Space-based gravitational wave detection requires a strict level of residual acceleration ($\sim$$10^{-15}\;\mathrm{m/s}^{2} / \sqrt{\text{Hz}}$ in $\text{0.1}\;\text{mHz}\text{--} {1}\;\text{Hz}$) on the test masses along the sensitive axes. Because of the configuration of the detection spacecraft with two test masses, there are complex couplings between different loops in the drag-free, and attitude control system. Moreover, the space environment disturbances and the limited noise levels of the actuators and sensors make it difficult to meet all the index requirements. Currently, proportional-integral-derivative (PID) and $H_\infty$ methods are mainly used for its controller design, where the system is decoupled into relatively independent loops, and the controllers are designed separately. However, parameter tuning usually requires empirical trial and error, leading to the low design efficiency. And the coupling relationships between loops cannot be well described and treated mathematically. Therefore, a controller design method for drag-free spacecraft multiple loops is proposed in this article, where the index requirements are transformed into frequency domain constraints and the optimization objectives are designed for better performances according to the control characteristics of different loops. Then, the controllers are tuned by multipopulation genetic algorithm improving the design efficiency. As mentioned, under the premise that the index requirements are all met, the couplings between loops are considered and some of the performances of the system can be optimized, such as the residual acceleration acting on the test masses. Numerical simulation and comparison verify the effectiveness of this method. 

A Controller Design Method for Drag-Free Spacecraft Multiple Loops With Frequency Domain Constraints

Finite-time stabilization for a novel non-contact spacecraft with a small air-clearance range constraint

TianQin is a proposed mission for space-based gravitational-wave detection that features a triangular constellation in circular high Earth orbits. The mission entails three drag-free controlled satellites and long-range laser interferometry with stringent beam pointing requirements at remote satellites. For the payload architecture and pointing control strategies, having two test masses per satellite, one for each laser arm, and rotating entire optomechanical assemblies (each consisting of a telescope, an optical bench, an inertial sensor, etc.) for constellation breathing angle compensation represent an important option for TianQin. In this paper, we examine its applicability from the perspectives of test mass and satellite control in the science mode, taking into account of perturbed orbits and orbital gravity gradients. First, based on the orbit-attitude coupling relationship, the required electrostatic forces and torques for the test mass suspension control are estimated and found to be sufficiently small for the acceleration noise budget. Further optimization favors configuring the centers of masses of the two test masses collinear and equidistant with the center of mass of the satellite, and slightly offsetting the assembly pivots from the electrode housing centers forward along the sensitive axes. Second, the required control forces and torques on the satellites are calculated, and thrust allocation solutions are found under the constraint of having a flat-top sunshield on the satellite with varying solar angles. The findings give a green light to adopting the two test masses and telescope pointing scheme for TianQin. 

Payload architecture and pointing control strategies for TianQin

The cablelessness of non-contact close-proximity formation satellites can fundamentally avoid the influence of non-contact interface coupling effects and can further enhance the attitude pointing accuracy and stability of the payload module (PM). However, it also brings the problem of limited on-board resources and system latency. In this paper, an event-triggered attitude tracking controller of the support module (SM) that avoids the Zeno phenomenon was proposed. The update time of the control signal was determined by the event-triggering mechanism based on intermediate variables, thus, reducing the communication burden and actuator asynchrony between the two modules. The feasibility and effectiveness of the proposed approach was demonstrated by numerical simulations.

/pdf/event-triggered-attitude-tracking-control-for-a-cableless-6ssbihbl.pdf

Event-Triggered Attitude-Tracking Control for a Cableless Non-Contact Close-Proximity Formation Satellite

GKYP-Based Finite Frequency Control for Relative Motion of Drag-Free Satellite

Tunable single-photon routing between two single-mode waveguides by a giant Λ-type three-level atom

The determination for ideal release point of test masses in drag-free satellites for the detection of gravitational waves

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Tunable single-photon routing between two single-mode waveguides by a giant Λ-type three-level atom

The determination for ideal release point of test masses in drag-free satellites for the detection of gravitational waves