Disclosure of Invention
In view of the defects in the prior art, the present invention aims to provide a distributed SAR formation configuration autonomous maintenance control method that solves the above technical problems.
In order to solve the technical problem, the distributed SAR formation configuration autonomous maintenance control method comprises the following steps:
step 1, acquiring a relative motion relation of a configuration, and establishing a relation between a base line and the configuration;
step 2, acquiring an autonomous maintenance control threshold;
and 3, adjusting the configuration according to the deviation value of the control threshold and the current configuration.
Preferably, step 1 comprises:
step 1.1, acquiring a relative movement relation of configuration;
step 1.2, establishing a relation between a base line and configuration;
step 1.3, acquiring the relation between space perturbation force and configuration;
and 1.4, acquiring the maximum deviation amount from the vertical track to the baseline and the maximum deviation amount from the track to the baseline.
Preferably, step 1.1 comprises: the description vector δ α defining the configuration satisfies:
wherein a is the major axis of the orbit of the main satellite, a
dIs the minor axis of the orbit of the slave satellite, e is the eccentricity of the master satellite, e
dThe eccentricity of the satellite is determined, i is the inclination angle of the orbit of the main satellite, M is the mean and near point angle of the orbit of the main satellite, f is the true and near point angle of the orbit of the main satellite, omega is the amplitude angle of the perigee of the main satellite, omega is
dThe amplitude angle of the satellite in the vicinity of the satellite, omega, the right ascension and the right ascension of the main satellite
dIs the right ascension from the star rising point, and u is the latitude argument of the orbit of the main star; u. of
dIs the latitude argument from the star orbit; e.g. of the type
x=ecosω,e
y=esinω;
Delta is the root number difference of the double-star orbit of formation, delta a is the semimajor axis difference of the slave star and the master star, delta lambda is the difference of the slave star and the master star along the flight path, delta e
xIs the x-component, deltae, of the two-star E vector difference
yThe y-component of the two-star E vector difference, δ i
xIs the x-component, δ I, of the two-star I-vector difference
yIs the y-component of the two-star I vector difference.
Preferably, step 1.2 comprises:
BECT=|δrrsinφ+δrncosφ|
in the formula, B
ECTAs a vertical effective baseline, B
ATIs along the track baseline, phi is the radar beam projection angle, delta r
r、δr
nAnd δ r
tRespectively satisfy:
in the formula (I), the compound is shown in the specification,
to shape the initial phase in the plane, and
θ=arctan(δi
y/δi
x) Configuring an out-of-plane initial phase;
preferably, step 1.3 comprises:
analyzing the influence of the spatial perturbation on the configuration, the influence of the configuration on the spatial perturbation can be obtained as follows:
in the formula:
the atmospheric drag on the topography effect can be expressed as:
in the formula (I), the compound is shown in the specification,
delta B is the surface-to-mass ratio difference of two satellites, rho is the atmospheric density, v is the in-orbit running speed of the satellite, J2 is the earth aspheric harmonic constant, R
eIs the equatorial radius of the earth; n is the angular velocity of the principal star in formation, u (t) is the latitude argument of the principal star at time t, u
0The latitude argument of the principal star at the initial moment is t, which represents the running time of the formation from the initial moment.
Preferably, step 1.4 comprises:
obtaining maximum deviation of vertical track to baseline
In the formula (I), the compound is shown in the specification,
to shape the in-plane phase angle divergence, Δ i
yConfiguring the out-of-plane divergence;
obtaining maximum deviation from track to baseline
In the formula, δ rr2Long-term offset, δ r, along the track for perturbation configurationraLong-term offset along track, δ r, caused for semi-major axis control residualrIs the atmospheric resistance long-term offset.
Preferably, step 2 comprises:
step 2.1, obtaining an in-plane maintenance control threshold;
and 2.2, acquiring an out-of-plane maintenance control threshold.
Preferably, step 2.1 comprises: selecting the in-plane configuration to maintain a control period of Ti,TiSatisfies the following conditions:
an in-plane control period threshold can be obtained
In the formula,. DELTA.B'
ECTxK is a reserved safety factor for configuring the vertical effective divergence amount caused by radial divergence,
to maintain the control period T
iThe configuration created by the perturbation of J2 over time is offset long-term along the track,
to maintain the control period T
iThe long-term offset along the track caused by the semi-major axis control residual in time,
to maintain the control period T
iLong-term offset of atmospheric resistance in time;
step 2.2 comprises: obtaining out-of-plane maintenance control threshold
In the formula,. DELTA.B'ECTzThe vertical effective baseline variation for out-of-plane amplitude divergence.
Preferably, step 3 comprises:
step 3.1, in-plane control;
and 3.2, controlling outside the plane.
Preferably, step 3.1 comprises: obtaining expected value delta e after two times of pulse controlman;
δe
manSatisfies the following conditions:
in the formula (I), the compound is shown in the specification,
the maximum allowable offset of the vector argument of the relative eccentricity is shown, and nom is a nominal variable for maintaining control reference;
step 3.2 comprises: obtaining ignition later expectation value delta iman;
δi
manSatisfies the following conditions:
compared with the prior art, the invention has the following beneficial effects:
1) the threshold is set for starting control, so that collision of formation satellites caused by mis-ignition can be avoided;
2) based on the strategy of maintaining the regional separation of application and ignition, the use efficiency of the satellite is improved;
3) the area can not be imaged by the ignition of the satellite, and the damage to satellite-borne electronic components caused by mutual shooting of double satellites can be avoided.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
As shown in fig. 1 to 3, the present invention includes the steps of:
(1) formation configuration mathematical description
According to the C-W equation of formation configuration relative kinematics, the distributed SAR near-circular orbit formation configuration described by using the orbit root number difference can be described as
In the formula, rrRepresenting the x-dimension, r, of the configurationtRepresenting the dimension of the configuration y, rnRepresenting a configurational z-dimension; a is a major axis of the orbit of the main satellite, e is the eccentricity of the main satellite, i is the inclination angle of the orbit of the main satellite, M is the mean anomaly angle of the orbit of the main satellite, f is the true anomaly angle of the orbit of the main satellite, and omega is the argument of the perigee of the main satellite. And delta represents the difference of the orbit parameters of the configuration master star and the slave star. As shown in equation (1), a new configuration description vector δ α is defined as
In the formula, no subscript represents the master star orbit parameter, and subscript d represents the slave star orbit parameter. Omega is the right ascension of the main star, and u-omega + f is the latitude argument of the main star orbit; e.g. of the typex=ecosω,eyEsin ω; delta represents the root number difference of the two-star orbit of formation, delta a represents the semimajor axis difference of the slave star and the master star, delta lambda represents the difference of the slave star and the master star along the flight path, delta exThe x-component, δ E, representing the two-star E vector differenceyThe y-component of the two-star E vector difference, δ ixRepresenting the x-component, δ I, of a two-star I-vector differenceyRepresenting the y-component of the two-star I-vector difference. δ λ is a synthetic variable, which has been described in equation 2 and will not be described. Constraint condition of close formation on near-circular orbit, delta exAnd δ eyCan be simplified into
The simplified formula (3) is substituted into the formula (1), and the kinematic equation of the formation configuration described based on the E/I vector can be obtained as
Further, the formula can be simplified into
In the formula (I), the compound is shown in the specification,
to shape the initial phase in the plane, and
θ=arctan(δi
y/δi
x) For shaping the out-of-plane initial phase, there are
Definition of
Is a nominal configuration parameter, wherein i is 1,2, …, 6.
(1) Formation configuration baseline definition
According to the requirements of mapping and GMTI tasks of a distributed SAR satellite system DEM, two interference baselines are generated by formation configuration, namely a vertical effective baseline (effective cross TrackBasine) for DEM, which projects the relative position between satellites in a radar beam radial plane and projects the projection again to the radial vertical direction of the beam; the second is the along-track baseline (AlongTrackBaseline) for GMTI, which is the projection of the relative inter-satellite position in the along-track direction. According to the definition of the interference baseline, the vertical effective baseline BECTIs composed of
BECT=|δrr sinφ+δrn cosφ| (12)
Wherein phi is the radar beam projection angle, a plus sign is taken when projecting to the left side, and a minus sign is taken when projecting to the right side.
Along track baseline BATIs defined as:
(2) topographic uptake divergence analysis
The influence of the spatial perturbation force on the configuration is then analyzed. In general, the average orbital radical variation caused by J2 perturbation can be described as
In the formula (I), the compound is shown in the specification,
j2 is the earth's aspheric harmonic constant, R
eThe equatorial radius of the earth. The substitution of equation (18) into (2) simplifies to yield:
based on the above formula, the variation situation of the J2 perturbation configuration parameter described based on the E/I vector can be obtained after integration
In the formula:
deltaa represents the minor to major axis difference,
for configuring the initial phase in the plane, n is the angular velocity of the principal star in formation, u (t) is the latitude argument of the principal star at time t, u
0The latitude argument of the principal star at the initial moment is t, which represents the running time of the formation from the initial moment.
(a) E vector shot change (b) I vector shot change
The E/I vector is perturbed by J2, and although the atmospheric density of the environment of the low earth orbit satellite is relatively thin, the satellite still has the orbit falling influence caused by the atmospheric resistance when in orbit operation. In general, the divergent acceleration along the track caused by the influence of atmospheric drag on a low earth orbit satellite can be described as
Where ρ is the atmospheric density, v is the in-orbit running speed of the satellite, and B ═ CDA/m is the satellite surface-to-mass ratio. The resulting radial (semi-major axis) drift rate and its long term drift error up the track can be expressed as
Delta B is the surface quality ratio difference of two satellites.
(3) Analysis of baseline divergence mechanisms
As can be seen from the definition of the vertical effective baseline and the along-track baseline, the influence of the spatial perturbation on the formation configuration causes the change of the baseline, and the goal of configuration-based maintenance control is to ensure that the satellite always provides a baseline meeting the requirements of the mapping task in the orbit life cycle. Therefore, the choice of the maintenance control strategy has a direct relationship with the change of the baseline, and the baseline divergence mechanism needs to be analyzed.
1. Vertical effective baseline divergence mechanism
According to the definition of the vertical effective baseline, under the influence of the space perturbation force, the vertical effective baseline is mainly influenced by the initial phase in the configuration plane
And the vertical track direction δ i
yThe influence of the amount of ingested change. The two types of shot change are substituted into formula (12) for simplification processing to obtain
In the formula (I), the compound is shown in the specification,
to shape the in-plane phase angle divergence, Δ i
yTo shape the amount of out-of-plane divergence. As can be seen from equation (24), as the formation system flies in orbit, the maximum deviation of the vertical track from the baseline can be further reduced to
From the above, it can be seen that the effective vertical divergence Δ B 'is caused by the radial divergence of the configuration'ECTxMainly determined by the configuration dimension in the configuration plane and the phase angle deviation caused in the maintenance control period; perpendicular effective amount of divergence Δ B 'due to out-of-plane divergence of the topography'ECTzMainly determined by the amount of dimensional change out of the plane of the topography.
2. Mechanism of divergence along track baseline
Similarly, according to the definition of the effective baseline along the track, under the influence of the space perturbation force, the effective baseline along the track is mainly subjected to the configuration radial phase
Shot variation, long-term offset δ r of J2 perturbation configuration along track
r2Long-term offset delta r along track caused by semi-major axis control residual error
raAnd long-term offset δ r of atmospheric resistance
rThe influence of (c). The change of several types of shooting can be substituted into formula (13) to simplify the processing
According to the above formula, as the formation system flies on the track, the maximum deviation from the baseline along the track can be further simplified to
From the above formula, the maximum deviation along the track baseline is respectively the periodic deviation in the configuration plane caused by perturbation of J2, and the long-term drift along the track; the long-term drift along the flight path caused by the semi-long axis control residual error and the long-term drift along the flight path caused by the atmospheric resistance.
(4) Configuration autonomic maintenance control threshold selection
According to the research results of two types of baseline divergence mechanisms of the distributed SAR formation system, the configuration maintenance control threshold value can be selected to take a vertical effective baseline as a target, and can also be selected to take a baseline along a flight path as a target; even if the vertical effective base line or the effective base line along the flight path exceeds the mapping task requirement, the ignition pulse can be planned and maintained under any condition. However, from the perspective of ensuring the relative stability of the maintenance control period, as the deviation of the configuration along the track to the baseline is greatly influenced by the control residual error of the semi-long axis of the configuration, and great uncertainty exists, the configuration maintenance control threshold is selected mainly to meet the application requirement of the vertical effective baseline, and meanwhile, the requirement along the track baseline is considered, so that the requirement of a surveying and mapping task can be met along the track effective baseline all the time when the distributed SAR satellite system performs maintenance control according to the vertical effective baseline. According to the principle, in-plane and out-of-plane configuration maintaining control threshold selection strategies are planned respectively below.
1. In-plane maintenance control threshold selection
From the research results of the vertical effective baseline and the configuration divergence mechanism, the in-plane configuration initial phase divergence amount is only a partial factor causing the divergence of the vertical effective baseline, but the out-of-plane configuration dimension has relatively slow divergence speed, so that the configuration plane can be ensuredThe control effect can be maintained within this range. Suppose that the vertical effective divergence amount caused by configuration radial divergence at the time of mission design is delta B'ECTxThe vertical effective baseline variation from the out-of-plane amplitude of the formation is Δ B'ECTzThe desired configuration maintenance control period is Ti, and the above variables are substituted (25) to obtain a maintenance control threshold value delta e in the configuration planemaxIs composed of
In the formula, k is more than or equal to 1, and k is 1.5 generally taken as a reserved safety factor. From the equation (28), the in-plane configuration maintenance control threshold δ emaxAnd maintaining the control period TiThe proportionality coefficient is determined by the in-plane configuration scale and the phase divergence rate. At this time, the configuration is required to be formed into a vertical effective baseline divergence delta B 'along the track'ATSatisfy the requirement of
In the formula (I), the compound is shown in the specification,
indicates the sustain control period T
iThe configuration created by the perturbation of J2 over time is offset long-term along the track,
indicates the sustain control period T
iThe long-term offset along the track caused by the semi-major axis control residual in time,
indicates the sustain control period T
iLong-term offset of atmospheric resistance over time.
2. Out-of-plane maintenance control threshold selection
Similarly, from the research results of the vertical effective baseline and the configuration divergence mechanism, the out-of-plane configuration dimension divergence can be knownThe amount is another partial factor that contributes to the divergence of the perpendicular effective baseline. Estimated baseline variation delta B 'if control threshold selection is maintained according to in-plane configuration'ECTzThe out-of-plane topography maintains the control threshold δ imaxIs composed of
According to the above formula, if the out-of-plane dimension divergence rate of the topography is combined, when the out-of-plane maintenance control threshold value is given, the out-of-plane topography maintenance control period T is also indirectly giveno。
(5) Autonomous maintenance control strategy
The distributed SAR system firstly calculates configuration dynamic parameters delta alpha according to the inter-satellite state measurement data
i(i 1,2, …,6) and based on the nominal configuration parameters uploaded by the satellite-ground large loop
Respectively generating an inside deviation value and an outside deviation value of a configuration plane; secondly, the on-satellite orbit control system judges the current configuration deviation value based on the perturbation control threshold value, starts configuration maintaining control operation when the configuration deviation value exceeds the set threshold value, and calculates and generates the maintaining control ignition pulse quantity and moment by a configuration maintaining control algorithm. And finally, driving the hydrazine thruster to perform maintenance control ignition operation to complete the maintenance control task.
1. In-plane control
When | | | delta e-delta enom| | exceeds δ emaxOn-time control, nom denotes the nominal variable that maintains the control reference.
According to the Gaussian perturbation equation, two ignition pulse quantities delta v in a plane can be controlledt1、δvt2And the corresponding time is:
in the formula, δ eman、δamanIs the expected value after two pulse controls, δ e, δ a are the real values before the first pulse control, uM1And uM2Respectively latitude argument, δ e, of applying two pulsesmanThe method specifically comprises the following steps:
in the formula (I), the compound is shown in the specification,
is the maximum allowable offset relative to the eccentricity vector argument:
δamanthe method specifically comprises the following steps:
in the formula (I), the compound is shown in the specification,
denotes J
2The term results in a change of δ u within one control cycle and has:
Δ t is the control period. Delta uDRepresents the change of delta u in a control cycle caused by atmospheric resistance, and comprises:
2. out-of-plane control
When | | | delta i-delta inomI exceeds delta imaxAnd (5) starting control.
According to the Gaussian perturbation equation, the quantity and the moment of the ignition pulse out of the plane can be controlled as follows:
in the formula, δ imanFor the ignition end expectation, there are:
the foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.