Capture Maneuver Research Articles

Aerogravity-assist capture into the three-body system: A preliminary design

Aero-gravity assist (AGA) is a low-cost maneuver for an interplanetary vehicle since it can potentially replace thrust with aerodynamic force to save fuel consumption. In this study, an AGA-maneuver capture scheme to deliver a vehicle into a three-body system is presented, and a successive approximation-based method is proposed to optimize atmospheric trajectories. Based on the analysis of the aerodynamic deceleration process, the AGA capture maneuver is first formulated as a coplanar atmospheric flight process with fixed time and strict endpoint-state constraints. Then, the lossless convexification and successive approximation techniques are applied to construct the solving process of iteratively optimizing the AGA trajectories. Finally, the relaxation strategy to the strict terminal state constraints and the heavily penalized-function method are developed to avoid the artificial infeasibility of the problem and improve the convergence. Numerical simulations, demonstrated by the AGA-capture into Sun-Mars L2 Halo orbits and Sun-Mars backward stable orbits, show the effectiveness and reliability of the proposed method. It is the first time that the AGA-maneuver is combined with the dynamic property of the three-body system, and the proposed method can potentially enrich the possibility of the low-energy interplanetary transfer.

Percutaneous Trans-venous Femoropopliteal Bypass in Long Occlusions of the Superficial Femoral Artery.

This technical note describes a total percutaneous technique to perform ultrasound and fluoroscopy-assisted femoropopliteal bypass in long superficial femoral artery (SFA) lesions, using standard equipment, through a juxta-anatomical superficial femoral vein (SFV) tunnel. Three percutaneous accesses were obtained under ultrasound guidance. The first was retrograde, with crossover maneuver, at the contralateral groin. The second was a proximal SFV-to-SFA stump puncture. The third was a distal popliteal artery-to-popliteal vein puncture. Through the described snaring and capture maneuvers, one single 0.018″ guide wire entered the femoral vein through the SFA stump and re-entered the popliteal artery distally. The fistulous tracts were then dilated and covered stents deployed and post-dilated. Three patients aged 68 ± 3years and presenting Rutherford 4 chronic limb ischemia were treated with this technique. The mean SFA lesion length was 22.6 ± 3cm. The mean procedure duration was 88 ± 18min. No intraoperative complication occurred. The postoperative course was uneventful. In particular, no deep vein thrombosis occurred. Rutherford stage decreased from 4 to 1 in all patients, with a mean follow-up duration of 6.6 ± 2months. The main advantage of the technique is avoiding calcification issues by abandoning the trans-arterial recanalization approach for long calcified lesions. The second interest is its feasibility by simple endovascular means without any particular or dedicated device. However, longer follow-up is needed to assess safety and durability.

A convex-programming-based guidance algorithm to capture a tumbling object on orbit using a spacecraft equipped with a robotic manipulator

An algorithm to guide the capture of a tumbling resident space object by a spacecraft equipped with a robotic manipulator is presented. A solution to the guidance problem is found by solving a collection of convex programming problems. As convex programming offers deterministic convergence properties, this algorithm is suitable for onboard implementation and real-time use. A set of hardware-in-the-loop experiments substantiates this claim. To cast the guidance problem as a collection of convex programming problems, the capture maneuver is divided into two simultaneously occurring sub-maneuvers: a system-wide translation and an internal re-configuration. These two sub-maneuvers are optimized in two consecutive steps. A sequential convex programming procedure, overcoming the presence of non-convex constraints and nonlinear dynamics, is used on both optimization steps. A proof of convergence is offered for the system-wide translation, while a set of structured heuristics—trust regions—is used for the optimization of the internal re-configuration sub-maneuver. Videos of the numerically simulated and experimentally demonstrated maneuvers are included as supplementary material.

Control of a Noncooperative Approach Maneuver Based on Debris Dynamics Feedback

Space Debris removal is a critical issue related to space research. One of the key requirements for a removal mission is the assessment of the target rotational dynamics. Ground observations are not sufficient for reaching the accuracy level required to guide the chaser spacecraft during the capture maneuver. Moreover, the guidance and control strategy for the chaser to approach the target is a critical aspect of such missions. This paper presents simulation results of two complementary methods, one for estimating the entire rotational dynamic state of the target and the other for accurately controlling the approach maneuver. In particular, the information coming from the identification and prediction of the actual motion of the tumbling axis of the target is exploited by the second method for aligning the docking interface of the chaser with that axis at the instant of capture. The dynamics estimation is based on Kalman filtering in an original combination with compressive sampling techniques for making the method robust to failures of observation sensors. The guidance of the chaser is based on a model predictive control law. The combined simulation of the employment of the methods has revealed the feasibility of the global approach.

Control System for Free-Floating Space Manipulator Based on Nonlinear Model Predictive Control (NMPC)

Manipulator mounted on an unmanned satellite could be used for performing orbital capture maneuver in order to repair satellites or remove space debris from orbit. Use of manipulators for such purposes presents unique challenges, as high level of autonomy is required and the motion of the manipulator influences the position and orientation of the manipulator-equipped satellite. This paper presents a new control system that consists of two modules: trajectory planning module (based on trajectory optimization algorithm) and Model Predictive Controller. Both modules take into account the free-floating nature of the satellite-manipulator system. Proposed control system was tested in numerical simulations performed for a simplified planar case. In the first set of simulations Nonlinear Model Predictive Control (NMPC) was used to ensure realization of a square reference end-effector trajectory, while in the second set control system was used for optimizing and then ensuring realization of the trajectory that leads to grasping of the rotating target satellite. Simulations were performed with disturbances and with the assumed non-perfect knowledge of parameters of the satellite-manipulator system. Results obtained with NMPC are better than results obtained with the controller based on the Dynamic Jacobian inverse and with the Modified Simple Adaptive Control (MSAC).

Control of asteroid retrieval trajectories to libration point orbits

The fascinating idea of shepherding asteroids for science and resource utilization is being considered as a credible concept in a not too distant future. Past studies identified asteroids which could be efficiently injected into manifolds which wind onto periodic orbits around collinear Lagrangian points of the Sun-Earth system. However, the trajectories are unstable, and errors in the capture maneuver would lead to complete mission failure, with potential danger of collision with the Earth, if uncontrolled. This paper investigates the controllability of some asteroids along the transfers and the periodic orbits, assuming the use of a solar-electric low-thrust system shepherding the asteroid. Firstly, an analytical approach is introduced to estimate the stability of the trajectories from a dynamical point of view; then, a numerical control scheme based on a linear quadratic regulator is proposed, where the gains are optimized for each trajectory through a genetic algorithm. A stochastic simulation with a Monte Carlo approach is used to account for different perturbed initial conditions and the epistemic uncertainty on the asteroid mass. Results show that only a small subset of the considered combinations of trajectories/asteroids are reliably controllable, and therefore controllability must be taken into account in the selection of potential targets.

INVERITAS: A facility for hardware-in-the-loop long distance movement simulation for rendezvous and capture of satellites and other autonomous objects

This paper describes the hardware-in-the-loop (HIL) long distance movement simulation system that was designed and built at the DFKI RIC for the INVERITAS project. It can simulate rendezvous and capture maneuvers between a Client satellite and a Servicer satellite in Earth orbit for scenarios where the semi-autonomous Servicer repairs, refuels, or re-orbits the Client which can otherwise become inoperable and eventually end up as space debris. The simulation system is a hardware-in-the-loop simulation system, meaning it incorporates real hardware like mock-ups of the Client and the Servicer, real sensors like stereocamera systems, a LIDAR, as well as sensor data processing hardware. Controlled by the simulation, the mock-ups are moved in reality so that the Servicer׳s sensors perceive the Client like in the real situation. One of the main tasks in the development of the simulator was the reduction of the twelve unconstrained degrees of freedom of two free-floating objects to ten constrained degrees of freedom of the INVERITAS movement hardware. A number of behaviors of the control system described in this paper enable it to use the given workspace efficiently to fit trajectories of the two satellites into it. The system reaches an accuracy of a few centimeters that is sufficient to test sensor data processing and navigation algorithms of the Servicer in closed-loop, meaning that the autonomous decisions of the Servicer can be based on the real sensor input. We also present methods and HIL test results concerning the sensors, sensory data processing and GNC (guidance, navigation and control) software of the functional Servicer mock-up that was developed in the INVERITAS project. Finally, the paper includes future plans of how the HIL simulator can be improved in accuracy and flexibility.

Study of the gravitational capture of a spacecraft by Jupiter

An extensive analysis of the gravitational capture of a spacecraft by Jupiter is performed for the main regions of interest around this planet. Four different dynamical models are used to study the problem. Our methodology is analogous to the one used to study the gravitational capture maneuvers in the Earth-Moon system. However, here the motion of the spacecraft is free to occupy the three-dimensional space rather than been limited to the orbital plane of the primaries, that is the most usual approach available in the literature. Similarly to what was done in the Earth-Moon system, the two-body energy Jupiter-spacecraft is monitored all the time and an impulsive maneuver should be applied to complete the capture when the spacecraft reaches the periapsis of the close approach trajectory. Our results show that the presence of the oblateness of Jupiter in the dynamical model is essential to obtain lower values for the two-body energy in times that are not too long for practical missions. The Galilean satellites are also very important, and despite their contribution in the gravitational capture maneuver itself, they can be used as a source of swing-bys that decrease the two-body energy Jupiter-spacecraft.

Low-Thrust Interplanetary Transfers, Including Escape and Capture Trajectories

O PTIMAL low-thrust interplanetary transfers in the heliocentric frame have been studied in many documented articles in which the planetary escape and capture maneuvers were not addressed. For example, [1–4] demonstrated different methods to find optimum steering programs for heliocentric orbital transfers. Moreover, a number of state-of-the-art low-thrust trajectory optimization tools are also available for mission designers. The Jet Propulsion Laboratory (JPL) developed the well-known SEPTOP and VARITOP [5] (SEPTOP’s predecessor) programs that have been used for decades. More recently, JPL has demonstrated devotion to developing new low-thrust programs such as MYSTIC [6] and MALTO [7], which are more sophisticated and capable of designing complicated low-thrust trajectories. On the other hand, optimizing low-thrust planetocentric escape and capture trajectories has also been studied (see [8–11]). These prior efforts and studies reveal that mission designers are interested in low-thrust transfers from a lowEarth orbit (LEO) to a low-planet orbit. However, the literature dealing with optimizing the entire mission, including both heliocentric and planetocentric transfer trajectories, still appears to be somewhat limited. The most commonly used method is the patched-conic approximation, which was used by Melbourne and Sauer [12] in the 1960s. The interplanetary leg and planetocentric spirals are optimized separately and then patched together. Currently, this approximation method is still in wide use by mission designers. In this Note, an approach is proposed to estimate the mission performances (e.g., flight time and propellant mass) of low-thrust interplanetary transfers, including escape and capture trajectories. During the escape or capture phases, the continuous tangential or antitangential thrust (null in shadow) is used and J2 perturbations are considered. The low-thrust escape or capture spirals are computed by a fast algorithm (an analytic orbital averaging technique plus a shortduration integration process) that significantly reduces the trajectory propagation time. With the patched-conic approximation, the proposed approach makes it possible to formulate the entire lowthrust interplanetary transfer trajectory in a single nonlinear programming parameter optimization problem. It should be noted that the shadow conditions may significantly affect propellant consumption, flight time, and the ephemeris time that the capture or escape begins. The inclusion of shadowing distinguishes this work from most previous research. The purpose of the proposed approach is not to generate highfidelity trajectory solutions but to provide a preliminary analysis tool for mission designers to quickly estimate the mission performances of low-thrust interplanetary transfers that include escape and capture trajectories. Themany-revolution planetocentric spiral trajectories in the presence of shadowing and J2 perturbations are propagated using orbital averaging, which results in much fewer steps than precise numerical integration. The proposed approach is particularly useful for determining a particular mission’s trendwith respect to variations in system parameters. An optimal Earth–Mars transfer is obtained in this Note to provide an example. Furthermore, the preliminary solutions obtained with the proposed method could be used as good initial guesses for further trajectory optimization to generate highfidelity solutions.

Indirect Optimization of Low-Thrust Capture Trajectories

The theory of optimal control is used to find the best trajectories for the capture maneuver of an interplanetary probe, which employs electric propulsion. The thrust magnitude and direction are optimized to exploit the spacecraft continuous steering capabilities and maximize the spacecraft final mass. Strategies, which involve propelled and coast arcs, are analyzed. The influence on the optimal trajectories of some parameters, such as the thrust, the specific impulse, and the initial velocity, is also discussed

The Neptune/Triton Explorer mission: A concept feasibility study

Technological advances over the next 10 – 15 years promise to enable a number of smaller, more capable science missions to the outer planets. With the inception of miniaturized spacecraft for a wide range of applications, both in large clusters around Earth, and for deep space missions, NASA is currently in the process of redefining the way science is being gathered. Technologies such as 3-dimensional multi-chip modules, micro-machined electromechanical devices, multi functional structures, miniaturized transponders, miniaturized propulsion systems, variable emissivity thermal coatings, and artificial intelligence systems are currently in research and development, and are scheduled to fly (or have flown) in a number of missions. This study will leverage on these and other technologies in the design of a lightweight Neptune orbiter unlike any other that has been proposed to date. The Neptune/Triton Explorer (NExTEP) spacecraft uses solar electric earth gravity assist and aero capture maneuvers to achieve its intended target orbit. Either a Taurus or Delta-class launch vehicle may be used to accomplish the mission.

Spacecraft Planetary Capture Using Gravity-Assist Maneuvers

If the arrival speed at a target body can be increased from the very low hyperbolic excesses required to perform a low-thrust capture maneuver, then potentially significant savings can be made in the heliocentric mission duration if a bound orbit about the target planet can be maintained. We define a bound orbit as having an apoapsis that is positive but less than infinity; however, because this is not a practical limit and is instead a theoretical limit we examine the impact of reducing the target apoapsis to more realistic and useful values within specific case studies. Furthermore, an increase in arrival velocity can be expected to yield a benefit in mission launch mass.

Neural ensemble coding of target identity in echolocating bats.

Most insectivorous bats use echolocation to determine the identity of flying insects. Among the many target features that are so extracted, the insect's wingbeat pattern and frequency appear to serve as useful cues for identification. Biosonar pulses impinging on the fluttering wings of an insect are returned as echoes whose amplitudes vary with time, thus providing a characteristic signature of the insect. It has been shown previously that neurons in the inferior colliculus, a midbrain auditory nucleus, of the little brown bat respond to sound stimuli that mimic echoes from fluttering targets. To examine the manner in which target identity is represented in the inferior colliculus, an ensemble coding analysis using a filter-based approach was undertaken. The analysis indicates that a discrete subset of neurons in the inferior colliculus, the onset units, are strongly tuned to wingbeat frequencies of targets that the bat hunts, and that ensemble response reaches a maximum at a distinct phase of the prey capture maneuver: the late approach stage. On the basis of the analysis it is hypothesized that inferior colliculus neurons may play an important role in target detection-identification processing. Although ensemble coding of temporally sequenced information has not been analyzed in the auditory system so far, this study indicates that this method of coding may provide the information necessary to detect and identify targets during prey capture.