In Samara, Chinese Scientist Has Developed the Program for Efficient Control over Satellites in Course of Exploration of The Moon

At Samara University, a member-university of the National Project “Science and Universities,” Du Chunzhui, a young Chinese scientist, developed the software package for efficient control over satellites in the circumlunar space. The development will be useful later, when exploring the Moon, for ensuring full operation of the future Lunar Space Station, and creating satellite communication, navigation and monitoring systems on the Moon.

At Samara University, Du Chunzhui graduated from the postgraduate school, and this year successfully defended his dissertation for Candidate of Technical Sciences in the University Dissertation Council. In future, he intends to work as a researcher and a teacher at one of universities in China.

“Currently, many countries work on a concept of Lunar Space Station (LSS). The station will be able to be used as a base platform for exploring the Moon, other planets, as well as for studying problems that may arise during long-term human flights into deep space. For operating the station and conducting research missions on the Moon surface, servicing spacecraft, i.e. satellites to perform communication, reconnaissance, monitoring and navigation tasks will be required, no doubt about it,” said the author of the project Du Chunzhui. “The program I have developed will make it possible to efficiently control movement of such spacecrafts in the circumlunar space, calculating optimal variants for them to move between different orbits. The optimal control selection methods developed by me together with my scientific supervisor will reduce the need for additional launches of electric rocket engines for orbit adjustment, which means that fuel reserves aboard will be enough for longer operation of the spacecraft, and the active operation time of the satellite system will increase.”

As the scientist noted, the program will help change working orbits of satellites more quickly, depending on the emerging tasks: for example, if there is an urgent need for examining some area of the Moon, which has not been previously included in the coverage area of a satellite, or it will be required to provide this area with stable communication and navigation signals, because of sending there, for instance, a lunar expedition.

The program automatically calculates the parameters of the control law for moving spacecrafts, considering a lot of data — the satellite mass, its movement trajectory, its current and future orbit type, gravitational effects of the Moon and Earth, etc. The orbit types to be selected and calculated are very different, starting from the simple elliptical orbit and ending with the orbit resembling movement of butterfly wings, so called “butterfly orbit.”

 

Important scientific and practical novelty of Du Chunzhui’s project is that the program calculates satellite flights not around the Moon, but near it — in the circumlunar space, around so-called Lagrange points, or libration points. In these special points of outer space, various physical forces compensate for each other’s mutual effects in such a way that a small object locating at the point appears to be in gravitational “weightlessness” or gravitational equilibrium: it does not gravitate towards either of the two massive rotating celestial bodies that seem to affect it (for example, the Earth – Moon or the Earth – Sun pairs). But “miracles” of the Lagrange points do not end there. As scientists have found out, if spacecrafts are launched in orbits around these points, then their trajectories will be very stable and little affected by external effects, i.e. they will be reliable and stable.

In total, there are five libration points for each system of a rotating pair of celestial bodies. The Chinese scientist’s program calculates orbits for two points, the most important in the future exploration of the Moon: these are the points with the laconic names L1 and L2 in the Earth – Moon system. Point L1 is located between the Earth and the Moon and, in most space researchers’ general opinion, is an ideal place to host the Lunar Space Station. Point L2 is located behind the far side of the Moon, and satellites can be placed in orbits around this point, which will help explore this part of the Moon invisible from the Earth. By the way, back in 2018, China placed its Queqiao communication relay satellite at Point L2, which provided communication to the Chang’e 4 Lunar Station.

“No one has developed such programs before to calculate movements between various orbits around Lagrange points, this is the key novelty of this project. The fact is that orbits around Lagrange points are much more steady, stable and reliable, and they are better to be used for placing satellite groupings in the near-lunar space than unstable orbits around the Moon. The reason is gravitational anomalies of the Moon: it geometrically differs so much from the symmetrical spherical shape that the orbital movement in low near-lunar orbits is unstable. The trajectory of a satellite moving around the Moon will be constantly distorted, you will have to turn on its engines every now and then to correct the orbit, i.e. the fuel and the life of the satellite will run out much faster than, say, its near-Earth “colleague.” Stable orbits around Lagrange points are devoid of these disadvantages, and I even think that in future, we may expect competition for the use of orbits near these points as very important, but spatially limited locations of outer space,” explained Olga Starinova, Scientific Supervisor of Du Chunzhui, Head of the Department of Flight Dynamics and Control Systems, Samara University.

For reference

Lagrange points (libration points) exist in systems consisting of two massive celestial bodies (for example, the Earth – Moon or the Earth – Sun pairs), where the body with its smaller mass rotates around the body with its larger mass. Due to the mutual balancing of centrifugal force and gravitational forces in these systems, there are five spatial points, in which a third body with a very small mass (for example, a satellite or interplanetary dust particles) can remain stationary in the rotating frame of reference associated with the massive bodies. Lagrange points got their name in honour of the French mathematician Joseph Louis Lagrange, who concluded existence of these singular points in 1772 by mathematical calculations.