Citation: Wang, X.; Zhu, H.; Shen, Q.;
Wu, S.; Wang, N.; Liu, X.; Wang, D.;
Zhong, X.; Zhu, Z.; Damaren, C.
Trigger-Based K-Band Microwave
Ranging System Thermal Control
with Model-Free Learning Process.
Electronics 2022, 11, 2173. https://
doi.org/10.3390/electronics11142173
Academic Editor: Nunzio Cennamo
Received: 28 May 2022
Accepted: 4 July 2022
Published: 1 July 2022
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Article
Trigger-Based K-Band Microwave Ranging System Thermal
Control with Model-Free Learning Process
Xiaoliang Wang
1,†,‡
, Hongxu Zhu
1
, Qiang Shen
1
, Shufan Wu
1,
*, Nan Wang
2
, Xuan Liu
3
, Dengfeng Wang
3,‡
,
Xingwang Zhong
3
, Zhu Zhu
4
and Christopher Damaren
5
1
School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai 200240, China;
xlwang12321@sjtu.edu.cn (X.W.); livewith_blackcat@sjtu.edu.cn (H.Z.); qiangshen@sjtu.edu.cn (Q.S.)
2
University of Michigan—Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University,
Shanghai 200240, China; wn19951113@sjtu.edu.cn
3
Institute of Space Radio Technology, Xi’an 710100, China; liuxuan0229@126.com (X.L.);
dfwang_aero@163.com (D.W.); zhongxw1391@163.com (X.Z.)
4
Shanghai Institute of Satellite Engineering, Shanghai 200240, China; annieapple1985@sina.com
5
Institute for Aerospace Studies, University of Toronto, Toronto, ON M1C 1A4, Canada;
damaren@utias.utoronto.ca
* Correspondence: shufan.wu@sjtu.edu.cn; Tel.: +86-186-2956-2996
† Current address: East Dongchuan Rd. No. 800, Shanghai 200241, China.
‡ These authors contributed equally to this work.
Abstract:
Micron-level accuracy K-band microwave ranging in space relies on the stability of the
payload thermal control on-board; however, large quantities of thermal sensors and heating devices
around the deployed instruments consume the precious inner communication resources of the central
computer. Another problem arises, which is that the payload thermal protection environment can
deteriorate gradually through years operating. In this paper, a new trigger-based thermal system
controller design is proposed, with consideration of spaceborne communication burden reduction
and actuator saturation, which guarantees stable temperature fluctuations of microwave payloads in
space missions. The controller combines a nominal constant sampling PID inner loop and a trigger-
based outer loop structure under constraints of heating device saturation. Moreover, an iterative
model-free reinforcement learning process is adopted that can approximate the estimation of thermal
dynamic modeling uncertainty online. Via extensive experiment in a laboratory environment, the
performance of the proposed trigger thermal control is verified, with smaller temperature fluctuations
compared to the nominal control, and obvious efficiency in system communications. The online
learning algorithm is also tested with deliberate thermal conditions that deviate from the original
system—the results can quickly converge to normal when the thermal disturbance is removed. Finally,
the ranging accuracy is tested for the whole system, and a 25% (RMS) performance improvement
can be realized by using a trigger-based control strategy—about 2.2
µ
m, compared to the nominal
control method.
Keywords:
K-band ranging system; event trigger; saturation control; reinforcement learning;
actor/critic policy
1. Introduction
K-band microwave ranging (MWR) technology can provide micron-level precise
ranging measurements between spacecraft in space, which has potential applications in the
fields of Earth elevation surveying, gravity field detection, and other space missions [
1
,
2
].
The accuracy ranging performance (time delay) of the MWR system is mainly affected by
the payload thermal condition in space. The state-of-the-art payload thermal controller
should be well designed with tiny temperature fluctuations during orbiting; however, the
spacecraft thermal control system is a large-scale system that involves hundreds, even
Electronics 2022, 11, 2173. https://doi.org/10.3390/electronics11142173 https://www.mdpi.com/journal/electronics
