Synchronous Addition of Antenna Field Signals with a Shift of Sampling Pulses during Spacecraft Tracking by Target Designations with Allowance for the Inertia of Antenna Motion

The method of synchronous addition of signals of separate antennas was proposed previously for the aggregation of relatively small-scale aperture antennas into a single digital antenna array (digital antenna field) with a combined area for receiving telemetry signals from spacecraft when antennas are mutually spaced by a distance big enough for them not to shade one another. The method is based on the idea of compensating mutual delays between the antennas of the received signal by a corresponding shift of the sampling pulses of the signals of different antennas. The present paper demonstrates the efficacy of the method in the mode of spacecraft tracking by target designations in orbits of global navigation systems with allowance for the inertia of antenna motion. It is shown that in spacecraft tracking mode, which is close to the real one, this method gives a signal-to-noise ratio and bit-error probability closer to the theoretical limit than the values obtained for the idealized mode (analyzed earlier), which equates the angular coordinates and velocities of the antennas to the calculated angles and velocities of spacecraft in target designation nodes.

Evaluation of Time Difference of Arrival (TDOA) Networks Performance for Launcher Vehicles and Spacecraft Tracking

Time Difference of Arrival (TDOA) networks could support spacecraft orbit determination or near-space (launcher and suborbital) vehicle tracking for an increased number of satellite launches and space missions in the near future. The evaluation of the geometry of TDOA networks could involve the dilution of precision (DOP), but this parameter is related to a single position of the target, while the positioning accuracy of the network with targets in the whole celestial vault should be evaluated. The paper presents the derivation of the MDOP (minimum dilution of precision), a parameter that can be used for evaluating the performance of TDOA networks for spacecraft tracking and orbit determination. The MDOP trend with respect to distance, number of stations and target altitude is reported in the paper, as well as examples of applications for network performance evaluation or time precision requirement definitions. The results show how an increase in the baseline enables the inclusion of more impactive improvements on the MDOP and the mean error than an increase in the number of stations. The target altitude is demonstrated as noninfluential for the MDOP trend, making the networks uniformly applicable to lower altitude (launchers and suborbital vehicles) and higher altitude (Low and Medium Earth Orbits satellites) spacecraft.

Adaptive Fixed-Time Terminal Sliding Mode Control on SE(3) for Coupled Spacecraft Tracking Maneuver

In this paper, a reaching law-based adaptive fixed-time terminal sliding mode control law, which is used for coupled spacecraft tracking maneuver in the presence of large inertia parametric uncertainties and external disturbances, is proposed. The coupled 6-DOF kinematics and dynamics for spacecraft motion are modeled on Lie group SE(3). The relative configuration is expressed by a local coordinate (exponential coordinate) of SE(3). In order to estimate the inertia parameters and external disturbances, we also propose a novel adaptive update law, which can make the control law be applied without the inertia parameters of the spacecraft a priori. Fixed-time convergence property of the closed-loop feedback system is proved in the framework of Lyapunov. Numerical simulations are performed to demonstrate the performances of the proposed control scheme for coupled spacecraft tracking maneuver.

Synchronous Addition of Antenna Signals with a Shift of Sampling Pulses in Idealized Mode of Spacecraft Tracking by Target Designations

The method of synchronous addition of signals of separate antennas was proposed previously for the aggregation of relatively small-scale aperture antennas into a single digital antenna array (digital antenna field) with a combined area for receiving telemetry signals from spacecraft. In this case, the antennas are mutually spaced by a big enough distance in order to not shade one another. The method is based on the idea of compensating the mutual delays between the antennas of the received signal by a corresponding shift of the sampling pulses of the signals of different antennas. This article demonstrates the method’s workability in idealized mode of spacecraft tracking by target designations on orbits of global navigation systems. It is shown that with the up-to-date level of impulse technology development the method of synchronous addition of antenna signals with a shift of sampling pulses is potentially capable of ensuring the reception of telemetry information from deep-space spacecraft at rates approximately 6 times higher than those of the classic Delta-DOR method.

Research on the operational regional coverage of satellite and spacecraft tracking and controlling

In view of the problem of building ground stations for tracking and controlling of satellites and spacecraft, considering the fixed angle between the orbit of the satellite or spacecraft and the equatorial surface of the earth, and the difference of longitude between the two circles in succession of the satellite or spacecraft caused by the rotation of the earth, the operation area of the satellite or spacecraft was calculated by using the method of spherical projection of satellite orbit rotation, taking the earth as the reference system. The minimum number of ground stations needed for satellite tracking and controlling was calculated in three cases, by using the mathematical model of sphere ring area and honeycomb coverage. This model was validated by the launch and operation data of Shenzhou 7.

Catching the wave

This chapter introduces the idea behind the technology used to detect gravitational waves, and places these ideas in a historical context. It explains the need for an international network of intruments and provides an idea of future possibilities. The notions of using spacecraft tracking and pulsar timing to search for low-frequency gravitational wave signals are also discussed.

Adaptive Saturated Neural Network Tracking Control of Spacecraft: Theory and Experimentation

An adaptive saturated neural network (NN) controller is developed for 6 degree-of-freedom (6DOF) spacecraft tracking, and its hardware-in-the-loop experimental validation is tested on the ground-based test facility. To overcome the dynamics uncertainties and prevent the large control saturation caused by the large tracking error at the beginning operation, a saturated radial basis function neural network (RBFNN) is introduced in the controller design, where the approximate error is counteracted by an adaptive continuous robust term. In addition, an auxiliary dynamical system is employed to compensate for the control saturation. It is proved that the ultimate boundedness of the closed-loop system is achieved. Besides, the proposed controller is implemented into a testbed facility to show the final operational reliability via hardware-in-the-loop experiments, where the experimental scenario describes that the simulator is tracking a planar trajectory while synchronizing its attitude with the desired angle. Experimental results illustrate that the proposed controller ensures that the simulator can track a preassigned trajectory with robustness to unknown inertial parameters and disturbances.