JP2008302808A - Orbit control programming device for spacecraft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrict orbit control quantity and control frequency to low levels, and limit the value of an orbit parameter within a tolerable range even during an orbit control prohibited period. <P>SOLUTION: The device is provided with a target range setting part to set the lower limit and the upper limit of a target value, a holding period setting part to set a holding period to limit the value of the orbit parameters within a tolerable range, a control prohibited period setting part to set a period in which orbit control is prohibited, an orbit error prediction part to predict orbit error in the holding period and the control prohibited period, an index determination part to determine the value of an index composed of control quantity or control quantity and orbit error, and a control quantity determination part to determine such control quantity as to minimize the value of index computed by the index determination part among such control quantities that total of the predicted orbit error and current orbit parameter is held within the target range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an orbit control planning apparatus for a spacecraft such as an artificial satellite orbiting around a central celestial body.

  The orbit of spacecraft such as artificial satellites deviates from the ideal orbit by receiving disturbances such as the flatness of the central celestial body and attractive forces from other celestial bodies. For this reason, trajectory holding control for correcting this error and holding the trajectory is required.

  In general, the orbit of a satellite is represented by a plurality of orbit parameters. For example, deviations from the ideal orbit of geostationary satellites are usually expressed as orbital parameters in the north-south and east-west directions, and in order to keep these within the allowable range, the north-south and east-west directions are maintained. It is necessary to perform control periodically.

  Also, the deviation of the earth observation satellite from the ideal orbit is usually expressed as the orbital parameters of the longitude and inclination of the descending point where the satellite's direct locus follows the equator from north to south. In order to keep these within the allowable range, it is necessary to periodically control the orbit period and the orbit inclination angle.

As described above, in order to maintain the orbit of the satellite, it is necessary to perform control so that the error from the ideal value of the orbit parameter remains within a certain range. The processing required for this control is
(1) Processing to obtain current trajectory parameters,
(2) A process of setting a trajectory cycle for control,
(3) A process for determining a target value of a trajectory parameter realized after control,
(4) a process for calculating a control amount and a control time to be changed from the current trajectory parameter to the target trajectory parameter;
(5) It can be divided into processing for calculating the operating conditions of the thrusters mounted on the artificial satellite.

  The devices that perform the processing from (1) to (5) are collectively referred to as the trajectory control device, but the trajectory control planning device that performs the processing from (1) to (4), and the trajectory control execution device that performs the processing of (5). I will call it separately as follows. Some or all of the orbit control execution device and the orbit control planning device are installed in an artificial satellite or a ground station, respectively.

  The processing of (1) is easy to obtain on-board current orbital parameters by installing a GPS receiver on an artificial satellite if it is a low or medium altitude orbit around the earth. In the orbit of the celestial body, it is possible to transmit the orbit determination value at the ground station to the artificial satellite and propagate the orbit on board, and in either case, it can be realized by a known technique.

  In the case of an artificial satellite that is operated based on an observation plan, such as the Earth observation satellite, the processing of (2) follows a predetermined period of orbit maintenance control. In the case of other artificial satellites, a method is generally used in which an error tolerance is set for each orbit parameter, and when the error exceeds the tolerance, orbit control is performed in the immediately preceding orbital period.

  The process (3) is a simple method in which the target value of the trajectory parameter is matched with the ideal value so that the trajectory is returned to the ideal trajectory after the trajectory control.

  For the process (4), for example, when the controllable time is not fixed, for example, the technique described in Patent Document 1 can be used. Further, when the controllable time is fixed, for example, the method described in Patent Document 2 can be used.

  Moreover, the process of patent document 3 can also be used for the process of (5).

  However, when the control amount for maintaining the orbit is increased, a limited amount of propellant is consumed to reduce the mission life of the satellite. Therefore, it is important to keep the control amount as small as possible. Also, considering the impact on the mission of the satellite and the operational load, it is not desirable to perform orbit control frequently, and it is necessary to keep the control frequency as low as possible throughout the mission period.

  As an example of a technique for reducing the control amount and control frequency in the orbit maintenance control of an artificial satellite, the conventional orbit control device disclosed in Patent Document 2 has an error tolerance value or less given in advance for each orbit parameter. Arbitrary values are set as control necessity thresholds, and when there are trajectory parameters whose error exceeds the allowable value, the trajectory control amount and trajectory control time are calculated for the trajectory parameters whose error exceeds the threshold, and the trajectory is calculated. Take control.

  Further, as an example of a technique for fixing the control frequency in the orbit maintenance control of the artificial satellite and reducing the control amount, the conventional orbit control planning device disclosed in Patent Document 4 fixes the control cycle and controls each control. A temporary target value is set based on an expression that approximates the effect of the disturbance that occurs until the next control cycle at the time. The trajectory prediction simulation is performed using the provisional target value as an initial value to predict the trajectory parameter in the next control cycle, and adjustment of the provisional target value is repeated until the deviation from the ideal trajectory parameter falls within the allowable value. After falling within the allowable value, the trajectory control amount and trajectory control time for realizing the target value are calculated and trajectory control is performed.

JP 11-139400 A JP 2006-213089 A JP-A-62-59200 JP 2003-212200 A

  However, in the trajectory control planning apparatus as in Patent Document 2, since the target value is fixed to an ideal value, for example, the difference from the ideal value with time is reduced due to the influence of disturbance. Even in this case, there is a problem that the control is performed so that the current trajectory parameter value is reduced to an ideal value, and as a result, the control amount increases.

  In addition, there may be a period during which orbit control cannot be performed. When there is such a control prohibition period, there is no means to determine in advance whether or not the value of the trajectory parameter is within the allowable range, so the trajectory parameter cannot be used during trajectory control. There is also a problem that the value of may deviate from the allowable range.

  Further, in the trajectory control planning apparatus as in Patent Document 4, since the trajectory error after the control cycle is predicted using the temporary target value as the initial value and the adjustment of the target value is repeated until it falls within the allowable range, In addition to the possibility that a large amount of control may be required to realize the set target value, there are a large number of trajectory parameters that need to be within an allowable range (two in the description of Patent Document 4). Adjustment itself becomes difficult.

  Furthermore, when there is a period during which the trajectory control cannot be performed, and in the case of no control, the trajectory control can be performed even when the trajectory parameter value is predicted to deviate from the allowable range during the period. There is also a problem that the trajectory control cannot be planned by shifting the control time within the possible period.

  The present invention has been made to solve the above-described problems. The track control amount and the control frequency are suppressed to be small, and the track parameter value is kept within an allowable range even during the track control prohibition period. The purpose is to obtain a spacecraft orbit control planning device that can do this.

  The spacecraft orbit control planning apparatus according to the present invention includes a target area setting unit that sets a lower limit and an upper limit of a target value, a holding period setting unit that sets a holding period that keeps the value of the orbit parameter within an allowable range, A control prohibition period setting unit for setting a control prohibition period for prohibiting the trajectory control, a trajectory error prediction unit for predicting a trajectory error in the holding period and the control prohibition period, and a value of an index composed of a control amount are calculated. An index calculation unit, and a control amount that minimizes the value of the index calculated by the index calculation unit among the control amounts such that the sum of the predicted trajectory error and the current trajectory parameter is held in the target region And a control amount calculation unit for calculating.

  According to the present invention, the index value calculated by the index calculation unit is minimized among the control amounts such that the sum of the trajectory error predicted during the holding period and the control prohibition period and the current trajectory parameter is held in the target region. The amount of control that can be converted into a constant is calculated, so that the amount of track control and the frequency of track control can be kept small, and the value of the track parameter can be kept within the allowable range even during the track control prohibition period. This is a remarkable effect that has never been seen before.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of the orbit control planning apparatus for a spacecraft according to Embodiment 1 of the present invention. As shown in the figure, the orbit control planning apparatus 100 of the artificial satellite 200 as a spacecraft has a target area setting unit 101 for setting a lower limit and an upper limit of a target value, and a holding period for keeping orbit parameter values within an allowable range. A holding period setting unit 102 for setting, a trajectory error prediction unit 103 for predicting a trajectory error in the holding period and a control prohibiting period to be described later, a control prohibiting period setting unit 104 for setting a control prohibiting period for prohibiting trajectory control, Of the control amounts such that the sum of the trajectory error and the current trajectory parameter is held in the target region, the control amount calculation unit 105 calculates a control amount that minimizes the index value calculated by the index calculation unit described later. And an index calculation unit 106 for calculating an index value composed of a control amount, a trajectory error, and the like. In FIG. 1, reference numeral 110 denotes an orbit control execution device 110, which is composed of a thruster 111. The thruster 111 gives propulsive force to the artificial satellite 200 according to the supplied control time and control amount and executes orbit control. To do.

  In the first embodiment, in order to facilitate understanding of the present invention, the trajectory control is planned in units of trajectory periods, and the trajectory control time is set in advance in one orbital period. Further, as a general assumption in the design of a satellite orbit control system, it is assumed that the total number of control axes that can be controlled at each control time is equal to or greater than the number of orbit parameters to be controlled.

  The orbit of the artificial satellite 200 is expressed by using six orbit parameters including an orbital length radius a, an eccentricity e, an orbit inclination angle i, an ascending intersection red longitude Ω, a near point argument ω, and an average near point separation angle M at the time of epoch. . A trajectory parameter vector b composed of these six trajectory parameters is defined by equation (1). The superscript T on the right shoulder represents the transpose of the vector.

  Other trajectory parameters may be used.

Next, the operation will be described. The target area setting unit 101 sets an allowable upper limit and a lower limit for each trajectory parameter. Orbital parameter vectors b _U and b _L composed of upper and lower limits are defined by Equation (2). The lower right subscripts U and L represent the upper and lower limits, respectively.

  For example, when the elevation angle of a satellite viewed from a plurality of cities in Japan is required to be greater than a certain value such as a quasi-zenith satellite, the upper and lower limits are determined for all six orbit parameters. On the other hand, when it is required that the satellite direction seen from the ground is within the range of north-south and east-west like a geostationary satellite, the upper limit and the lower limit are determined for two or three orbit parameters.

  In addition, when a satellite is required to be seen in the same direction at the same time every day like a GPS satellite, an upper limit and a lower limit are determined for one orbit parameter. When the upper and lower limits are not determined for some of the trajectory parameters as described above, values that are far from the ideal values may be set. At this time, the target region is defined as a trajectory parameter vector b that satisfies inequality (3).

  The retention period setting unit 102 sets a retention period. The holding period is a request for each trajectory parameter to fall within the target area during the holding period without further control during the holding period. For observation satellites that have an orbit control period determined from the operation plan, it may be possible to set the orbit control period as the retention period. For artificial satellites that require a low control frequency, such as GPS satellites and quasi-zenith satellites, the reciprocal of the frequency less than the average expected control frequency can be set as the holding period. It is conceivable to make the control frequency less than the value.

  The control prohibition period setting unit 104 predicts in advance a period during which it is not desirable or difficult to perform orbit control at the request of a mission, a bus, or the like, using the current orbit parameter value. In the case of a certain satellite, when the angle between the orbital plane and the sun direction (β angle) is large, it is pointed out that taking an earth-oriented attitude for orbit control is not preferable from the viewpoint of securing power and thermal control. Yes. The time when the β angle increases can be easily predicted from the current orbital parameters and the solar ephemeris, and such a period is set as the control prohibition period.

  In the orbit error prediction unit 103, for a period including the holding period and the control prohibition period, the current orbit parameter value is used as an initial value, and future orbital deviation due to the lunar or solar attraction, atmospheric resistance, solar radiation, etc. Use to predict. In order to predict a future trajectory shift, ideal trajectory parameter values may be used. In this way, the deviation of the trajectory parameter after the elapsed time t is given as the vector Δb (t).

The operation of the control amount calculation unit 105 will be described with reference to FIG. FIG. 2 is a flowchart of the operation of the control amount calculation unit 105 according to the first embodiment. In step ST 101, in addition to the deviation of the trajectory parameters of the elapsed time t to the value b ₀ of the current orbital parameters △ b (t), the trajectory parameters after elapse time when not controlled t b _{0 +} △ b ( t).

In step ST102, the current trajectory deviation b ₀ is compared with a target area with a margin m ₁ (0 ≦ m ₁ ≦ 1). Here, the target area b with the margin m ₁ is defined by Expression (4). In equation (4), b _IDEAL is an ideal trajectory parameter.

For example, 0.10 is set as the value of the margin m ₁ . Determining required maneuver if even one element of trajectory parameters does not fit within the target region of the margin m ₁ with the proceeds to step ST 104. Otherwise, the process proceeds to step ST103.

In step ST103, the time until the start of the track control prohibited section is compared with a predetermined time. If the time is shorter than the predetermined time, the predicted value of the track parameter in the track control prohibited section and the margin m ₂ (0 ≦ m ₂ ≦ 1) Compare with the target area marked. Determining required maneuver if even one fit elements not within the target area of the margin m ₂ with is, the process proceeds to step ST 104. In other cases, the trajectory control is unnecessary and this process is terminated. For example, 0.10 is set as the value of the margin m ₂ .

  Steps ST104 to ST109 perform a series of processes for calculating the trajectory control amount. In step ST104, an initial value of the holding period T is set. For example, a reciprocal with a frequency less than the control frequency expected on average is set.

In step ST105, a target area with a margin m ₃ (0 ≦ m ₃ ≦ 1) is set as a range for holding the trajectory parameter in the holding period T. For example, 0.45 is set as the initial value of the margin m ₃ .

In step ST106, a matrix E and vectors f and h necessary for calculating the trajectory control amount are prepared. The contents of preparation are as follows.
When the trajectory parameter is selected as in the formula (1), the trajectory parameter change amount δb ₀ by the trajectory control is defined by the formula (5).

The change amount of the trajectory parameter by the trajectory control is very small, and the control is performed by adding this change amount to the trajectory parameter b ₀ + Δb (t) after the elapsed time t when the control obtained previously is not performed. In this case, the trajectory parameters after the elapsed time t can be obtained. However, since the orbital period becomes longer as the orbital length radius a becomes longer, the influence that the average near point separation angle is delayed with time cannot be ignored. Calculate in 6).

In equation (6), n ₀ is the average motion of the artificial satellite 200.

  If the trajectory parameters in Equation (1) are taken, the control amount and the change in the trajectory parameters are linearly related, and the calculation method is known (for example, Nobuyuki Hamada: Introduction to Space Systems, Chapter 10). , See University of Tokyo Press (1993)). That is, when the control amount is a vector x, there is a relationship of Expression (7), and each element of the matrix A is determined by the trajectory parameter and the control time in the control cycle (or the phase representing the position on the trajectory).

  Here, when the acceleration amount for each machine axis is used as the control amount, the vector x is configured separately in the + direction and the − direction, and the corresponding column vectors of the matrix A are also configured in the + direction and the − direction. However, it can be considered that each component of the vector x is required to be 0 or more. Or when using the injection quantity for every thruster as a control quantity, it cannot be overemphasized that the attachment direction of a thruster is reflected on the matrix A. Also in this case, each component of the vector x is required to be 0 or more.

  What is necessary is just to obtain | require the vector x which satisfy | fills Formula (8) from Formula (4), (6), (7).

  If there is no restriction on the magnitude of the control amount, there are generally innumerable vectors x that satisfy this inequality. Therefore, for example, when the sum of the control amounts x is selected as the index J, and the index calculation unit 106 calculates the value of this index using Equation (9), the optimal vector x in the sense of minimizing the total control amount Exists.

  When the equations (8) and (9) are rearranged as in the equation (10), the vector x can generally be solved using general-purpose software as a linear programming problem with inequality constraints.

When time t is appropriately discretized from 0 to a period T including a holding period and a control prohibition period as t = t ₁ , t ₂ ,..., T _n , (t ₁ = 0, t _n = T), By performing the trajectory control of the control amount x obtained by solving Equation (11), the trajectory parameters are held in the target region from time 0 to T.

  Furthermore, it goes without saying that a restriction on the range of the vector x is added when the component of the vector x is required to be 0 or more, or when there is an upper limit to the thrust that can be generated. Further, for convenience of explanation, the case where the component of the vector x is requested to be 0 or more has been described. However, even when there is no restriction on the sign of the vector x, the expression (10) or the expression It goes without saying that it can be reduced to the form (11).

  In step ST107, the equation (10) or the equation (11) is solved as a linear programming problem with inequality constraints to obtain a vector x. If the range of the vector x is restricted, there may be no solution. In that case, the process proceeds to step ST108. If a solution is obtained, the process proceeds to step ST110.

In step ST 108, close to 0 margin m ₃ at an appropriate step size. For example, 0.05 is used as the step size. If it can no longer approach 0, the process proceeds to step ST109. Otherwise, the process returns to step ST106.

  In step ST109, the holding period T is shortened by an appropriate step size. As the step size, for example, 10 times the orbital period is used. The process returns to step ST105.

  In step ST110, the control amount at each control time is supplied to the trajectory control execution device 110, and this process is terminated.

If the margin m ₁ is set sufficiently larger than the maximum value expected to occur due to natural disturbance or trajectory control error in the trajectory control calculation cycle, the following trajectory control is performed at least during the current trajectory period. Since the trajectory parameters are within the target region even during the trajectory period, the solution of the vector x is always obtained in this processing.

  The trajectory control execution device 110 includes a thruster 111. The thruster 111 applies propulsive force to the artificial satellite 200 according to the supplied control time and control amount, and performs orbit control.

  In this example, the simple sum of the control amounts is selected as the index of the index calculation unit 106, and all the elements of the coefficient vector f in Expression (8) are set to 1, but the elements of the vector f corresponding to a specific control axis are reduced. Alternatively, the control axis can be preferentially used or refrained from being used by increasing it, or the control time can be used preferentially by reducing or increasing the element of the vector f corresponding to a specific control time. It is conceivable to achieve or refrain from use.

  Also, it is divided into in-plane components such as major radius, eccentricity, near-point argument and average near-point separation angle, and out-of-plane components such as orbital inclination angle and ascending intersection red angle, and for each of the equations (10) or The formula (11) is configured, or the formula (10) or the formula (11) is configured only for the trajectory parameters for which the lower limit and the upper limit are set, thereby reducing the number of columns of the matrix E and reducing the computer load. It is possible.

  In addition, the number of rows of the matrix E is reduced by making the step of discretization at time t finer for trajectory parameters having a large time change, and by making the step of discretization at time t coarser for trajectory parameters having a small time change. It may be possible to reduce the computer load.

  Also, in this example, the trajectory control amount was calculated so that each trajectory parameter was within the target area, but design parameters that can be expressed by a linear combination of trajectory parameters, such as latitude argument, ascending intersection longitude, or descending intersection longitude By newly defining and extending the matrix E and the vector h, the newly defined parameters can also be held in the target area during the holding period.

  In this example, the control amount at each control time is supplied to the trajectory control execution device 110 in step 110 and the process is terminated. However, the deviation of the trajectory parameter after the elapsed time t is calculated based on the obtained control amount. It goes without saying that further optimization of the control amount and control frequency can be realized by performing re-prediction and improving the prediction accuracy of the deviation of the trajectory, or by re-executing steps ST101 to ST110 using the prediction result. .

  As described above, according to the first embodiment, the sum of the control amounts is minimized among the control amounts such that the sum of the trajectory error predicted in the holding period and the control prohibition period and the current trajectory parameter is held in the target region. Therefore, the trajectory control amount and the trajectory control frequency can be kept small, and the trajectory parameter value can be kept within the allowable range even during the trajectory control prohibition period.

  In addition, paying attention to the fact that the orbit parameter correction by orbit control is very small and that the phase change accompanying the orbit length radius correction increases in proportion to the orbit length radius correction amount, Since the trajectory parameter after control is expressed by the linear sum of the current trajectory parameter and trajectory control amount, it is not necessary to re-estimate the trajectory error after obtaining the trajectory control amount, and the number of trajectory parameters increases. However, the trajectory control amount can be easily obtained.

  FIG. 3 shows an example of a track maintenance plan according to the first embodiment. The horizontal axis is the elapsed time from the start of the plan and corresponds to three years. The upper row represents the time history of the β angle and the lower row the trajectory length radius. In this example, trajectory control is prohibited when the β angle is 40 degrees or more. In the prior art, the trajectory error deviates from the allowable range during the control prohibition period and the trajectory control is required. However, according to the first embodiment, the trajectory control is performed before the trajectory error is predicted and the trajectory control prohibition period starts. Since the control timing is reset so as to perform the orbit, the trajectory error can be within the allowable range during the control prohibition period.

Embodiment 2. FIG.
FIG. 4 is a block diagram showing the configuration of the orbit control planning apparatus for a spacecraft according to Embodiment 2 of the present invention. In the orbit control planning apparatus 100 for the artificial satellite 200 according to the second embodiment shown in FIG. 4, the control amount calculation unit 106 counts the elapsed time from the previous orbit control with respect to the configuration of the first embodiment shown in FIG. Is further provided with a control period counting unit 107, and the same parts are denoted by the same reference numerals and description thereof is omitted.

  The operation of the control amount calculation unit 106 in the second embodiment will be described with reference to the flowchart of FIG. ST201 to ST210 in the flowchart of FIG. 5 are the same as ST101 to ST110 in the flowchart of the operation of the control amount calculation unit 106 in the first embodiment, respectively, but only step ST202 is different from step ST102. Behave differently. Hereinafter, the operation of step ST202 will be described.

In step ST202, the elapsed time from the previous trajectory control is compared with a threshold value. The threshold value is set sufficiently larger than the inverse of the control frequency expected on average. If it is less than the threshold value, the same processing as step ST102 is performed. That is, if the current trajectory deviation b ₀ is compared with the target area with the margin m ₁ (0 ≦ m ₁ ≦ 1), and there is even one element of the trajectory parameter that does not fall within the target area with the margin m _1. It is determined that the trajectory control is necessary, and the process proceeds to step ST204. Otherwise, the process proceeds to step ST203. When the threshold is greater than or equal to the threshold, the current trajectory deviation b ₀ is compared with the target area with the margin m ₄ (0 ≦ m ₁ <m ₄ ≦ 1), and the trajectory parameter that does not fall within the target area with the margin m ₁ If there is even one element, it is determined that the trajectory control is necessary, and the process proceeds to step ST204. Otherwise, the process proceeds to step ST203. For example, 0.60 is set as the value of the margin m ₄ .

  As described above, according to the second embodiment, the elapsed time from the previous trajectory control is counted, and when the size is large, the margin of the target area is increased. As time increases, trajectory control can be performed to correct the deviation of the trajectory accumulated so far to ensure a margin with respect to the target region and to equalize the trajectory control interval.

Further, to set the control interval as a target as a threshold for comparing the elapsed time from the previous orbit control at step ST 202, when set, for example, 1 as the value of the margin m _4, the effect of keeping the distance to target control interval can get.

It is a block diagram which shows the structure of the orbit control plan apparatus of the spacecraft by Embodiment 1 of this invention. It is a flowchart which shows the operation | movement content of the control amount calculation part by Embodiment 1 of this invention. It is a figure which shows the track | orbit maintenance control plan example by Embodiment 1 of this invention. It is a block diagram which shows the structure of the orbit control plan apparatus of the spacecraft by Embodiment 2 of this invention. It is a flowchart which shows the operation | movement content of the control amount calculation part by Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Trajectory control planning apparatus, 101 Target area setting part, 102 Holding period setting part, 103 Trajectory error prediction part, 104 Control prohibition period setting part, 105 Control amount calculation part, 106 Index calculation part, 107 Control period counting part, 110 Trajectory Control execution device, 111 thruster, 200 artificial satellite (spacecraft).

Claims (2)

A target area setting unit for setting a lower limit and an upper limit of the target value;
A holding period setting unit for setting a holding period for keeping the value of the orbital parameter within an allowable range;
A control prohibition period setting unit for setting a control prohibition period for prohibiting orbit control, and
A trajectory error prediction unit that predicts trajectory errors in the holding period and the control prohibition period;
An index calculation unit that calculates an index value composed of control amounts;
Control amount calculation for calculating a control amount that minimizes the value of the index calculated by the index calculation unit among the control amounts such that the sum of the predicted trajectory error and the current trajectory parameter is held in the target region Spacecraft orbit control planning device with In the orbit control planning apparatus for a spacecraft according to claim 1,
A control period counting unit that counts the elapsed time from the previous trajectory control,
The control amount calculation unit changes a criterion for determining whether or not orbit control is necessary according to the elapsed time.

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