Light small SAR satellite level flight mode construction method and system

Abstract

The application provides a light and small SAR satellite flat flight mode construction method and system, comprising the following steps: step 1: according to user demand, inputting a target area visible observation bandwidth range in a satellite flat flight mode, and determining a field of view range; step 2: performing SAR plane phased array antenna capacity design on a load, so that antenna beam scanning capacity covers the target field of view range; step 3: performing integrated electric, attitude control and load subsystem working time sequence design; and step 4: performing on-board radar working parameter calculation on the load subsystem. The light and small SAR satellite flat flight mode design method provided by the application realizes efficient observation of multiple targets in the satellite visible observation range through load antenna beam electric scanning, does not need satellite attitude maneuvering cooperation, saves satellite attitude maneuvering energy, additionally, one-dimensional electric scanning is designed for the satellite SAR antenna, the number of component channels is reduced, the whole satellite weight and cost are reduced, and the use demand of a user for a light and small SAR satellite is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aerospace systems, in particular, to a light and small SAR satellite flat flight mode construction method and system. BACKGROUND

[0002] Space-borne synthetic aperture radar is an all-weather and all-day active observation means, which can discover, identify and confirm important land and ocean targets. At present, the main imaging modes of space-borne SAR mainly include strip mode, spotlight mode and scan mode, and the target observation modes of the satellites implementing these SAR imaging modes are two, one is left-right side view and the other is flat flight. The traditional space-borne SAR satellite usually adopts left-right side view mode, which completes left-right side swing by relying on satellite platform attitude maneuvering, and completes beam scanning by cooperating with the load antenna. When multiple targets are dispersed on the left and right sides of the orbit, if all targets are observed at one time, the satellite attitude must be frequently maneuvered in the roll direction, which will increase the mission time, thus reducing the observation efficiency of multiple targets in one pass, consuming satellite attitude maneuvering energy, and the frequent changes of satellite attitude may also affect the pointing of the data transmission antenna and the relay antenna, and even affect the real-time transmission of data on the satellite.

[0003] At present, the existing research and invention mostly adopt satellite platform attitude side swing at a fixed angle, such as the left-right side view ±31.5° platform side swing mode for target observation of domestic GF-3 satellite (2014, document name: General Design and Key Technologies of GF-3 Satellite, Journal of Geomatics), the right positive side view platform side swing mode for target observation of environment 1C satellite (2016, document name: General Design of Environment 1C Satellite System and Its On-orbit Verification, Journal of Radars), and the left-right side view platform side swing mode for ground observation of fast-response SAR satellite in a patent document (2019, patent application number CN201910446779.2). In the above research and invention, the satellite platform attitude side swing mode is mostly adopted for stable observation of the earth, and no matter the satellite attitude is in left side view or right side view, when the target is located on one side of the orbit, the SAR antenna beam electrical scanning under the satellite attitude of the present invention can meet the observation efficiency of multiple targets; if the target is distributed on the other side of the orbit, the satellite attitude of the present invention cannot meet the target observation range, and in this case, the satellite attitude must be maneuvered to the other side of the orbit to observe the target; if the target appears again on the other side of the orbit, the present invention will need to repeatedly maneuver the satellite attitude, which will inevitably reduce the observation efficiency.

[0004] Patent document One parabolic body system satellite-borne SAR scene matching mode satellite control method (2021, patent application number CN20211118057.9) uses a parabolic body antenna to improve the satellite beam pointing method in pitch and roll, ensuring the integrity of the echo data. This invention completely relies on satellite two-dimensional direction attitude maneuver for target observation. Compared with the invention of this invention, the satellite attitude maneuver is frequent, which reduces the target observation efficiency and consumes a large amount of satellite maneuver energy; patent document Agile SAR small satellite and its overall design method (2017, patent application number CN201710343713.1), this invention uses attitude maneuver for earth observation in load design, and has almost no scanning capability in range and azimuth. In view of the design of this invention, satellite flat flight efficient observation cannot be realized.

[0005] After searching, there is no relevant invention patent on the design method of satellite-borne SAR flat flight mode at present. In order to improve the observation efficiency of satellite-borne SAR on multiple targets, it is urgent to conduct flat flight observation on multiple targets in one pass. SUMMARY

[0006] In view of the defects in the prior art, the purpose of the present application is to provide a light and small SAR satellite flat flight mode construction method and system.

[0007] According to the light and small SAR satellite flat flight mode construction method provided by the present application, the following steps are included:

[0008] Step 1: According to the user demand, input the target area visible observation bandwidth range in satellite flat flight mode, determine the required field of view range of the target area;

[0009] Step 2: Perform SAR plane phased array antenna capability construction for the load to meet the effective coverage of the target area field of view range in satellite flat flight mode;

[0010] Step 3: Perform working time sequence construction of the integrated electric system, attitude and orbit control subsystem and load subsystem in flat flight mode, set the satellite roll angle to zero when the integrated electric system receives the satellite flat flight mode command sent by the ground, and send it to the attitude and orbit control subsystem to make the satellite attitude advance from the sun state to the flat flight state on the ground, and send the satellite platform roll angle, downward angle and target point coordinates to the load subsystem;

[0011] Step 4: The load subsystem performs on-board radar working parameter calculation, calculates the wave position according to the satellite platform roll angle, downward angle and target point coordinates, then calculates the imaging parameters according to the satellite platform, radar system and imaging performance constraint conditions, and performs flat flight mode imaging according to the imaging parameters.

[0012] Preferably, the step 1 comprises: inputting the target area visual observation bandwidth range ±S_min~S_max, ± being the left and right field of view directions, and calculating the required field of view range ±θ of the satellite according to the target area observation bandwidth, the orbit height and the orbit radius v _min~θ v _max.

[0013] Preferably, the step 2 comprises: the SAR planar phased array antenna is designed to be one-dimensional range direction electric scanning, and the number of T / R components channels is increased in the antenna range direction.

[0014] Preferably, the step 3 comprises:

[0015] Step 3.1: when the integrated electric receives the satellite flat flying mode instruction sent by the ground, the satellite platform yaw angle is first written as 0 degree, and then the satellite platform yaw angle is sent to the attitude and orbit control subsystem in advance by T1 seconds, so that the satellite platform attitude is changed from the sun direction to the ground flat flying state;

[0016] Step 3.2: the integrated electric calculates the satellite downward looking angle according to the received target point coordinates and the orbit prediction data, and sends the satellite downward looking angle, the platform yaw angle and the target point to the load subsystem at T2 seconds;

[0017] Step 3.3: if the integrated electric receives multiple target point information, the target points meeting the constraint in the visual observation band range are first screened out, and then sorted according to the observation overtop time of the target, and then the target point information is sent to the load subsystem in turn, and it is ensured that the orbit prediction data corresponding to the central time of all target points are valid; the load subsystem calculates multiple groups of radar working parameters according to the target point position, the task time length and the orbit prediction time, and performs one-time start and multiple imaging.

[0018] Preferably, the step 4 comprises:

[0019] Step 4.1: calculating the downward looking angle and the imaging start and stop time required for the target area imaging according to the target point information and the current satellite position information;

[0020] Step 4.2: selecting the wave position number according to the downward looking angle, and calculating the near end slant range and the far end slant range corresponding to the wave position;

[0021] Step 4.3: selecting the pulse repetition frequency and the pulse width according to the input range of the distance direction beam width, the transmitting signal sampling frequency, the pulse repetition frequency range and the pulse width range, and the selection principle is to avoid signal transmission interference, meet the requirements of the SAR system constraints and imaging performance;

[0022] Step 4.4: selecting the optimal group of parameters for flat flying mode imaging under the input condition range and multiple parameter constraints of step 4.3.

[0023] According to the application, a light and small SAR satellite flat flying mode construction system is provided, comprising:

[0024] Module M1: according to user demand, inputting a target region visible observation bandwidth range in a satellite flat flying mode, determining a required field of view range of the target region;

[0025] Module M2: performing SAR plane phased array antenna capability construction of a load, satisfying effective coverage of the field of view range of the target region in the satellite flat flying mode;

[0026] Module M3: performing working time sequence construction of an integrated electric system, an attitude and orbit control subsystem and a load subsystem in the flat flying mode, setting a satellite side swing angle to zero when the integrated electric system receives a satellite flat flying mode instruction sent by the ground, sending the satellite side swing angle to the attitude and orbit control subsystem, making the satellite attitude advance from a sun state to a ground flat flying state, and sending a satellite platform side swing angle, a downward viewing angle and a target point coordinate to the load subsystem;

[0027] Module M4: performing on-board radar working parameter calculation of the load subsystem, calculating a wave position according to the satellite platform side swing angle, the downward viewing angle and the target point coordinate, then calculating imaging parameters according to satellite platform, radar system and imaging performance constraint conditions, and performing flat flying mode imaging according to the imaging parameters.

[0028] Preferably, the module M1 comprises: inputting a target region visible observation bandwidth range ±S_min~S_max, ± being left and right field of view directions, calculating a required field of view range ±θ v _min~θ v _max of the satellite according to the target region observation bandwidth, an orbit height and an orbit radius.

[0029] Preferably, the module M2 comprises: the SAR plane phased array antenna being one-dimensional distance direction electric scanning, and a number of T / R component channels in the antenna distance direction being increased by hundreds.

[0030] Preferably, the module M3 comprises:

[0031] Module M3.1: when the integrated electric system receives a satellite flat flying mode instruction sent by the ground, first setting the satellite platform side swing angle to 0 degrees, then sending the satellite platform side swing angle to the attitude and orbit control subsystem T1 seconds in advance, making the satellite platform attitude advance from a sun state to a ground flat flying state;

[0032] Module M3.2: the integrated electric system calculating a satellite downward viewing angle according to received target point coordinates and orbit prediction data, and sending the satellite downward viewing angle, the platform side swing angle and the target point to the load subsystem at T2 seconds;

[0033] Module M3.3: If multiple target point information is received by the integrated control system, first, the target points meeting the range constraint of the visual observation zone are screened out, and are sorted according to the observation overtop time of the target, and then the target point information is sent to the payload subsystem in turn, and it is ensured that the orbit prediction data corresponding to the central time of all targets are valid; the payload subsystem calculates multiple groups of radar working parameters according to the target point position, task duration and orbit prediction time, and performs one-time start and multiple imaging.

[0034] Preferably, the module M4 comprises:

[0035] Module M4.1: calculating the downward angle and imaging start and end time required for imaging of the target area according to the target point information and the current satellite position information;

[0036] Module M4.2: selecting the wave position number according to the downward angle, and calculating the near end slant range and far end slant range corresponding to the wave position;

[0037] Module M4.3: selecting the pulse repetition frequency and pulse width according to the input distance direction beam width, the sampling frequency of the transmitted signal, the pulse repetition frequency range and the pulse width range, and the selection principle is to avoid signal transmission interference, meet the constraints and imaging performance requirements of the SAR system;

[0038] Module M4.4: selecting an optimal group of parameters for flat flight mode imaging under the condition of the input range of module M4.3 and multiple parameter constraints.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] The method proposed in the present application fully utilizes the advantages of the large-angle electric scanning capability of the payload antenna without the need for satellite attitude maneuver, and improves the observation efficiency of multiple targets within one satellite pass through SAR antenna distance direction beam electric scanning and fast switching;

[0041] The method proposed in the present application adopts on-board radar parameter calculation, does not need to perform ground command arrangement, simplifies the satellite use process, and improves the intelligent working capability of the payload system;

[0042] The method proposed in the present application designs the SAR planar phased array antenna as one-dimensional electric scanning, greatly simplifies the antenna structure, reduces the weight and cost of the whole satellite, and meets the user's use demand for lightweight and low-cost SAR satellites;

[0043] The method proposed in the present application can realize real-time transmission of on-board data during earth observation, improves the timeliness of data transmission, and meets the user's demand for rapid processing of satellite data. BRIEF DESCRIPTION OF DRAWINGS

[0044] Other features, objects, and advantages of the application will become apparent from the following detailed description of non-limiting embodiments, when read in connection with the following accompanying drawings:

[0045] Figure 1 Flow chart of the method of the present application;

[0046] Figure 2 Schematic diagram of the flat flight mode of the method of the present application;

[0047] Figure 3 Satellite flat flight mode system sensitivity curve results of the method of the present application;

[0048] Figure 4 Satellite flat flight mode distance ambiguity curve results of the method of the present application;

[0049] Figure 5 Satellite flat flight mode azimuth ambiguity curve results of the method of the present application. DETAILED DESCRIPTION

[0050] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but in no way limit the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These are within the scope of the present application.

[0051] Reference Figure 1 , Figure 1 is a flow chart of a light and small SAR satellite flat flight mode design method provided by the present embodiment, and the method steps are as follows:

[0052] Step 1: According to the user's demand, input the target area's visible observation bandwidth range in the satellite flat flight mode, and determine the required field of view range of the target area;

[0053] Step 2: Perform SAR plane phased array antenna capability design for the load, so that the antenna has large-angle beam scanning capability, and meets the effective coverage of the satellite flat flight mode target area field of view range;

[0054] Step 3, satellite comprehensive power, attitude control and load working time sequence design. When the comprehensive power receives the satellite flat flight mode command sent by the ground, first set the satellite roll angle to zero and send it to the attitude and orbit control subsystem, so that the satellite attitude is converted from the sun state to the flat flight state. At the same time, send the satellite platform roll angle, downward angle, target point coordinates and other parameters to the load subsystem;

[0055] Step 4, the payload subsystem performs on-board radar operating parameter calculation. The payload calculates the wave position according to the target downward-looking angle sent by the integrated power supply, and then calculates imaging parameters such as pulse repetition frequency, pulse width and frame length according to satellite platform, radar system and imaging performance constraints.

[0056] Further, in step 1, according to user requirements, first input the target area visual observation bandwidth range ±S_min~S_max (considering the satellite subsatellite point range), unit: kilometers, ± is the left and right field of view direction, as shown in Figure 2 Further, in step 2, according to the characteristics of the satellite flat flight mode, no satellite platform attitude maneuvering is required, only the SAR antenna beam electrical scanning is relied on to realize the effective coverage of the target area observation bandwidth ±S_max kilometers, so the SAR antenna beam is required to have the electrical scanning ability of ±θ v _max degrees. v

[0057] Further, in step 2, according to the characteristics of the satellite flat flight mode, no satellite platform attitude maneuvering is required, only the SAR antenna beam electrical scanning is relied on to realize the effective coverage of the target area observation bandwidth ±S_max kilometers, so the SAR antenna beam is required to have the electrical scanning ability of ±θ v _max degrees. In order to meet the user's demand for target area observation in the satellite flat flight mode, while considering the constraints of SAR system sensitivity and image quality indicators, as well as the limitations of satellite weight, volume and development cost, the SAR antenna capability is designed in the present application, the SAR planar phased array antenna is designed as one-dimensional distance electrical scanning, and the number of T / R component channels in the antenna distance direction is increased by hundreds, which can meet the rapid scanning and shaping of any beam within the target visual observation bandwidth.

[0058] Further, in step 3, the satellite integrated power supply and attitude control, payload working time sequence design mainly includes the following steps:

[0059] Step 3.1: when the integrated power supply receives the satellite flat flight mode instruction sent by the ground, first write the satellite platform side swing angle as 0 degrees, and then send the satellite platform side swing angle to the attitude and orbit control subsystem T1 seconds in advance, so that the satellite platform attitude is changed from the sun to the ground flat flight state;

[0060] Step 3.2: the integrated power supply calculates the satellite downward-looking angle according to the received target point coordinates and orbit prediction data, and sends the satellite downward-looking angle, platform side swing angle, target point and other information to the payload subsystem at T2 seconds;

[0061] ​Step 3.3: If the integrated computer receives multiple target point information, first, the target points meeting the range constraint of the visible observation zone are screened out, and then the target point information is sent to the payload in sequence according to the observation top time of the target, and the orbit prediction data corresponding to the central time of all targets are ensured to be valid; the payload calculates multiple groups of radar working parameters according to the target point position, task duration and orbit prediction time, and performs one start and multiple imaging.

[0062] Further, in step 4, the on-board radar working parameter calculation mainly includes the following steps:

[0063] Step 4.1: Calculate the downward-looking angle and imaging start and stop time required for the target area according to the target point information and the current satellite position information;

[0064] Step 4.2: Select the wave position number according to the downward-looking angle, and calculate the near-end slant range and far-end slant range corresponding to the wave position;

[0065] Step 4.3: Select the pulse repetition frequency and pulse width according to the input range of the distance direction beam width, the sampling frequency of the transmitted signal, the pulse repetition frequency range, the pulse width range and other parameters, and the selection principle is to avoid signal transmission interference, meet the requirements of SAR system constraints (duty cycle and data rate) and imaging performance (ambiguity and NESZ);

[0066] Step 4.4: Select the optimal set of parameters for flat flight mode imaging under the input condition range and multi-parameter constraint of step 4.3, wherein the output parameters include the number of distance direction sampling points, the start time of echo sampling, PRF, pulse width, delay pulse number, etc.

[0067] Further, the method of the present application can be applied to high-resolution strip flat flight mode and wide-scan flat flight mode. In the design of the strip flat flight mode, the one-dimensional large-angle electrical scanning capability of the antenna in the distance direction is fully utilized, and the antenna electrical beam scanning and widening are performed according to the set target downward-looking angle and electrical scanning angle. Compared with the traditional satellite, the strip flat flight mode does not need satellite attitude yaw. When multiple targets are distributed on the left and right sides of the orbit, the oblique flight mode used by the traditional satellite can only observe the ground on the left side or the right side of the orbit, and when the targets are distributed on the other side of the orbit, the satellite attitude must be maneuvered to the other side for observation, which greatly reduces the observation efficiency of the satellite. The method of the present application fully utilizes the advantages of satellite flat flight electrical scanning, can perform left and right side observation, and improves the observation efficiency of multiple targets. When multiple targets are distributed on one side of the orbit and are dispersed and sparse, the width of the strip flat flight mode may not meet the coverage of multiple targets. The flat flight scanning mode performs ScanSAR scanning and splicing imaging in the distance direction based on the strip flat flight mode, and utilizes the advantages of satellite flat flight electrical scanning to not only improve the observation efficiency of multiple targets, but also realize large-width scanning imaging in the distance direction.

[0068] Further, compared with the use of other satellites, the method of the application is more intelligent in satellite use operation, only needs to input target position information, and automatically calculates satellite downward viewing angle, side swing angle and task starting time according to current orbit information. Meanwhile, the satellite selects a suitable flat flight imaging mode according to the number, characteristics and distribution of the targets. The application does not need the ground to perform task planning, instruction preparation and other work according to orbit parameters in advance, thereby simplifying the satellite on-orbit use method.

[0069] Further, the satellite flat flight mode designed by the application does not need satellite attitude maneuvering, and does not need to consider the influence of satellite attitude on satellite communication and data satellite-ground transmission link. Therefore, the real-time transmission of on-board data can be realized when the satellite flat flight mode observes the earth, the timeliness of data transmission is improved, and the rapid processing demand of users for satellite data is met.

[0070] The effect of the application will be further described below in combination with simulation data.

[0071] Here, the orbit height of the satellite-borne SAR is about 510km, the incidence angle range is designed to be 13-50°, the satellite platform side swing angle is selected to be 0°, the working mode is selected to be a strip imaging mode, the load working PRF is designed to be 4730-6110Hz, the range resolution is designed to be 2m, and the range imaging width is designed to be 21km. The above parameter values are shown in Table 1.

[0072] Table 1 Input parameters in the embodiment

[0073]

[0074] According to the given input system requirement parameters in Table 1, the main imaging performance index simulation is performed according to the method proposed in the application, and the results are shown in Figures 3-5 .

[0075] Figure 3 The NESZ curve estimation results of the method proposed in the paper in the full incidence angle range of 13-50° are given, and the worst NESZ is better than -19.327dB; Figure 4 The RASR curve estimation results of the method proposed in the paper in the full incidence angle range of 13-50° are given, and the worst RASR is better than -19.331dB; Figure 5 The AASR curve estimation results of the method proposed in the paper in the full incidence angle range of 13-50° are given, and the worst AASR is better than -20.412dB. The above image estimation results all meet the use requirements.

[0076] The application further provides a light and small SAR satellite flat-flying mode construction system, which can be realized by performing the flow steps of the light and small SAR satellite flat-flying mode construction method, i.e., the light and small SAR satellite flat-flying mode construction method can be understood as the preferred embodiment of the light and small SAR satellite flat-flying mode construction system by those skilled in the art.

[0077] The light and small SAR satellite flat-flying mode construction system comprises:

[0078] Module M1: according to the user demand, input the target area visible observation bandwidth range in the satellite flat-flying mode, and determine the field of view range required by the target area.

[0079] Module M2: the load performs SAR plane phased array antenna capability construction, and meets the effective coverage of the field of view range of the target area in the satellite flat-flying mode.

[0080] Module M3: the working time sequence construction of the integrated electric system, the attitude and orbit control subsystem and the load subsystem in the flat-flying mode is performed, when the integrated electric system receives the satellite flat-flying mode instruction sent by the ground, the satellite roll angle is set to zero, and is sent to the attitude and orbit control subsystem, so that the satellite attitude is advanced from the sun state to the ground flat-flying state, and the satellite platform roll angle, the downward angle and the target point coordinates are sent to the load subsystem.

[0081] Module M4: the load subsystem performs on-board radar working parameter calculation, calculates the wave position according to the satellite platform roll angle, the downward angle and the target point coordinates, then calculates the imaging parameters according to the satellite platform, the radar system and the imaging performance constraint conditions, and performs flat-flying mode imaging according to the imaging parameters.

[0082] Those skilled in the art know that, in addition to realizing the system and each device, module and unit thereof provided by the application in the form of pure computer readable program code, the same function can also be realized by logically programming the method steps in the form of logic gates, switches, special integrated circuits, programmable logic controllers and embedded microcontrollers. Therefore, the system and each device, module and unit thereof provided by the application can be considered as a hardware component, and the devices, modules and units included therein for realizing various functions can also be considered as structures in the hardware component; the devices, modules and units for realizing various functions can also be considered as both software modules realizing the method and structures in the hardware component.

[0083] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A small and light SAR satellite level flight mode construction method, characterized in that, The method comprises the following steps: Step 1: according to the user demand, inputting a visible observation bandwidth range of a target area in a satellite flat-flying mode, determining a required field of view range of the target area; Step 2: constructing a SAR plane phased array antenna capability of a load to meet effective coverage of the field of view range of the target area in the satellite flat-flying mode; Step 3: constructing a working time sequence of an integrated power system, an attitude and orbit control subsystem and the load in the flat-flying mode, setting a satellite side swing angle to zero when the integrated power system receives a satellite flat-flying mode instruction sent by the ground, sending the satellite side swing angle to the attitude and orbit control subsystem, making the satellite attitude advance from a sun-facing state to a ground flat-flying state, and sending a satellite platform side swing angle, a downward-looking angle and a target point coordinate to the load subsystem; Step 4: the load subsystem performs on-board radar working parameter calculation, calculates a wave position according to the satellite platform side swing angle, the downward-looking angle and the target point coordinate, then calculates imaging parameters according to satellite platform, radar system and imaging performance constraint conditions, and performs flat-flying mode imaging according to the imaging parameters.

2. The method according to claim 1, wherein, The step 1 includes: inputting target area visual observation bandwidth range ±S_min~S_max, ± being left and right field of view directions, calculating required field of view range ±θ v _min~θ v _max of the satellite according to target area observation bandwidth, orbit height and orbit radius.

3. The method according to claim 1, wherein, In the step 2, the SAR plane phased array antenna is designed as one-dimensional distance direction electric scanning, and the number of T / R component channels is increased in the distance direction of the antenna.

4. The method according to claim 1, wherein, The step 3 comprises the following steps: Step 3.1: when the integrated power system receives the satellite flat-flying mode instruction sent by the ground, first, the satellite platform side swing angle is written as 0 degree, then the satellite platform side swing angle is sent to the attitude and orbit control subsystem in advance by T1 seconds, so that the satellite platform attitude is changed from the sun-facing state to the ground flat-flying state; Step 3.2: the integrated power system calculates a satellite downward-looking angle according to the received target point coordinate and orbit prediction data, and sends the satellite downward-looking angle, the platform side swing angle and the target point to the load subsystem at T2 seconds; Step 3.3: if the integrated power system receives multiple target point information, first, target points meeting the constraint in the visible observation band range are screened out, and are sorted according to observation over-the-top time of the target, then the target point information is sent to the load subsystem in sequence, and it is ensured that orbit prediction data corresponding to a central time of all targets are valid; the load subsystem calculates multiple groups of radar working parameters according to the target point position, the task duration and the orbit prediction time, and performs one-time start-up multiple imaging.

5. The method according to claim 1, wherein, The step 4 comprises the following steps: Step 4.1: calculating a downward-looking angle and imaging start-stop time required for target area imaging according to the target point information and current satellite position information; Step 4.2: selecting a wave position number according to the downward-looking angle, and calculating a near-end slant range and a far-end slant range corresponding to the wave position; Step 4.3: selecting a pulse repetition frequency and a pulse width according to input distance direction beam width, transmission signal sampling frequency, pulse repetition frequency range and pulse width range, and the selection principle is to avoid signal transmission interference, meet the SAR system constraint and the imaging performance requirement; Step 4.4: selecting an optimal group of parameters for flat-flying mode imaging under the input condition range and multiple parameter constraints in step 4.

3.

6. A small and light SAR satellite level flight mode construction system, characterized by, The method comprises the following steps: Module M1: according to the user demand, inputting a visible observation bandwidth range of a target area in a satellite flat-flying mode, determining a required field of view range of the target area; Module M2: the load performs SAR plane phased array antenna capability construction, and effective coverage of a target area field of view range in a satellite flat flight mode is met; Module M3: the working time sequence construction of an integrated power system, an orbit control subsystem and a load subsystem in the flat flight mode is performed, when the integrated power system receives a satellite flat flight mode instruction sent by the ground, the satellite side swing angle is set to zero, and is sent to the orbit control subsystem, so that the satellite attitude is converted from the sun state to the ground flat flight state in advance, and the satellite platform side swing angle, the downward looking angle and the target point coordinates are sent to the load subsystem; Module M4: the load subsystem performs satellite radar working parameter calculation, calculates the wave position according to the satellite platform side swing angle, the downward looking angle and the target point coordinates, then calculates the imaging parameters according to the satellite platform, the radar system and the imaging performance constraint conditions, and performs flat flight mode imaging according to the imaging parameters.

7. The light small-sized SAR satellite steady flight mode construction system according to claim 6, characterized in that, The module M1 includes: input target area visual observation bandwidth range ±S_min~S_max, ± is left and right field of view direction, according to target area observation bandwidth, orbit height, orbit radius, the required field of view range ±θ of satellite is calculated v _min~θ v _max. 8.The small-sized SAR satellite flying-in-mode construction system according to claim 6, characterized in that, The module M2 comprises: the SAR plane phased array antenna is designed as one-dimensional distance direction electric scanning, and the number of T / R component channels is increased in the antenna distance direction. 9.The small-sized SAR satellite flying-in-mode construction system according to claim 6, wherein, The module M3 comprises: Module M3.1: when the integrated power system receives a satellite flat flight mode instruction sent by the ground, the satellite platform side swing angle is first written as 0 degree, and then the satellite platform side swing angle is sent to the orbit control subsystem T1 seconds in advance, so that the satellite platform attitude is converted from the sun state to the ground flat flight state; Module M3.2: the integrated power system calculates the satellite downward looking angle according to the received target point coordinates and orbit prediction data, and sends the satellite downward looking angle, the platform side swing angle and the target point to the load subsystem at T2 seconds; Module M3.3: if the integrated power system receives multiple target point information, first, the target points meeting the constraint in the visible observation band range are screened out, and are sorted according to the observation overtop time of the target, then the target point information is sent to the load subsystem in turn, and it is ensured that the orbit prediction data corresponding to the central time of all targets are valid; the load subsystem calculates multiple groups of radar working parameters according to the target point position, the task duration and the orbit prediction time, and performs multiple imaging once. 10.The small-sized SAR satellite flying-in-mode construction system according to claim 6, wherein, The module M4 comprises: Module M4.1: the target area imaging required downward looking angle and imaging start and stop time are calculated according to the target point information and the current satellite position information; Module M4.2: the wave position number is selected according to the downward looking angle, and the near end slant range and the far end slant range corresponding to the wave position are calculated; Module M4.3: the pulse repetition frequency and the pulse width are selected according to the input distance direction beam width, the transmitted signal sampling frequency, the pulse repetition frequency range and the pulse width range, and the selection principle is to avoid signal transmission interference, and meet the requirements of the SAR system constraint and the imaging performance; Module M4.4: an optimal group of parameters is selected for flat flight mode imaging under the input condition range and multiple parameter constraints of module M4.3.

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