CN102243311A - Pulsar selection method used for X-ray pulsar navigation - Google Patents

Abstract

A pulsar selection method used for X-ray pulsar navigation is disclosed, which comprises the steps of: (1) removing pulsars capable of flickering; (2) eliminating the unusable pulsars by predicting the usability of pulsars according to a flight mission orbit of a spacecraft; (3) calculating the TOA (Time Of Arrival) estimated accuracy of the usable X-ray pulsars in a pulsar catalog database; (4) in combination with the flight mission orbit and season of the spacecraft, calculating the influence of a pulsar catalog position error of the usable pulsars in the pulsar catalog database on pulsar signal measurement precision; (5) calculating the comprehensive influence of the TOA estimated accuracy and the pulsar catalog position error on pulsar signal measurement; and (6) calculating the optimal navigation X-ray pulsar combination according to a navigation location error matrix of the X-ray pulsars to cause the navigation location error matrix to be the smallest, wherein the X-ray pulsars of the optimal combination can be used for navigation. The method disclosed by the invention is easy to popularize and use, and has the advantages of simple principle, strong operability, the capacity of increasing navigation stability and reliability, etc.

Description

The satellite selection method that a kind of X ray pulsar navigation uses

Technical field

The present invention is mainly concerned with the air navigation aid field, refers in particular to a kind of satellite selection method that is used for the X ray pulsar navigation, is applicable to that the high precision X ray pulsar navigation of different aerial missions uses.

Background technology

The X ray pulsar navigation is a kind of perspective navigate mode, its navigation ultimate principle is that the pulse of relatively forecasting in solar system barycenter inertial system arrives the pulse that measures on true origin time and the spacecraft arrives initial point through extrapolation time, the difference of the two has reflected actual position and has estimated the deviation of position on the pulsar direction, utilize the measurement result of a plurality of different pulsars, adopt the navigation filtering algorithm just can realize the navigation calculating of spacecraft simultaneously in conjunction with the spacecraft dynamics equation.

X ray pulsar navigation principle and GPS navigation are similar.For improving navigation accuracy, GPS needs to consider the GDOP problem in navigation, promptly select suitable nautical star.For the X ray pulsar navigation, different pulsars has different waveform signal features and star catalogue positional accuracy measurement, and pulsar signal waveform character paired pulses time of arrival (TOA) estimated accuracy has a direct impact.The star catalogue site error is relevant in the position of solar system geocentric coordinate system with spacecraft to the influence of navigation accuracy.Therefore pulsar navigation is different from GPS navigation again, need take all factors into consideration various influence factors such as TOA estimated accuracy and star catalogue azimuthal error, does not still have the satellite selection method that is applicable to that high precision X ray pulsar navigation uses at present.

Summary of the invention

The technical problem to be solved in the present invention is: at the technical matters that prior art exists, the invention provides the satellite selection method that a kind of principle X ray pulsar navigation simple, workable, that easily promote and use, can improve navigation stability and reliability uses.

For solving the problems of the technologies described above, the present invention by the following technical solutions:

The satellite selection method that a kind of X ray pulsar navigation uses is characterized in that step is:

(1), removes the pulsar that flickering can take place based on the astronomical sight data;

(2) according to the availability of the aerial mission orbit prediction pulsar of spacecraft, remove out of use pulsar;

(3) calculate the TOA estimated accuracy of available X ray pulsar in the star catalogue database by following formula:

${\mathrm{\σ}}_1=\frac{\sqrt{\frac{1}{4}{T}_{50}^2+T_b^2}}{\sqrt{A\·\mathrm{\Δt}}}\·\frac{\sqrt{{\mathrm{\λ}}_n+{\mathrm{\λ}}_p}}{{\mathrm{\λ}}_p}$

Wherein, T ₅₀It is the X ray pulse signal semi-fluid metric density duration; T _bIt is the detector temporal resolution; λ _pAnd λ _nBe respectively the average discharge density of pulse signal and ground unrest, A is the detector useful area, and Δ t is the observation duration;

(4), calculate the influence of the star catalogue site error pulse signals measuring accuracy of available pulsar in the star catalogue database in conjunction with the aerial mission track and season of spacecraft; Star catalogue site error pulse signals measuring accuracy influence Normal Distribution, its mean square deviation is:

$\left\{\begin{array}{c}{\mathrm{\σ}}_2=\sqrt{A^2+B^2}\\ A=[-(X_B+x)\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}+(Y_B+y)\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}]{\mathrm{\σ}}_{\mathrm{\α}}\\ B=[(X_B+x)\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}+(Y_B+y)\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}-(Z_B+z)\cos \widetilde{\mathrm{\δ}}]{\mathrm{\σ}}_{\mathrm{\δ}}\end{array}\right.$

Wherein, it is zero normal distribution that right ascension and declination error are obeyed average, and their mean square deviation is (σ _α, σ _δ); X _B, Y _BAnd Z _BBe the location components of center gravitation celestial body in solar system geocentric coordinate system of spacecraft, obtain by accurate astronomical ephemeris computation; X, y and z are respectively spacecrafts with respect to the position of the center gravitation celestial body component on three change in coordinate axis direction in solar system geocentric coordinate system;

Be X ray pulsar right ascension,

It is X ray pulsar declination;

(5) combined influence of calculating TOA estimated accuracy and star catalogue site error paired pulses star signal measurement, the measurement mean square deviation of X ray pulsar navigation signal is:

$\mathrm{\σ}=\sqrt{C^2\·{\mathrm{\σ}}_1^2+{\mathrm{\σ}}_2^2}$

Wherein C is the light velocity;

(6) calculate the combination of optimum navigation X ray pulsar, at an X ray pulsar number of selecting to use, navigation positioning error matrix in the calculating star catalogue database under all permutation and combination of available X ray pulsar, the X ray pulsar combination of minimum positioning error matrix correspondence is optimum X ray pulsar combination, uses as the navigation pulsar.

As a further improvement on the present invention:

The navigation positioning error matrix is in the described step (6):

Wherein, H is the observing matrix of X ray pulsar navigation system; The following footnote of σ is represented the X ray pulsar sequence number in the star catalogue database.

Compared with prior art, the invention has the advantages that: the satellite selection method that X ray pulsar navigation of the present invention uses, principle is simple, workable, easily promote and use, by taking all factors into consideration aspect factors such as star catalogue site error, spacecraft position, the degree of stability of signal period, signal characteristic, TOA estimated accuracy and detector performance X ray pulsar navigation precision is influenced, guaranteed the bearing accuracy of X ray pulsar navigation under each season, the reliability and stability of pulsar navigation have been improved greatly, for its popularization provides condition.

Description of drawings

Fig. 1 is the schematic flow sheet of the concrete Application Example of the present invention;

Fig. 2 be in the concrete application implementation of the present invention celestial body to the availability impact synoptic diagram of X ray pulsar.

Embodiment

Below with reference to the drawings and specific embodiments the present invention is described in further detail.

In concrete application example, the spacecraft that is adopted is a kind of lunar orbiter.

As shown in Figure 1, the concrete steps of satellite selection method of the present invention are as follows:

1,, removes the pulsar that glitches takes place based on the astronomical sight data.

The X ray pulsar is the neutron star of high speed rotation, and its rotation period is very stable, and long-time stability are extremely stable galaxy beacons with now the same good as the cesium-beam atomic clock of time standard.But some pulsars self rotary speed has irregular variation, be called " flickering " (glitches), if flickering is bigger, then being unsuitable for navigation uses, therefore at first need remove the X ray pulsar that glitches may take place in the spacecraft run duration nautical star database based on the stability of astronomical sight data forecast pulsar signal.

For example, there are a large amount of X ray pulsar observation datas in astronomical observatory and regularly publish result, can by in official website of the astronomical observatory enquiry navigation X ray pulsar database or the X ray pulsar of glitches may take place in a short time, removing these pulsars need not.

2, usability analyses.

Although the X ray pulsar is very remote apart from the solar system, when spacecraft enters in the shadow region of certain celestial body, promptly anyly all can stop the observability of spacecraft detection device to the X ray pulsar through the celestial body between spacecraft and the X ray pulsar.In addition, because X ray pulsar ray flow is lower, and the relative X ray pulsar of X-radiation of other celestial bodies such as fixed star and Jupiter is very high, so X-ray detector should be avoided pointing to these celestial bodies in order to avoid detector is saturated.So, will be according to the availability of the aerial mission orbit prediction pulsar of spacecraft, promptly take all factors into consideration the influence that celestial bodies such as celestial body blocks, the sun/Jupiter cause aspects such as detector is saturated,, remove out of use pulsar according to the availability of the aerial mission orbit prediction pulsar of spacecraft.

As shown in Figure 2, in the time of in lunar orbiter enters moon shadow region, a month club stops that X-ray detector receives the X ray pulsar signal.Angle [alpha] is a spacecraft with respect to the angle between the direction n of the position vector r of the moon and X ray pulsar among the figure, and a month radius of a ball is R, works as α ₁＜α＜α ₂The time, spacecraft is arranged in the shade of the moon, and this moment, this pulsar was unavailable, and spacecraft is positioned at when blocking the celestial body shaded side and will satisfies:

$\mathrm{\π}-\arccos \left(\frac{\sqrt{{\left|r\right|}^2-R^2}}{\left|r\right|}\right)\≤\arccos (n\·r)\≤\mathrm{\π}+\arccos \left(\frac{\sqrt{{\left|r\right|}^2-R^2}}{\left|r\right|}\right)---\left(1\right)$

In addition, because X ray pulsar ray flow is lower, and the sun is very high with the relative X ray pulsar of X-radiation of other celestial bodies such as Jupiter, will be saturated when X-ray detector points to these celestial bodies, effective measured X ray pulse star signal, therefore also to analyze the availability of other celestial body, guarantee that X-ray detector can successfully measure pulsar signal according to formula (1) to the X ray pulsar.

3, calculate the TOA estimated accuracy of available X ray pulsar in the star catalogue database.

Detector measurement to the photon arrival event be to obey Poisson distribution, equal the character of variance according to the Poisson distribution average, can use following model to calculate the estimated accuracy of TOA:

${\mathrm{\σ}}_1=\frac{{\mathrm{HWHM}}^{*}}{S/\sqrt{S+B}}---\left(2\right)$

${\mathrm{HWHM}}^{*}=\sqrt{{\mathrm{HWHM}}^2+T_b^2}---\left(3\right)$

Wherein, HWHM is a pulse signal semi-fluid metric density duration T ₅₀Half; S is the photon number from pulsar that detects during the observation; B is the photon number of the ground unrest that detects; T _bIt is the detector temporal resolution.

S＝Aλ _pΔt (4)

B＝Aλ _nΔt (5)

Wherein, λ _pAnd λ _nBe respectively the average discharge density of pulse signal and ground unrest, A is the detector useful area, and Δ t is the observation duration.

With (3) to (5) formula substitutions (2) formula, then have the TOA estimated accuracy of X ray pulsar to be:

${\mathrm{\σ}}_1=\frac{\sqrt{\frac{1}{4}{T}_{50}^2+T_b^2}}{\sqrt{A\·\mathrm{\Δt}}}\·\frac{\sqrt{{\mathrm{\λ}}_n+{\mathrm{\λ}}_p}}{{\mathrm{\λ}}_p}---\left(6\right)$

Wherein, T ₅₀It is the X ray pulse signal semi-fluid metric density duration; T _bIt is the detector temporal resolution; λ _pAnd λ _nBe respectively the average discharge density of pulse signal and ground unrest, A is the detector useful area, and Δ t is the observation duration.

4,, calculate the influence of the star catalogue site error pulse signals measuring accuracy of available pulsar in the star catalogue database based on the aerial mission track and season of spacecraft.

The right ascension of pulsar is α, and declination is δ, and then the unit vector of pulsar direction is in inertial system:

$n=\left[\begin{array}{c}\cos \mathrm{\δ}\cos \mathrm{\α}\\ \cos \mathrm{\δ}\sin \mathrm{\α}\\ \sin \mathrm{\δ}\end{array}\right]---\left(7\right)$

The position of X ray pulsar is in the star catalogue

Its error is (Δ α, Δ δ), has

$\left\{\begin{array}{c}\mathrm{\α}=\widetilde{\mathrm{\α}}+\mathrm{\Δ\α}\\ \mathrm{\β}=\widetilde{\mathrm{\β}}+\mathrm{\Δ\β}\end{array}\right.---\left(8\right)$

With (8) formula substitution (7) formula, can get

$n=\left[\begin{array}{c}\cos (\widetilde{\mathrm{\δ}}+\mathrm{\Δ\δ})\cos (\widetilde{\mathrm{\α}}+\mathrm{\Δ\α})\\ \cos (\widetilde{\mathrm{\δ}}+\mathrm{\Δ\δ})\sin (\widetilde{\mathrm{\α}}+\mathrm{\Δ\α})\\ \sin (\widetilde{\mathrm{\δ}}+\mathrm{\Δ\δ})\end{array}\right]---\left(9\right)$

Following formula is carried out Taylor expansion, be taken to the single order item, have

$n=\left[\begin{array}{c}\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}-\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}-\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}+\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α\Δ\δ}\\ \cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}+\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}\\ -\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}-\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α\Δ\δ}\\ \sin \widetilde{\mathrm{\δ}}+\cos \widetilde{\mathrm{\δ}}\·\mathrm{\Δ\δ}\end{array}\right]---\left(10\right)$

Ignore the second order event, can get

$n=\left[\begin{array}{c}\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\\ \cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\\ \sin \widetilde{\mathrm{\δ}}\end{array}\right]+\left[\begin{array}{c}-\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}-\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}\\ \cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}-\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}\\ \cos \widetilde{\mathrm{\δ}}\·\mathrm{\Δ\δ}\end{array}\right]---\left(11\right)$

Note

$\mathrm{\Δn}=\left[\begin{array}{c}-\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}-\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}\\ \cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}\·\mathrm{\Δ\α}-\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}\·\mathrm{\Δ\δ}\\ \cos \widetilde{\mathrm{\δ}}\·\mathrm{\Δ\δ}\end{array}\right]---\left(12\right)$

Then (11) formula can be converted into

$n=\tilde{n}+\mathrm{\Δn}---\left(13\right)$

Arrive the impulse phase φ of satellite _kThe time that propagates into the SSB initial point is

${\tilde{t}}_{\mathrm{SSB}}=t_{\mathrm{sc}}+\frac{\tilde{n}\·(R_B+r)}{c}---\left(14\right)$

In the formula, t _ScBe the pulse arrival time of measuring on the satellite; C is the light velocity; R _B=[X _BY _BZ _B] ^TBe the position vector of center gravitation celestial body with respect to the SSB coordinate system; R=[x y z] ^TBe the position vector of spacecraft with respect to center gravitation celestial body.

By (13) Shi Kede

With its substitution (14) formula, have

${\tilde{t}}_{\mathrm{SSB}}=t_{\mathrm{sc}}+\frac{n\·(R_B+r)}{c}-\frac{\mathrm{\Δn}\·(R_B+r)}{c}---\left(15\right)$

In order to carry out the precise time conversion, (15) formula need be considered the influence of various factors, then arrives the pulse signal φ of satellite _kThe time that propagates into the SSB initial point is

${\tilde{t}}_{\mathrm{SSB}}=t_{\mathrm{sc}}+\frac{n\·(R_B+r)}{c}-\frac{\mathrm{\Δn}\·(R_B+r)}{c}+{\mathrm{\δt}}_a+{\mathrm{\δt}}_v+{\mathrm{\δt}}_D+{\mathrm{\δt}}_G---\left(16\right)$

Wherein, δ t _aIt is the annual parallax influence; δ t _vIt is the kinetic Doppler shift influence of pulsar; δ t _DIt is the chromatic dispersion time delay; δ t _GIt is the crooked and gravitation time delay of light path.

Because the influence of Δ n in back four is a small amount of, its influence can be ignored, and then can obtain the pulsar site error by (16) formula to the influence of measuring equation to be

$\mathrm{\δt}=\frac{\mathrm{\Δn}\·r_{\mathrm{sc}}}{c}=[-(X_B+x)\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}+(Y_B+y)\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}]\mathrm{\Δ\α}...$ $\left(17\right)$

$-[(X_B+x)\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}+(Y_B+y)\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}-(Z_B+z)\cos \widetilde{\mathrm{\δ}}]\·\mathrm{\Δ\δ}$

Because right ascension and declination error are separate and obey average is zero normal distribution, their mean square deviation is (σ _α, σ _δ), then the star catalogue site error to the measurement mean square deviation of X ray pulsar navigation observation equation influence is:

$\left\{\begin{array}{c}{\mathrm{\σ}}_2=\sqrt{A^2+B^2}\\ A=[-(X_B+x)\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}+(Y_B+y)\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}]{\mathrm{\σ}}_{\mathrm{\α}}\\ B=[(X_B+x)\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}+(Y_B+y)\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}-(Z_B+z)\cos \widetilde{\mathrm{\δ}}]{\mathrm{\σ}}_{\mathrm{\δ}}\end{array}\right.---\left(18\right)$

Wherein, (σ _α, σ _δ) be the mean square deviation of X ray pulsar right ascension and declination measuring error; X _B, Y _BAnd Z _BBe the location components of center gravitation celestial body in solar system geocentric coordinate system of spacecraft, obtain by accurate astronomical ephemeris computation; X, y and z are respectively the location components of spacecraft with respect to the center celestial body.

5, calculate the combined influence of TOA estimated accuracy and star catalogue site error paired pulses star signal measurement.

Though the site error of X ray pulsar is fixed in a short time, can only provide the statistical information of position and variance by long-term observation.Because TOA estimated accuracy and star catalogue site error are separate to the influence of measuring equation, then the mean square deviation of TOA estimated accuracy and star catalogue site error paired pulses star signal measurement combined influence is

$\mathrm{\σ}=\sqrt{C^2\·{\mathrm{\σ}}_1^2+{\mathrm{\σ}}_2^2}---\left(19\right)$

Wherein C is the light velocity.

6, calculate the combination of optimum navigation X ray pulsar.

Requirement observation X ray pulsar number n according to aerial mission calculates the navigation positioning error matrix P under all permutation and combination of residue X ray pulsar in the star catalogue database, and concrete model is:

Wherein, H is the observing matrix of X ray pulsar navigation system; The following footnote of σ is represented the X ray pulsar sequence number in the star catalogue database.The X ray pulsar combination of minimum positioning error matrix correspondence is optimum X ray pulsar combination, uses as the navigation pulsar.At an X ray pulsar number of selecting to use, navigation positioning error matrix in the calculating star catalogue database under all permutation and combination of available X ray pulsar, the X ray pulsar combination of minimum positioning error matrix correspondence is optimum X ray pulsar combination, can be used as the navigation pulsar and uses.

The above only is a preferred implementation of the present invention, and protection scope of the present invention also not only is confined to the foregoing description, and all technical schemes that belongs under the thinking of the present invention all belong to protection scope of the present invention.Should propose, for those skilled in the art, in the improvements and modifications that do not break away under the principle of the invention prerequisite, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (2)

1. the satellite selection method that uses of an X ray pulsar navigation is characterized in that step is:

(1), removes the pulsar that flickering can take place the spacecraft run duration based on the astronomical sight data;

(2) according to the availability of the aerial mission orbit prediction pulsar of spacecraft, remove out of use pulsar;

(3) calculate the TOA estimated accuracy of available X ray pulsar in the star catalogue database by following formula:

${\mathrm{\σ}}_1=\frac{\sqrt{\frac{1}{4}{T}_{50}^2+T_b^2}}{\sqrt{A\·\mathrm{\Δt}}}\·\frac{\sqrt{{\mathrm{\λ}}_n+{\mathrm{\λ}}_p}}{{\mathrm{\λ}}_p}$

Wherein, T ₅₀It is the X ray pulse signal semi-fluid metric density duration; T _bIt is the detector temporal resolution; λ _pAnd λ _nBe respectively the average discharge density of pulse signal and ground unrest, A is the detector useful area, and Δ t is the observation duration;

(4), calculate the influence of the star catalogue site error pulse signals measuring accuracy of available pulsar in the star catalogue database in conjunction with the aerial mission track and season of spacecraft; Star catalogue site error pulse signals measuring accuracy influence Normal Distribution, its mean square deviation is:

$\left\{\begin{array}{c}{\mathrm{\σ}}_2=\sqrt{A^2+B^2}\\ A=[-(X_B+x)\cos \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}+(Y_B+y)\cos \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}]{\mathrm{\σ}}_{\mathrm{\α}}\\ B=[(X_B+x)\sin \widetilde{\mathrm{\δ}}\cos \widetilde{\mathrm{\α}}+(Y_B+y)\sin \widetilde{\mathrm{\δ}}\sin \widetilde{\mathrm{\α}}-(Z_B+z)\cos \widetilde{\mathrm{\δ}}]{\mathrm{\σ}}_{\mathrm{\δ}}\end{array}\right.$

Wherein, it is zero normal distribution that right ascension and declination error are obeyed average, and their mean square deviation is (σ _α, σ _δ); X _B, Y _BAnd Z _BBe the location components of center gravitation celestial body in solar system geocentric coordinate system of spacecraft, obtain by accurate astronomical ephemeris computation; X, y and z are respectively spacecrafts with respect to the position of the center gravitation celestial body component on three change in coordinate axis direction in solar system geocentric coordinate system;

Be X ray pulsar right ascension,

It is X ray pulsar declination;

(5) combined influence of calculating TOA estimated accuracy and star catalogue site error paired pulses star signal measurement, the measurement mean square deviation of X ray pulsar navigation signal is:

$\mathrm{\σ}=\sqrt{C^2\·{\mathrm{\σ}}_1^2+{\mathrm{\σ}}_2^2}$

Wherein C is the light velocity;

(6) calculate the combination of optimum navigation X ray pulsar, at an X ray pulsar number of selecting to use, navigation positioning error matrix in the calculating star catalogue database under all permutation and combination of available X ray pulsar, the X ray pulsar combination of minimum positioning error matrix correspondence is optimum X ray pulsar combination, uses as the navigation pulsar.

2. the satellite selection method that X ray pulsar navigation according to claim 1 uses is characterized in that: the navigation positioning error matrix is in the described step (6):

Wherein, H is the observing matrix of X ray pulsar navigation system; The following footnote of σ is represented the X ray pulsar sequence number in the star catalogue database.