Auxiliary data for satellite control

Abstract

The present invention relates to a method of generating assistance data for controlling a satellite moving in an Earth orbit, the method comprising the steps of receiving (101) tracking data for the satellite, applying an orbit determination algorithm including the steps of estimating (102) an orbit of the satellite based on the tracking data and predicting (103) future ephemeris data of the satellite based on the estimated orbit, generating (105) assistance data including the predicted future ephemeris data, and transmitting (106) the assistance data to the satellite for use in attitude and orbit control of the satellite.

Description

Background Art

[0001] The present invention relates to a method and a ground segment for generating auxiliary data for controlling a satellite moving in an Earth orbit, and a satellite moving in an Earth orbit using the auxiliary data.

[0002] Onboard knowledge of the satellite's position is very important for all space missions. In Earth observation missions, especially when using small satellites, very accurate knowledge of the satellite's position is required. A positioning error exceeding 500 m may already be unacceptable for certain payloads such as synthetic aperture radar (SAR) images. A satellite equipped with a global positioning system (GPS) receiver can accurately determine its orbital state without the assistance of a ground segment. Therefore, an onboard GPS receiver can provide an accurate navigation solution. However, this system depends on periodic GPS measurements and is not always available.

[0003] The interruption of GPS can occur for various reasons, such as where the availability and quality of GPS signals deteriorate or in certain directions of the satellite. Other reasons may include improper installation of the GPS equipment and antennas on the satellite. Furthermore, GPS signals may be degraded or blocked, resulting in inaccurate data or a complete loss of GPS signals.

[0004] Without periodic updates from the GPS receiver, the internal orbit propagator within the satellite's attitude determination and control system “ADCS” may start to deviate from the true orbit. For example, if the satellite loses GPS signal lock for just one hour, an error of up to 6 km may occur in the satellite's trajectory. Therefore, it is necessary to more accurately grasp the current position of the satellite when GPS is interrupted.

[0005] To control a satellite moving in Earth orbit, it is desirable to obtain accurate information about the satellite's position onboard. This applies, for example, to situations where measurements from the onboard GPS receiver may be unavailable or inaccurate. Therefore, accurate information about the satellite's position needs to be provided onboard to ensure necessary ADCS functionality even when GPS is down.

[0006] The embodiments described below are not limited to implementations that address some or all of the shortcomings of the known approaches described above. [Overview of the Initiative]

[0007] This summary is provided to introduce a selection of concepts in a simplified form, which will be further elaborated upon in the detailed description. This summary is not intended to identify the main or essential features of the requested subject matter.

[0008] In a first embodiment, the present invention provides a method for generating auxiliary data for controlling a satellite moving in Earth orbit, the method comprising the steps of: receiving tracking data for the satellite; applying an orbit determination algorithm which includes the steps of: estimating the satellite's orbit based on the tracking data; and predicting future ephemeris data of the satellite based on the estimated orbit; generating auxiliary data which includes the predicted future ephemeris data; and transmitting the auxiliary data to the satellite for use in attitude and orbit control of the satellite.

[0009] In some embodiments, the tracking data includes Global Navigation Satellite System (GNSS) sensor data, Satellite Laser Rangefinder (SLR) measurements, or satellite radar measurements.

[0010] In some embodiments, tracking data shows a sequence of times for the satellite and its corresponding position and velocity.

[0011] In some embodiments, the method further includes the step of determining the satellite's current position based on auxiliary data if data from a GNSS or GPS sensor onboard the satellite is unavailable or unreliable.

[0012] In some embodiments, at least the steps of applying the orbit determination algorithm and generating auxiliary data are performed on the ground.

[0013] In some embodiments, estimating the satellite's orbit is based further on a previously estimated orbit.

[0014] In some embodiments, the tracking data corresponds to a predetermined time interval and optionally to the time between two ground station paths of the satellite.

[0015] In some embodiments, the tracking data includes one or more gaps corresponding to one or more tracking stops within a given time interval.

[0016] In some embodiments, this method is repeated for each satellite pass, and optionally, tracking data is received for each satellite pass, while generated auxiliary data is transmitted for each consecutive satellite pass.

[0017] In some embodiments, this method is arbitrarily repeated in parallel for a second satellite and for multiple satellites.

[0018] In some embodiments, the auxiliary data includes predicted future ephemeris over a period of at least 6 hours, optionally at least 12 hours, and optionally at least 24 hours, at time intervals of up to 1 minute, optionally 2 minutes, and optionally 5 minutes.

[0019] In some embodiments, the supplementary data includes predicted future ephemeris covering at least one orbital period of the satellite.

[0020] In some embodiments, this method further includes a step of verifying the accuracy of the results of the orbit determination algorithm before generating and transmitting auxiliary data.

[0021] In some embodiments, the step of estimating the orbit includes filtering the tracking data to provide a filtered ephemeris of the satellite.

[0022] In some embodiments, a Kalman filter is used to process the tracking data sequentially.

[0023] In some embodiments, the step of predicting future ephemeris data of a satellite includes the step of propagating the filtered ephemeris forward in time.

[0024] In some embodiments, dynamic models are used to predict future ephemeris data from satellites.

[0025] In some embodiments, this method is implemented by a computer.

[0026] In a second aspect, the disclosure provides a ground segment that generates auxiliary data for controlling a satellite moving in Earth orbit, and the ground station system is configured to perform the method according to the first aspect.

[0027] In a third aspect, the present disclosure provides a ground segment for generating auxiliary data for controlling a satellite moving in an earth orbiting trajectory, the ground segment comprising a receiving module configured to receive tracking data for the satellite, an orbit determination tool kit "ODTK" configured to apply an orbit determination algorithm including estimating the orbit of the satellite based on the tracking data and predicting future ephemeris data of the satellite based on the estimated orbit, an auxiliary data module configured to generate auxiliary data including the predicted future ephemeris data, and a transmitting module configured to transmit the auxiliary data to the satellite for use in the satellite's attitude determination and control system "ADCS" unit.

[0028] In some embodiments, the components of the ground segment are distributed at multiple locations, optionally different terrestrial locations.

[0029] In a fourth aspect, the present disclosure provides for the use of a ground segment according to the second or third aspect to generate auxiliary data for controlling one or more satellites moving in an earth orbiting trajectory, each of the one or more satellites being configured to determine its position based on the auxiliary data.

[0030] In a fifth aspect, the present disclosure provides a satellite moving in an earth orbiting trajectory, the satellite comprising a receiving module configured to receive auxiliary data generated for the satellite according to the method of the first aspect, and an attitude determination and control system "ADCS" unit for controlling the satellite in orbit, the ADCS unit being configured to determine the current position of the satellite based on the auxiliary data.

[0031] In some embodiments, the satellite includes an onboard computer configured to select the latest predicted ephemeris data from auxiliary data based on the satellite's current onboard time, and an orbital propagator that forms part of the ADCS unit and is configured to numerically propagate the selected predicted ephemeris data based on the current onboard time to determine the satellite's current position.

[0032] In some embodiments, the satellite further includes a tracking module for tracking the satellite, optionally the tracking module being a GPS sensor module, and the ADCS unit is further configured to determine the satellite's current position based on the sensor data of the tracking module, and if the tracking module is not functioning, the ADCS unit is configured to switch from sensor data to auxiliary data.

[0033] In some embodiments, the satellite is a small satellite for Earth observation and / or a radar satellite.

[0034] Some embodiments of the present disclosure provide a system comprising one or more computing systems, each including at least one processor and memory, the system being configured to implement any of the methods or processes described herein.

[0035] Some embodiments of the present invention further provide a computer-readable medium containing instructions, for example in the form of algorithms, which, when implemented in a computing system forming part of a satellite operating system, cause the system to perform any of the methods or processes described herein.

[0036] The features of different aspects and embodiments of the present invention can be appropriately combined and combined with any aspect of the present invention, as will be obvious to those skilled in the art. Embodiments of the present invention will be described by reference to the following drawings. [Brief explanation of the drawing]

[0037] [Figure 1] This block diagram shows the process of generating auxiliary data to control a satellite moving in Earth orbit. [Figure 2] This is a schematic diagram of the satellite and ground segment, where the ground segment is configured to generate auxiliary data, and the satellite is configured to use the auxiliary data to obtain accurate knowledge about its position on the satellite. [Figure 3] This visualizes the use of onboard auxiliary data in a scenario where the satellite's GPS receiver is temporarily inactive. [Figure 4] This is a perspective view of a satellite, including the ADCS unit used to control the satellite as it moves in Earth orbit. [Figure 5] Figure 4 is a partial perspective view of the satellite, showing the components for controlling the satellite's attitude. [Figure 6] This shows test results comparing the position determined by the onboard propagator based on auxiliary data with the actual trajectory data based on GPS measurements. [Figure 7] This graph compares predicted future ephemeris data with actual trajectories. [Figure 8] This graph shows the residual measurement of 24 hours of GPS data. [Figure 9] Figure 8 shows a graph illustrating the positional consistency statistics. [Modes for carrying out the invention]

[0038] To illustrate similar characteristics, a common reference number is used throughout the figure.

[0039] Embodiments of the present invention are described below only as examples. These examples represent the best way the applicant currently knows how to practice the invention, but this is not the only way it can be achieved. The description shows the function of the examples and a set of steps for constructing and operating them. However, the same or equivalent functions and sequences may be achieved by different examples.

[0040] The present invention provides a method and ground segment for generating auxiliary data to obtain accurate onboard knowledge regarding a satellite's position. For this purpose, a ground-based orbit determination (OD) can be implemented, estimating the satellite's state using received tracking data such as GPS receiver measurements, and then predicting the satellite's state for a certain period in the future using a propagation algorithm. Auxiliary data is generated based on the future prediction. The auxiliary data is suitable for use in the satellite's ADCS unit instead of GPS measurements to obtain accurate information regarding the satellite's onboard position. The present invention further provides a satellite equipped with an ADCS unit configured to receive auxiliary data and to determine the satellite's position based on the auxiliary data.

[0041] This invention is based on the discovery that improved accuracy can be achieved by using auxiliary data instead of unfiltered GPS measurements, because noise inherent in GPS measurements can be filtered out before auxiliary data is generated and fed to the internal orbit propagator onboard the satellite. The most significant consequence of not filtering out noise from GPS measurements is that the orbit propagator deviates from its true orbit.

[0042] Figure 1 illustrates the method for generating auxiliary data. First, in operation 101, tracking data for the satellite is received. The tracking data may indicate a series of times and corresponding position and velocity points of the satellite. The tracking data can be used to determine the satellite's orbit. The tracking data may be acquired using radar or laser ranging equipment at an earth station. Alternatively, the tracking data may be acquired by a Global Navigation Satellite System (GNSS) receiver onboard the satellite. A well-known example of GNSS is the Global Positioning System (GPS). For simplicity, in the following description, the tracking data is described as GPS data acquired by a GPS receiver onboard the satellite. The GPS receiver module is described in more detail with reference to Figure 5.

[0043] In operation 101, tracking data may be received from the satellite itself or from a tracking station that tracks the satellite. The tracking data may be received directly from the satellite or tracking station, or indirectly, for example, through one or more ground stations. The tracking data may be received each time the satellite passes a ground station. Typically, GPS measurements are transmitted via telemetry each time a ground station is passed. In the case of GPS data, the tracking data consists of at least position and velocity vectors and a timestamp. The GPS data may correspond to GPS measurements spaced 30 seconds apart. The GPS data may correspond to at least one complete orbital period.

[0044] In operation 110, the orbit determination (OD) method is applied to the tracking data. In this step, the orbit is (re)estimated based on the received tracking data (and previously estimated orbits). OD is a method for estimating the state of an object in orbit, such as a satellite, including its position and velocity. OD is well known in the field of satellite operations and can be described as a filtering method that integrates observations and orbital dynamics equations to estimate the satellite's position and velocity. In other words, it estimates the satellite's state variables (position and velocity) based on measured data such as tracking data. The OD method can be applied by an OD process tool generally called a filter, which will be explained in more detail with reference to Figure 2. Numerical OD methods can achieve a significant improvement in accuracy, but at the cost of requiring stepwise propagation over time and having a high computational load.

[0045] In the first step 102 of OD operation 110, the satellite's orbit is estimated based on at least the tracking data received in step 101. The output of step 102 is also called the filtered ephemeris. In the second step 103, future ephemeris data is predicted based on the estimated orbit (or filtered ephemeris). The predicted future orbital ephemeris can correspond to the satellite's future state at any time, such as in the near future or more than 24 hours ahead. The predicted future ephemeris data may provide a resolution of 5 seconds or include data for more than 24 hours. The predicted future ephemeris data may include data corresponding to at least two or more complete orbital periods.

[0046] One example of OD operation 110 applies two types of filters (statistical processes) in a process that includes the following steps:

[0047] 1) BWLS (Bayesian Weighted Least Squares): This is essentially a curve fitting process. It does not use dynamic models and is used to make better initial inferences before proceeding to the next filtering step. Here, all tracking data is processed at once.

[0048] 2) The next step is ordered statistical filtering (OSF). This is a Kalman filter, where the data is processed sequentially. A dynamic model is used here to make the most accurate updates. The optimal state minimizes uncertainty in state estimation. The uncertainty of the model is determined by the size and variability of this uncertainty (process noise). Here, we are moving from old data to new data.

[0049] 3) Second OSF: Also called a smoother. It is the same as (2), but the time is reversed. Kalman filters generally use dynamic models to create the best possible predictions by recognizing the convergence (uncertainty level) of the previous state and attempting to minimize the uncertainty of the state.

[0050] In operation 104, the accuracy of the results of the OD method in operation 110 is verified. For the prediction to be accurate, the uncertainty must be low. Only then can sufficient knowledge of the orbit be established and the prediction be accurate enough to be used as a basis for controlling the satellite in orbit. Verification step 104 is optional and may be applied before generating and transmitting the auxiliary data in steps 105 and 106. For example, verification step 104 may only be performed if the tracking data received in step 101 contains one or more gaps. If the verification accuracy is low, the OD method in operation 110 may be repeated or paused until further tracking data for the satellite is received. If the prediction is verified to be accurate, the satellite's auxiliary data is generated.

[0051] Operation 105 generates auxiliary data containing the satellite's predicted future ephemeris data. The resolution of the auxiliary data will be lower than the resolution of the future ephemeris predicted in step 103. The resolution of the auxiliary data represents a compromise between the amount of data that can be successfully uploaded and stored on the satellite (such as uplink bandwidth limitations and onboard memory constraints) and the amount of data required to ensure the satellite does not deviate from its actual orbit. The auxiliary data may, for example, provide a resolution of 5 minutes or include ephemeris data for at least one complete orbital period.

[0052] In operation 106, the generated auxiliary data is transmitted to the satellite and used for satellite attitude and orbit control. The auxiliary data may be transmitted to the satellite for each ground station pass, each ground station pass, or according to other schedules. For example, since the auxiliary data is only used when the GPS signal is lost, it may only be transmitted to the satellite if there is time remaining after other priority transmissions have been made. The satellite may also pass over one or more ground stations during its orbit. Therefore, the auxiliary data may be transmitted to the satellite once per orbit, less than once per orbit, or more than once per orbit. Onboard use of auxiliary data to obtain precise knowledge about the satellite's position is described in more detail with reference to Figures 2 and 3. The auxiliary data is configured, for example, to substitute GPS measurements when GPS is down and is used to initialize the internal orbit propagator.

[0053] Method 100 prevents satellites from deviating from their actual orbits when GPS is unavailable. Auxiliary data allows for the maintenance of accurate attitude and orbital control even when GPS is disabled or unavailable for extended periods. During this time, the satellite can perform payload and orbit maintenance operations, which would normally be impossible. Method 100 ensures that satellites always have accurate orbital information onboard, regardless of GPS availability. This allows for the execution of planned payload activities with extremely high geolocation accuracy. Furthermore, it avoids the prohibitively high computational load required to constantly estimate and predict the orbital information onboard the satellite.

[0054] Figure 2 shows a system consisting of a ground segment 200 and a satellite 300. Tracking and auxiliary data can be exchanged between the ground segment 200 and the satellite 300 for each ground station pass. Figure 2 shows the components required to generate the auxiliary data and how the auxiliary data is used on the satellite to control the satellite 300. The ground segment 200 is configured to perform method 100, as described with reference to Figure 1. The same ground segment 200 can be used to generate and provide auxiliary data to multiple satellites in a constellation, also known as a fleet, for example.

[0055] As shown in Figure 2, the (distributed) ground segment 200 consists of a ground station 201 located at a different ground location from the ground automation 202. Alternatively, the ground station 201 may be located at the same location as the ground automation 202 of the ground segment 200. Furthermore, the ground automation 202 of the ground segment 200 may be hosted and run using a cloud computing provider. The ground station 201 is configured to receive tracking data from the satellite 300. In this embodiment, the tracking data originates from the satellite 300. In another example, the ground automation 202 may use tracking data from a radar or laser rangefinder from the earth station. The tracking data is routed from the ground station 201 to the ground automation 202.

[0056] Ground automation 202 includes a receiving module (not shown as a separate component) configured to receive tracking data from satellite 300, an orbit determination toolkit "ODTK" 210 configured to apply an orbit determination algorithm, an auxiliary data module 260 configured to generate auxiliary data, and a transmitting module (not shown as a separate component) configured to transmit the auxiliary data to satellite 300. Similarly, as described for the receiving ground station 201, auxiliary data from the transmitting module may be transmitted to the satellite via a ground station, for example, a ground station 201 located at a different or the same ground location as ground automation 202.

[0057] Each time new tracking data is received from satellite 300, the OD server 220 coordinates the execution of the OD process tool 210 to determine the orbit. For example, commercially available software for performing the OD method is the orbit determination toolkit "ODTK". The OD server 220 is configured to control the OD process tool 210, as illustrated in Figure 2. The OD process tool 230 may be a software module integrated into the OD server or it may be standalone. Tracking data is also supplied to the OD process tool 210. The OD process tool 210 consists of a filter module 212, a storage module 213, and a prediction module 214. The filter module 212, commonly referred to as the OD filter, is configured to filter the tracking data in one or more filtering stages, which are further described below. The filter module 212 performs filtering of the tracking data and, if available, previously estimated orbital knowledge to (re)estimate the satellite's orbit. The estimation results (such as previously estimated orbital knowledge) are provided to the storage module 213. For filtering, the OD process tool may maintain a dynamic model of the satellite's motion. This model can be used to predict the satellite's position and velocity at any point in the future and is dynamic in the sense that it is updated periodically. The predictions are performed by the prediction module 214. In some examples, the model may be updated whenever one or more tracking data points are filtered by the OD process tool's filter module 212. Alternatively, the model may be manually updated by the system user.

[0058] The desired / predicted attitude of the spacecraft is also used in the OD process to fit the satellite's dynamic model. This attitude data can be collected each time the satellite passes. The attitude data can be stored, for example, in an attitude file that is added each time the satellite passes. By including the attitude data in the state vector data, the satellite's precise motion can be modeled. This precise position model can be combined with state vector measurements (such as GPS measurements) and satellite dimensions to improve the reliability and accuracy of the dynamic model, resulting in more accurate data filtering by the OD filter. As a result, the accuracy of predictions made based on the dynamic model is improved, orbital maneuvering planning is improved, and the accuracy of post-processing of orbital information is improved.

[0059] The orbit is defined by six orbital parameters: 1. the semi-major axis of the solar eclipse (representing altitude), 2. the inclination, 3. the eccentricity of the solar eclipse, 4. the argument of perigee (the location of the point closest to Earth on the orbital arc), 5. the longitude of the ascending node, and 6. the angle of true perigee. Since information about the orbital state and energy can be obtained by estimating the satellite's acceleration, the orbit can also be described using a state vector (position, velocity, time).

[0060] Next, the OD server 220 performs predictions based on the estimated orbit and forecasts future ephemeris data for the satellite. The forecast module 214 may be configured to forecast future ephemeris for more than 24 hours. The forecast module 214 may also be configured to forecast future ephemeris at any desired resolution, such as between 1 and 5 seconds.

[0061] Furthermore, the ground automation 202 includes an OD application programming interface "API" 230. Here, tracking data for the satellite is typically stored in separate files, possibly received from different ground stations, and aggregated into a dataset accessible via API 230 and searchable by time range. For this purpose, the data may be organized in chronological order. An evaluation process may be triggered via the API. For this purpose, the API may access data from the filter module 212, the storage module 213, and / or the prediction module 214. Slackbot 240 and / or operator 250 may assist in verifying the accuracy of the results generated by the OD process tool 210. Slackbot 240 may provide links for downloading filtered ephemeris and / or predicted ephemeris, and the results of a filter consistency test. The auxiliary data module 260 may be configured to generate auxiliary data based on predicted future ephemeris only if the results generated by the OD process tool are acceptable and / or approved. The auxiliary data module 260 may include a downconverter (not shown) to reduce the resolution of future predicted ephemeris, if necessary.

[0062] Satellite 300 receives new auxiliary data from ground segment 200, for example, after each ground station pass or according to a different schedule. The new auxiliary data may include future predicted ephemeris covering at least one complete orbital period or a partial orbital period until the next ground station pass. For this purpose, satellite 300 includes a receiving module (not shown). A data file containing the auxiliary data is stored in memory 311 of the onboard computer 340. Each time satellite 300 receives new auxiliary data, the entire auxiliary data file stored in memory 311 is replaced, which can save memory resources. If the onboard computer 340 receives information 321a that GPS is functioning, the auxiliary data stored in memory 311 may not be used. If the onboard computer 340 receives information 321b that GPS is not functioning, the processor 312 of the onboard computer 340 adjusts the internal orbit propagator to initialize it with the ephemeris data predicted from the auxiliary data. For this purpose, the processor 312 of the onboard computer 340 selects an appropriate predicted ephemeris from memory 311 and provides it to the satellite's ADCS subsystem 302. The predicted ephemeris is selected to be closest to the current time on the onboard computer. The internal orbit propagator of ADCS 302 performs orbit propagation using the predicted ephemeris instead of the latest GPS measurement data. In other words, if GPS fails, auxiliary data is used instead of actual tracking data.

[0063] An example of a GPS outage that could trigger the use of auxiliary data is a situation where some satellites may lose or be unable to maintain a lock on one or more GPS satellites for a relatively long period, such as more than an hour. Furthermore, this problem can be repeated multiple times throughout the day. In particular, this problem can occur when satellites are performing complex operations such as downlink operations. Before and after this activity, the number of tracked GPS satellites may suddenly drop from the nominal value of approximately 15 to zero. In addition, if the GPS antenna is pointed towards the zenith, it may take some time for the GPS lock to be restored even after returning to the nominal flight attitude, in which case the GPS satellite constellation should be clearly visible.

[0064] The use and availability of satellite-onboard auxiliary data for determining the satellite's current position based on the auxiliary data is further explained with reference to Figure 3. In this scenario, the satellite's GPS is down. That is, the GPS module transitions from a functioning 321a to a non-functioning 321b and then back to a functioning 321a. The auxiliary data file contains future predicted ephemeris for each Δt, for example, at a 5-minute resolution. Thus, the auxiliary data file contains predicted ephemeris x, v (including both position and velocity data) for times t1, t2, t3, etc. At a 5-minute resolution, there is a 5-minute gap Δt between consecutive ephemeris. 停止 If tracking data is lost, that is, if the onboard GPS receiver cannot maintain a lock on the GPS satellite signal, the onboard computer's flight software (OBC) selects the latest predicted ephemeris (x1,v1) corresponding to time t1 and provides this to the ADCS system. The ADCS system calculates the current position and velocity based on the predicted ephemeris (x1,v1) from the OBC and numerically propagates the orbital information until it receives an update. 停止A short offset period may exist between the GPS stop at time t and the ADCS system calculating the current position based on auxiliary data at the start of time t. The next update is performed on the tracking data when the tracking data becomes available again, but if the tracking data is not available again, the OBC continues to provide the ADCS system with the predicted ephemeris. After a predetermined time interval Δt' (which may be the same as the time interval Δt shown in Figure 3) has elapsed, the onboard computer may again select the latest predicted ephemeris (x2,v2) corresponding to time t2. Thus, the ADCS system selects the latest predicted ephemeris (x2,v2) corresponding to time t 更新 Then, based on the ephemeris (x2,v2) provided by the OBC from the auxiliary data, the current orbital information for the current time is calculated, and this information is then independently propagated numerically until the next update is provided by the OBC. This process may be repeated as long as GPS cannot obtain GPS information about the satellite's position. In the scenario shown in Figure 3, GPS is t GPS The lock is then reacquired, and the ADCS system receives GPS measurements and calculates the current position and speed based on the latest GPS measurements. In this case, the predicted ephemeris (x3,v3) of t3 is not sent to the ADCS system.

[0065] Figure 4 is a perspective view of satellite 300 orbiting the Earth, as an example of a platform that can utilize onboard auxiliary data. The ground segment containing all the ground elements of the spacecraft system is shown as 200. The ground segment 200 enables control of satellite 300 as it moves in Earth orbit, and the delivery of payload data and telemetry. Satellite 300 consists of a body 310, solar panels 350, and "wings" 360. Satellite 300 also includes an attitude determination and control system "ADCS" unit, which may be equipped with one or more reaction wheels, one of which is shown as 370. The ADCS unit is described further with reference to Figure 5. The reaction wheel 370 applies a torque force to the satellite body 310. The ADCS unit is used to control the satellite as it moves in orbit, that is, to guide satellite 300 in a desired direction and maintain it.

[0066] Satellites, such as satellite 300 in Figure 4, are typically equipped with a propulsion system 390 for steering the satellite with the thrust generated. The propulsion system 390 shown in Figure 3 is mounted on the body 310 on the opposite side of the solar panel 350. The propulsion system 390 comprises multiple thrusters 305. The four thrusters 305 shown in the example in Figure 4 are configured to generate thrust for steering the satellite as needed. The thrusters 305 are typically operated to maintain satellite 300 in a specific orbit. For example, the thrusters 305 may be used to propel satellite 300 in a specific direction relative to the Earth's surface.

[0067] The satellite shown in Figure 4 may be a microsatellite or small satellite, and due to its small size and high agility, its attitude can be changed by manipulating the entire satellite. This type of operation can be performed using an ADCS unit. For example, satellite 300 may be a microsatellite with a mass of 100 kg. A regular satellite with a mass of about 1000 kg is generally more expensive and less agility than a microsatellite. Satellites can be classified according to their mass. For example, satellites with a mass of about 1 kg to about 10 kg are classified as cube satellites, satellites with a mass of about 50 kg to about 250 kg are classified as microsatellites, satellites with a mass of about 500 kg are classified as small satellites, and satellites with a mass of about 800 kg to about 1200 kg can be classified as regular satellites.

[0068] Large satellites may offer opportunities to implement numerical methods called "orbital filters" onboard the satellite, but for small satellites such as nanosatellites, implementing orbital filters that yield satisfactory results may not be feasible. For small, inexpensive satellites, design options are limited by weight and size constraints, as well as the use of commercially available off-the-shelf components.

[0069] Figure 5 is a partial perspective view of the satellite. The ADCS 302 is typically located within the satellite body 310 and is used to control the satellite's orientation. The components of the ADCS 302 unit are described with reference to Figure 5.

[0070] The ADCS unit 302 consists of a set of three reaction wheels 370a, 370b, and 370c located within the satellite body 310. Reaction wheels are also called momentum wheels. The reaction wheels 370a, 370b, and 370c are controlled by the ADCS controller 341. The reaction wheels 370a, 370b, and 370c function by using electric motors to rotate the wheels within the spacecraft body 310. Due to the conservation of angular moment, rotating the wheels in one direction will cause the spacecraft to rotate in the opposite direction. Using reaction wheels is a well-known method for determining the orientation of spacecraft such as satellites. In this example, three reaction wheels 370a, 370b, and 370c are provided, one for each axis to orient the satellite 300. The reaction wheels 370a, 370b, and 370c are shown to have orthogonal axes. In another example, especially for satellites with large moments of inertia, four or more reaction wheels may be used to better control various aspects of satellite dynamics, such as slew rate and fine positioning control.

[0071] The ADCS unit shown in Figure 5 further includes torque rods 305a, 305b, and 305c. The torque rods are also used for satellite attitude control. The torque rods 305a, 305b, and 305c are typically operated to maintain the satellite 300 in a specific attitude, and this operation is controlled by the ADCS controller 341, which is described below.

[0072] The ADCS unit 302 further includes an ADCS controller 341. The ADCS controller 341 communicates with an onboard computing system 340. The onboard computing system 340 consists of a processor 349, memory 348, and a telemetry unit 345. Memory 348 can be used to store auxiliary data (similar to memory 311 in Figure 2). The telemetry unit 345 may be configured to transmit telemetry data, including tracking data, to a ground station, such as ground station 201 in Figure 2, each time it passes a ground station. The ADCS controller 341 is further configured to receive information from one or more sensors 347. One or more sensors 347 are configured to measure various quantities during the satellite's flight, such as a solar sensor and a magnetometer for measuring local magnetic fields. The ADCS controller 341 further communicates with a GPS receiver module, which includes a GPS receiver 352 and a GPS antenna 353. The GPS receiver module may be a commercially available GPS receiver.

[0073] To properly control satellite 300 moving in Earth orbit, the ADCS controller needs to know the satellite's actual position as accurately as possible. For this purpose, the ADCS controller 341 also runs orbital propagator software, also called the (internal) orbital propagator. The ADCS controller 341, including the orbital propagator, may be a commercially available off-the-shelf product. When the GPS module is functioning, the ADCS controller 341 is configured to calculate the current position and velocity based on the latest GPS measurements received from the GPS receiver 352. While the GPS module maintains lock, GPS measurements are typically repeated every 30 seconds. Therefore, the internal orbital propagator is repeatedly initialized with the new GPS measurements and continues to perform numerical propagation based on the GPS measurements. If the GPS module temporarily or permanently stops working for any reason, as in the example in Figure 3, the onboard computing system 340 selects ephemeris data points from the auxiliary data stored in memory 348 according to the satellite's onboard time. In one example, the auxiliary data consists of predicted future ephemeris data every 5 minutes. When the onboard computing system 340 receives notification from the ADCS controller 341 that the GPS is not functioning, it selects the most recent ephemeris data based on the onboard time and provides it to the ADCS controller 341. The ADCS controller 341 then calculates the current position and velocity based on the ephemeris data received from the onboard computing system 341 and numerically propagates the orbital information until it receives the next update. The next update may be either a GPS measurement if the GPS module regains lock, or the next predicted ephemeris data point for the auxiliary data. In the latter case, the internal orbital propagator is initialized with the new predicted ephemeris data every 5 minutes, or whenever a new ephemeris data point becomes available.

[0074] As an example, the certainty of future ephemeris predictions and the results determined by the internal orbit propagator based on uploaded auxiliary data were tested by simulation. Therefore, it is assumed that the measurements from the filtered GPS receiver are significantly more accurate than predictions and can be considered "true" compared to the results. The simulation results are explained with reference to Figures 6-9.

[0075] Figure 6 shows a plot of the positional difference between the positional data determined by the onboard orbit propagator based on auxiliary data (onboard information regarding the satellite's position) and the actual orbit (filtered tracking data, such as filtered GPS measurements). In Figure 6, increments on the y-axis correspond to 20 meters, and increments on the x-axis correspond to 2 hours. To evaluate the deviation between the onboard knowledge based on auxiliary data and the actual orbit, the GPS lock was unlocked for at least 12 hours. As shown in Figure 6, when the ADCS internal orbit propagator is initialized with auxiliary data generated according to the method described with reference to Figure 1, the satellite's onboard information is very accurate for approximately 15 hours. Although a peak deviation was observed to increase during this period, the positional deviation still did not exceed 80 meters, which is acceptable for many payload requirements. An 80-meter positional error is well below the 500-meter requirement specified for SAR imaging. Without auxiliary data, the deviation could be much larger, such as 6000 meters, over a similar timeframe. The auxiliary data provides sufficient accuracy in knowing the satellite's position even if GPS fails, allowing the satellite to continue its mission.

[0076] Figure 7 shows a graph comparing predicted future ephemeris data acquired by ODTK with the actual orbit measured by the onboard GPS receiver and filtered by ODTK to reduce noise. Lines (a) and (b) in the figure correspond to the radial and cross-track directions, respectively. From Figure 7, it can be seen that deviations in both directions are negligible over the entire 24-hour forecast. Line (c) corresponds to the in-orbit direction. As expected, the error in the satellite's orbit is slightly noticeable. Looking at Figure 7, it can be seen that the deviation in the trajectory direction is small (less than 100 meters) for at least 12 hours and remains within approximately 400 meters for the entire 24-hour forecast. Therefore, the predicted future ephemeris data provides very high accuracy for at least the first 12 hours and also provides acceptable accuracy for the entire 24-hour forecast.

[0077] The results of an example of an orbit determination algorithm are evaluated by the following simulation, as explained with reference to Figures 8 and 9.

[0078] Figure 8 is a graph showing the measurement residual ratios of multiple GPS measurements over a 24-hour period (approximately 17–18 hours are displayed in Figure 8). As can be seen from Figure 8, there are at least two gaps in the GPS data that exceed one hour (the first gap is from approximately 9:30 to 11:30, and the second gap is from approximately 21:30 to 23:30). The gaps may correspond to the cessation of GPS tracking onboard satellites. In Figure 8, data points of different shapes and styles represent the x, y, and z components of the position and velocity vectors, respectively. Measurement residual ratios outside the 3-sigma limit (the boundary line in Figure 8) are not considered accurate measurements and are ignored.

[0079] Figure 9 is a graph showing the positional consistency statistics (test statistics) of the orbit determination results based on GPS measurements shown in Figure 8. The consistency test is used to evaluate the quality of the orbit determination. As can be seen from Figure 9, the estimation algorithm functions without actual measurements even during periods corresponding to GPS downtime (such as between approximately 9:30 and 11:30 and between approximately 21:30 and 23:30, as shown in Figure 8). Therefore, the impact of GPS downtime on orbit estimation is not significant. In Figure 9, line (a) corresponds to the in-orbit direction, line (b) to the radial direction, and line (c) to the cross-orbit direction. The deviation in the cross-track direction is very small over the entire 18-hour estimation. The deviations in the radial and trajectory directions are slightly noticeable, but remain stable over the 18-hour propagation time despite being generated from GPS measurements with gaps of more than two hours. Based on the test statistics shown in Figure 9, there is almost no difference between the GPS measurement period and the non-GPS measurement period. Since orbit determination is based on uploaded auxiliary data, including predicted future ephemeris data, these predictions can be inferred to be accurate even if the tracking data contains gaps due to GPS outages. This demonstrates the accuracy of orbit determination and the resulting auxiliary data, even when based on an incomplete record of actual GPS measurements.

[0080] For clarity, the above description has referred to a single user in describing embodiments of the present invention. In practice, it should be understood that the system may be shared by multiple users, and may be shared by many users simultaneously.

[0081] The above embodiments are fully automated. In some examples, the system user or operator may manually instruct some steps of the process to be carried out.

[0082] In embodiments described in the present invention, the system may be implemented as any form of computing and / or electronic device. Such a device may include one or more processors, which are microprocessors, controllers, or other suitable types of processors that process computer executable instructions that control the operation of the device in order to collect and record routing information. In some examples, for example, when a system-on-chip architecture is used, the processor may include one or more fixed-function blocks (also called accelerators) that implement parts of the method in hardware (rather than software or firmware). Platform software, including an operating system or other suitable platform software, may be provided to the computing-based device so that application software can run on the device.

[0083] The various functions described herein may be implemented in hardware, software, or any combination thereof. If implemented in software, these functions may be stored or transmitted on a computer-readable medium as one or more instructions or codes. A computer-readable medium may include, for example, a computer-readable storage medium. A computer-readable storage medium may include volatile or non-volatile, removable or inremovable media implemented by any method or technique for storing information such as computer-readable instructions, data structures, program modules, or other data. A computer-readable storage medium may be any available storage medium accessible by a computer. Such a computer-readable storage medium may include, but not limited to, RAM, ROM, EEPROM, flash memory or other storage devices, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, or any other medium accessible by a computer and used to transport or store desired program code in the form of instructions or data structures. The optical discs and discs used herein include optical discs (CDs), laser discs, optical discs, digital multipurpose discs (DVDs), floppy disks (registered trademarks), and Blu-ray discs (BDs). Furthermore, propagated signals are not included within the scope of computer-readable storage media. Computer-readable media also include communication media, including any medium that facilitates the transmission of computer programs from one location to another. Connections may, for example, be communication media. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave, it falls within the definition of communication media. Any combination of the above must also be included within the scope of computer-readable media.

[0084] Furthermore, or alternatively, the functions described herein may be performed at least partially by one or more hardware logic components. For example, usable hardware logic components may include field-programmable gate arrays (FPGAs), specific programmable integrated circuits (ASICs), specific programmable standard products (ASSPs), system-on-chip systems (SOCs), and composite programmable logic devices (CPLDs).

[0085] While the diagram shows a single system, it should be understood that computing devices can be part of a distributed system. Therefore, for example, multiple devices may communicate via a network connection and collaboratively perform tasks described as being executed by the computing device.

[0086] While the illustration shows a local device, please understand that computing devices may be located and accessed remotely via a network or other communication link (e.g., using a communication interface).

[0087] It should be understood that the above advantages and benefits may relate to one embodiment or to several embodiments. Multiple embodiments are not limited to those that solve any or all of the problems mentioned or that possess the advantages and benefits mentioned. Variations should be considered to fall within the scope of the invention.

[0088] A reference to an item means one or more of those items. The term "contains" is used here to mean including the identified method steps or elements, but these steps or elements do not include an exclusive list, and the method or device may include additional steps or elements.

[0089] As used herein, the terms “component” and “system” are intended to include a computer-readable data store consisting of computer-executable instructions that, when executed by a processor, perform a specific function. Computer-executable instructions may include routines, functions, and so on. It should also be understood that a component or system may reside on a single device or be distributed across multiple devices.

[0090] Furthermore, as used herein, the term “exemplary” is intended to mean “as an example or illustration of something.”

[0091] The attached diagram illustrates an exemplary method. While the method is presented and described as a series of actions performed in a specific order, it should be understood that the method is not limited by order. For example, some operations may occur in a different order than those described herein. Furthermore, some actions may occur simultaneously with others. Moreover, in some cases, not all actions may be necessary to perform the method described herein.

[0092] Furthermore, the actions described herein may include computer-executable instructions implemented by one or more processors and / or stored on a computer-readable medium. Computer-executable instructions include routines, subroutines, programs, execution threads, and the like. In addition, the results of operations performed by these methods may be stored in a computer-readable medium and displayed on a display device and / or on a similar device.

[0093] The order of steps in the methods described herein is illustrative, but these steps may be performed in any suitable order, or, where appropriate, simultaneously. Furthermore, steps may be added to or replaced in any method, or a single step may be removed from any method, without departing from the scope of the subject matter described herein. An aspect of any example described above may be combined with an aspect of any other example to form further examples without losing the desired effect.

[0094] The above description of preferred embodiments is presented for illustrative purposes only, and it should be understood that those skilled in the art can make various modifications. The above description comprises one or more examples of embodiments. Of course, for the purpose of illustrating the aforementioned embodiments, it is impossible to describe all possible modifications and changes to the above apparatus or method, but those skilled in the art will recognize that many more modifications and combinations of various embodiments are possible. Accordingly, the embodiments described are intended to include all such modifications, changes, and variations that fall within the scope of the appended claims.

Claims

1. A computer-based method for generating auxiliary data to control a satellite moving in Earth orbit, The steps include receiving tracking data for the satellite, A step in which an orbit determination algorithm is applied, The steps include: estimating the satellite's orbit based on the aforementioned tracking data, and The step includes predicting future ephemeris data of the satellite based on the estimated orbit, The steps include generating auxiliary data including the predicted future ephemeris data, The steps include transmitting auxiliary data to the satellite for use in controlling the satellite's attitude and orbit, If data from the GNSS or GPS sensor mounted on the satellite is unavailable or unreliable, the current position of the satellite is determined based on the predicted future ephemeris data included in the auxiliary data. The steps include using the current position to control the orbit and attitude of the satellite, At least the application of the orbit determination algorithm and the generation of the auxiliary data are performed on the ground. If data from the GNSS or GPS sensor mounted on the satellite is available and reliable, the current position of the satellite is determined based on the data from the GNSS or GPS sensor. method.

2. The method according to claim 1, wherein the tracking data includes Global Navigation Satellite System (GNSS) sensor data, satellite laser ranging (SLR) measurements, or satellite radar measurements.

3. The method according to claim 1, wherein the tracking data indicates a series of times and corresponding positions and speeds of the satellite.

4. The method according to claim 1, wherein the orbit of the satellite is estimated based on a previously estimated orbit.

5. The method according to claim 1, wherein the tracking data corresponds to a predetermined time interval and optionally corresponds to the time between the satellite's two ground station paths.

6. The method according to claim 5, wherein the tracking data includes one or more gaps corresponding to one or more tracking stops within a predetermined time interval.

7. The method according to claim 1, wherein the method is repeated for each pass of the satellite, the tracking data is received for each pass of the satellite, and the generated auxiliary data is transmitted for each consecutive pass of the satellite.

8. The method according to claim 1, wherein the method is repeated in parallel for multiple satellites.

9. The method according to claim 1, wherein the auxiliary data includes predicted future ephemeris over a period of time equal to or shorter than 6 hours, 12 hours, or 24 hours, up to a maximum interval equal to one of 1 minute, 2 minutes, and 5 minutes.

10. The method according to claim 1, wherein the auxiliary data includes predicted future ephemeris covering at least one orbital period of the satellite.

11. The method according to claim 1, wherein the step of estimating the orbit includes the step of filtering the tracking data to provide a filtered ephemeris of the satellite.

12. The method according to claim 11, wherein the step of predicting future ephemeris data of the satellite includes the step of propagating forward in time from the filtered ephemeris.

13. A ground segment that generates auxiliary data for controlling a satellite moving in Earth orbit, wherein the ground segment is configured to perform the method of claim 1.

14. A ground segment that generates auxiliary data for controlling a satellite moving in Earth orbit, wherein the ground segment is A receiving module configured to receive tracking data for a satellite, Estimating satellite orbits based on tracking data, and This includes predicting future ephemeris data of the satellite based on the estimated orbit, The orbit determination toolkit "ODTK" is configured to apply orbit determination algorithms, An auxiliary data module configured to generate auxiliary data including the predicted future ephemeris data, A transmitting module is configured to transmit auxiliary data to the satellite for use in the satellite attitude determination and control system "ADCS" unit, and, if data from the GNSS or GPS sensors on board the satellite is unavailable or unreliable, to determine the satellite's current position based on the predicted future ephemeris data contained in the auxiliary data, and to use the current position to control the satellite's orbit and attitude, At least the application of the orbit determination algorithm and the generation of the auxiliary data are performed on the ground. If data from the GNSS or GPS sensor mounted on the satellite is available and reliable, the current position of the satellite is determined based on the data from the GNSS or GPS sensor. Ground segment.

15. The ground segment according to claim 14, wherein the components of the ground segment are distributed to multiple locations.

16. Use of a ground segment according to claim 14 for generating auxiliary data for controlling one or more satellites moving in Earth orbit, wherein each of the one or more satellites is configured to determine its position based on the auxiliary data.

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