Abstract: A novel, empirically-validated method for robust initial orbit determination from two or more observations of an object’s angles and angle rates is presented. The method can be applied for all orbital regimes including those where traditional methods, such as Gauss and double-r, fail. It also works for all times-of-flight to produce the corresponding set of feasible orbit solutions using admissible regions. The method uses a cost function that has a unique non-trivial zero at the correct orbit solution for the single revolution case and a set of zeros for the multi-orbit case. Applying admissible regions to both observations allows the state space to be further constrained with a corresponding improvement to the computational efficiency. The proposed method overcomes the shortcomings of many traditional initial orbit determination methods and has been empirically verified to find solutions to cases well-approximated by two-body dynamics. Furthermore, this work includes a comparison of the proposed and existing methods for initial orbit determination to highlight the domains that the various methods excel. While the global optimizer approach of the proposed method sacrifices computation time in comparison to the single iteration of the previously established methods, it consistently converges to the correct solution or set of possible solutions independent of the orbital regime. PubDate: 2021-05-06

Abstract: This work presents a comparison study using a constant bitrate (CBR) and variable bitrate (VBR) configuration on lossy audio formats, which can be chosen as suitable option to compress spacecraft onboard acoustic data. The acoustic data measured during a rocket motor firing test is assessed by comparing the signal compression rates and information distortions yielded by using those configurations. As a result, the compression algorithm to be used for launch vehicle onboard acoustic measurements is defined. The results have shown that among the lossy formats presented, the OPUS format using the VBR configuration has achieved a compression rate of 254:1 at 5 kbps, saving up to 99.6% the required amount of data to be transmitted through a telemetry link when compared to a non compressed data. PubDate: 2021-05-04

Abstract: The electrodynamic tether (EDT) is a type of propulsion system that uses the geomagnetic field and ionospheric plasma and has the potential to conduct a space-debris removal mission without consuming a large amount of propellant. To understand the dynamic properties of the bare EDT system, an orbital dynamic model based on a detailed environmental space model and the real discharge characteristics of a hollow cathode plasma contactor (HCPC) was built. By numerical simulation, the differences in the bare tether performance caused by various orbital conditions and HCPC voltage models (at constant or various voltages) were compared and discussed. The results suggest that dynamic distinctions generated by the two bias voltage models increased as the latitude increased from 0° to 60°. PubDate: 2021-04-13

Abstract: Classical Floquet theory describes motion near a periodic orbit. But comparing Floquet theory to action angle methods shows which Jordan form is desirable. A new eigenvector algorithm is developed ensuring a canonical transform and handling the typical for the case of repeated eigenvalues, a chronic problem in conservative Hamiltonian systems. This solution also extends the Floquet decomposition to adjacent trajectories, and is fully canonical. This method yields the matrix of frequency partial derivatives, extending the solution’s validity. Some numerical examples are offered. PubDate: 2021-03-25

Abstract: The NASA DART and ESA Hera missions to binary asteroid 65803 Didymos have generated a lot of interest in the study of spacecraft dynamics in the vicinity of binary asteroids. The combination of the effect of the irregular shape and the rotation of the primary bodies makes them not only non-linear, but also non-autonomous systems. This study uses a technique to design reference trajectories in the context of a mission to a binary asteroid system using a fourth-order gravitational potential model for the two primary bodies. The rotation of the primary bodies, their elliptical mutual motion and the solar radiation pressure are also considered in the model, which makes this study unique. It then compares the control effort required when these reference trajectories are used with that required when reference trajectories are built with simpler models. The goal is to examine how the choice of the model used to compute reference trajectories influences the control effort required to keep the spacecraft close to them. PubDate: 2021-03-04 DOI: 10.1007/s40295-021-00248-1

Abstract: The endgame scenario that was explored in this analysis consisted of the part of the trajectory starting at the last Ganymede flyby and ending at the final Europa approach. The basic design components included computing the phasing for the final Ganymede encounter, computing the required intermediate Europa flybys, determining the required maneuvers to transition between the intermediate resonances, and interfacing with a computed portal prior to the final approach. The JPL optimization software, COSMIC, was used in the ephemeris model to optimize solutions computed in the circular restricted three-body problem and compute bounds on the attainable set of solutions by sweeping various design parameters. PubDate: 2021-03-01

Abstract: We develop a Gravity Assist Mapping to quantify the effects of a flyby in a two-dimensional circular restricted three-body situation based on Gaussian Process Regression (GPR). This work is inspired by the Keplerian Map and Flyby Map. The flyby is allowed to occur anywhere above 300 km altitude at the Earth in the system of Sun-(Earth+Moon)-spacecraft, whereas the Keplerian map is typically restricted to the cases outside the Hill sphere only. The performance of the GPR model and the influence of training samples (number and distribution) on the quality of the prediction of post-flyby orbital states are investigated. The information provided by this training set is used to optimize the hyper-parameters in the GPR model. The trained model can make predictions of the post-flyby state of an object with an arbitrary initial condition and is demonstrated to be efficient and accurate when evaluated against the results of numerical integration. The method can be attractive for space mission design. PubDate: 2021-03-01

Abstract: Successful tracking and detection of resident space objects (RSOs) requires selection of spectral filters that are capable of compensating for the effects of wavelength dependent atmospheric scattering, and material reflectance properties. When operating in an urban environment such as Atlanta, GA the emitted city light pollution is also an important factor. In this study, we perform a multi-spectral optimization for the Georgia Tech Space Object Research Telescope across the visible through infrared spectrum that accounts for atmospheric turbulence, atmospheric transmission, and background sky radiance. The first contribution of this work is the development of a wavelength-dependent performance metric for the detection of RSOs under different atmospheric conditions. The second contribution is the derivation of a simplified model for light pollution that is based on existing astronomy models. This simplified model accounts for double scattering of light and can be used for adding a light pollution component to sky background results that are generated by complex atmospheric simulation tools. The final contribution is the derivation of novel spectral filters that are tuned to the sub-optimal atmospheric seeing conditions of Atlanta, GA and the RSO materials that are considered in this study. While this study is developed for the geographic region of Atlanta, GA and uses simplified bidirectional reflectance distribution models models for spacecraft materials, the framework is generalizable to different geographic regions, weather conditions, and satellite orientations. PubDate: 2021-03-01

Abstract: A cell-mapping approach is implemented and parallelized to analyze three-body problem orbits in the vicinity of icy moons (Europa and Enceladus). The cell-mapping method is developed for studying nonlinear dynamics with periodic motions. The method does not require previously known solutions as inputs, which is an essential requirement of continuation approaches, and does not impose symmetric constraints. As major strengths of the method, multiple-period periodic solutions and bifurcation studies can be easily performed. This method is especially applicable to a systematic periodic orbit search over a region of interest using an integration time of one period. The parallelized cell-mapping method facilitates a rapid understanding of the global dynamics. PubDate: 2021-03-01

Abstract: Thispaper investigates the micro-satellite cluster long-distance gathering control problem including initialization, orbit maintenance and collision avoidance operations. This problem is formulated using absolute orbital elements and newly developed quadratic artificial potential function based on these elements. Incorporating with the artificial potential function, a distributed autonomous low-thrust control method is proposed to solve the cluster gathering problem. Comparing with the fuel-optimal control problem formulated by equations established in Cartesian coordinates, the proposed method demonstrates geometrical intuition and possesses a low-cost computation burden. These advantages make the proposed method more suitable for controlling micro-satellite clusters. The stability of the autonomous low-thrust control method is proved using the Lyapunov method. Additionally, a Monte Carlo analysis is applied to demonstrate both the effectiveness and the collision avoidance ability of the presented algorithm. PubDate: 2021-03-01

Abstract: This paper deals with the existence and stability of libration points in linear sense in central square configuration of restricted six-body problem when small perturbations υ and ρ are given to the coriolis and the centrifugal forces, respectively. This is observed that there exist twelve libration points out of which four libration points are collinear and eight are non-collinear and all libration points lie on the concentric circles C1, C2 and C3 centered at origin. This is also observed that the eight libration points are on the axes and four are off the axes, i.e., L1, L2, L3 and L4 are on x-axis, L5, L6, L7 and L8 are on y-axis and rest are off the axes. Also, the locations of all the libration points are only influenced by a small change in the centrifugal force. It is further observed that the stability of libration points lying on circles C1 and C3 is not influenced by the perturbations and they remain unstable for all values of mass parameter μ while the libration points lying on circle C2 are influenced by the perturbations and stable for the critical mass parameter μc. PubDate: 2021-03-01

Abstract: Current active satellite maneuver detection techniques can resolve maneuvers as quickly as fifteen minutes post maneuver for large Δv when using angles-only optical tracking. Medium to small magnitude burn detection times range from 6 to 24 h or more. Small magnitude burns may be indistinguishable from natural perturbative effects if passive techniques are employed. Utilizing a photoacoustic signature detection scheme can allow for near real time maneuver detection and spacecraft parameter estimation. We define the acquisition of hypertemporal photometric data as photoacoustic sensing because the data can be played back as an acoustic signal. Studying the operational frequency spectra, profile, and aural perception of an active satellite event such as a thruster ignition or any subsystem operation can provide unique signature identifiers that support resident space object characterization efforts. A thruster ignition induces vibrations in a satellite body which can modulate reflected sunlight. If the reflected photon flux is sampled at a sufficient rate, the change in light intensity due to the propulsive event can be detected. Sensing vibrational mode changes allows for a direct timestamp of thruster ignition and shut-off events and thus makes possible the near real time estimation of spacecraft Δv and maneuver type if coupled with active observations immediately post maneuver. This research also investigates the estimation of other impulse related spacecraft parameters such as mass, specific impulse, exhaust velocity, and mass flow rate using impulse-momentum and work-energy methods. Experimental results to date have not yet demonstrated an operator-correlated detection of a propulsive event; however, the application of photoacoustic sensing has exhibited characteristics unique to hypertemporal photometry that are discussed alongside potential improvements to increase the probability of active satellite event detection. Simulations herein suggest that large, potentially destructive modal displacements are required for optical sensor detection and thus more comprehensive vibration modeling and signal-to-noise ratio improvements should be explored. PubDate: 2021-03-01

Abstract: In the current research, a novel approach or solving procedure for equations of the trapped motion for small mass m near the primary mplanet in case of the elliptic restricted problem of three bodies (ER3BP) is presented. We consider two primaries MSun and mplanet which are orbiting around their barycenter on elliptic orbits. Our aim of investigating such the class of motions is to obtain the coordinates of the aforementioned satellite (in the synodic co-rotating Cartesian coordinate system \( \overrightarrow{r} \) ={x, y, z}) which will always maintain its orbit located near the second of these primaries, mplanet. We obtain a family of semi-analytical (approximated) solutions as follows: 1) equation for x is given via coordinate y and true anomaly f, with help of the additional variable parameter α, which determines a Riccati-type character of solution for coordinate z (which means possibility of sudden jumping of the magnitude of solution), 2) expression for y is given via coordinate x, true anomaly f, and the chosen parameter α, 3) coordinate z is to be quasi-oscillating with small amplitude depending on true anomaly f which is tracing the motion of small mass (satellite) around primary mplanet. Besides, the additional ways of semi-analytical solving equations of motion are illuminated. PubDate: 2021-03-01

Abstract: Two-line elements are widely used for space operations to predict orbits with a moderate accuracy for 2-3 days. Local optimization methods can estimate a TLE as long as there exists an initial estimate, whereas global optimization methods are computationally intensive, and estimating a large number of them is prohibitive. In this paper, the feasibility of predicting the initial estimates within the radius of convergence of the actual TLEs using machine learning methods is investigated. First, a Monte-Carlo approach to estimate a TLE, when there is no initial estimate that is within the radius of convergence of the actual TLE, is introduced. The proposed Monte-Carlo method is leveraged for demonstrating the behavior of the fitting error between the realistic trajectory and the trajectory propagated by SGP4 theory during the TLE estimation processes and evaluating the unbiased performance of the proposed machine learning models. Second, gradient boosting decision trees and fully-connected neural networks are trained to map the orbital evolution of space objects to the associated TLEs using 9.5 million publicly available TLEs from the US space catalog. The desired precision in the mapping to estimate a TLE is achieved for one of the three test cases, which is a low area-to-mass ratio space object. PubDate: 2021-02-09 DOI: 10.1007/s40295-021-00249-0

Abstract: This study proposes a near-optimal, impulsive control method for overflying ground targets. A set of impulses, which adjusts the satellite ground trajectory to enable the overflight, is derived. The proposed impulsive solution is expressed in closed-form which only consists of orbital revolution numbers and target overflight errors. It allows not only simplifying the search for a minimum delta-v solution but also facilitating its extension to the multiple-target overflight problem. It is also provided in this paper an insight connecting the overflight problem to a relative orbit transfer problem controlling a phase angle or mean anomaly. Numerical examples for single-, two-, and three-target overflight verify that the controlled trajectory with the proposed impulsive solution successfully overflies the designated targets within a prescribed time. It is also demonstrated that the total delta-v required for the proposed method is near-optimal based on the performance comparison with a numerical optimization-based method which employs a very large set of initial guesses. PubDate: 2021-02-02 DOI: 10.1007/s40295-020-00240-1

Abstract: With the advent of the Deep Space Atomic Clock, operationally accurate and reliable one-way radiometric data sent from a radio beacon (i.e., a DSN antenna or other spacecraft) and collected using a spacecraft’s radio receiver enables the development and use of autonomous radio navigation. This work examines the fusion of radiometric data with optical data (i.e. OpNav) to yield robust and accurate trajectory solutions that include selected model reductions and computationally efficient navigation algorithms that can be readily adopted for onboard, autonomous navigation. The methodology is characterized using a representative high-fidelity simulation of deep space cruise, approach, and delivery to Mars. The results show that the combination of the two data types yields solutions that are almost an order of magnitude more accurate than those obtained using each data type by itself. Furthermore, the combined data solutions readily meet representative entry navigation requirements (in this case at Mars). PubDate: 2021-01-22 DOI: 10.1007/s40295-020-00244-x

Abstract: Low-thrust, optimal strategies are investigated for making a smooth landing on a uniformly rotating, homogeneous rectangular parallelepiped while avoiding the sharp corners during the approach. The individual effects of principal spherical harmonic coefficients on the stability against impact are determined numerically. An iterative predictor-corrector algorithm is utilized to find a direct and retrograde family of equatorial orbits. Stability analysis of equatorial orbits confirms the fact that retrograde orbits are less prone to disturbances than direct orbits. For an optimal landing, each approach trajectory begins from a stable equatorial orbit, and terminates at a prescribed landing point. The optimality conditions are given by Euler-Lagrange equations, and the associated two-point boundary value problem is solved by a collocation method with additional path constraints, and its results are compared with those of a direct nonlinear programming search technique. It is observed that a smaller energy expenditure is required for a landing made further away from the initial location such that sufficient time is allowed for the spacecraft to remain in an unforced orbital trajectory for a majority of the trajectory. A sample inclined orbit is also studied for a possible non-planar optimal approach in the body-fixed frame, and further investigated for various landing locations. PubDate: 2020-12-02 DOI: 10.1007/s40295-020-00243-y

Abstract: Deep Space Gateway is a NASA program planned to support deep space human exploration and prove new technologies needed to achieve it. One Gateway requirement is the ability to operate in the absence of communications with the Deep Space Network (DSN) for a period of at least three weeks. In this paper, three types of onboard sensors (a camera for optical navigation, a GPS receiver, and X-ray navigation) are considered to enhance its autonomy and reduce the reliance on DSN. A trade study is conducted to explore alternatives on how to achieve autonomy and how to reduce DSN dependency while satisfying navigation performance requirements. Using linear covariance analysis, error budgets, and sensitivity analysis, the performance of navigation systems using combinations of DSN with the aforementioned onboard sensors is shown. PubDate: 2020-12-01 DOI: 10.1007/s40295-020-00224-1