Have you ever looked up into the night sky and saw the erratic flash of one and wondered what the space vehicle you were gazing at actually looked like? It varies-Sputnik was the size of a beach ball, and the Hubble Space Telescope is the size of a school bus. There are thousands of satellites orbiting the planet; each of those costs an immense amount of money to build, and deliver, but also to maintain.
A solution to this problem lies in the next generation of satellites, which tend to become smaller and smaller. These satellites, first conceived in the early 1990’s, are now much more advanced as they are designed to orbit the earth in a formation, and work as a network to do the job of much larger satellites. Not only do they require less expensive materials and technology, substantially reducing the costs, but they are also more reliable, because the risk of failure is spread out across many satellites, instead of just one. But a new fix sometimes brings new problems. How do you keep a network of small satellites from crashing into each other? Such a crash would be catastrophic for the owners of the satellites, and would create even more space debris. An article published recently in Open Physics may have an answer.
The traditional method of controlling satellites is called a Linear Quadratic Regulator (LQR), and the new approach is called a state-dependent Riccati equation (SDRE). The LQR has been used for decades in the field of space exploration and technology, but it is linear.
In the paper, the authors – Zhang Ke, He Zhenqi, and Lv Meibo, designed a LQR controller, and an SDRE controller and compared the reaction and adaption time of both.
SDRE is nonlinear, and has several other advantages: it proves a much quicker method in most situations in which it has been tested. As it is quicker, it requires less movement from the spacecraft. The less movement that is required from the spacecraft, the less fuel. Of course, less fuel means less money, so cheaper and more efficient satellites. Low-cost satellites mean that the services that depend on satellites, such as internet and GPS, will go down in price. It further results in development of space technology because the money saved on spacecraft maintenance can go into research.
Dr. HE Zhenqi says, “The SDRE control method is a kind of efficient and low energy consumption control method in the flight control satellites formation. It has certain practical value and such study may play a guiding role in the future deep space exploration activities.”
The original article is available fully in open access to read, download and share on De Gruyter Online.
The research was supported by the Natural Science Foundation of China (Grant No. 61174202, 61502391), China Space Foundation(No. 2015KC020121), National Key Laboratory of Aerospace Flight Dynamics Open Foundation(No. 2015KC020214)