Theoretical and experimental application of neural networks in spaceflight control systems

“Spaceflight systems can enable advanced mission concepts that can help expand our understanding of the universe. To achieve the objectives of these missions, spaceflight systems typically leverage guidance and control systems to maintain some desired path and/or orientation of their scientific instrumentation. A deep understanding of the natural dynamics of the environment in which these spaceflight systems operate is required to design control systems capable of achieving the desired scientific objectives. However, mitigating strategies are critically important when these dynamics are unknown or poorly understood and/or modelled. This research introduces two neural network methodologies to control the translation and rotation dynamics of spaceflight systems. The first method uses a neural network to perform nonlinear estimation in the control space for both translational and attitude control. The second method uses an observer with a neural network to perform estimation outside the control space, and input-output feedback linearization using the estimated dynamics for both translational and attitude control. The methods are demonstrated for attitude control through simulation and hardware testing on the Wallops Arc-Second Pointer, a high-altitude balloon-borne spaceflight system. Results show that the two new methodologies can provide improved attitude control performance over the heritage control system. The methods are also demonstrated for translational and attitude control of two small spacecraft in a deep space environment, where they provide improved position and attitude control performance as compared to a traditional control method. This work demonstrates, through simulation and hardware testing, that the two neural network methods presented can offer improved translational and attitude control performance of spaceflight systems where the dynamic environment may be unknown or poorly understood and/or modeled”--Abstract, page iv

GTOSat: Radiation Belt Dynamics from the Inside

GTOSat, a 6U SmallSat integrated and tested at NASA Goddard Space Flight Center (GSFC), has a scheduled launch date of July 31st, 2022, on an Atlas V. From a low inclination geosynchronous transfer orbit (GTO), GTOSat has the primary science goal of advancing our quantitative understanding of acceleration and loss of relativistic electrons in the Earth’s outer radiation belt. It will measure energy spectra and pitch angles of both the seed and the energized electron populations simultaneously using a compact, high-heritage Relativistic Electron Magnetic Spectrometer (REMS) built by The Aerospace Corporation. A boom-mounted Fluxgate Magnetometer (FMAG), developed by NASA GSFC, will provide 3-axis knowledge of the ambient local magnetic field. The spacecraft bus uses a combination of commercial and in-house/custom designed components. Design, integration, and testing of the spacecraft bus was performed by a small, dedicated team at GSFC. Throughout development GTOSat has encountered numerous challenges, expected and unexpected, that we’re ready to share with the community

Scanning Tunneling Microscopy of Intermediate Transformation Structures in Electric Arc Surfacing Modified with Titanium Carbonitrides on Pipe Steel

In the present paper, the structure of electric arc coatings modified with nanodispersed titanium carbonitride additives on low-carbon pipe steel is studied using optical, scanning tunneling, and transmission electron microscopy. The obtained “substrate-modified surface” compositions are tested for fracture toughness, and the derived test results are compared with the data for the compositions formed using commercial electrodes. It is found that the introduction of titanium carbonitride nanoparticles with the estimated content from 0.15 to 1 wt% refines the ferrite–pearlite structure. Scanning tunneling microscopy reveals acicular and lamellar structures in local regions of ferrite grains, which, by morphological features, are identified as lower bainite and acicular ferrite. It is concluded that the increase in fracture toughness of the “substrate-modified surface” composition is of a complex nature. First of all, this increase is associated with grain refinement, while the formation of intermediate transformation structures plays a secondary role

ETNAC Design Enabling Formation Flight at Liberation Points

This study considers the feasibility of an event-triggered neuro-adaptive controller (ETNAC) providing precision flying control for microsatellites used for deep space missions. For \u27smallsats\u27 factors including limited capabilities of the microsatellite platform, minimal communication, restricted controls and actuation, overly sensitive response to uncertainties, etc. make the controller design challenging. To cope with such challenges, an ETNAC design is proposed in this study. Its performance analysis is given along with its derivation and implementation. ETNAC is based on an observer, known as Modified State Observer (MSO), which is used for online approximation of the uncertainties in the system. The MSO formulation has two tunable gains that allow for fast estimation without inducing high frequency oscillations in the system. At the same time, an event triggering mechanism (ETM) is used in an aperiodic fashion to transmit state information and update the control only when required. In this way, it reduces communication and computational efforts, simplifying onboard implementations. A Lyapunov analysis is used to prove stability. Simulation and performance results show that ETNAC can be an excellent solution for highly nonlinear resource-constrained problems

Development and Flight of a Stereoscopic Imager for Use in Spacecraft Close Proximity Operations

Proximity operations about noncooperative resident space objects (RSOs) is a current area of research with the intent to enable many useful on-orbit missions. One method of performing passive proximity operations about a noncooperative RSO uses two cameras to obtain stereo line-of-sight data to the RSO in order to fully resolve the relative position and velocity of the RSO and navigate about it. An overview of the MR and MRS SAT mission, in which a stereoscopic imager is used aboard MR SAT to navigate about MRS SAT (a mock noncooperative RSO) is presented. The developed hardware and algorithms used by the stereoscopic imaging sensor, as well as the guidance, navigation, and control subsystems, are presented. A software-in-the-loop simulation is presented to demonstrate the expected on-orbit performance of the MR and MRS SAT mission