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9. A New Spacecraft Attitude Stabilization Mechanism Using Deep Reinforcement Learning Method

Author

WANG, Yuejiao, MA, Zhong, YANG, Yidai, WANG, Zhuping, and TANG, Lei

Subjects
FLIGHT CONTROL, AI ARTIFICIAL INTELLIGENCE
Abstract

Aiming at the problem of sudden changes in the attitudes and the mass parameters encountered by spacecrafts when performing complex tasks such as discarding a payload or capturing a target, this paper proposes a new attitude stabilization mechanism based on the deep reinforcement learning method to restore the spacecraft to a stable attitude. Specifically, a three-dimensional space simulation environment which simulates the spacecraft\'s attitude is firstly established according to the real-time control torque. A neural network model based on the segmented weighted reward function is then built, which takes the attitude of the spacecraft as input, and outputs the discretized control torque to control the spacecraft. Moreover, the Deep Q Network algorithm performs the attitude stabilization training for the spacecraft in the simulation environment, the parameters of the neural network model are continuously updated in the training phase. Simulation experiments illustrate that, by continuous self-learning and self-evolution, deep reinforcement learning method gradually learns to re-stabilize spacecraft\'s attitude after unknown disturbance. As a contrast, we compare the proposed method with PD controller and backstepping controller. The PD controller is unable to re-stabilize the attitude due to its dependence on the mass parameters. The backstepping controller has robustness against mass parameter uncertainty, but it can only handle the constant control cycle. Compared with two controllers, our attitude stabilization mechanism based on deep reinforcement learning has competitive performance for uncertainties in the mass parameters, while allows the control cycle changes during the training phase. The proposed mechanism is an innovative application of artificial intelligence technology in attitude stabilization field, which provides support for achieving the intelligent control and makes the technical foundation for completing the service and maintenance of spacecrafts on-orbit. For future work, we plan to train and validate the mechanism on a semi-physical simulation platform consisting of a three-dimensional turntable and an actuator under the complex space simulation environment.

Published
2019
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11. Structural Analysis of the Ash2L/Dpy-30 Complex Reveals a Heterogeneity in H3K4 Methylation

Author

Haddad, John Faissal, primary, Yang, Yidai, additional, Takahashi, Yoh-hei, additional, Joshi, Monika, additional, Chaudhary, Nidhi, additional, Woodfin, Ashley R., additional, Benyoucef, Aissa, additional, Yeung, Sylvain, additional, Brunzelle, Joseph S., additional, Skiniotis, Georgios, additional, Brand, Marjorie, additional, Shilatifard, Ali, additional, and Couture, Jean-François, additional

Published
2018
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22. PakB binds to the SH3 domain of DictyosteliumAbp1 and regulates its effects on cell polarity and early development

Author

Yang, Yidai, Roche, Marc de la, Crawley, Scott W., Li, Zhihao, Furmaniak-Kazmierczak, Emilia, and Côté, Graham P.

Abstract

DictyosteliumPakB, a p21-activated kinase implicated in the activation of class I myosins, is shown to bind directly to actin filaments and to the SH3 domain of actin-binding protein 1 (dAbp1). The interaction with PakB is needed to localize dAbp1 to actin-rich sites in the cell and control its activity during chemotaxis and early development.

Published
2013
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24. Autophosphorylation activates Dictyostelium myosin II heavy chain kinase A by providing a ligand for an allosteric binding site in the alpha-kinase domain.

Author

Crawley SW, Gharaei MS, Ye Q, Yang Y, Raveh B, London N, Schueler-Furman O, Jia Z, and Côté GP

Subjects
Calcium-Calmodulin-Dependent Protein Kinases genetics, Dictyostelium genetics, Enzyme Activation physiology, Mutation, Phosphorylation physiology, Protein Structure, Tertiary, Protozoan Proteins genetics, Calcium-Calmodulin-Dependent Protein Kinases metabolism, Dictyostelium enzymology, Protozoan Proteins metabolism
Abstract

Dictyostelium discoideum myosin II heavy chain kinase A (MHCK A), a member of the atypical α-kinase family, phosphorylates sites in the myosin II tail that block filament assembly. Here we show that the catalytic activity of A-CAT, the α-kinase domain of MHCK A (residues 552-841), is severely inhibited by the removal of a disordered C-terminal tail sequence (C-tail; residues 806-841). The key residue in the C-tail was identified as Thr(825), which was found to be constitutively autophosphorylated. Dephosphorylation of Thr(825) using shrimp alkaline phosphatase decreased A-CAT activity. The activity of a truncated A-CAT lacking Thr(825) could be rescued by P(i), phosphothreonine, and a phosphorylated peptide, but not by threonine, glutamic acid, aspartic acid, or an unphosphorylated peptide. These results focused attention on a P(i)-binding pocket located in the C-terminal lobe of A-CAT. Mutational analysis demonstrated that the P(i)-pocket was essential for A-CAT activity. Based on these results, it is proposed that autophosphorylation of Thr(825) activates ACAT by providing a covalently tethered ligand for the P(i)-pocket. Ab initio modeling studies using the Rosetta FloppyTail and FlexPepDock protocols showed that it is feasible for the phosphorylated Thr(825) to dock intramolecularly into the P(i)-pocket. Allosteric activation is predicted to involve a conformational change in Arg(734), which bridges the bound P(i) to Asp(762) in a key active site loop. Sequence alignments indicate that a comparable regulatory mechanism is likely to be conserved in Dictyostelium MHCK B-D and metazoan eukaryotic elongation factor-2 kinases.

Published
2011
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25. Crystal structure of the alpha-kinase domain of Dictyostelium myosin heavy chain kinase A.

Author

Ye Q, Crawley SW, Yang Y, Côté GP, and Jia Z

Subjects
Adenine Nucleotides metabolism, Adenosine Monophosphate metabolism, Amino Acid Sequence, Amino Acid Substitution, Animals, Calcium-Calmodulin-Dependent Protein Kinases genetics, Calcium-Calmodulin-Dependent Protein Kinases metabolism, Catalytic Domain, Crystallography, X-Ray, Dictyostelium genetics, Hydrolysis, Magnesium metabolism, Mice, Models, Molecular, Molecular Sequence Data, Mutagenesis, Site-Directed, Protein Conformation, Protein Structure, Tertiary, Protozoan Proteins genetics, Protozoan Proteins metabolism, Recombinant Proteins chemistry, Recombinant Proteins genetics, Recombinant Proteins metabolism, Sequence Homology, Amino Acid, TRPM Cation Channels chemistry, TRPM Cation Channels genetics, Calcium-Calmodulin-Dependent Protein Kinases chemistry, Dictyostelium enzymology, Protozoan Proteins chemistry
Abstract

Dictyostelium discoideum myosin II heavy chain kinase A (MHCK A) disrupts the assembly and cellular activity of bipolar filaments of myosin II by phosphorylating sites within its alpha-helical, coiled-coil tail. MHCK A is a member of the atypical alpha-kinase family of serine and threonine protein kinases and displays no sequence homology to typical eukaryotic protein kinases. We report the crystal structure of the alpha-kinase domain (A-CAT) of MHCK A. When crystallized in the presence of adenosine triphosphate (ATP), A-CAT contained adenosine monophosphate (AMP) at the active site. However, when crystallized in the presence of ATP and a peptide substrate, which does not appear in the structure, adenosine diphosphate (ADP) was found at the active site and an invariant aspartic acid residue (Asp(766)) at the active site was phosphorylated. The aspartylphosphate group was exposed to the solvent within an active-site pocket that might function as a docking site for substrates. Access to the aspartylphosphate was regulated by a conformational switch in a loop that bound to a magnesium ion (Mg(2+)), providing a mechanism that allows alpha-kinases to sense and respond to local changes in Mg(2+).

Published
2010
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