{"project":{"acronym":"","projectId":91755,"title":"Low Thrust Trajectory Optimization in Cislunar and Translunar Space","primaryTaxonomyNodes":[{"taxonomyNodeId":10979,"taxonomyRootId":8816,"parentNodeId":10973,"level":3,"code":"TX17.2.6","title":"Rendezvous, Proximity Operations, and Capture Trajectory Design and Orbit Determination","definition":"Spacecraft trajectory design and orbit determination to support rendezvous and proximity operations in several specific orbital regimes. Trajectory design for missions performing rendezvous and proximity operations includes the inertial motion of a spacecraft starting and launch, and continuing to the design of relative motion to achieve rendezvous, proximity operations, capture, and departure from another space object (spacecraft or small body). Orbit determination is the inertial navigation function (ground or onboard) required to allow onboard systems to acquire the relative navigation estimate required to complete the mission.","exampleTechnologies":"LEO Rendezvous and Proximity Operations (RPO) trajectory design and orbit determination; Geosynchronous Earth Orbit (GEO) RPO trajectory design and orbit determination; Sun-Earth Lagrange Point RPO trajectory design and orbit determination; Lunar Near Rectilinear Halo Orbit (NRHO) RPO trajectory design and orbit determination; Lunar Distant Retrograde Orbit (DRO) RPO trajectory design and orbit determination; Lunar Orbit RPO trajectory design and orbit determination; Highly Elliptical Orbit (HEO) (aka Phasing Orbit) RPO trajectory design and orbit determination","hasChildren":false,"hasInteriorContent":true}],"startTrl":2,"currentTrl":3,"endTrl":3,"benefits":"The goal of this project is to advance the state of the art with regard to low thrust trajectory optimization in 3-body and 4-body force models, specifically in Earth-Moon space.","description":"The goal of this project is to advance the state of the art with regard to low thrust trajectory optimization in 3-body and 4-body force models, specifically in Earth-Moon space. The proposed research will bring together two areas of space exploration capability that have each brought new kinds of missions to the table: electric propulsion (equivalently referred to as “low thrust propulsion” or “solar electric propulsion”) and low-energy transfers. These two areas of study have mostly existed in isolation from each other. The proposed research will explore how bringing them together can be an enabling space technology, and it will quantify the resulting mission benefits and risks. This research will be conducted at the University of Colorado using high fidelity numerical simulations, using code developed specifically for this research and also code that has been developed in the research center to address many similar problems. The trajectory solutions will be validated with NASA software. Some of the questions that will be addressed include: What existing optimization methods for low-thrust trajectories are most suitable for onboard computation? What new missions can be enabled with active thrusting to transfer between halo orbits? Some of the perceived benefits are: reduced mission design time; reduced time of flight, traded with fuel cost; and new types of missions enabled.","startYear":2015,"startMonth":8,"endYear":2018,"endMonth":7,"statusDescription":"Completed","principalInvestigators":[{"contactId":98992,"canUserEdit":false,"firstName":"Daniel","lastName":"Scheeres","fullName":"Daniel Scheeres","fullNameInverted":"Scheeres, Daniel","primaryEmail":"scheeres@colorado.edu","publicEmail":false,"nacontact":false}],"programDirectors":[{"contactId":84634,"canUserEdit":false,"firstName":"Claudia","lastName":"Meyer","fullName":"Claudia M Meyer","fullNameInverted":"Meyer, Claudia M","middleInitial":"M","primaryEmail":"claudia.m.meyer@nasa.gov","publicEmail":true,"nacontact":false}],"programExecutives":[{"contactId":84634,"canUserEdit":false,"firstName":"Claudia","lastName":"Meyer","fullName":"Claudia M Meyer","fullNameInverted":"Meyer, Claudia M","middleInitial":"M","primaryEmail":"claudia.m.meyer@nasa.gov","publicEmail":true,"nacontact":false}],"programManagers":[{"contactId":183514,"canUserEdit":false,"firstName":"Hung","lastName":"Nguyen","fullName":"Hung D Nguyen","fullNameInverted":"Nguyen, Hung D","middleInitial":"D","primaryEmail":"hung.d.nguyen@nasa.gov","publicEmail":true,"nacontact":false}],"projectManagers":[{"contactId":506184,"canUserEdit":false,"firstName":"Steven","lastName":"Hughes","fullName":"Steven P Hughes","fullNameInverted":"Hughes, Steven P","middleInitial":"P","primaryEmail":"steven.p.hughes@nasa.gov","publicEmail":true,"nacontact":false}],"coInvestigators":[{"contactId":351711,"canUserEdit":false,"firstName":"Nathan","lastName":"Re","fullName":"Nathan P Re","fullNameInverted":"Re, Nathan P","middleInitial":"P","primaryEmail":"nathan.re@advancedspace.com","publicEmail":false,"nacontact":false}],"website":"https://www.nasa.gov/strg#.VQb6T0jJzyE","libraryItems":[],"transitions":[{"transitionId":75855,"projectId":91755,"transitionDate":"2018-07-01","path":"Closed Out","details":"Low-thrust propulsion technologies such as electric propulsion and solar sails are key to enabling many space missions which would be impractical with chemical propulsion. With exhaust velocities 10x higher than chemical rockets, electric propulsion systems can deliver a spacecraft to its target state for a fraction of the fuel. Due to the low thrust, the control must remain active for weeks or even years. When three-body dynamics are considered, the change in dynamics over the course of a trajectory can be extreme. This greatly complicates low-thrust mission design and navigation in cislunar and translunar space, making it an area of active research. Deterministic strategies for trajectory design and optimization solve a series of linearized problems. In regimes with simple or slowly-varying dynamics, the linearization holds “true enough”, and existing algorithms can easily arrive at a solution. However, three-body environments readily provide real cases where the linearization for all but the most carefully-chosen problem descriptions break down. The objectives for this research come directly from the limitations of the current state of the art. Modifications to existing algorithms are presented which improve convergence, especially when good initial guesses are not available. Initial work was also completed to enhance spacecraft onboard navigation capabilities, through the use of artificial neural networks for optimal trajectory correction. The approach begins with one optimal low-thrust transfer. Then, thousands of transfers in the neighborhood of the nominal transfer are optimized. These transfers are described in the language of indirect optimal control, with the optimal control given as a function of Lawden’s primer vector. We see that for a slightly different initial condition, the states and the costates both follow a slightly different trajectory to the target. A feedforward artificial neural network is trained to map the difference in states to the difference in costates, with a high degree of accuracy. The novel application of neural networks pioneered in this research sets the stage for spacecraft that can navigate themselves autonomously in the presence of errors. Future spacecraft may use this technique to optimally correct their trajectories without ground contacts. Neural network navigation is demonstrated in two simplified dynamical environments: two-body heliocentric gravity, and the Earth-Moon circular restricted three body problem. Transition of the results to NASA and/or industry flight projects is being explored.","infoText":"Closed out","infoTextExtra":"","dateText":"July 2018"}],"responsibleMd":{"acronym":"STMD","canUserEdit":false,"city":"","external":false,"linkCount":0,"organizationId":4875,"organizationName":"Space Technology Mission Directorate","organizationType":"NASA_Mission_Directorate","naorganization":false,"organizationTypePretty":"NASA Mission Directorate"},"program":{"acronym":"STRG","active":true,"description":"
\tThe Space Technology Research Grants Program will accelerate the development of "push" technologies to support the future space science and exploration needs of NASA, other government agencies and the commercial space sector. Innovative efforts with high risk and high payoff will be encouraged. The program is composed of two competitively awarded components.
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