Restricted Four-Body Problem

The upcoming Lunar IceCube (LIC) mission will deliver a 6U CubeSat to a low lunar orbit via a ride-share opportunity during NASAs Artemis 1 mission. This presents a challenging trajectory design scenario, as the vast change in energy required to transfer from the initial deployment state to the destination orbit is compounded by the limitations of the LICs low-thrust engine. This investigation addresses these challenges by developing a trajectory design framework that utilizes dynamical structures available in the Bicircular Restricted Four-Body Problem (BCR4BP) along with a robust direct collocation algorithm. Maps are created that expedite the selection of invariant manifold paths from a periodic staging orbit in the BCR4BP that offer favorable connections between the LIC transfer phases. Initial guesses assembled from these maps are passed to a direct collocation algorithm that corrects them in the BCR4BP while including the variable low-thrust acceleration of the spacecraft engine. Results indicate that the ordered motion provided by the BCR4BP and the robustness of direct collocation combine to offer an efficient and adaptable framework for designing a baseline trajectory for the LIC mission.

Pritchett, Robert↗

NASA NTRS2019

Low-Thrust Trajectory Design for A Cislunar CubeSat Leveraging Structures from the Bicircular Restricted Four-Body Problem

The upcoming Lunar IceCube (LIC) mission will deliver a 6U CubeSat to a low lunar orbit via a ride-share opportunity during NASAs Artemis 1 mission. This presents a challenging trajectory design scenario, as the vast change in energy required to transfer from the initial deployment state to the destination orbit is compounded by the limitations of the LICs low-thrust engine. This investigation addresses these challenges by developing a trajectory design framework that utilizes dynamical structures available in the Bicircular Restricted Four-Body Problem (BCR4BP) along with a robust direct collocation algorithm. Maps are created that expedite the selection of invariant manifold paths from a periodic staging orbit in the BCR4BP that offer favorable connections between the LIC transfer phases. Initial guesses assembled from these maps are passed to a direct collocation algorithm that corrects them in the BCR4BP while including the variable low-thrust acceleration of the spacecraft engine. Results indicate that the ordered motion provided by the BCR4BP and the robustness of direct collocation combine to offer an efficient and adaptable framework for designing a baseline trajectory for the LIC mission.

Pritchett, Robert↗

NASA NTRSDate not supplied

Low-Thrust Transfer to Interplanetary Trajectories from Lunar Trajectories with Rideshare

Accessing interplanetary space is challenging when using low thrust systems. Injecting spacecraft onto interplanetary trajectories is difficult with small launch vehicles, but it is possible to instead transfer to an interplanetary trajectory from a lunar flyby. Such cases are useful, for example, in rideshares between lunar and interplanetary missions. This work examines the problem of rideshare for small satellites onto lunar flyby trajectories, with transfers to an interplanetary trajectory. Low thrust interplanetary trajectories are examined starting from a rideshare mission on a lunar trajectory using delivery systems based on a modified Rocket Lab USA Electron vehicle and Photon stage.

Darcey R Graham↗

NASA NTRS2019

Designing Low-Thrust Enabled Trajectories for a Heliophysics Smallsat Mission to Sun-Earth L5

A small satellite deployed to Sun-Earth L5 could serve as a low-cost platform to observe solar phenomena such as coronal mass ejections. However, the small satellite platform introduces signiﬁcant challenges in the trajectory design process via limited thrusting capabilities, power and operational constraints, and ﬁxed deployment conditions. To address these challenges, a strategy employing dynamical systems theory is used to design a low-thrust-enabled trajectory for a small satellite to reach the Sun-Earth L5 region. This procedure is demonstrated for a small satellite that launches as a secondary payload with a larger spacecraft destined for a Sun-Earth L2 halo orbit.

Stuart, Jeffrey↗

NASA NTRS2019

Efficient computation of optimal low thrust gravity perturbed orbit transfers

We have developed a new method for solving low-thrust fuel-optimal orbit transfer problems in the vicinity of a large body (planet or asteroid), considering a high-fidelity spherical harmonic gravity model. The algorithm is formulated via the indirect optimization method, leading to a two-point boundary value problem (TPBVP). We make use of a hyperbolic tangent smoothing law for performing continuation on the thrust magnitude to reduce the sharpness of the control switches in early iterations and thus promote convergence. The TPBVP is solved using the method of particular solutions (MPS) shooting method and Picard-Chebyshev numerical integration. Application of Picard-Chebyshev integration affords an avenue for increased efficiency that is not available with step-by-step integrators. We demonstrate that computing the particular solutions with only a low-fidelity force model greatly increases the efficiency of the algorithm while ultimately achieving near machine precision accuracy. A salient feature of the MPS is that it is parallelizable, and thus further speedups are available. It is also shown that, for near Earth orbits and over a small number of en-route revolutions around the Earth, only the zonal perturbation terms are required in the costate equations to obtain a solution that is accurate to machine precision and optimal to engineering precision. The proposed framework can be used for trajectory design around small asteroids and also for orbit debris rendezvous and removal tasks.

Junkins, John L.↗

NASA NTRS2017

Low-Thrust Trajectory Maps (Bacon Plots) to Support a Human Mars Surface Expedition

Planning the logistics of multiple launches to support a Mars surface expedition requires good trajectory design tools. Traditional ballistic transfers are well characterized by performance maps known as pork-chop plots. However, the transportation of cargo can benefit from the use of low-thrust solar electric propulsion, both in terms of mass delivered and the flexibility of flight durations and dates. This paper describes the design and use of bacon plots (the low-thrust analog to pork-chop plots) and their application to the architectural design of a human Mars surface expedition.

Post, Kevin E.↗

NASA NTRSDate not supplied

Lightweight Thrust Chamber Composite Overwrap Lessons Learned

Filament winding a polymer/carbon fiber composite overwrap onto an additively manufactured copper combustion chamber will allow it to act as a light-weight structural jacket, significantly reducing weight for high pressure thrust chamber assemblies and reducing overall cost and fabrication schedules. Chamber assemblies for 2k lb. and 7k lb. of thrust have been successfully tested at NASA’s Marshall Space Flight Center. Multiple lessons were learned throughout the overwrap process development and manufacturing trials. The lessons learned on small scale hardware will guide further composite manufacturing technologies and enable a progression to larger scale assemblies with greater structural loads. Material performance requirements, manufacturing process development, and surface preparation were evaluated during the small chamber trials, with the broad thermal requirements of the resin being the primary driver for material selection and processing. Both epoxy and bismaleimide materials were evaluated with respect to both performance in the hot-fire test and ease of fabrication. Separately, surface preparation procedures were studied with the goal of providing a smooth chamber surface to promote a non-bonded overwrap. The recent testing of the 7k trust chamber has provided data in Non-Destructive Evaluation (NDE) and processing in order to continue to evaluate the performance requirements stated.

composite overwrap↗

NASA NTRSDate not supplied

MULTI-OBJECTIVE REINFORCEMENT LEARNING FOR LOW-THRUST TRANSFER DESIGN BETWEEN LIBRATION POINT ORBITS

Multi-Reward Proximal Policy Optimization (MRPPO) is a multi-objective reinforcement learning algorithm used to construct low-thrust transfers between periodic orbits in multi-body systems. Previous implementations of MRPPO have relied on a predefined reference transfer to successfully train each policy. In this paper, an algorithmic modification labeled the ‘moving reference’, is introduced to autonomously construct these reference trajectories during training. With this modification, MRPPO is used to recover various low-thrust transfers between two periodic orbits in the Earth-Moon circular restricted three-body problem to solve a multi-objective optimization problem. These results are then compared with the solutions recovered via a traditional optimization formulation.

algorithm↗

NASA NTRSDate not supplied

Lightweight Thrust Chamber Composite Overwrap Lessons Learned

The manufacturing, design, and analysis of filament wound carbon fiber/polymer composite overwraps for additively manufactured, copper combustion chambers are a critical part of NASA’s Rapid Analysis and Manufacturing Propulsion Technology (RAMPT) project. Ideally, the composite overwrap acts as a light-weight structural jacket and allows significant weight reduction of the high pressure thrust chamber assembly, reduction of overall cost, and reduced fabrication schedules. Chamber assemblies for 2000 lb. (2k) and 7000 lb. (7k) of thrust have been successfully tested at NASA’s Marshall Space Flight Center. Multiple lessons were learned throughout the overwrap process development and manufacturing trials. The lessons learned on small scale hardware, such as the 2k and 7k chambers, will guide further composite manufacturing technologies and enable a progression to larger scale assemblies with greater structural loads. Material performance requirements, manufacturing process development, and surface preparation were evaluated during the small chamber trials, with the broad thermal requirements of the resin being the primary driver for material selection and processing. Both epoxy and bismaleimide (BMI) materials were evaluated with respect to both performance in the hot-fire test and ease of fabrication. Separately, surface preparation procedures were studied with the goal of providing a smooth chamber surface to promote a non-bonded overwrap. Recent testing of the 7k trust chamber has provided data in Non-Destructive Evaluation (NDE) and processing in order to continue to evaluate the performance requirements stated.

Allison Clark↗

NASA NTRSDate not supplied

MULTI-OBJECTIVE REINFORCEMENT LEARNING FOR LOW-THRUST TRANSFER DESIGN BETWEEN LIBRATION POINT ORBITS

Multi-Reward Proximal Policy Optimization (MRPPO) is a multi-objective reinforcement learning algorithm used to construct low-thrust transfers between periodic orbits in multi-body systems. Previous implementations of MRPPO have relied on a predefined reference transfer to successfully train each policy. In this paper, an algorithmic modification labeled the ‘moving reference’, is introduced to autonomously construct these reference trajectories during training. With this modification, MRPPO is used to recover various low-thrust transfers between two periodic orbits in the Earth-Moon circular restricted three-body problem to solve a multi-objective optimization problem. These results are then compared with the solutions recovered via a gradient descent optimization scheme to validate the performance of MRPPO with the moving reference modification.

Christopher J. Sullivan↗

NASA NTRSDate not supplied

MULTI-OBJECTIVE REINFORCEMENT LEARNING FOR LOW-THRUST TRANSFER DESIGN BETWEEN LIBRATION POINT ORBITS

Multi-Reward Proximal Policy Optimization (MRPPO) is a multi-objective reinforcement learning algorithm used to construct low-thrust transfers between periodic orbits in multi-body systems. Previous implementations of MRPPO have relied on a predefined reference transfer to successfully train each policy. In this paper, an algorithmic modification labeled the ‘moving reference’, is introduced to autonomously construct these reference trajectories during training. With this modification, MRPPO is used to recover various low-thrust transfers between two periodic orbits in the Earth-Moon circular restricted three-body problem to solve a multi-objective optimization problem. These results are then compared with the solutions recovered via a gradient descent optimization scheme to validate the performance of MRPPO with the moving reference modification

Christopher John Sullivan↗

NASA NTRSDate not supplied

Navigation and Mission Design for Low-Thrust Insertion into Near Rectilinear Halo Orbits

Near Rectilinear Halo Orbits, the target of NASA’s Gateway, are slightly unstable and therefore require minimal insertion delta-V. This makes insertion using highly efficient low-thrust systems a viable and attractive option; however, it also may require the spacecraft to approach the insertion on a dynamically sensitive trajectory with multiple perilune passes. This study focuses on a low-thrust NRHO insertion from a spiral-out, Earth-to-Moon transfer that involves this type of dynamically sensitive approach. Correction maneuver and navigation strategies are found that are robust to initial state, navigation, and maneuver execution errors prior to and through insertion. Further, it is demonstrated that these maneuver and navigation strategies allow the spacecraft to transition to nominal NRHO stationkeeping after insertion, without the need for specially designed clean-up maneuvers or a significant amount of additional delta-V.

Ethan W Kayser↗

NASA NTRS2020

Optimal Low Thrust Orbit Transfers for Space Telescope Refueling at SEL2

The James Webb Space Telescope (JWST), a ten billion-dollar infrared telescope with a 6.5m primary mirror to be launched in 2021, is designed to operate in a Halo orbit around the second Sun-Earth Lagrange point (SEL2) for five to ten years. At that point fuel for station keeping and attitude maneuvers will run out. Refueling missions to JWST, as well as to similar space telescope missions proposed for SEL2, could greatly enhance the “science-per-dollar” value and promote a more sustainable use of space assets. In this paper, we present a novel approach to designing fuel optimal trajectories that will allow the refueling spacecraft to arrive at the SEL2 Halo orbit with maximum final mass (i.e. fuel payload). The low thrust optimal control problem is formulated using an indirect optimization method, leading to a two-point boundary value problem with a bang-bang control structure. We make use of a hyperbolic tangent smoothing technique for performing continuation on the thrust magnitude to reduce the sharpness of the control switches in early iterations and, thus, promote convergence. The problem is posed and solved in the circular restricted three-body problem. In this dynamical system, invariant manifolds exist that can be utilized to reduce fuel consumption. The here presented methodology to this challenging and important problem in astrodynamics demonstrates a significant potential for low-cost refueling mission design.

Woollands, Robyn↗

NASA NTRS2020

Missed Thrust Requirements for Psyche Mission

The Psyche Mission, part of NASA’s Discovery Mission Program, will explore the metal asteroid (16) Psyche which orbits the sun at ~3 AU. The spacecraft uses solar electric propulsion (SEP) as its primary propulsion system during the ~3.5 year trajectory to (16) Psyche and 21 month orbital operations period around the asteroid. As the first NASA mission to use Hall thrusters for deep space exploration, unique challenges have been identified and resolved in how we plan to accommodate unplanned coast (missed thrust time) during the trajectory and orbital operations and still meet the mission objectives. This paper describes the projects missed thrust requirements in detail, along with the accompanying rationale and analysis plan for the Psyche mission.

Snyder, John Steven↗

NASA NTRSDate not supplied

Efficient Variable-Pitch Propeller Aerodynamic Model Development for Vectored-Thrust eVTOL Aircraft

This paper describes a variable-pitch propeller testing and aerodynamic modeling methodology for electric vertical takeoff and landing (eVTOL) aircraft using wind tunnel testing. Propellers used for eVTOL aircraft propulsion systems experience a wide range of operating conditions resulting in significant variation of axial thrust and torque, as well as off-axis forces and moments, across a typical flight envelope. An experimental design is developed to collect informative wind tunnel data in an efficient manner using response surface methods. System identification methods are then applied to isolated propeller wind tunnel data to develop a mathematical model of the propeller valid throughout the transition envelope of a vectored-thrust eVTOL aircraft. Multiple explanatory variable definitions are postulated and compared using modeling and prediction performance metrics. Modeling results validated against data withheld from the modeling process indicate good predictive capability and agree with theoretical expectations. All identified propeller models are provided, which allows the models to be used in future eVTOL aircraft flight dynamics simulations.

aerodynamic modeling↗