A satellite electric propulsion system and angular momentum unloading method

Abstract

The present invention provides a satellite electric propulsion system, including: electric thrusters, the number of which is four, each of which is installed on the satellite back floor through a dual-axis vector adjustment mechanism, and its thrust direction points to the center of mass of the satellite, wherein: two electric thrusters are arranged on each side of the satellite back floor, symmetrically installed relative to a center line of the satellite back floor; the two electric thrusters on the same side are symmetrically installed relative to another center line of the satellite back floor; the satellite back floor is rectangular. The angular momentum unloading method, used for the above-mentioned satellite electric propulsion system, includes: initializing the dual-axis vector adjustment mechanism and angular momentum unloading. This scheme can complete the angular momentum unloading of the momentum wheel while the electric propulsion performs position holding, and improve the efficiency of the use of propellant, which can meet the on-orbit angular momentum unloading requirements of GEO satellites. This patent is applicable to geosynchronous orbit satellites that use electric thrusters for angular momentum unloading.

Description

Technical Field

[0001] The present invention relates to an on-orbit angular momentum unloading technology for a geostationary orbit satellite, and in particular to a satellite electric propulsion system and an angular momentum unloading method. Background Art

[0002] During the on-orbit operation phase, geostationary orbit (GEO) satellites are affected by the disturbance torque of solar radiation pressure, which causes the angular momentum of the momentum wheel to accumulate. When the accumulated angular momentum exceeds the nominal angular momentum of the momentum wheel, a control torque needs to be applied to unload the angular momentum of the momentum wheel.

[0003] GEO satellites generally use chemical thrusters to provide the control torque required for unloading the angular momentum of the momentum wheel. With the rapid development of electric propulsion technology in space applications, electric thrusters can be used to complete the angular momentum unloading of the momentum wheel.

[0004] The thrust of chemical thrusters is relatively large, generally reaching 10N. The distance from the satellite's center of mass to the thrust application point is generally more than 1m. Therefore, the control torque provided by chemical thrusters can generally reach more than 10Nm. Only short pulse ignition is required to unload the momentum wheel angular momentum. The thrust of electric thrusters is relatively small, generally less than 100mN. Since electric thrusters are mainly used to maintain the position of satellites, their thrust direction generally points to the satellite's center of mass position. The thrust direction of the electric thrusters can be adjusted by the vector adjustment mechanism, but the adjustment angle is generally small. The distance from the satellite's center of mass to the thrust application point is small, resulting in a very small control torque generated by the electric thrusters. Unloading the momentum wheel angular momentum requires the electric thrusters to work for a long time. Therefore, the method of achieving angular momentum unloading by electric propulsion is different from the method using chemical thrusters.

[0005] Although most GEO satellites already use electric thrusters for north-south position maintenance, chemical thrusters are mainly used for angular momentum unloading of momentum wheels, such as the A2100 platform, E3000 platform, and SpaceBus4000 platform.

[0006] However, chemical propulsion systems have low specific impulse and low propellant efficiency. Summary of the invention

[0007] 1. Purpose:

[0008] In order to improve the propellant usage efficiency of GEO satellites equipped with electric propulsion for on-orbit angular momentum unloading, electric thrusters are needed to replace traditional chemical thrusters to complete the on-orbit angular momentum unloading of GEO satellites.

[0009] This patent proposes a satellite electric propulsion system and angular momentum unloading method, which can complete the angular momentum unloading of the momentum wheel while performing position holding by electric propulsion, and improve the efficiency of propellant use, which can meet the on-orbit angular momentum unloading requirements of GEO satellites. This patent is applicable to geosynchronous orbit satellites that use electric thrusters for angular momentum unloading.

[0010] 2. Technical solution:

[0011] The technical solution of the present invention is:

[0012] The present invention provides a satellite electric propulsion system, comprising:

[0013] There are four electric thrusters, each of which is installed on the back floor of the satellite through a dual-axis vector adjustment mechanism, and its thrust direction points to the center of mass of the satellite, wherein:

[0014] A rectangular area is defined on the satellite back floor. The geometric center of the rectangle is located at the intersection of the projection of the satellite's center of mass on the back floor. The four sides of the rectangle are perpendicular to the satellite's X-axis and Y-axis respectively. Four electric thrusters are symmetrically installed at the four vertices of the rectangle.

[0015] The dual-axis vector adjustment mechanism can point the thrust direction of the electric thruster toward the center of mass of the satellite. At this time, each electric thruster can generate thrust in the north-south and east-west directions at the same time.

[0016] Furthermore, there is a certain distance between the two electric thrusters on the same side.

[0017] The present invention provides an angular momentum unloading method for the above-mentioned satellite electric propulsion system, comprising:

[0018] Initialize the dual-axis vector adjustment mechanism, first rotate the vector adjustment mechanism around the pitch axis by an angle of θ, then rotate around the roll axis of the vector adjustment mechanism When the thrust direction of the electric thruster points to the satellite mass center, the corresponding θ0 and

[0019] Angular momentum unloading is carried out simultaneously with electric propulsion position maintenance, and each electric propulsion angular momentum unloading only unloads the angular momentum in a single axis direction, and two electric thrusters work in pair to avoid interfering with the angular momentum of other axes.

[0020] Furthermore, the ignition duration of the electric thruster is determined by the electric propulsion position keeping requirement, and the pointing direction of the electric thruster is calculated based on the angular momentum unloading value required by the control system, and the pointing direction is adjusted by a dual-axis vector adjustment mechanism.

[0021] Furthermore, in the angular momentum unloading step, the method of unloading the X-axis angular momentum is: controlling Δθ to 0, by adjusting the appropriate The required rolling control torque is generated by the angle, and the additional yaw control torque generated is eliminated by pairing two electric thrusters. The actual rotation angle is compared with θ0 and Angle of deviation.

[0022] Furthermore, in the angular momentum unloading step, the method of unloading the Y-axis angular momentum is: The control is 0, and the required pitch control torque is generated by adjusting the appropriate Δθ angle. The additional rolling and yaw interference torques are eliminated by pairing the two electric thrusters. The actual rotation angle is compared with θ0 and Angle of deviation.

[0023] Furthermore, in the angular momentum unloading step, the method of unloading the Z-axis angular momentum is: The control is 0, and the required yaw control torque is generated by adjusting the appropriate Δθ angle, and the additional rolling and pitch control torques generated are eliminated by pairing the two electric thrusters. Among them, Δθ, The actual rotation angle is compared with θ0 and Angle of deviation.

[0024] 3. Effect

[0025] This method adjusts the thrust direction of the electric thruster through a vector adjustment mechanism before the electric thruster performs east-west and north-south position keeping control, so that during the ignition of the electric thruster, not only the thrust required for position keeping is generated, but also the control torque required for momentum wheel unloading is generated, thereby improving the use efficiency of propellant and meeting the on-orbit angular momentum unloading requirements of GEO satellites. This optimization strategy has the following advantages:

[0026] 1) Electric propulsion is used to unload the angular momentum of GEO satellites. The thrust generated during the unloading process is small, which has little impact on the attitude of the entire satellite and is beneficial to avoid exciting the vibration of large flexible accessories carried by GEO mobile communication satellites.

[0027] 2) Electric propulsion is used to unload the angular momentum of GEO satellites. Since the specific impulse of electric propulsion is much higher than that of traditional chemical thrusters, it greatly reduces the consumption of propellant and is beneficial to extending the service life of GEO satellites.

[0028] 3) In the process of electric propulsion position maintenance, electric propulsion is simultaneously used to complete angular momentum unloading, avoiding the need to arrange additional electric propulsion ignition positions for angular momentum unloading, simplifying the on-orbit working procedures of electric propulsion, and facilitating project implementation.

[0029] For both the normal operation of the electric thruster and the failure of a single electric thruster, the method can achieve angular momentum unloading of the electric thruster. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the definition of a geostationary orbit satellite coordinate system in an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of thrust direction adjustment of an electric thruster in an embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of the layout of the electric thruster of the geostationary orbit satellite in an embodiment of the present invention;

[0033] Figure 4 is an angular momentum variation curve without angular momentum unloading in an embodiment of the present invention;

[0034] Figure 5 is an angular momentum variation curve for angular momentum unloading in an embodiment of the present invention;

[0035] Figure 6 is a curve of external torque variation for angular momentum unloading in an embodiment of the present invention;

[0036] Figure 7 is an angular momentum variation curve without angular momentum unloading in an embodiment of the present invention;

[0037] Figure 8 is an angular momentum variation curve without angular momentum unloading in an embodiment of the present invention;

[0038] Fig. 9 This is a curve of angular momentum change during angular momentum unloading in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be fully described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0041] The specific impulse of chemical thrusters is relatively low, generally around 300s; the specific impulse of electric thrusters is relatively high, generally around 3000s. Therefore, the specific impulse of electric thrusters is more than 10 times that of chemical thrusters. The fuel efficiency of electric thrusters in achieving angular momentum unloading is greatly improved, which is conducive to further improving the payload carrying capacity of satellites.

[0042] The present invention proposes a method for angular momentum unloading using an electric thruster, which can complete the angular momentum unloading of the momentum wheel while maintaining the position by electric propulsion, and improve the efficiency of propellant use, thereby meeting the on-orbit angular momentum unloading requirements of GEO satellites.

[0043] First, some coordinate systems and calculation formulas required for the present invention are given.

[0044] For the convenience of description, it is necessary to establish a satellite mechanical coordinate system, which is defined as follows: the coordinate origin O is located in the mechanical separation plane between the lower end frame of the satellite and the launch vehicle, and coincides with the theoretical center of the docking ring interface; the OX axis (roll axis) passes through the origin O, is parallel to the theoretical normal direction of the satellite's east plate, and its positive direction is consistent with the outer normal direction of the east plate; the OZ axis (yaw axis) passes through the origin O, is parallel to the satellite axis, and its positive direction points to the ground; the OY axis (pitch axis) forms a right-handed rectangular coordinate system with the OX and OY axes, and its positive direction is consistent with the outer normal direction of the south plate. The payload module is located on top of the propulsion service module, see Figure 1 .

[0045] The electric thruster is fixed on the vector adjustment mechanism. The installation coordinate system of the electric thruster is defined as follows: the coordinate origin is located at the intersection of the rotation axis of the vector adjustment mechanism. When the roll axis and pitch axis rotation angles of the vector adjustment mechanism are both 0 degrees, the +Y axis (pitch axis) of the vector adjustment mechanism is consistent with the +Y axis direction of the satellite mechanical coordinate system, the +X axis (roll axis) of the vector adjustment mechanism is consistent with the +X axis direction of the satellite mechanical coordinate system, and the +Z axis of the vector adjustment mechanism is consistent with the +Z axis direction of the satellite mechanical coordinate system. The thrust direction of the electric thruster passes through the coordinate origin of the vector adjustment mechanism and is always consistent with the +Z axis direction of the vector adjustment mechanism, see Figure 2 .

[0046] The process of adjusting the thrust direction of the electric thruster by the vector adjustment mechanism is as follows: first rotate the pitch axis of the vector adjustment mechanism by an angle of θ, then rotate the roll axis of the vector adjustment mechanism by an angle of θ. When the thrust direction of the electric thruster points to the satellite mass center, the corresponding θ0 and To generate the control torque, the actual vector control mechanism rotates θ and The difference between the two is Δθ = θ-θ0 and

[0047] The specific implementation process of the present invention is as follows:

[0048] (1) Electric thruster layout: 4 electric thrusters are used

[0049]

[0050] Where L0 is the distance from the origin of the vector control mechanism coordinate system to the satellite mass center, F0 is the output thrust of a single electric thruster, It is the control torque generated by a single electric thruster.

[0051] (2) Electric thrust unloading X-axis angular momentum strategy: Electric thrust unloading and electric thrust position maintenance are performed simultaneously. The ignition duration of the electric thruster is determined by the electric thrust position maintenance. Control Δθ to 0 and adjust the appropriate The required rolling control torque is generated by the angle, and the additional yaw control torque generated is eliminated by pairing two electric thrusters. When all four electric thrusters can work normally, the thrusters that can be paired are WN+EN, WN+ES, WS+EN, and WS+ES. For the failure of a single electric thruster: when WN fails, select WS+EN or WS+ES; when EN fails, select WN+ES and WS+ES; when WS fails, select WN+EN and WN+ES; when ES fails, select WN+EN and WS+EN.

[0052] (3) Electric thrust unloading Y-axis angular momentum strategy: Electric thrust unloading and electric thrust position maintenance are performed simultaneously, and the ignition duration of the electric thruster is determined by the electric thrust position maintenance. Control is 0, and the required pitch control torque is generated by adjusting the appropriate Δθ angle, and the additional rolling and yaw interference torques are eliminated by pairing the two electric thrusters. When all four electric thrusters can work normally, the thrusters that can be paired are WN+WS, WN+ES, WS+EN, and EN+ES. For the failure of a single electric thruster: when WN fails, select WS+EN or EN+ES; when EN fails, select WN+ES and WN+ES; when WS fails, select WN+ES and EN+ES; when ES fails, select WN+WS and WS+EN.

[0053] (4) Electric thrust unloading Z-axis angular momentum strategy: Electric thrust unloading and electric thrust position maintenance are performed simultaneously, and the ignition duration of the electric thruster is determined by the electric thrust position maintenance. Control is 0, and the required yaw control torque is generated by adjusting the appropriate Δθ angle, and the additional roll and pitch control torques generated are eliminated by pairing the two electric thrusters. When all four electric thrusters can work normally, the thrusters that can be paired are WN+WS, WN+ES, WS+EN, and EN+ES. For the failure of a single electric thruster: when WN fails, select WS+EN or EN+ES; when EN fails, select WN+WS and WN+ES; when WS fails, select WN+ES and EN+ES; when ES fails, select WN+WS and WS+EN.

[0054] In a specific embodiment, it is assumed that a GEO satellite is equipped with four electric thrusters, each of which is controlled by a thrust vector control mechanism. The indicators of a single electric thruster are: thrust 80mN, specific impulse 3800s. The installation positions of the electric thrusters are: ES electric thruster is (500,1500,0)mm, EN electric thruster is (500,-1500,0)mm, WS electric thruster is (-500,1500,0)mm, and WN electric thruster is (-500,-1500,0)mm. The satellite center of mass height is 2000mm.

[0055] (1) X-axis angular momentum unloading

[0056] Consider unloading the angular momentum of the X-axis for 5 days, using the WN electric thruster at the ascending node and the ES electric thruster at the descending node. The angular momentum unloading and electric thrust position maintenance are carried out simultaneously. Adjust is -0.3 degrees, then the angular momentum change curves without angular momentum unloading and angular momentum unloading are as follows: Figure 4 and Figure 5 Before unloading, the X-axis angular momentum accumulation reaches 30Nms; after unloading, the Y-axis angular momentum accumulation is controlled within 20Nms.

[0057] (2) Y-axis angular momentum unloading

[0058] Consider unloading the angular momentum of the Y axis for 5 days, using the WN electric thruster at the ascending node and the ES electric thruster at the descending node. The angular momentum unloading and electric thruster position retention are performed simultaneously. Adjust Δθ to -0.46 degrees. The angular momentum change curves without angular momentum unloading and angular momentum unloading are as follows: Figure 6 and Figure 7 Before unloading, the Y-axis angular momentum accumulation reaches 80Nms; after unloading, the Y-axis angular momentum accumulation is controlled within 22Nms.

[0059] (3) Z-axis angular momentum unloading

[0060] Consider unloading the Z-axis angular momentum for 5 days, using WN electric thrusters at the ascending node and ES electric thrusters at the descending node. Angular momentum unloading and electric thrusting are performed simultaneously. Adjust Δθ to -0.65 degrees. The angular momentum change curves without angular momentum unloading and angular momentum unloading are as follows: Figure 8 and Fig. 9 Before unloading, the accumulated angular momentum of the Z axis reaches 12Nms; after unloading, the accumulated angular momentum of the Z axis is controlled within 1Nms.

[0061] In the description of this specification, reference to the terms "one embodiment" and "example" means that the specific features, structures or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the combination in a suitable manner in the relative embodiment or example.

[0062] It must be pointed out that the description of the above embodiments is not intended to be limiting but only to help understand the core idea of ​​the present invention. For ordinary technicians in this technical field, any improvements to the present invention and alternatives equivalent to the product, without departing from the principles of the present invention, also fall within the scope of protection of the claims of the present invention.

Claims

1. An angular momentum unloading method, characterized in that: For use in a satellite electric propulsion system, the system comprising: There are four electric thrusters, each of which is installed on the back floor of the satellite through a dual-axis vector adjustment mechanism, and its thrust direction points to the center of mass of the satellite, wherein: A rectangular area is defined on the back floor of the satellite, the geometric center of the rectangle is located at the intersection of the projection of the satellite's centroid on the back floor, the four sides of the rectangle are perpendicular to the satellite's X-axis and Y-axis respectively, and the four electric thrusters are symmetrically installed at the four vertices of the rectangle; there is a certain distance between the two electric thrusters on the same side; The method includes: Initialize the dual-axis vector adjustment mechanism, first rotate the vector adjustment mechanism around the pitch axis by an angle of θ, then rotate around the roll axis of the vector adjustment mechanism When the thrust direction of the electric thruster points to the satellite mass center, the corresponding angle is θ0 and Angular momentum unloading is carried out simultaneously with the electric propulsion position keeping, and each electric propulsion angular momentum unloading is only for the angular momentum of a single axis, and two electric thrusters are paired to work to avoid interfering with the angular momentum of other axes; The ignition duration of the electric thruster is determined by the electric propulsion position keeping requirement, and the pointing direction of the electric thruster is calculated based on the angular momentum unloading value required by the control system, and the pointing direction is adjusted by a dual-axis vector adjustment mechanism; In the angular momentum unloading step, the method of unloading the X-axis angular momentum is to control Δθ to 0 and adjust the appropriate The required rolling control torque is generated by the angle, and the additional yaw control torque generated is eliminated by pairing two electric thrusters. The actual rotation angle is compared with θ0 and Angle of deviation; In the angular momentum unloading step, the method of unloading the Y-axis angular momentum is: The control is 0, and the required pitch control torque is generated by adjusting the appropriate Δθ angle. The additional rolling and yaw interference torques are eliminated by pairing the two electric thrusters. The actual rotation angle is compared with θ0 and Angle of deviation; In the angular momentum unloading step, the method of unloading the Z-axis angular momentum is: The control is 0, and the required yaw control torque is generated by adjusting the appropriate Δθ angle, and the additional rolling and pitch control torques generated are eliminated by pairing the two electric thrusters. Among them, Δθ, The actual rotation angle is compared with θ0 and Angle of deviation.

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