# Multi-Satellite Observation-Relay Transmission-Downloading Coupling Scheduling Method
## 1 Introduction  
The earth observation satellite (EOS) acquires Earth's surface data from space, offering the advantage of extensive detection coverage. EOS finds widespread applications in disaster monitoring, environmental surveillance, and resource exploration [1]. Accompanying the increment in the number of in-orbit satellites, the collaboration of multiple EOSs has strengthened the Earth's observation ability, expanded coverage, and increased the number of observation targets, which is beyond what a single EOS could accomplish. Typical multi-EOS projects include Pleiades [2], World View [3], H [4], etc. Multi-EOS mission scheduling involves the rational scheduling of on-board actions during satellite observation processes to maximize profit while satisfying the satellite's constraints [5]. Based on single-EOS mission scheduling, multi-EOS mission scheduling also needs to schedule multi-EOS cooperative work [6]. In recent years, the multi-EOS scheduling problem has received extensive attention and research efforts. The process of satellite earth observation involves capturing ground target information through a camera, storing it in storage, and subsequently transmitting it to a ground station. The observation data acquisition ability and data transmission of a single satellite are constrained by the satellite-station data transmission window and satellite storage capacity. With the continuous advancement of satellite communication technology, the number of satellites capable of inter-satellite communication is increasing, and the inter-satellite data transmission capacity is constantly improving. Projects such as Starlink, OneWeb, and Telesat [7] exhibit strong inter-satellite data communication capabilities. Inter-satellite data transmission enables observation satellites to relay data to ground stations through other satellites when they are not within the satellite-station data transmission window, thereby reducing the occupancy of satellite storage resources and enhancing their target observation capabilities. Integrating multiple capabilities in a single satellite, including target observation, inter-satellite data transmission, and satellite-ground data transmission, is a development trend, as it can maximize the collective capabilities of the satellite cluster. However, this integration also presents scheduling challenges for the satellite cluster. The processes of multi-satellite observation, inter-satellite data transmission, and satellite-ground data downloading are coupled, and they are coupled in terms of electricity consumption and storage occupancy. Effectively coordinating the entire coupled process of multi-satellite observation, relay transmission, and downloading is the key to the problem. In prior research, scholars have conducted investigations into the single-satellite observation scheduling problems [8; 9; 10; 11; 12; 13], the multi-satellite observation scheduling problems [14; 15; 16; 17], the schedule problems of multi-satellite observation and downloading data through a single satellite [18; 19; 20; 21], and the multi-satellite data relay transmission scheduling problems [22; 23; 24; 25]. There is relatively limited research that discusses multi-satellite observation and the entire coupled process involving multi-satellite observation, relay transmission, and data downloading. Therefore, this article delves into the study of the coupled scheduling problem for the entire process of multi-satellite observation, relay transmission, and downloading. The multi-satellite observation-relay transmission-download coupling scheduling problem includes the multi-satellite observation scheduling process and the data transmission planning process, whereas the data transmission planning process includes determining which satellite will be involved in the process of transmitting observation data between satellites and which satellite will be responsible for downloading the data to the ground station.