A Joint Fixed-Point Capture Method Based on Continuous Small Thrust

Abstract

This invention discloses a joint fixed-point acquisition method based on continuous small thrust. This method, targeting geostationary orbit satellites using continuous small thrust for orbit transfer, employs a multi-step strategy to gradually approach the satellite's mean longitude to a fixed position. First, before the semi-major axis reaches its final position, the satellite's longitude is continuously moved eastward by manipulating the arrival time, until the semi-major axis reaches the geostationary orbit and is at the fixed longitude position. Then, while correcting inclination and eccentricity isolation residuals, the effects of ground shadows and unexpected ignition failures are overcome by manipulating the stop-fire arc segment, maintaining the satellite's mean longitude at the fixed position. Finally, once the inclination and eccentricity are both in place, a short high-precision fixed-point acquisition is performed, ensuring that the satellite's geographic latitude and longitude are entirely within the dead zone controlled by the geostationary orbit.

Description

Technical Field

[0001] This invention relates to a joint stationary acquisition method based on continuous small thrust, belonging to the field of satellite attitude and orbit control technology. Background Technology

[0002] When geostationary satellites separate from the launch vehicle, they are often not directly in geosynchronous orbit, but in geosynchronous transfer orbit. Their semi-major axis, inclination, and eccentricity all need to be adjusted by orbit control, and they need to be captured at the end of the orbit transfer.

[0003] Continuous low-thrust orbit transfer and station-keeping capture is a novel mission execution method that can effectively save propellant fuel consumption compared to traditional high-thrust engine orbit control. However, there are fundamental differences: First, high-thrust orbit capture is typically combined with apogee maneuvering pulse control for orbit selection, a scheme that cannot be implemented under continuous low-thrust orbit transfer control. Second, continuous low-thrust orbit transfer takes a long time, and changes in geographical longitude are more sensitive to thrust magnitude and direction, requiring long-term corrections and making it difficult to balance orbit control efficiency and station-keeping time. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a joint fixed-point acquisition method based on continuous small thrust. The fixed-point acquisition is carried out in a step-by-step and multiple-correction manner to meet the requirements of orbit transfer and fixed-point acquisition missions of geostationary satellites.

[0005] The technical solution of this invention is:

[0006] A joint positioning and acquisition method based on continuous low thrust is applied to satellites configured with continuous low thrust and capable of adjusting orbit control thrust pointing. The joint positioning and acquisition method includes:

[0007] When the satellite is in transfer orbit and its semi-major axis, inclination, and eccentricity are not yet in place, joint control of the semi-major axis, inclination, and eccentricity is carried out and the longitude is adjusted to ensure that the semi-major axis is at a fixed longitude position when it reaches the geosynchronous orbit.

[0008] By aligning the in-plane thrust component perpendicular to the perigee direction, eccentricity is eliminated; by igniting the out-of-plane component in the orbital normal direction, the orbital inclination is reduced; and by eliminating the aforementioned inclination and eccentricity residuals, the satellite's longitude is maintained at its fixed position.

[0009] Once the satellite's semi-major axis, inclination, and eccentricity are all in place, it will be fired twice along the orbital tangential direction to achieve pinpoint capture and precisely control the longitude and drift rate.

[0010] Preferably, when the satellite is in transfer orbit and its semi-major axis, inclination, and eccentricity are not yet in place, joint control of the semi-major axis, inclination, and eccentricity is performed, along with adjustment of the longitude. This is achieved by igniting the in-plane thrust component in the orbital tangential direction to increase the semi-major axis; igniting the out-of-plane component in the orbital normal direction to decrease the orbital inclination; stopping ignition in the perigee region to eliminate the orbital eccentricity; and controlling the time it takes for the semi-major axis to reach the target semi-major axis to control the satellite's longitude to drift eastward, ensuring that the semi-major axis is at a fixed longitude position when it reaches the geosynchronous orbit.

[0011] Preferably, the semi-major axis, inclination angle, and eccentricity are jointly controlled and adjusted together with the horizontal longitude. The adjustment method is as follows:

[0012] The small thrust continuously ignites within one orbital cycle. The thrust is in the plane formed by the velocity direction and the orbital angular momentum, and there is an angle ψ1 between the thrust and the orbital plane. The absolute value remains unchanged, but the sign changes at 90° and 270°. Ignition stops at the approximate point angle of 0°±ΔM. In each orbital cycle, fuel consumption is minimized by traversing ψ1 within ±90° and ΔM within 0 to 180°. When the orbital cycle is more than 90% of the target orbital cycle, the time for the semi-major axis to reach the target semi-major axis is controlled.

[0013] Preferably, the timing of the semi-major axis reaching the target semi-major axis is controlled by the following method: for each orbital period, the magnitude of the thrust is calibrated according to the changing trend of the orbital semi-major axis and inclination angle. The target fixed-point longitude is obtained by numerical integration using the calibrated thrust. By extending or shortening the ΔM value, the satellite's longitude is located at the fixed-point accuracy at the same time as the semi-major axis reaches the target semi-major axis.

[0014] Preferably, the eccentricity is eliminated by aligning the in-plane thrust component perpendicular to the perigee direction; the orbital inclination is reduced by igniting the out-of-plane component in the orbital normal direction. The specific method is as follows:

[0015] When the small thrust is continuously ignited within one orbital period, and the angle between the thrust component in the orbital plane and the perigee vector direction is -90°, the angle ψ2 between the out-of-plane component and the orbital plane remains unchanged in absolute value. The sign changes around 90° and 270°.

[0016] Set the orbital angle 90°±Δu1 region and the orbital angle 270°±Δu2 region, and stop ignition to reduce fuel consumption;

[0017] Each orbital cycle updates the angle ψ2 between the out-of-plane component and the orbital plane by traversing ±90°, thus minimizing fuel consumption.

[0018] Preferably, when affected by the Earth's shadow season, initial orbital conditions, or unplanned ignition shutdown, the relationship between Δu1 and Δu2 is set to correct the fixed-point longitude:

[0019] If the orbital angle u = 90° is closer to the perigee: when the drift rate increases, set Δu1 > Δu2; when the drift rate decreases, set Δu1 < Δu2.

[0020] If the orbital angle u = 270° is closer to the perigee: when the drift rate increases, set Δu1 < Δu2; when the drift rate decreases, set Δu1 > Δu2.

[0021] When the drift rate enables the satellite to reach its fixed position at the end of the fixed-point acquisition, set Δu1 = Δu2.

[0022] Preferably, once the satellite's semi-major axis, inclination, and eccentricity are all in place, two fires are performed along the orbital tangential direction for pinpoint capture, specifically including:

[0023] After receiving the fixed-point acquisition command, the satellite orbit is first determined, the latest mean longitude and mean longitude drift rate of the satellite are obtained, and then the thrust is adjusted to the start-up direction to start ignition, with a duration of T1.

[0024] After the T1 stage ignition ends, the spark drift phase begins, lasting for T seconds. draft ;

[0025] After the drifting phase ends, adjust the thrust to the braking direction and perform braking ignition for a duration of T2.

[0026] After braking and ignition, the satellite reached the target longitude with a drift rate of 0.

[0027] Preferably, if the satellite is performing a deorbiting mission at the end of its lifespan, only an initial ignition is performed, and the capture is considered complete after the T1 ignition is completed.

[0028] The advantages of this invention compared to the prior art are:

[0029] (1) This invention performs preliminary fixed-point capture control while transferring orbits with low thrust, eliminating most of the fixed-point longitude difference without consuming additional fuel. After the orbit transfer is completed, the geographic longitude of the nadir point is basically in place, requiring only minor adjustments.

[0030] (2) The fixed-point capture method described in this invention has the advantages of updating the track control parameter angle multiple times and adjusting it in stages, and has a high success rate.

[0031] (3) The invention adjusts the geographical longitude during orbit transfer, at which time the inclination and eccentricity are greater, and the distance from other geostationary orbit satellites is greater, realizing inclination and eccentricity isolation during the positioning process, which is more secure. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0033] Figure 1 This is a flowchart of the joint fixed-point capture method based on continuous small thrust of the present invention;

[0034] Figure 2 The following are fixed-point capture correction curves for embodiments of the present invention: (a) is the curve corresponding to calculation example 1, and (b) is the curve corresponding to calculation example 2.

[0035] Figure 3 The following are curves for the fixed-point capture start-drift-braking of an embodiment of the present invention: (a) is a curve showing the change of the orbital semi-major axis over time; (b) is a curve showing the change of eccentricity over time; and (c) is a curve showing the change of geographical longitude over time. Detailed Implementation

[0036] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0037] In view of the practical characteristics of continuous low-thrust orbit transfer and taking into full account the actual engineering constraints and the convenience of on-orbit operation, this invention proposes a joint fixed-point capture method based on continuous low thrust. It is mainly applied to geostationary orbit satellites equipped with continuous low-thrust actuators and capable of adjusting the direction of orbit control thrust during orbit transfer and fixed-point capture.

[0038] This method is as follows Figure 1 As shown, when the satellite is in transfer orbit and its semi-major axis, inclination, and eccentricity are not yet in place, the following steps are performed during the entire low-thrust orbit transfer:

[0039] S1: When the orbital period is greater than 21 hours, the semi-major axis, inclination, and eccentricity are combined and the longitude is adjusted.

[0040] By igniting the in-plane thrust component tangentially to the orbit, the semi-major axis is increased; by igniting the out-of-plane thrust component normally to the orbit, the orbit inclination angle is reduced; and by stopping ignition near the perigee, the orbital eccentricity is eliminated.

[0041] (1) During this stage, the small thrust is continuously ignited for most of the orbital period. The thrust is in the plane formed by the velocity direction (or vertical radial direction) and the orbital angular momentum, and has a certain angle ψ1 with the orbital plane. Its absolute value remains unchanged, but the sign changes around 90° and 270°.

[0042] (2) Near the perigee, set the ignition stop near the horizontal perigee angle of 0°±ΔM to reduce the track eccentricity.

[0043] (3) Regularly update ψ1 and ΔM in the above two processes to keep fuel consumption at a minimum.

[0044] (4) When the orbital period is more than 90% of the target orbital period, the longitude is drifted eastward. The method is to periodically calibrate the thrust by observing the changing trends of the orbital semi-major axis and inclination, and on this basis, extend or shorten the magnitude of ΔM so that the longitude is at the fixed point accuracy when the satellite reaches the target semi-major axis.

[0045] Under the above strategy, when the orbital semi-major axis is about to be in place, the satellite phase is continuously drifted eastward by adjusting the time when the semi-major axis reaches the target semi-major axis, i.e., the stop point fire control eccentricity time, so as to gradually approach the fixed point phase.

[0046] S2: Eliminate tilt angle and eccentricity residuals.

[0047] After completing the joint control of semi-major axis, inclination angle, and eccentricity, a large residual inclination angle and eccentricity are left to ensure the safety of pinpoint capture. At the current stage, eccentricity is eliminated by making the in-plane thrust component perpendicular to the perigee direction; the orbital inclination angle is reduced by igniting the out-of-plane component in the orbital normal direction.

[0048] (1) During this stage, the small thrust is continuously ignited for most of the orbital cycle. The thrust direction is in the J2000 coordinate system. The thrust component in the orbital plane makes an angle of -90° with the perigee vector direction, and the thrust component out of the orbital plane makes an angle ψ2 with the orbital plane. Its absolute value remains unchanged, but the sign changes around the 90° and 270° angles. Set up an orbital angle of 90°±Δu1 region and an orbital angle of 270°±Δu2 region, and stop ignition to reduce fuel consumption.

[0049] (2) Regularly update ψ2 in the above two processes to keep fuel consumption at a minimum.

[0050] (3) When affected by the Earth's shadow season, initial orbital conditions, or unplanned ignition shutdown, the symmetry of Δu1 and Δu2 is set to correct the fixed-point longitude:

[0051] If the orbital angle u = 90° is closer to the perigee: when the drift rate increases, set Δu1 > Δu2; when the drift rate decreases, set Δu1 < Δu2.

[0052] If the orbital angle u = 270° is closer to the perigee: when the drift rate increases, set Δu1 < Δu2; when the drift rate decreases, set Δu1 > Δu2.

[0053] When the drift rate is appropriate, Δu1 = Δu2.

[0054] (4) Regularly update ψ2 in the above two processes to keep fuel consumption at a minimum.

[0055] Under the above strategy, the deviation of longitude and drift rate from the fixed position caused by ground shadow or other ignition interruption events is corrected by stopping ignition near the near and far points.

[0056] S3: Perform low-thrust fixed-point capture control.

[0057] Once the satellite's semi-major axis, inclination, and eccentricity are all in place, the longitude and drift rate are precisely controlled by two ignitions along the tangential direction of the orbit.

[0058] (1) The design for geostationary acquisition is divided into the following five states. After receiving the geostationary acquisition command, the satellite orbit is first determined, and the latest satellite longitude and longitude drift rate are obtained. Then, the thrust is adjusted to start pointing east or west, and ignition is initiated for a duration of T1. After the ignition in the T1 stage, the satellite enters the stationary ignition drift stage, with a drift duration of T. draft After the satellite drift ends, the thrust will be adjusted to a westward or eastward braking direction for braking ignition, lasting for T2. After braking ignition, the satellite will reach the target longitude with a drift rate of 0.

[0059] (2) If the satellite is performing a deorbit mission at the end of its lifespan, only the initial ignition is performed. After the T1 ignition is completed, the capture is considered complete.

[0060] Example 1

[0061] Assume the thrust of the small thruster is 320 mN, the satellite's semi-major axis is located near 42165 km, the inclination is 4.5°, the eccentricity is 0.07, and the fixed longitude is 135°E. During the inclination and eccentricity elimination phase, the following conditions are set: (1) Δu1 = 30°, Δu2 = 30°; (2) Δu1 = 28.1°, Δu2 = 31.0°. The time to reach geostationary orbit is 31 days for both sets of examples. In example 1, the longitude drifts eastward; in example 2, the longitude is consistently stabilized near 135° by adjusting the ignition stop time. See curves for details. Figure 2 Figures (a) and (b) are shown in the image.

[0062] Example 2

[0063] Set the satellite's current geographic longitude to 150°E. Using the start-ignition-braking procedure, first initiate the process to raise the semi-major axis, then drift the satellite, and finally brake to return the semi-major axis to its nominal position in the geostationary orbit, while simultaneously controlling the satellite to its target geostationary position at 134°E. See the curve for details. Figure 3 (a) to (c) in the text.

[0064] Simulation results show that the method of this invention can achieve fixed-point capture based on continuous small thrust, and can be used for fixed-point capture control of orbit transfer in geosynchronous orbit.

[0065] In summary, by utilizing the joint fixed-point capture method based on continuous small thrust of the present invention, a multi-step strategy can be adopted to gradually approach the longitude of a geostationary orbit satellite with a continuous small thrust orbit transfer actuator to a fixed position.

[0066] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for combined station keeping and pointing based on continuous low thrust, applied to a satellite equipped with continuous low thrust and with the ability to adjust the pointing of the orbit control thrust, characterized in that, The combined spot capture method comprises: When the satellite is in a transfer orbit and the semi-major axis, inclination and eccentricity are not in place, semi-major axis, inclination and eccentricity are jointly controlled and combined with the adjustment of the mean longitude, so that the semi-major axis is in a spot longitude position when reaching the synchronous orbit; The eccentricity is eliminated by the in-plane thrust component being perpendicular to the perigee direction, the inclination is reduced by the out-of-plane component firing in the orbit normal direction, and the residual inclination and eccentricity are eliminated, so that the mean longitude of the satellite is continuously maintained at the spot position; When the semi-major axis, inclination and eccentricity of the satellite are all in place, the spot capture is performed by twice firing in the tangential direction of the orbit, so that the mean longitude and the drift rate are accurately controlled to be in place; When the satellite is in a transfer orbit and the semi-major axis, inclination and eccentricity are not in place, semi-major axis, inclination and eccentricity are jointly controlled and combined with the adjustment of the mean longitude, the semi-major axis is increased by the in-plane thrust component firing in the tangential direction of the orbit, the inclination is reduced by the out-of-plane component firing in the normal direction of the orbit, and the eccentricity is eliminated by stopping firing in the perigee region, and the longitude of the satellite is controlled to drift eastward by controlling the time when the semi-major axis reaches the target semi-major axis, so that the semi-major axis is in a spot longitude position when reaching the synchronous orbit.

2. The method of claim 1, wherein the method is a method of combined on- target capture based on continuous small pushes. The adjustment method for the combined control of the semi-major axis, inclination and eccentricity and the adjustment of the mean longitude is as follows: The small thrust is continuously fired in one orbit period, the thrust in the plane formed by the velocity direction and the angular momentum of the orbit has an angle ψ1 with the orbit plane, the absolute value is unchanged, but at the amplitude angles of 90° and 270°, the positive and negative are changed, the mean anomaly 0°±ΔM is set to stop firing, and in each orbit period, ψ1 is traversed at ±90° and ΔM is traversed in 0-180°, so that the fuel consumption is at a minimum value, and when the orbit period is above 90% of the target orbit period, the time when the semi-major axis reaches the target semi-major axis is controlled.

3. The method of claim 2, wherein the method is a combined method of continuous low thrust based station keeping and station capture. The control method for the time when the semi-major axis reaches the target semi-major axis is as follows: the thrust size is calibrated according to the change trend of the semi-major axis and the inclination in each orbit period, the target spot longitude is obtained by numerical integration using the calibrated thrust, and by lengthening or shortening the ΔM value, the satellite is located at the spot position with a high precision when the semi-major axis reaches the target semi-major axis.

4. The method of claim 1, wherein the method is a combined method of continuous low-impulse based spot capture. The eccentricity is eliminated by the in-plane thrust component being perpendicular to the perigee direction, the inclination is reduced by the out-of-plane component firing in the normal direction of the orbit, and the specific method is as follows: The small thrust is continuously fired in one orbit period, the in-plane thrust component has an angle of -90° with the perigee vector direction in the orbit plane, the out-of-plane component has an angle ψ2 with the orbit plane, the absolute value is unchanged, and at the amplitude angles of 90° and 270°, the positive and negative are changed; The orbit amplitude angles 90°±Δu1 region and the orbit amplitude angles 270°±Δu2 region are set to stop firing and reduce the fuel consumption; In each orbit period, the out-of-plane component is updated by traversing at ±90°, so that the fuel consumption is at a minimum value.

5. The method of claim 4, wherein the method is a combined method of continuous low-impulse based spot capture. When the satellite is in a transfer orbit and the semi-major axis, inclination and eccentricity are not in place, semi-major axis, inclination and eccentricity are jointly controlled and combined with the adjustment of the mean longitude, the semi-major axis is increased by the in-plane thrust component firing in the tangential direction of the orbit, the inclination is reduced by the out-of-plane component firing in the normal direction of the orbit, and the eccentricity is eliminated by stopping firing in the perigee region, and the longitude of the satellite is controlled to drift eastward by controlling the time when the semi-major axis reaches the target semi-major axis, so that the semi-major axis is in a spot longitude position when reaching the synchronous orbit. The adjustment method for the combined control of the semi-major axis, inclination and eccentricity and the adjustment of the mean longitude is as follows: The small thrust is continuously fired in one orbit period, the thrust in the plane formed by the velocity direction and the angular momentum of the orbit has an angle ψ1 with the orbit plane, the absolute value is unchanged, but at the amplitude angles of 90° and 270°, the positive and negative are changed, the mean anomaly 0°±ΔM is set to stop firing, and in each orbit period, ψ1 is traversed at ±90° and ΔM is traversed in 0-180°, so that the fuel consumption is at a minimum value, and when the orbit period is above 90% of the target orbit period, the time when the semi-major axis reaches the target semi-major axis is controlled. The control method for the time when the semi-major axis reaches the target semi-major axis is as follows: the thrust size is calibrated according to the change trend of the semi-major axis and the inclination in each orbit period, the target spot longitude is obtained by numerical integration using the calibrated thrust, and by lengthening or shortening the ΔM value, the satellite is located at the spot position with a high precision when the semi-major axis reaches the target semi-major axis. The eccentricity is eliminated by the in-plane thrust component being perpendicular to the perigee direction, the inclination is reduced by the out-of-plane component firing in the normal direction of the orbit, and the specific method is as follows: The small thrust is continuously fired in one orbit period, the in-plane thrust component has an angle of -90° with the perigee vector direction in the orbit plane, the out-of-plane component has an angle ψ2 with the orbit plane, the absolute value is unchanged, and at the amplitude angles of 90° and 270°, the positive and negative are changed; The orbit amplitude angles 90°±Δu1 region and the orbit amplitude angles 270°±Δu2 region are set to stop firing and reduce the fuel consumption; In each orbit period, the out-of-plane component is updated by traversing at ±90°, so that the fuel consumption is at a minimum value. When the satellite is in a transfer orbit and the semi-major axis, inclination and eccentricity are not in place, semi-major axis, inclination and eccentricity are jointly controlled and combined with the adjustment of the mean longitude, the semi-major axis is increased by the in-plane thrust component firing in the tangential direction of the orbit, the inclination is reduced by the out-of-plane component firing in the normal direction of the orbit, and the eccentricity is eliminated by stopping firing in the perigee region, and the longitude of the satellite is controlled to drift eastward by controlling the time when the semi-major axis reaches the target semi-major axis, so that the semi-major axis is in a spot longitude position when reaching the synchronous orbit. If the orbit argument u = 90° is closer to the perigee: when the drift rate increases, set Δu1 > Δu2; when the drift rate decreases, set Δu1 < Δu2; If the orbit argument u = 270° is closer to the perigee: when the drift rate increases, set Δu1 < Δu2; when the drift rate decreases, set Δu1 > Δu2; When the drift rate enables the satellite to reach the station-keeping position at the end of the station-keeping acquisition, set Δu1 = Δu2.

6. The method of claim 1, wherein the method is a combined method of continuous low-impulse based spot capture. After the semi-major axis, inclination and eccentricity of the satellite are all in place, perform station-keeping acquisition by firing twice in the tangential direction of the orbit, specifically including: After receiving the station-keeping acquisition instruction, first perform satellite orbit determination to obtain the latest mean longitude and mean longitude drift rate of the satellite, then adjust the thrust to the start pointing, perform start firing, and the duration is T1; After the ignition of the T1 section is over, the star drift phase with stopped ignition is entered, and the star drift time T draft ; After the drift is completed, adjust the thrust to the braking pointing, perform braking firing, and the duration is T2; After the braking firing is completed, the satellite reaches the target mean longitude, and the drift rate is 0.

7. The method according to claim 6, wherein, If the satellite performs an end-of-life deorbit mission, only start firing, and after the T1 segment firing is completed, it is considered that the acquisition is completed.

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