Modulating retro-reflectors for space, tracking, acquisition, and ranging using multiple quantum-well technology

Autonomous rendezvous and proximity operations between a chaser spacecraft and a target space object, consist of autonomous controlled approach and controlled docking with or controlled capture of the target by the chaser. Guidance, navigation and control problems during autonomous rendezvous and proximity maneuvers between spacecraft are challenging, particularly when the target spacecraft or space object is not cooperating with the chaser spacecraft. In this work, we present a guidance scheme and a control scheme for a chaser spacecraft that is tasked to synchronize its motion with a target space object during close proximity maneuvers. The guidance scheme generates a desired state trajectory based on remote measurements of the motion states of the target from the chaser and motion prediction of the target. The tracking control scheme for the chaser results in asymptotic tracking of the desired state trajectory with an almost global domain of convergence on the state space. These schemes are applied to the situation where the chaser spacecraft synchronizes its attitude motion with the target, while maintaining a constant relative position with respect to the target at the end of the maneuver. Numerical simulation results are presented to show the performance of these guidance and tracking control schemes.

This paper investigates the problem of relative motion control for spacecraft rendezvous on an arbitrary elliptical orbit. The simplified dynamic model describing the relative motion between the chaser spacecraft and the target spacecraft is established via using transformed variables. Due to the presence of time variant parameters in this novel model, robust control scheme and adaptive control scheme are designed to solve the rendezvous problem. Theoretical analyses and simulation results demonstrate the effectiveness of the proposed methods.

<p dir="ltr">The paper addresses a significant challenge in on-orbit robotics servicing and assembly, which is to overcome the saturation setback of force/torque on robot joint and spacecraft actuators during the post-capture stage while controlling a target spacecraft with uncontrolled large angular and linear momentums. The authors propose a novel solution based on two robust and efficient control algorithms: Optimal Control Allocation (OCA) and Non-linear Model Predictive Control (NMPC). Both algorithms aim to minimize joint torques, spacecraft actuator moments, contact forces, and moments of a compound redundant system that includes a common payload (target spacecraft) grasped by dual n-degree space robotics manipulators mounted on a chaser spacecraft. The OCA algorithm minimizes a quadratic cost function using only the current states and the system dynamics, but the NMPC also considers the future state estimates and the control inputs over a specified prediction horizon. It is computationally more involved but provides superior results in reducing joint torques. The literature to date in application of MPC to robotics mainly focuses on linear models but the dual arm coordination is highly non-linear and there is no MPC application on dual arm coordination. The proposed discretized technique offers exact realizations (of a non-linear model) with elegance and simplicity and yet considers the full non-linear model of the dual arm coordinating system. It is computationally very efficient. The computer simulation results show that the proposed algorithms work efficiently, and the minimum torques, contact forces, and moments are realized. The developed algorithm also is very efficient in tracking problems.</p>

A method of estimating the relative position and rate between a chaser spacecraft and a target spacecraft is discussed. An extended Kalman algorithm is used for the estimation. The stale variables are described in a reference frame which is not accelerating. The relative position control is based on the multiple arc transfer method. The thruster ON time and the instant of thruster firing is based on these estimates. The simulation results with and without the filter in the control loop are discussed. The effect of noise modelling is also described.

Model Predictive Control (MPC) based relative motion control is developed for rendezvous of a follower spacecraft with a leader spacecraft. Debris Avoidance Maneuver operates in rendezvous phase and Line of Sight Maneuvers during terminal phase. In this approach, the optimal control sequence is generated over finite horizon by considering the measurement of the state in every guidance step for different rendezvous phases. Various equality and inequality constraints are included. These constraints are thrust magnitude limit, chaser spacecraft positioning with in Line-of-Sight (LOS) while approaching the target spacecraft, and chaser spacecraft terminal velocity limit for soft-docking with target spacecraft. In addition debris avoidance constraints are also considered along the rendezvous path. The robustness of this control has been verified using nonlinear dynamics with J2 perturbation model. Pulse Width and Pulse Frequency modulator (PWPFM) are used to generate the impulse velocity change by on/off thrusters as actuators. The MPC Controller is validated on nonlinear and elliptical orbit model by simulations.

Formation Flying is revolutionizing Earth and Space science and the way the space community conducts science missions. This technological transformation provides new, innovative techniques in spacecraft guidance, navigation, and control, and how the science community gathers and shares information between space vehicles and the ground. These technologies will also expedite the human exploration of space. Once fully matured, this technology will result in swarms of space vehicles flying as virtual platforms or distributed space systems and sensor webs which gather significantly more and better science data than is possible today. Formation flying will be enabled through the development and deployment of automated spaceborne guidance, navigation, and control (GN&C) systems integrated with intrasatellite communications infrastructure. Innovative spacecraft autonomy techniques, such as differential Global Positioning System (GPS) technology, optical, and vision-based navigation and celestial navigation allow autonomous navigation while other technologies provide for the autonomous control methods to maintain and optimize these formations. This paper provides a vision of the future of space exploration in the context of GN&C technology, and an overview of the current status of NASA technology development and its partnerships with the Department of Defense (DoD), Industry, and University to bring formation flying technology to the forefront as quickly as possible. We address the impediments that need to be overcome to achieve the distributive spacecraft vision and NASA GSFC's approach to transfer this technology to space. We will also describe some of the formation flying testbeds, such as the on-orbit Air Force Research Laboratory (AFRL) University Nanosats, and Orion test beds and ground based GSFC Formation Flying Test Bed, which are being developed to demonstrate and validate innovative position sensing and formation control technologies.

This chapter studies the spacecraft rendezvous problem and the spacecraft formation flying problem by using the TPF approaches. For the spacecraft rendezvous problem, the target spacecraft can be in arbitrary eccentric orbits, and for the spacecraft formation flying problem, the reference spacecraft is assumed to be in a circular orbit. By clarifying that the T-H equation and C-W equation are both ANCBC and NCE, the TPF approach for stabilization and consensus of linear systems with input and output delays built in the previous chapters are extended to solve the considered problems. Some simulations are carried out to validate the effectiveness of the proposed approaches.

We demonstrate parametric wavelength conversion via four-wave mixing using ultra-low peak pump powers of a few milliwatts in a micrometer-scale silicon device. The response time of our device is 100 ps allowing for implementation in high-bandwidth optical communications. At these ultra-low power levels and microscale sizes, it should be possible to realize hundreds of these devices operating simultaneously on a single chip.

The article proposes the concept of joint navigation and communication for a heterogeneous group of autonomous uncrewed vehicles located in different environments. The theory of multi-agent systems forms the basis for this concept. The authors present a block diagram for a multi-agent system, a scheme of object integration based on the data from geophysical fields, beacons, and other available meters.

A single InGaN/GaN multiple quantum wells microwire light-emitting diode with high efficiency current injection and spreading

Automated aerial surveillance and detection of hostile ground events, and the tracking of the perpetrators have become of critical importance in the prevention and control of insurgent uprisings and the global war on terror. Yet a basic understanding of the limitations of sensor system coverage as a function of aerial platform position and attitude is often unavailable to program managers and system administrators. In an effort to better understand this problem we present some of the design tradeoffs for two applications: 1) a 360° viewing focal-plane array sensor system modeled for low altitude aerostat applications, and 2) a fixed diameter area of constant surveillance modeled for high altitude fixed wing aircraft applications. Ground coverage requirement tradeoffs include the number of sensors, sensor footprint geometry, footprint coverage variability as a function of platform position and attitude, and ground surface modeling. Event location specification includes latitude, longitude, altitude for the pixel centroid and corners, and line-of-sight centroid range.

This paper studies the spacecraft multi-target tracking. Firstly, the spacecraft expected attitude angle is designed according to the mission requirement, namely having the camera on the chaser spacecraft point strictly to the target spacecraft and maximizing the communication time between the antenna on the chaser spacecraft and the Earth. Then, the appropriate antenna installation angle is calculated based on task constraints. Finally, numerical simulation is presented to verify the effectiveness of the design of expected attitude angle and antenna installation angle. Index Terms - Fixed Antenna, Installation Angle Design, Multi- target Tracking, Expected Attitude Angle

In recent decades, the increased space debris around Earth’s orbit has become a severe problem due to the increased risk of collisions with spacecraft. Therefore, the development of technology to remove this debris is one of the most urgent issues. This study takes up a real-time method of estimating the decommissioned spacecraft’s periodic attitude motion using video taken from the chaser spacecraft. In terms of high estimation accuracy and low calculation load, the proposed method visually tracks the feature points of the target spacecraft, and the attitude motion of the spacecraft is estimated by Extended Kalman Filter using the quaternion as the state vairable, in which both the posture direction and angular speed are instantly specified, and the singular point is accessible. The proposed method has the assumption that the target is in the nutation motion or the geometry is known. This article reports numerical simulation examples in which the proposed method estimates the nutation motion.

Although commercial Si-based photodetectors have been widely developed and are highly mature for weak-light detection, GaN photodetectors with multiple quantum wells (MQWs) structures still demonstrate remarkable advantages in weak visible-light sensing due to their inherent spectral selectivity, low dark current, and high reliability. These features make them particularly suitable for challenging scenarios such as long-distance transmission, underwater environments, and rainfall conditions. To investigate their potential for weak-light detection, high-responsivity GaN-based MQWs PDs were fabricated and implemented in VLC systems under challenging environments. Under a -20 V bias and 66.4 mW of 405 nm laser irradiation, a peak photocurrent of 7.23 mA was observed. Responsivities of 1.24 A/W and 1.15 A/W were obtained under biases of -20 V and -5 V, respectively. Initially, a 20 m free-space communication scenario was simulated, yielding a maximum data rate of 5.74 Gbps. Subsequently, a 3.38 m rain environment was constructed with simulated light, moderate and heavy rain conditions, where maximum data rates of 7.77 Gbps, 6.11 Gbps, and 6.03 Gbps were achieved, respectively. Finally, underwater optical communication was evaluated in a 3.38-m-long water tank, resulting in a maximum data rate of 6.57 Gbps. These experimental results indicate significant potential for high-response current GaN-based MQWs PDs in enabling high-speed, multi-scenario optical communication networks.

Modulating retro-reflectors (MRR) couple passive optical retro-reflectors with electro-optic modulators to allow free-space optical communication with a laser and pointing/acquisition/tracking system required on only one end of the link. In operation a conventional free space optical communications terminal, the interrogator, is used on one end of the link to illuminate the MRR on the other end of the link with a cw beam. The MRR imposes a modulation on the interrogating beam and passively retro-reflects it back to the interrogator. These types of systems are attractive for asymmetric communication links for which one end of the link cannot afford the weight, power and expense of a conventional free-space optical communication terminal. Recently, MRR using multiple quantum well (MQW) modulators have been demonstrated using a large area MQW placed in front of the aperture of a corner-cube. For the MQW MRR, the maximum modulation can range into the gigahertz, limited only by the RC time constant of the device. This limitation, however, is a serious one. The optical aperture of an MRR cannot be too small or the amount of light retro-reflected will be insufficient to close the link. For typical corner-cube MQW MRR devices the modulator has a diameter between 0.5-1 cm and maximum modulation rates less than 10 Mbps. In this paper we describe a new kind of MQW MRR that uses a cat's eye retro-reflector with the MQW in the focal plane of the cat's eye. This system decouples the size of the modulator from the size of the optical aperture and allows much higher data rates. A 50 Mbps device has been demonstrated.