CN102997922A - Method for determining pulse arrival time difference by utilizing optical navigation information - Google Patents

Abstract

The invention discloses a method for determining pulse arrival time difference by utilizing optical navigation information. The method comprises the basic processes of: establishing a time transformation equation through spacecraft position information obtained by an optical navigation sensor on a spacecraft, and performing time transformation through the X-ray photon arrival time observed quantity obtained by observing an X-ray detector; obtaining an observing pulse outline based on the X-ray photon arrival time data subjected to time transformation through a period folding method; and comparing the observing pulse outline and the known standard pulse outline, and calculating to obtain pulsar signal arrival time difference, wherein the obtained pulsar signal arrival time difference can serve as the observed quantity of an autonomous spacecraft navigation system. According to the method, the pulsar signal arrival time difference can be accurately calculated, and the accurate pulsar signal arrival time difference observed quantity is provided for the autonomous spacecraft navigation system.

Description

A kind of poor definite method of pulse arrival time of utilizing optical guidance information

Technical field

The present invention relates to a kind of pulsar signal poor definite method time of arrival based on optical guidance information, belong to the Spacecraft Autonomous Navigation Technology field.

Background technology

The Spacecraft Autonomous Navigation system determines position and the speed of spacecraft can alleviate space mission to the dependence of ground observing and controlling by the instrument and equipment of himself, reduces the frequency of star ground communication, improves the autonomous viability of spacecraft.In in the past 20 years, GPS (Global Positioning System/GPS) becomes the important navigation means of low rail earth satellite gradually.But because gps system mainly provides navigation Service on a surface target, for high rail satellite or deep space probe, gps signal is often very faint, even can't receive effective gps signal.In addition, also to tackle the situation that GPS is interfered or is destroyed.Therefore, when utilizing GPS to navigate, be necessary to explore new independent navigation mode.

The X ray pulsar navigation is a kind of emerging spacecraft autonomous astronomical navigation mode.Pulsar is the compact object that the most of nuclear fuel of fixed star has formed by outburst when having exhausted.Fixed star no longer during combustion nucleus fuel, can not support the gravitation of self to subside in the mode of thermal pressure, causes celestial body to shrink, and under huge graviational interaction, electronics and proton in the celestial body are combined into neutron, thereby forms the neutron star of high speed rotation.Neutron star can be along pole orientation emitted radiation wave beam, because its axis of rotation and pole orientation are inconsistent, the rotation of pulsar is with radiation beam inswept huge taper in universe, when radiation beam is inswept when being installed in ground or spaceborne detecting devices, detecting devices just receives a pulse signal, be the beacon of marine navigation just as the sea, as shown in Figure 1.Because pulsar has extremely densification and stable structure, therefore, its rotation period is highly stable, and the pulse signal of institute's radiation has good stability of period.

The X ray pulsar can be launched the X ray pulse signal with stable period, is desirable navigation celestial source, is described as " beacon in the universe ", " natural celestial clock ".Pulsar signal poor observed quantity time of arrival that measures by X-ray detector on the spacecraft has reflected the projection of spacecraft site error on the pulsar line of sight, can be used for the site error of spacecraft is revised, thereby realize Spacecraft Autonomous Navigation.Successfully detect pulsar soon, just having the scholar to propose the concept of pulsar navigation.In the last few years, constantly have new pulsar to be found and catalogue, and as the X-ray detector technology of pulsar navigation sensor the development of making rapid progress had been arranged also, when X-ray detector sensitivity improved, its quality volume constantly reduced; The X ray pulsar navigation becomes the study hotspot in Spacecraft Autonomous Navigation field gradually.

The original observed quantity of obtaining by X-ray detector on spacecraft is x-ray photon observed quantity time of arrival.By the processing of x-ray photon observed quantity time of arrival being obtained pulsar signal poor observed quantity time of arrival, it is one of core technology link in the X ray pulsar navigation process.Traditional signal processing method is by the cycle method for folding, utilize x-ray photon observed quantity time of arrival to make up the observation pulse profile, to observe pulse profile and known full sized pules profile masterplate compare, the phase differential between the two has reflected that pulsar signal is poor time of arrival again.It should be noted that, in order to eliminate the factors such as relativistic effect and Doppler effect to the impact of X ray pulsar signal, before application cycle method for folding obtains the observation pulse profile, need and to be converted to a certain spatial reference point time of arrival at the x-ray photon that spacecraft observation obtains, need to use the spacecraft positional information in the time transfer process.Yet if the position of spacecraft is unknown, so, the time conversion can't effectively be carried out.At this moment, the observation pulse profile can thicken, and pulsar signal difference time of arrival that obtains by observation pulse profile and full sized pules profile masterplate contrast conting will be inaccurate.

Summary of the invention

Technology of the present invention is dealt with problems and is: for the inaccurate problem of pulsar signal poor calculating time of arrival in the situation that solves the unknown of spacecraft positional information, a kind of pulsar signal poor definite method time of arrival based on optical guidance information is proposed, realize pulsar signal poor accurate calculating time of arrival, provide accurately pulsar signal poor observed quantity time of arrival for follow-up independent navigation resolves.

Technical solution of the present invention is:

A kind of poor definite method of pulse arrival time of utilizing optical guidance information, step is as follows:

(1) at an observations of pulsar in the period, by spaceborne X-ray detector record x-ray photon time of arrival;

(2) by the earth's core direction and the earth's core distance of spaceborne optical guidance sensor measurement spacecraft, the earth's core direction and the earth's core distance are multiplied each other and negate, obtain the spacecraft position vector;

(3) utilize spacecraft position vector transfer equation Time Created that obtains by step (2), by the time transfer equation x-ray photon that obtains in the step (1) is carried out the time conversion time of arrival, x-ray photon is transformed into solar system barycenter as spatial reference point time of arrival;

(4) by the cycle method for folding x-ray photon data time of arrival of the conversion of elapsed time described in the step (3) are processed structure observation pulse profile function;

(5) the observation pulse profile function that utilizes full sized pules profile function and step (4) to obtain is set up cost function, carries out nonlinear optimization based on described cost function, thereby obtains the poor observed quantity of pulse arrival time that independent navigation needs.

The time transfer equation is in the described step (3):

${\hat{t}}_k^{\left(b\right)}=t_k^{\left(\mathrm{obs}\right)}+\frac{1}{c}n\·{\hat{r}}_{\mathrm{sc},k}+\frac{1}{{2\mathrm{cD}}_o}[{\hat{r}}_{\mathrm{sc},k}^2-{(n\·{\hat{r}}_{\mathrm{sc},k})}^2]$

$-\frac{{2\mathrm{\μ}}_s}{c^3}\ln |\frac{n\·{\hat{r}}_{\mathrm{sc},k}+{\hat{r}}_{\mathrm{sc},k}}{n\·b+b}+1|$

Wherein,

Be the x-ray photon time of arrival of recording on the spacecraft, i.e. the x-ray photon of pulsar emission arrives the time of spacecraft; The x-ray photon time of arrival of expression elapsed time conversion, c represents the light velocity, and unit vector n is the pulsar line of sight, D _oExpression solar system barycenter is to the distance of pulsar, μ _sExpression solar gravitation field coefficient, b represents solar system barycenter with respect to the position vector at solar system center,

The projection of expression spacecraft position vector in solar system barycenter inertial system.

By the cycle method for folding x-ray photon data time of arrival of elapsed time conversion are processed in the described step (4), structure observation pulse profile function is specially:

Pass through formula $\widehat{\mathrm{\λ}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)=\frac{1}{N_p{T}_b}{\mathrm{\Σ}}_{j=1}^{N_p}C\left({\hat{t}}_{k,j,i}^{\left(b\right)}\right),$ i＝1，2，...，N _b

Calculate observation pulse profile function

Wherein, N _pThe recurrence interval number that the indicating impulse star comprised in the observation period, N _bThe time window number that represents division in the recurrence interval, T _bThe length of expression time window.

Be illustrated in Centered by time window in the photon number that detects,

With The time that expression is discrete.

Described cost function is

$J\left({\mathrm{\Δt}}_k^{\left(b\right)}\right)=\underset{i=1}{\overset{N_b}{\mathrm{\Σ}}}{[\widehat{\mathrm{\λ}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)-\mathrm{\λ}({\hat{t}}_{k,i}^{\left(b\right)}-{\mathrm{\Δt}}_k^{\left(b\right)})]}^2$

Wherein, Expression full sized pules profile function;

Describedly carry out nonlinear optimization based on cost function and undertaken by following formula:

$\mathrm{\Δ}{\hat{t}}_k^{\left(b\right)}=\arg \underset{\mathrm{\Δ}{t}_k^{\left(b\right)}\∈(0,T_p)}{\min }J\left(\mathrm{\Δ}{t}_k^{\left(b\right)}\right)$

Wherein,

Indicating impulse star signal arrival time difference, T _pRepresent the known recurrence interval,

For pulsar signal poor observed quantity time of arrival, namely at (0, T _p) in the scope, make cost function

Minimum

The present invention's beneficial effect compared with prior art is:

In order accurately to calculate pulsar signal poor observed quantity time of arrival, need to carry out the time conversion to x-ray photon data time of arrival that X-ray detector measures.In the situation of spacecraft positional information the unknown, the time transfer process can not effectively be carried out, and this can cause observing the pulse profile distortion, thereby affects the computational accuracy of pulsar signal poor observed quantity time of arrival.Pulsar signal poor definite method time of arrival based on optical guidance information that adopts the present invention to propose, spacecraft positional information transfer equation Time Created that utilizes optical sensor to measure, x-ray photon data time of arrival are carried out the time conversion, can obtain steady and audible observation pulse profile, thereby improve the computational accuracy of pulsar signal poor observed quantity time of arrival.

Description of drawings

Fig. 1 is process flow diagram of the present invention;

Fig. 2 for without the optics navigation information time observation pulse profile and full sized pules profile compare;

Compare by time observation pulse profile and full sized pules profile in order optical guidance information to be arranged for Fig. 3.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is further described in detail.

For the inaccurate problem of pulsar signal poor calculating time of arrival in the situation that solves the unknown of spacecraft positional information, the present invention proposes a kind of pulsar signal poor definite method time of arrival based on optical guidance information: at first, to be used for transfer equation Time Created by the spacecraft positional information that the optical guidance sensor obtains, the time conversion is carried out in observed quantity time of arrival to x-ray photon; Secondly, based on x-ray photon data time of arrival through conversion, obtain the observation pulse profile by the cycle method for folding; Again, it is poor time of arrival to obtain pulsar signal by observation pulse profile and the comparison of full sized pules profile masterplate, and pulsar signal difference time of arrival that obtains can be used for subsequent navigation and resolves.

As shown in Figure 1, the present invention proposes a kind of pulsar signal poor definite method time of arrival based on optical guidance information, and step is as follows:

(1) measures x-ray photon time of arrival based on X-ray detector

At an observations of pulsar in the period, by spaceborne X-ray detector record x-ray photon time of arrival.The x-ray photon that records on the spacecraft is used time of arrival Expression, i.e. the x-ray photon of pulsar emission arrives the time of spacecraft.

(2) determine the spacecraft position vector based on optical sensor

Measure the earth's core direction and the earth's core distance of spacecraft by the optical guidance sensor.The earth's core direction can be expressed as

Wherein

Expression spacecraft position vector, subscript k is used for distinguishing the different moment, and the earth's core is apart from being expressed as

The earth's core direction and the earth's core apart from multiplying each other and negate, are obtained spacecraft with respect to the position vector in the earth's core:

${\hat{r}}_k=-(-{\hat{r}}_k/|{\hat{r}}_k|\·|{\hat{r}}_k\left|\right)$

(3) x-ray photon conversion time of arrival

The spacecraft position vector that measures based on optical sensor

Time Created transfer equation, by the x-ray photon time of arrival of time transfer equation to measuring

The time of carrying out conversion is transformed into a certain spatial reference point with x-ray photon time of arrival, usually selects solar system barycenter as spatial reference point.The time transfer equation is as follows:

${\hat{t}}_k^{\left(b\right)}=t_k^{\left(\mathrm{obs}\right)}+\frac{1}{c}n\·{\hat{r}}_{\mathrm{sc},k}+\frac{1}{{2\mathrm{cD}}_o}[{\hat{r}}_{\mathrm{sc},k}^2-{(n\·{\hat{r}}_{\mathrm{sc},k})}^2]$

$-\frac{{2\mathrm{\μ}}_s}{c^3}\ln |\frac{n\·{\hat{r}}_{\mathrm{sc},k}+{\hat{r}}_{\mathrm{sc},k}}{n\·b+b}+1|$

Wherein,

The x-ray photon time of arrival of expression elapsed time conversion, c represents the light velocity, be known constant, unit vector n is the pulsar line of sight, can calculate by known pulsar angle position information, Li Ming, the Chen Shaolong flat by the general that the computing method of pulsar line of sight can be published with reference to Chinese Yuhang Publishing House 2009, " X ray pulsar navigation system principle and method " book that yellow shake is write; D _oExpression solar system barycenter is to the distance of pulsar, μ _sExpression solar gravitation field coefficient, b represents that solar system barycenter is with respect to the position vector at solar system center, D _o, μ _sWith b all be known,

The projection of expression spacecraft position vector in solar system barycenter inertial system can be calculated as follows

${\hat{r}}_{\mathrm{sc},k}=r_{E,k}+{\hat{r}}_k$

Wherein, r _{E, k}Be the earth's core with respect to the position vector of solar system barycenter, can obtain according to known ephemeris computation, Be based on the spacecraft position vector that optical sensor measures.

(4) observation pulse profile structure

By the cycle method for folding, and utilize x-ray photon data time of arrival of elapsed time conversion Structure observation pulse profile.The mathematical description of observation pulse profile is as follows:

$\widehat{\mathrm{\λ}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)=\frac{1}{N_p{T}_b}{\mathrm{\Σ}}_{j=1}^{N_p}C\left({\hat{t}}_{k,j,i}^{\left(b\right)}\right),$ i＝1，2，...，N _b

Wherein, Expression observation pulse profile function, N _pThe recurrence interval number that the indicating impulse star comprised in the observation period, N _bRepresent the artificial time window number of dividing in the recurrence interval, T _bThe length of expression time window, T _bCan be calculated as follows

$T_b=\frac{T_p}{N_b}$

Wherein, T _pRepresent the known recurrence interval. Be illustrated in

Centered by time window in the photon number that detects, can obtain function by the photon counting function of X-ray detector

In be used for the symbol of expression discrete time

Shown in being defined as follows:

${\hat{t}}_{k,i}^{\left(b\right)}={\hat{t}}_k^{\left(b\right)}+(i-0.5)T_b,$ i＝1，2，...，N _b

Wherein,

It is the x-ray photon time of arrival of elapsed time conversion.Function In be used for the symbol of expression discrete time

Shown in being defined as follows:

${\hat{t}}_{k,j,i}^{\left(b\right)}={\hat{t}}_k^{\left(b\right)}+(j-1)T_p+(i-0.5)T_b,$ i＝1，2，...，N _b，j＝1，2，...，N _p

(5) pulsar signal poor calculating time of arrival

Utilize the observation pulse profile function that obtains by the cycle method for folding

Set up cost function with known full sized pules profile function

By finding the solution nonlinear optimal problem, calculate required pulsar signal poor observed quantity time of arrival of navigation

The formulation of nonlinear optimal problem is as follows:

$\mathrm{\Δ}{\hat{t}}_k^{\left(b\right)}-\arg \underset{\mathrm{\Δ}{t}_k^{\left(b\right)}\∈(0,T_p)}{\min }J\left(\mathrm{\Δ}{t}_k^{\left(b\right)}\right)$

Wherein,

Indicating impulse star signal arrival time difference,

Expression is by calculating

Estimated value, be called poor observed quantity pulsar signal time of arrival, namely at (0, T _p) in the scope, make cost function Minimum

Cost function

Be defined as observation pulse profile function

With the statistic of the difference of full sized pules profile function, its mathematic(al) representation is as follows:

$J\left({\mathrm{\Δt}}_k^{\left(b\right)}\right)=\underset{i=1}{\overset{N_b}{\mathrm{\Σ}}}{[\widehat{\mathrm{\λ}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)-\mathrm{\λ}({\hat{t}}_{k,i}^{\left(b\right)}-{\mathrm{\Δt}}_k^{\left(b\right)})]}^2$

Wherein, Expression full sized pules profile function.Pulsar signal poor observed quantity time of arrival Can be used for follow-up independent navigation resolves.

To implement the X ray observations of pulsar as example at near-circular orbit around the spacecraft of earth flight, by the validity of simulation example checking the method for the invention.

The spacecraft orbit semi-major axis is 7471km, and orbit inclination is 63 °, and the X-ray detector of installing on the spacecraft carries out timing observation to the X ray pulsar that is numbered B0531+21, and the recurrence interval of X ray pulsar B0531+21 is T _p=0.0334s.Only utilize 1 X-ray detector to observe, suppose that X-ray detector is installed on the 2 dimension directing mechanisms, can realize the tracking observation to X ray pulsar B0531+21.The full sized pules profile function of X ray pulsar B0531+21 is

λ(t)＝λ _b+λ _sg(t)

Wherein, t represents the time, λ _bAnd λ _sExpression derives from cosmic background and as the photon arrival rate of the pulsar in navigation signal source, for pulsar B0531+21, establishing the pulse rate constant is λ respectively _b=100ph/s and λ _s=1000ph/s.G (t) is periodic function, and its expression formula is:

$g\left(t\right)=\left\{\begin{array}{c}{p}_1{e}^{-q_{1}t}+p_2{e}^{-q_{2}t},t<{\mathrm{\&tau;}}_0\\ p_3{e}^{{-q}_3(t-{\mathrm{\&tau;}}_0)}+p_4{e}^{-q_4(t-{\mathrm{\&tau;}}_0)},t\&GreaterEqual;{\mathrm{\&tau;}}_0\end{array}\right.$

Wherein, each parameter value is respectively: p ₁=8.6336, p ₂=1.4172 * 10 ^-2, p ₃=4.6888, p ₄=2.5563 * 10 ^-9, q ₁=9.9090 * 10 ², q ₂=4.3888 * 10 ², q ₃=8.1196 * 10 ², q ₄=1.1092 * 10 ³, τ ₀=1.3219 * 10 ^-2If the recurrence interval that observations of pulsar comprised in the period is counted N _p=3000, at this moment, segment length is about 100s during an observations of pulsar, and the artificial time window of dividing is counted N in the recurrence interval _b=1000.Select UV navigation sensor as optical sensor, the spacecraft location positioning precision of utilizing UV navigation sensor to reach to be better than 1km.

In the situation of spacecraft positional information the unknown, can not effectively carry out the time conversion, at this moment, directly adopt the cycle stacking method that x-ray photon data time of arrival that X-ray detector measures are processed, the observation pulse profile that obtains and the contrast situation of full sized pules profile are as shown in Figure 2.Among the figure, the observation pulse profile represents that with solid line the full sized pules profile dots.Be not difficult to find out from figure, compare with the full sized pules profile that obvious distortion has appearred in the observation pulse profile.In this case, pulsar signal poor error of calculation time of arrival that obtains by the pulse profile comparison is amounted to into distance and is 114.4km.

The below adopts the method for the invention, based on optical guidance information transfer equation Time Created, x-ray photon data time of arrival that X-ray detector measures are processed, and the observation pulse profile that obtains and the contrast situation of full sized pules profile are as shown in Figure 3.Be not difficult to find out that from figure the observation pulse profile is very approaching with the full sized pules profile on waveform.In this case, pulsar signal poor error of calculation time of arrival that obtains by the pulse profile comparison is amounted to into distance and is 0.331km.

Obviously, compare with unfavorable situation with the optics navigation information, pulsar signal poor precision time of arrival that adopts the method for the invention to calculate has had largely lifting.Therefore, pulsar signal poor definite method time of arrival based on optical guidance information of the present invention's proposition is effective.

The main technical content of this patent can be used for designing X ray pulsar navigation system schema, realizes deep space probe and earth satellite independent navigation, has broad application prospects.

The content that is not described in detail in the instructions of the present invention belongs to this area professional and technical personnel's known technology.

Claims (4)

1. poor definite method of pulse arrival time of utilizing optical guidance information is characterized in that step is as follows:

(1) at an observations of pulsar in the period, by spaceborne X-ray detector record x-ray photon time of arrival;

(2) by the earth's core direction and the earth's core distance of spaceborne optical guidance sensor measurement spacecraft, the earth's core direction and the earth's core distance are multiplied each other and negate, obtain the spacecraft position vector;

(3) utilize spacecraft position vector transfer equation Time Created that obtains by step (2), by the time transfer equation x-ray photon that obtains in the step (1) is carried out the time conversion time of arrival, x-ray photon is transformed into solar system barycenter as spatial reference point time of arrival;

(4) by the cycle method for folding x-ray photon data time of arrival of the conversion of elapsed time described in the step (3) are processed structure observation pulse profile function;

(5) the observation pulse profile function that utilizes full sized pules profile function and step (4) to obtain is set up cost function, carries out nonlinear optimization based on described cost function, thereby obtains the poor observed quantity of pulse arrival time that independent navigation needs.

2. a kind of poor definite method of pulse arrival time of utilizing optical guidance information according to claim 1 is characterized in that: the time transfer equation is in the described step (3):

${\hat{t}}_k^{\left(b\right)}=t_k^{\left(\mathrm{obs}\right)}+\frac{1}{c}n\&CenterDot;{\hat{r}}_{\mathrm{sc},k}+\frac{1}{{2\mathrm{cD}}_o}[{\hat{r}}_{\mathrm{sc},k}^2-{(n\&CenterDot;\widehat{r_{\mathrm{sc},k}})}^2]$

$-\frac{{2\mathrm{\&mu;}}_s}{c^3}\ln |\frac{n\&CenterDot;{\hat{r}}_{\mathrm{sc},k}+{\hat{r}}_{\mathrm{sc},k}}{n\&CenterDot;b+b}+1|$

Wherein,

Be the x-ray photon time of arrival of recording on the spacecraft, i.e. the x-ray photon of pulsar emission arrives the time of spacecraft; The x-ray photon time of arrival of expression elapsed time conversion, c represents the light velocity, and unit vector n is the pulsar line of sight, D _oExpression solar system barycenter is to the distance of pulsar, μ _sExpression solar gravitation field coefficient, b represents solar system barycenter with respect to the position vector at solar system center, The projection of expression spacecraft position vector in solar system barycenter inertial system.

3. a kind of poor definite method of pulse arrival time of utilizing optical guidance information according to claim 1, it is characterized in that: by the cycle method for folding x-ray photon data time of arrival of elapsed time conversion are processed in the described step (4), structure observation pulse profile function is specially:

Pass through formula $\widehat{\mathrm{\&lambda;}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)=\frac{1}{N_p{T}_b}{\mathrm{\&Sigma;}}_{i=1}^{N_p}C\left({\hat{t}}_{k,j,i}^{\left(b\right)}\right),$ i＝1，2，...，N _b

Calculate observation pulse profile function

Wherein, N _pThe recurrence interval number that the indicating impulse star comprised in the observation period, N _bThe time window number that represents division in the recurrence interval, T _bThe length of expression time window.

Be illustrated in

Centered by time window in the photon number that detects,

With

The time that expression is discrete.

4. a kind of poor definite method of pulse arrival time of utilizing optical guidance information according to claim 1, it is characterized in that: described cost function is

$J\left({\mathrm{\&Delta;t}}_k^{\left(b\right)}\right)=\underset{i=1}{\overset{N_b}{\mathrm{\&Sigma;}}}{[\widehat{\mathrm{\&lambda;}}\left({\hat{t}}_{k,i}^{\left(b\right)}\right)-\mathrm{\&lambda;}({\hat{t}}_{k,i}^{\left(b\right)}-{\mathrm{\&Delta;t}}_k^{\left(b\right)})]}^2$

Wherein,

Expression full sized pules profile function;

Describedly carry out nonlinear optimization based on cost function and undertaken by following formula:

$\mathrm{\&Delta;}{\hat{t}}_k^{\left(b\right)}=\arg \underset{\mathrm{\&Delta;}{t}_k^{\left(b\right)}\&Element;(0,T_p)}{\min }J\left(\mathrm{\&Delta;}{t}_k^{\left(b\right)}\right)$

Wherein,

Indicating impulse star signal arrival time difference, T _pRepresent the known recurrence interval,

For pulsar signal poor observed quantity time of arrival, namely at (0, T _p) in the scope, make cost function

Minimum

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