## 1 Introduction  
Remote sensing satellites have been widely used in geological exploration, disaster monitoring, emergency rescue, environmental supervision, etc., promoting social and economic development [1, 2, 3]. In recent years, constellations for remote sensing have been developing rapidly, such as Dove [4], WorldView [5], Capella [6], Gaofen-1 [7], Jilin-1 [8], etc. The efficiency of remote sensing can be improved by compressing the imaging revisit time. However, the acquisition of remote sensing data generally takes several hours, which makes it difficult to meet the real-time requirements of remote sensing tasks. The traditional remote sensing system consists of remote sensing satellites, telemetry, tracking and control (TT&C) system, ground system, users of remote sensing, etc. The ground system includes the operations control and management (OC&M) system, and data processing system, which are responsible for task planning and management, data receiving and processing, and product generation and distribution [9]. In the traditional remote sensing process, the ground system operates in a periodic and batch manner. It usually takes several days from the user's request to the acquisition of remote sensing images, and several hours during urgent tasks. In addition to increasing the number of satellites and shortening the revisit cycle, there are two alternative ways to improve the timeliness of remote sensing applications: (i) increase the onboard processing capacity,including data compression, down-link data rate reduction, image interpretation, and effective information extraction, so as to complete multi-target recognition and monitoring with high confidence [10; 11]; (ii) use the Internet to provide ubiquitous access capability for remote sensing demand collection and data distribution, so as to improve the efficiency of satellite-terrestrial network collaboration [12]. In order to promote the timeliness of remote sensing, the company Maxar has proposed a series of methods for each phase of remote sensing. Maxar develops a Rapid Access Program (RAP) for demand collection [13]. The RAP provides online access to the ground system and constellation for time-sensitive tasks through a web interface, and allows for the assignment of prioritized tasks. A Direct Access Program (DAP) is developed for remote sensing data distribution [14]. The DAP supports the use of the customer's ground station for task planning, image acquisition, and data download. Maxar offers a \"mobile access terminal\" to provide remote sensing services with features of fast deployment (less than 1 h), low latency (imagery in hand in under 15 min), and operational anywhere (available in disconnected, intermittent, and limited-bandwidth environments) [15]. In recent years, large or even mega low Earth orbit (LEO) constellations have been constructed worldwide [16; 17]. Global coverage can be achieved by deploying hundreds or thousands of small LEO communication satellites [18; 19]. SpaceX plans to deploy a mega-constellation with about 42,000 satellites, providing global satellite Internet access. As of December 2022, more than 3500 satellites have been launched into orbit, and more than 1 million user terminals have been produced, providing satellite Internet access coverage to 40 countries [20; 21]. OneWeb has also submitted frequency applications for about 48,000 satellites. As of December 2022, a total of 502 satellites have been launched, providing high-speed and low-latency satellite network services across the US, Europe, much of the Middle East and Asia, South Africa, southern Australia, and parts of South America [22; 23]. According to incomplete statistics, the number of satellites in the planned constellations has reached 100,000. The remote sensing programs developed by Maxar are still based on the stations and communication networks on the ground.