CN103033188A - Navigation satellite autonomous time synchronization method based on synthetic aperture observation - Google Patents

Abstract

The invention provides a navigation satellite autonomous time synchronization method based on synthetic aperture observation. The method comprises the following steps: all the cooperative observation satellites and a reference satellite perform timing observation on the same millisecond pulsar at the same time; the reference satellite completes time delay correction between each cooperative observation satellite and the reference satellite by the relative position measurement data between satellites at different times, and stacks each group of observation data completing the time delay correction to obtain the observation waveform of a synthetic aperture timing observation system; the clock error of an onboard clock of the reference satellite is measured; and the clock error between each satellite of a navigation constellation and a standard time TCB is measured and the clock error correction value is broadcast in the broadcast ephemeris of each satellite so as to complete the autonomous time synchronization of the navigation satellite. The method achieves the technical effects of reducing the X-ray detector load of the navigation satellite, shortening the observation time, and improving the autonomous time synchronization precision and real-time property of the navigation satellite.

Description

The autonomous method for synchronizing time of Navsat based on synthetic aperture observation

Technical field

The invention belongs to the Spacecraft Autonomous Navigation Technology field, relate to a kind of x ray signal that utilizes the pulsar radiation carries out precise synchronization for Navsat method.

Background technology

Satellite navigation system is a kind of radio navigation location and time transmission system of space-based, be the space fundamental facilities of Real-time Obtaining high-acruracy survey information, the navigation information services such as round-the-clock, round-the-clock, high-precision Position, Velocity and Time can be provided for the users of earth surface and terrestrial space.Complete satellite navigation system comprises three large ingredients, i.e. space constellation part (navigation constellation), ground control section and user terminal part.Wherein, the ground control section is by a plurality of monitoring stations and the injection plant that are distributed in the whole world, and 1 main control centre station forms, be responsible for Navsat is carried out tracking observation, accurate definite satellite orbit and spaceborne clock parameter, work out navigation message and steering order, and be injected into Navsat via up data link.Navsat extracts up injection information, navigation message is broadcast to the user terminal receiver use.That is to say, the at present operation of navigation constellation, manage and keep all and be responsible for finishing by ground control system, daily requirement is done a uplink information and is injected (such as gps system).

If Navsat can be realized independent navigation and the operational management of long period, with effectively reducing the laying quantity of ground control station, alleviate the ground control system work load, reduce navigation constellation operational management and long term maintenance expense; Can Real-Time Monitoring navigation information integrity, greatly shorten the fault alarm time, improve continuity and the availability performance of navigation information; Reduce land station to the uplink information injection number of times of satellite, reduce navigation constellation to the degree of dependence of ground observing and controlling system, strengthen satellite navigation system in the autonomous viability of particular time.As seen, the navigation constellation independent navigation has extremely important practical engineering application value.

The U.S. has carried out modernization restructuring to its gps system for this reason, increased communication/range finding link between star at serial satellites such as GPS Block II R/II R-M, Block II F, process by bidirectional ranging, exchanges data and spaceborne computer filtering between star, constantly revise satellite Long-term forecasting ephemeris and timing parameter and autonomous navigation message and the steering order of generating, keep the stable of the basic configuration of constellation, to satisfy user's continuous precise navigator fix application demand.

Yet this navigation constellation independent navigation mode based on the inter-satellite link ranging information lacks outside space-time datum data, is difficult to solve two class unobservability errors and accumulates in time problem.One class is constellation integral-rotation error, and this error can cause constellation integral body to drift about with respect to inertial coordinates system; Another kind of is the non-homogeneous rotation error of the earth, causes the earth's core to connect firmly coordinate system and drifts about with respect to inertial coordinates system.Especially the constellation integral-rotation accumulation of error will cause satellite ephemeris and timing parameter error to increase gradually, user's navigation and positioning accuracy degradation.

At present, address the above problem two kinds of Basic Ways: ⑴ by setting up the Long-term prediction model of constellation integral-rotation and earth rotation, suppress the accumulation of error (such as gps satellite independent navigation mode).But this method does not thoroughly solve this technical barrier from practical application effect, can not satisfy the long-time autonomous navigation technology index request of constellation; ⑵ adopt the navigation constellation technology of " casting anchor ", regularly to constellation satellite launch distance measuring signal and modulation earth rotation parameter (ERP) information, carries out information processing by land station on the star, suppresses constellation unobservability error and accumulate in time.But this by setting up the settling mode of satellite-ground link, run counter to the principle of the long-time autonomous operation of Navsat.

In recent years, along with the home and abroad to the broad research based on the Spacecraft Autonomous Navigation Technology of X ray millisecond pulsars timing observation, for navigation satellite autonomous navigation provides a kind of new thinking and feasible way, especially for navigation constellation provides a kind of independently outside absolute space-time benchmark, can solve the long-time autonomous operation problem of constellation.Spacecraft Autonomous Navigation based on the observation of X ray millisecond pulsars timing is the effective model of realizing spacecraft high-precision independent navigation truly.The pulsar autonomous navigation technology is applied to GLONASS (Global Navigation Satellite System) (Global Navigation Satellite System, GNSS), can realizes the autonomous time synchronized of Navsat and autonomous measurement and the renewal of satellite ephemeris.This independent navigation is take pulsar inertia space-time frame of reference as reference, pulsar space-time frame of reference does not exist rotation and time drift with respect to the inertial reference frame, thereby can suppress or eliminate the long term drift error of constellation self rotation error and Navsat time reference.Apply pulse star airmanship also can accurately be measured constellation error averaging time and the constellation integral-rotation error that the GNSS independent navigation exists.

When navigation application, scope when utilizing the roentgenometer of equipping on the Navsat, one group of millisecond pulsar of selecting is in advance carried out Time of arrival, the pulse that records every pulsar arrives the moment of Navsat, utilize simultaneously the pulsar clock model can forecast the moment that same pulse arrives solar system barycenter, arrive Navsat and the comparison constantly of solar system barycenter by same pulse, again in conjunction with the space position parameter of this set of pulses star, just can calculate observation constantly Navsat with respect to the position vector (three-dimensional coordinate) of solar system barycenter and spaceborne clock with respect to standard time (solar system barycentric coordinate time, clock correction TCB).Its ultimate principle as shown in Figure 1.In Fig. 1, the X ray pulsar autonomous navigation system that the Navsat utilization is carried is measured Navsat with respect to the position of solar system barycenter and the spaceborne clock clock correction with respect to the standard time, realize autonomous location with regularly.X ray pulsar autonomous navigation system mainly comprises following a few part: 4 X-ray detectors, be used for surveying the X ray pulse signal from pulsar, and the integrated pulse profile that acquisition has satisfied signal to noise ratio (S/N ratio) within certain integral time; Satellite atomic clock is for the measurement of TOA provides the reference time; X ray pulsar and celestial body in solar system ephemeris database, the basic data that provides pulsar space-time frame of reference and navigation algorithm to need; TOA measures and processing module, adopts appropriate algorithm, utilizes the integrated pulse profile, obtains the pulse arrival time that observation obtains; Navsat Position, Velocity and Time algoritic module, the TOA that utilizes observation to obtain sets up the pulsar navigation observation equation, adopts appropriate algorithm to realize measurement and the forecast of spacecraft state parameter (position, speed, time).

X ray pulsar timing observation is the basis of pulsar autonomous navigation technology.The basic structure of recording geometry as shown in Figure 2 during roentgenometer, spacecraft is with the X-ray detector that the carries source that aims at the mark, observe and record (Time of Arrival time of arrival from the x-ray photon in target source and background sky district thereof, TOA), the measurement of time of arrival is the time signal that provides take satellite atomic clock as reference, then records original observation data by digital data recording system.Because the high-speed motion of spacecraft can cause observation signal to produce obvious Doppler effect; Because the impact of special relativity effect, the actual vibration frequency of satellite atomic clock also can change with respect to its nominal frequency; And the millisecond pulsar many places that are applicable to Spacecraft Autonomous Navigation of having found at present are in binary-star system, cause the pulsar of observing also can produce extra impact to observation signal around the revolution motion of binary-star system barycenter; In addition, also need consider the impact of the multinomial error sources such as Shapiro delay.Therefore original observation data will be through the further processing of observation data pretreatment system, to eliminate various error sources to the impact of observation data.After the correction of finishing every error source, observation sequence is carried out overlap-add procedure according to the rotation period of observation pulsar, to obtain integrated pulse profile with satisfied signal to noise ratio (S/N ratio).Add the initial time of this observation after the full sized pules profile that records in integrated pulse profile and the database compared, just obtain the TOA of this observation.

A large amount of observation datas show: for the strongest Crab(J0534+2200 of X ray wave band radiation) pulsar is 1m with a useful area ²X-ray detector, per second can receive approximately 7800 x-ray photons from pulsar (signal) and approximately 78000 photons from the place nebula (noise), namely the flashlight subnumber of a recurrence interval is about 260, and the noise light subnumber is about 2600.And the X ray flow intensity of other X ray pulsars only is the per mille of Crab pulsar even lower, that is to say every 1m ²The detector per second can only detect signal photon even still less about 10, and the background photon number is about 100.If obtain a clearly pulse profile, need at least tens hours line observation time.

The observation signal that signal to noise ratio (S/N ratio) is so low becomes the one of the main reasons of Limited Pulses star autonomous navigation technology practical application.If use it for the independent navigation of Navsat, just must take measures to improve signal to noise ratio (S/N ratio), two kinds of solutions are arranged at present: a kind of is to prolong observation time; Another kind is to use large-area detector.But two schemes all has its limitation, and for the first scheme, the prolongation of observation time can reduce the real-time of navigational solution, can't realize the quasi real time monitoring to the navigation information integrality, and prolongs the fault alarm time; For first scheme, because the useful load of Navsat is limited, therefore large-area X-ray detector is difficult to carry up.

Autonomous measurement for the Navsat position coordinates, a kind of comparatively feasible technical scheme is arranged at present, namely utilize on two Navsats the equipment X-ray detector to observe simultaneously same X ray become the source, line between these two satellites consists of between dynamic star measures baseline, the difference that same signal arrives the time of two satellites has namely reflected the direction of Inter-satellite Baseline with respect to pulsar, just can measure the direction of Inter-satellite Baseline in inertia space-time frame of reference by the simultaneous observation that many X ray is become source signal.Measure simultaneously the direction of many Inter-satellite Baselines in inertia space-time frame of reference, and in conjunction with measurement result and the dynamics of orbits equation of range finding/communication link between star, just can realize the autonomous mensuration of Navsat position coordinates.X ray becomes common high 5～6 magnitudes of flow of the throughput ratio X ray millisecond pulsar in source, does not therefore need to use large-area detector also not need the observation time of growing very much, just can obtain higher measuring accuracy.But utilize X ray to become the source and can't realize the autonomous time synchronized of Navsat, only have the X ray of utilization millisecond pulsar just can realize the autonomous time synchronized of Navsat.

In sum, if X ray pulsar autonomous navigation technology will be applied to Navsat to realize the autonomous time synchronized of navigation constellation, just must solve the excessively low problem of observation signal signal to noise ratio (S/N ratio).The method of existing raising observation signal signal to noise ratio (S/N ratio) mainly contains two kinds: increase the useful area of detector or prolong observation time, there is respectively following problem in two kinds of methods:

For Navsat, to carry atomic clock group, time frequency signal generation and keeping system, antenna, solar cell etc. on it and be used in a large number the equipment that navigation signal produces, keeps and launch.The useful load that can distribute to the X-ray detector system is very limited, and large-area X-ray detector volume is large, quality is large, power consumption is high, must take more Satellite Payloads, is difficult to carry out.And existing pulsar autonomous navigation technology usually requires to carry 4 X-ray detectors at satellite, and this is just so that carry more infeasible that the scheme of large area x-ray detector becomes at Navsat.

In the situation that detector size is limited, can also adopt the way that prolongs observation time to improve signal to noise ratio (S/N ratio).But except the Crab pulsar, the millisecond pulsar X-radiation flow that is generally used for navigating is all very low, even be 1m for useful area ²The large area x-ray detector, the photon signal that can receive within the time interval in 1 second also only is about 10 even still less, if will obtain a clearly pulse profile, needs at least tens hours Continuous Observation time.In so long observation time, Navsat along orbital flight a very long segmental arc or even a week, and the pulsar autonomous navigation system provides or motion state parameters and the clock correction parameter of satellite during the observation beginning.Therefore the prolongation of observation time can reduce the real-time of navigational solution greatly, can't realize the quasi real time monitoring to spaceborne mitriform attitude, and can prolong the fault alarm time.

Patent of invention 200710005043.9 has proposed that a kind of Navsat autonomous Orbit based on the X ray pulsar is determined, the System and method for of time synchronized and attitude measurement.This patent remains utilizes traditional X ray pulsar autonomous navigation method to realize the autonomous time synchronized of Navsat, can't thoroughly solve existing weak signal observation problem in the X ray pulsar navigation.

Summary of the invention

Cross deficiency low and that be difficult to identification in order to overcome the observation signal signal to noise ratio (S/N ratio) that exists in the existing pulsar autonomous navigation technology, the present invention proposes a kind of synthetic aperture observation program of X ray wave band, in the situation that do not increase detector area, do not prolong observation time, well solved based on existing Testing of Feeble Signals problem in the autonomous time synchronized of the navigation constellation of pulsar, measuring accuracy is high and easy to implement.

The technical solution adopted for the present invention to solve the technical problems may further comprise the steps:

Step 1, according to the ephemeris of each Navsat and the location parameter of millisecond pulsar, selected one group of Navsat that can observe simultaneously same millisecond pulsar, and therefrom choose one wantonly as reference satellite, remaining Navsat is as collaborative observation satellite, and the observation data of collaborative observation satellite wants reduction to the reference satellite place;

Step 2, all collaborative observation satellites and reference satellite are carried out timing observation to same millisecond pulsar simultaneously, and original observed data is separately preserved; Simultaneously collaborative observation satellite and reference satellite according to separately the Position And Velocity parameter finish Doppler effect, the special relativity effect and Shapiro delay correction of original observation signal;

Step 3, after each timing observation was finished, each collaborative observation satellite was sent to reference satellite with observation data separately;

Step 4, reference satellite are utilized different constantly relative position measurement data between star, finish each collaborative observation satellite to the time delay correction at reference satellite place, and concrete grammar is:

At t constantly, i collaborative observation satellite position vector with respect to reference satellite in inertial space is

The direction vector of the millisecond pulsar of observing is Then t constantly collaborative observation satellite to the TOA measurement data time delay corrected value of reference satellite be

Wherein c is the light velocity; The photon sequence time of arrival toa that collaborative observation satellite i observes _IjCorrect one by one, obtain one group of new observation sequence time of arrival, the detector that namely is equivalent to collaborative satellite i is placed on resulting TOA observation sequence on the reference satellite;

Step 5 is carried out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry to the observation data of respectively organizing of finishing the time delay correction;

Step 6 is measured the clock correction of the spaceborne clock of reference satellite, and concrete grammar is:

If the unit direction vector of the millisecond pulsar of observing in solar system geocentric coordinate system be

Wherein

Be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of the millisecond pulsar of observing, the solar system geocentric coordinate system position vector of reference satellite when epoch of observation is

Wherein

Be respectively three coordinate components of position vector in solar system geocentric coordinate system of reference satellite, the pulse arrival time that the observation of synthetic aperture timing recording geometry obtains is toa _Sat, the moment that the same pulse that is obtained by the clock model prediction of this millisecond pulsar arrives solar system barycenter is toa _SSB, then observation equation is

$({\mathrm{toa}}_{\mathrm{sat}}-{\mathrm{toa}}_{\mathrm{SSB}})\·c={\stackrel{\→}{k}}_x\·{\stackrel{\→}{r}}_x+{\stackrel{\→}{k}}_y\·{\stackrel{\→}{r}}_y+{\stackrel{\→}{k}}_z\·{\stackrel{\→}{r}}_z+\mathrm{\Δ}{t}_c\·c+\mathrm{\δ}\·c$

In the formula, Δ t _cBe the deviation of the spaceborne clock of reference satellite and standard time TCB, δ is the summation of all the other timing observational errors;

Step 7, calculate the clock correction of each satellite of navigation constellation and standard time TCB, the spaceborne clock of each Navsat is converted to clock correction with respect to terrestrial time with respect to the clock correction of TCB, and in every satellite broadcast ephemeris separately, the clock error correction value is broadcast away, just can guarantee user's navigation and time service service precision, namely finish the autonomous time synchronized of Navsat.

The invention has the beneficial effects as follows: the observed result of the little detector of Jiang Duotai carries out combining after time delay corrects, and forms the observation effect of a large detector.The X-ray detector load that reduces Navsat, the technique effect that shortens observation time, the raising autonomous timing tracking accuracy of Navsat and real-time have been reached.The present invention also is applicable to near-earth orbit, deep space and interplanetary flight Spacecraft formation, and without dense atmosphere celestial body lander is formed into columns and surperficial stroller is formed into columns precise synchronization application.

Description of drawings

Fig. 1 is the autonomous positioning timing schematic diagram of pulsar;

Fig. 2 is X ray pulsar timing layout chart;

Fig. 3 is that collaborative observation satellite to reference satellite time delay corrects schematic diagram;

Fig. 4 is synthetic aperture observation program process flow diagram.

Embodiment

The present invention includes following steps:

At first, according to long-term selected one group of millisecond pulsar that is applicable to the Navsat time synchronized of ground timing observation, Time Created is synchronous with millisecond pulsar database (the clock model parameter and the uranometry parameter that comprise every millisecond pulsar), and it is stored in the spaceborne computer of each Navsat.When practical application, according to the ephemeris of each Navsat and the location parameter of millisecond pulsar, selected one group of Navsat that can observe simultaneously same millisecond pulsar, from wherein selecting a Navsat as reference satellite, remaining Navsat is as collaborative observation satellite, and the observation data of collaborative observation satellite wants reduction to the reference satellite place.All collaborative observation satellites and reference satellite are carried out timing observation to same millisecond pulsar simultaneously, and original observed data is separately preserved.Simultaneously collaborative observation satellite and reference satellite according to separately the Position And Velocity parameter finish Doppler effect, the special relativity effect and Shapiro delay correction of original observation signal.After each timing observation was finished, each collaborative observation satellite was sent to reference satellite with observation data separately by range finding/communication link between star.By the different constantly relative position measurement data between star that reference satellite utilizes the inter-satellite link autonomous navigation system to provide, finish each collaborative observation satellite to the time delay correction at reference satellite place.Time delay correct process as shown in Figure 3:

At t constantly, i collaborative observation satellite position vector with respect to reference satellite in inertial space is

The direction vector of the pulsar of observing is Then t constantly collaborative satellite to the TOA measurement data time delay corrected value of reference satellite be Wherein c is the light velocity.Because i collaborative observation satellite is continually varying with respect to the dynamic position vector of reference satellite, so the photon sequence time of arrival (toa that collaborative observation satellite i observes _Ij) will correct accordingly one by one.Obtain one group of new observation sequence time of arrival, the detector that namely is equivalent to collaborative satellite i is placed on resulting TOA observation sequence on the reference satellite.

Secondly, the observation data of respectively organizing of finishing the time delay correction is carried out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry.

After the observation waveform that obtains synthetic aperture timing recording geometry, at first need the clock correction of the spaceborne clock of reference satellite is measured, measuring principle is as follows:

If the unit direction vector of the millisecond pulsar of observing in solar system geocentric coordinate system be

(wherein

Be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of the millisecond pulsar of observing), the solar system geocentric coordinate system position vector of reference satellite when epoch of observation is (wherein

Be respectively three coordinate components of position vector in solar system geocentric coordinate system of reference satellite), the pulse arrival time that the observation of synthetic aperture timing recording geometry obtains is toa _Sat, the moment that the same pulse that is obtained by the clock model prediction of this millisecond pulsar arrives solar system barycenter is toa _SSB, we can set up following observation equation.

$({\mathrm{toa}}_{\mathrm{sat}}-{\mathrm{toa}}_{\mathrm{SSB}})\·c={\stackrel{\→}{k}}_x\·{\stackrel{\→}{r}}_x+{\stackrel{\→}{k}}_y\·{\stackrel{\→}{r}}_y+{\stackrel{\→}{k}}_z\·{\stackrel{\→}{r}}_z+\mathrm{\Δ}{t}_c\·c+\mathrm{\δ}\·c$

In the formula, c is the light velocity, Δ t _cBe the deviation of the spaceborne clock of reference satellite and standard time TCB, δ is the summation of all the other timing observational errors.

After the measurement of finishing the spaceborne clock clock correction of reference satellite and since in the navigation constellation each satellite to have finished relative time synchronous, therefore can calculate the clock correction of each satellite of navigation constellation and standard time TCB.The spaceborne clock of each Navsat is converted to clock correction with respect to terrestrial time with respect to the clock correction of TCB, and in every satellite broadcast ephemeris separately, the clock error correction value is broadcast away, just can guarantee user's navigation and time service service precision, namely finish the autonomous time synchronized of Navsat.

The present invention is further described below in conjunction with drawings and Examples.

The invention provides a kind of navigation constellation method for synchronizing time based on X ray synthetic aperture observation program, have an observation time short, accuracy of observation is high, advantage easy to implement.

The present invention with the X ray millisecond pulsar as externally measured benchmark, utilize the X ray signal of its radiation as the input message of autonomous navigation system, in conjunction with communication between planets of the solar system ephemeris database, X ray pulsar clock model and characteristic parameter database, strapdown inertial navigation system (SINS), Autonomous Navigation Algorithm module, the star/link etc. of finding range, solved the problem of navigation constellation high-precision independent time synchronized.

The synthetic aperture observation of key point 1.X ray wave band.Namely carry an X-ray detector at every satellite, multi-satellite carries out timing observation to same pulsar simultaneously by the coordination of reference satellite, and records observation data separately.After observation is finished, communication/range finding link is sent to reference satellite with observation data separately between every passing of satelline star, reference satellite is after the time delay correction of finishing from the observation data of different satellites, all observation datas are carried out comprehensively, obtain the synthetic aperture timing observation data of reference satellite.The X-ray detector load that reduces Navsat, the technique effect that shortens observation time, the raising autonomous timing tracking accuracy of Navsat and real-time have been reached.

Resolving of key point 2. reference satellite clock correction parameters.On the basis that obtains reference satellite synthetic aperture observation data, utilize suitable algorithm, calculate the clock correction of the spaceborne clock of reference satellite with respect to the standard time.And utilize range finding/communication link between star, realize between other satellite carried clocks and the spaceborne clock of reference satellite synchronously, and then realize the autonomous time synchronized of navigation constellation.Arrived the technique effect of Navsat constellation high-precision independent time synchronized.

Navsat is after typing, and the equipment that carries on every satellite all is the same.According to these characteristics, the enforcement of technical solution of the present invention at first need to be carried an X-ray detector at every satellite.When utilizing after other technology finishes the autonomous measurement of Navsat position coordinates, utilize between star range finding/communication link to coordinate other multi-satellite (collaborative satellite) by reference satellite previously selected X ray millisecond pulsar is carried out timing observation, be that reference satellite and collaborative satellite all point to X-ray detector the measured pulse star, and record the x-ray photon time of arrival that receives separately.Simultaneously, all satellite utilization position, speed, attitude parameters separately that participate in observing are finished the correction of Doppler effect, special relativity effect, if the millisecond pulsar of observing is in binary-star system, need also then to consider that pulsar is around the revolve round the sun variation of caused apparent cycle of binary-star system barycenter.After observation was finished, each collaborative satellite was sent to reference satellite with observation data by range finding/communication link between star.

The time delays that reference satellite is at first finished the observation data that comes from different collaborative satellites correct, time delay correct process as shown in Figure 3:

At t constantly, i collaborative satellite position vector with respect to reference satellite in inertial space is

The direction vector of the pulsar of observing is

Then t constantly collaborative satellite to the TOA measurement data time delay corrected value of reference satellite be

Because i collaborative observation satellite is corded variations with respect to the dynamic position vector of reference satellite, so the photon sequence time of arrival (toa that collaborative observation satellite i observes _Ij) will correct accordingly one by one.Obtain one group of new observation sequence time of arrival, the detector that namely is equivalent to collaborative satellite i is placed on resulting TOA observation sequence on the reference satellite.

Finished from working in coordination with satellite to the time delay correction of reference satellite when the TOA observation sequence of all n collaborative observation satellite, just be equivalent to this n platform detector all is positioned over the reference satellite place, and obtained TOA observation sequence separately.Add the observation sequence of reference satellite detector, just obtain n+1 separate detectors at the TOA at reference satellite place observation sequence, the equivalent observation sequence that the observation sequence of this n+1 detector is superimposed and just can draws the synthetic aperture detector.

Compare with simple detector, the synthetic aperture detector is through the stack to n+1 sub-detector observation signal, the signal to noise ratio (S/N ratio) of observation signal can be promoted to the original signal signal to noise ratio (S/N ratio)

Doubly.Namely for same pulsar, for obtaining the integrated pulse profile of same signal to noise ratio (S/N ratio), utilize the synthetic aperture observation technology, observation time can be foreshortened to original

Fig. 4 is the process flow diagram of above-mentioned synthetic aperture observation program:

At first, all collaborative observation satellites are carried out timing observation to same millisecond pulsar simultaneously under the coordination of reference satellite, every satellite is preserved original observed data separately, and finishes the correction of the multinomial error sources such as Doppler effect, special relativity effect according to the Position And Velocity parameter of satellite.After this observation was finished, each collaborative observation satellite was sent to reference satellite with observation data separately by range finding/communication link between star.By the different constantly relative position measurement data between star that reference satellite utilizes the inter-satellite link autonomous navigation system to provide, finish each collaborative satellite to the time delay correction at reference satellite place.The observation data of respectively organizing of finishing the time delay correction is carried out the observation waveform that overlap-add procedure just can obtain synthetic aperture timing recording geometry.

After obtaining clearly pulse profile, at first need the clock correction of the spaceborne clock of reference satellite is measured, measuring principle is as follows:

If the unit direction vector of the pulsar of observing is

The solar system geocentric coordinate system position vector of Navsat when epoch of observation is The moment that the pulse that observation obtains arrives satellite is toa _Sat, the moment that the same pulse that is obtained by the clock model prediction arrives solar system barycenter is toa _SSB, we can set up following observation equation.

$({\mathrm{toa}}_{\mathrm{sat}}-{\mathrm{toa}}_{\mathrm{SSB}})\·c={\stackrel{\→}{k}}_x\·{\stackrel{\→}{r}}_x+{\stackrel{\→}{k}}_y\·{\stackrel{\→}{r}}_y+{\stackrel{\→}{k}}_z\·{\stackrel{\→}{r}}_z+\mathrm{\Δ}{t}_c\·c+\mathrm{\δ}\·c$

In the formula, c is the light velocity, Δ t _cBe the deviation of the spaceborne clock of reference satellite and standard time TCB, δ is the summation of all the other timing observational errors.Because Navsat has utilized other autonomous navigation technology to finish the measurement of solar system geocentric coordinate system position coordinates, therefore only has a unknown quantity Δ t in the situation that ignore measuring error following formula right-hand member _cIn theory, a millisecond pulsar is carried out the measurement that timing observation just can be finished the spaceborne clock clock correction of reference satellite, but in order better to eliminate observational error, also need many millisecond pulsars are carried out repeatedly observation, to improve accuracy of observation.After the measurement of finishing the spaceborne clock clock correction of reference satellite and since in the navigation constellation each satellite to have finished relative time synchronous, therefore can calculate the clock correction of each satellite of navigation constellation and standard time TCB.The spaceborne clock of each Navsat is converted to the terrestrial time with respect to TT(with respect to the clock correction of TCB) clock correction, and in every satellite broadcast ephemeris separately, the clock error correction value is broadcast away, just can guarantee user's navigation and time service service precision, namely finish the autonomous time synchronized of Navsat.

Claims (1)

1. the autonomous method for synchronizing time of Navsat based on synthetic aperture observation is characterized in that comprising the steps:

Step 1, according to the ephemeris of each Navsat and the location parameter of millisecond pulsar, selected one group of Navsat that can observe simultaneously same millisecond pulsar, and therefrom choose one wantonly as reference satellite, remaining Navsat is as collaborative observation satellite, and the observation data of collaborative observation satellite wants reduction to the reference satellite place;

Step 2, all collaborative observation satellites and reference satellite are carried out timing observation to same millisecond pulsar simultaneously, and original observed data is separately preserved; Simultaneously collaborative observation satellite and reference satellite according to separately the Position And Velocity parameter finish Doppler effect, the special relativity effect and Shapiro delay correction of original observation signal;

Step 3, after each timing observation was finished, each collaborative observation satellite was sent to reference satellite with observation data separately;

Step 4, reference satellite are utilized different constantly relative position measurement data between star, finish each collaborative observation satellite to the time delay correction at reference satellite place, and concrete grammar is:

At t constantly, i collaborative observation satellite position vector with respect to reference satellite in inertial space is

The direction vector of the millisecond pulsar of observing is

Then t constantly collaborative observation satellite to the TOA measurement data time delay corrected value of reference satellite be

Wherein c is the light velocity; The photon sequence time of arrival toa that collaborative observation satellite i observes _IjCorrect one by one, obtain one group of new observation sequence time of arrival, the detector that namely is equivalent to collaborative satellite i is placed on resulting TOA observation sequence on the reference satellite;

Step 5 is carried out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry to the observation data of respectively organizing of finishing the time delay correction;

Step 6 is measured the clock correction of the spaceborne clock of reference satellite, and concrete grammar is:

If the unit direction vector of the millisecond pulsar of observing in solar system geocentric coordinate system be

Wherein

Be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of the millisecond pulsar of observing, the solar system geocentric coordinate system position vector of reference satellite when epoch of observation is

Wherein

Be respectively three coordinate components of position vector in solar system geocentric coordinate system of reference satellite, the pulse arrival time that the observation of synthetic aperture timing recording geometry obtains is toa _Sat, the moment that the same pulse that is obtained by the clock model prediction of this millisecond pulsar arrives solar system barycenter is toa _SSB, then observation equation is

$({\mathrm{toa}}_{\mathrm{sat}}-{\mathrm{toa}}_{\mathrm{SSB}})\·c={\stackrel{\→}{k}}_x\·{\stackrel{\→}{r}}_x+{\stackrel{\→}{k}}_y\·{\stackrel{\→}{r}}_y+{\stackrel{\→}{k}}_z\·{\stackrel{\→}{r}}_z+\mathrm{\Δ}{t}_c\·c+\mathrm{\δ}\·c$

In the formula, Δ t _cBe the deviation of the spaceborne clock of reference satellite and standard time TCB, δ is the summation of all the other timing observational errors;

Step 7, calculate the clock correction of each satellite of navigation constellation and standard time TCB, the spaceborne clock of each Navsat is converted to clock correction with respect to terrestrial time with respect to the clock correction of TCB, and in every satellite broadcast ephemeris separately, the clock error correction value is broadcast away, just can guarantee user's navigation and time service service precision, namely finish the autonomous time synchronized of Navsat.

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