CN103033188B - The autonomous method for synchronizing time of Navsat based on synthetic aperture observation - Google Patents

Abstract

The invention provides the autonomous method for synchronizing time of a kind of Navsat based on synthetic aperture observation, all synergistic observation satellites and reference satellite are carried out timing to same millisecond pulsar simultaneously and are observed, reference satellite utilizes not relative position measurement data between star in the same time, carrying out each synergistic observation satellite to the time delay at reference satellite place to correct, having carried out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry to completing each group of observation data that time delay corrects; The clock correction of the spaceborne clock of reference satellite is measured, calculates the clock correction of each satellite of navigation constellation and standard time TCB and in the respective broadcast ephemeris of every satellite, clock error correction value broadcast away, namely completing the autonomous time synchronized of Navsat.Invention achieves the X-ray detector load reducing Navsat, the technique effect shortening observation time, improve the autonomous timing tracking accuracy of Navsat and real-time.

Description

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

Technical field

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

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, can provide round-the-clock for the users of earth surface and terrestrial space, the navigation information service such as round-the-clock, high-precision Position, Velocity and Time.Complete satellite navigation system comprises three large ingredient, i.e. space constellation part (navigation constellation), ground control segment and user terminal parts.Wherein, ground control segment is by the multiple monitoring station and the injection plant that are distributed in the whole world, and 1 main control centre station composition, be responsible for carrying out tracking observation to Navsat, precision determines satellite orbit and spaceborne clock parameter, establishment navigation message and steering order, and be injected into Navsat via up data link.Navsat extracts up injection information, is broadcast by navigation message to user terminal receiver and uses.That is, the operation of current navigation constellation, management and maintenance have all been responsible for by ground control system, and daily requirement does a uplink information and injects (as gps system).

If Navsat can realize independent navigation and the operational management of long period, will effectively reduce the laying quantity of ground control station, alleviate 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 the uplink information injection number of times of land station to satellite, reduce navigation constellation to the degree of dependence of ground observing and controlling system, strengthen the autonomous viability of satellite navigation system at particular time.Visible, navigation constellation independent navigation has extremely important practical engineering application and is worth.

The U.S. has carried out modernization restructuring to its gps system for this reason, the series of satellites such as GPSBlockIIR/IIR-M, BlockIIF add between star/range finding the link that communicates, by bidirectional ranging, exchanges data and spaceborne computer filtering process between star, continuous correction satellite Long-term forecasting ephemeris and timing parameter are also autonomous generates navigation message and steering order, maintain the stable of the basic configuration of constellation, to meet user's continuous precise navigator fix application demand.

But this navigation constellation independent navigation mode based on inter-satellite link ranging information, lacks outside space-time datum data, be difficult to solution two class unobservability error and accumulate problem in time.One class is constellation integral-rotation error, and this error can cause constellation entirety to drift about relative 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 relative 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, solve the problem two kinds of Basic Ways: (1) by setting up the Long-term prediction model of constellation integral-rotation and earth rotation, suppresses the accumulation of error (as gps satellite independent navigation mode).But this method is from practical application effect, thoroughly do not solve this technical barrier, the long-time autonomous navigation technology index request of constellation can not be met; (2) adopt navigation constellation " to cast anchor " technology, by land station regularly to constellation satellite launch distance measuring signal and modulation earth rotation parameter (ERP) information, star carries out information processing, suppresses constellation unobservability error to accumulate in time.But this settling mode by setting up satellite-ground link, has run counter to the principle of the long-time autonomous operation of Navsat.

In recent years, along with home and abroad is to the extensive research of the Spacecraft Autonomous Navigation Technology observed based on X ray millisecond pulsars timing, for navigation satellite autonomous navigation provides a kind of new thinking and feasible way, especially for navigation constellation provides one independently outside absolute space-time benchmark, the long-time autonomous operation problem of constellation can be solved.Spacecraft Autonomous Navigation based on the observation of X ray millisecond pulsars timing is the effective model of the spacecraft high-precision independent navigation realized truly.Pulsar autonomous navigation technology is applied to GLONASS (Global Navigation Satellite System) (GlobalNavigationSatelliteSystem, GNSS), the autonomous time synchronized of Navsat and the autonomous measurement of satellite ephemeris and renewal can be realized.This independent navigation with pulsar inertia space-time frame of reference for reference, there is not rotation and time drift relative to inertial reference frame in pulsar space-time frame of reference, thus can suppress or eliminate the long term drift error of constellation self rotation error and Navsat time reference.Apply pulse star airmanship also accurately can measure constellation mean timing error and the constellation integral-rotation error of the existence of GNSS independent navigation.

When navigation application, scope when utilizing the roentgenometer that Navsat is equipped, Time of arrival is carried out to one group of millisecond pulsar selected in advance, the pulse recording every pulsar arrives the moment of Navsat, utilize pulsar clock model to forecast moment that same pulse arrives solar system barycenter simultaneously, comparing of Navsat and solar system barycenter moment is arrived by same pulse, again in conjunction with the space position parameter of this set of pulses star, just can calculate observation moment Navsat relative to the position vector (three-dimensional coordinate) of solar system barycenter and spaceborne clock relative to standard time (solar system barycentric coordinate time, TCB) clock correction.Its ultimate principle as shown in Figure 1.In FIG, Navsat utilizes the X-ray pulsar autonomous navigation system carried to measure Navsat relative to the position of solar system barycenter and spaceborne clock relative to the clock correction of standard time, realizes autonomous location and timing.X-ray pulsar autonomous navigation system mainly comprises following a few part: 4 X-ray detectors, and for detecting the X-ray pulse signal from pulsar, and acquisition has the integrated pulse profile being satisfied with signal to noise ratio (S/N ratio) within certain integral time; Satellite atomic clock, for the measurement of TOA provides the reference time; X-ray pulsar and celestial body in solar system ephemeris data storehouse, provide the basic data that pulsar space-time frame of reference and navigation algorithm need; TOA measures and processing module, adopts appropriate algorithm, utilizes integrated pulse profile, obtains the pulse arrival time observed and obtaining; Navsat Position, Velocity and Time algoritic module, utilizes and observes the TOA obtained set up 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.During roentgenometer, the basic structure of recording geometry as shown in Figure 2, carried X-ray detector aims at the mark source by spacecraft, observe and record (TimeofArrival time of arrival of the x-ray photon from target source and background sky district thereof, TOA), the measurement of time of arrival is the time signal that provides with satellite atomic clock is reference, then records original observation data by digital data recording system.High-speed motion due to spacecraft can cause observation signal to produce obvious Doppler effect; Due to the impact of special relativity effect, the actual vibration frequency of satellite atomic clock also can change relative to its nominal frequency; And the millisecond pulsar many places being applicable to Spacecraft Autonomous Navigation found at present are in binary-star system, cause observed pulsar also can produce extra impact to observation signal around the revolution motion of binary-star system barycenter; In addition, the impact considering the multinomial error sources such as Shapiro delay is also needed.Therefore original observation data will through the further process of observation data pretreatment system, to eliminate the impact of various error source on observation data.After the correction completing every error source, according to the rotation period of observed pulsar, overlap-add procedure is carried out to observation sequence, to obtain the integrated pulse profile having and be satisfied with signal to noise ratio (S/N ratio).Add this initial time observed after being compared by the full sized pules profile recorded in integrated pulse profile and database, just obtain the TOA of this observation.

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

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.To use it for the independent navigation of Navsat, just must take measures to improve signal to noise ratio (S/N ratio), having two kinds of solutions at present: one extends observation time; Another kind uses large-area detector.But two schemes all has its limitation, for the first scheme, the prolongation of observation time can reduce the real-time of navigational solution, cannot realize the quasi real time monitoring to navigation information integrality, and extend 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.

For the autonomous measurement of Navsat position coordinates, there is a kind of comparatively feasible technical scheme at present, namely utilize and two Navsats equip X-ray detector and observe same X ray become source simultaneously, line between these two satellites forms dynamic Cross-Link measurement baseline, namely the difference that same signal arrives the time of two satellites reflects the direction of Inter-satellite Baseline relative to pulsar, just can measure the direction of Inter-satellite Baseline in inertia space-time frame of reference by the simultaneous observation many X ray being become to source signal.Measure the direction of many Inter-satellite Baselines in inertia space-time frame of reference simultaneously, and in conjunction with the measurement result of H_2O maser/communication link and motion dynamics equations, just can realize the autonomous mensuration of Navsat position coordinates.X ray becomes flow high 5 ~ 6 magnitudes usually 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 grown very much, just can obtain higher measuring accuracy.But utilize X ray to become source and cannot realize the autonomous time synchronized of Navsat, only have and utilize X ray millisecond pulsar just can realize the autonomous time synchronized of Navsat.

In sum, to X-ray pulsar autonomous navigation technology is applied to Navsat to realize the autonomous time synchronized of navigation constellation, the too low problem of observation signal signal to noise ratio (S/N ratio) must just be solved.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 extend observation time, two kinds of methods exist following problem respectively:

For Navsat, it to carry atomic clock group, the time frequency signal generation equipment that for navigation signal produces, keep and launch a large amount of with keeping system, antenna, solar cell etc.The useful load can distributing to X-ray detector system is very limited, and large-area X-ray detector volume is large, quality is large, power consumption is high, inherently takies more Satellite Payloads, is difficult to carry out.And existing pulsar autonomous navigation technology requires to carry 4 X-ray detectors usually on satellite, it is more infeasible that this just makes the scheme of carrying large area x-ray detector on Navsat become.

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

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

Summary of the invention

Too low and be difficult to the deficiency of identification in order to overcome the observation signal signal to noise ratio (S/N ratio) existed in existing pulsar autonomous navigation technology, the present invention proposes a kind of synthetic aperture observation scheme of X ray wave band, when not increasing detector area, not extending observation time, well solve Testing of Feeble Signals problem existing in the autonomous time synchronized of navigation constellation based on pulsar, measuring accuracy is high and easy to implement.

The technical solution adopted for the present invention to solve the technical problems comprises the following steps:

Step one, according to the ephemeris of each Navsat and the location parameter of millisecond pulsar, select the Navsat that a group can observe same millisecond pulsar simultaneously, and therefrom optional one as reference satellite, remaining Navsat is as synergistic observation satellite, and the observation data of synergistic observation satellite wants reduction to reference satellite place;

Step 2, all synergistic observation satellites and reference satellite are carried out timing to same millisecond pulsar simultaneously and are observed, and respective original observed data are preserved; Simultaneously synergistic observation satellite and reference satellite complete the Doppler effect of original observation signal, special relativity effect and Shapiro according to respective Position And Velocity parameter and postpone to correct;

Step 3, after each timing has been observed, respective observation data has been sent to reference satellite by each synergistic observation satellite;

Step 4, reference satellite utilizes not relative position measurement data between star in the same time, and carried out each synergistic observation satellite to the time delay at reference satellite place and corrected, concrete grammar is:

In t, i-th synergistic observation satellite relative to the position vector of reference satellite is in inertial space observe the direction vector of millisecond pulsar be then t synergistic observation satellite to the TOA measurement data time delay corrected value of reference satellite is wherein c is the light velocity; Photon sequence toa time of arrival that synergistic observation satellite i observes _ijcorrect one by one, obtain one group of new observation sequence time of arrival, be namely equivalent to and the detector of collaborative satellite i is placed on the TOA observation sequence that reference satellite obtains;

Step 5, carries out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry to each group of observation data completing time delay correction;

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

If observe the unit direction vector of millisecond pulsar in solar system geocentric coordinate system be wherein be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of observed millisecond pulsar, 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, timing recording geometry in synthetic aperture observes the pulse arrival time obtained be toa _sat, the moment that the same pulse 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 formula, Δ t _cfor 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, spaceborne for each Navsat clock is converted to clock correction relative to terrestrial time relative to the clock correction of TCB, and in the respective broadcast ephemeris of every satellite, clock error correction value is broadcast away, just can ensure that precision is served in navigation and the time service of user, namely complete the autonomous time synchronized of Navsat.

The invention has the beneficial effects as follows: combine after the observed result of little for multiple stage detector is carried out time delay correction, form the observation effect of a large detector.Reach the X-ray detector load reducing Navsat, the technique effect shortening observation time, improve the autonomous timing tracking accuracy of Navsat and real-time.The present invention is also applicable to near-earth orbit, deep space and interplanetary flight Spacecraft formation, and without the precise synchronization application that dense atmosphere celestial body lander is formed into columns and surperficial stroller is formed into columns.

Accompanying drawing explanation

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

Fig. 2 is X-ray pulsar timing layout chart;

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

Fig. 4 is synthetic aperture observation protocol procedures figure.

Embodiment

The present invention includes following steps:

First, the millisecond pulsar that one group is applicable to Navsat time synchronized is selected according to long-term ground timing observation, synchronously use millisecond pulsar database (comprising clock model parameter and the uranometry parameter of every millisecond pulsar) Time Created, and be 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, select the Navsat that a group can observe same millisecond pulsar simultaneously, from wherein selecting a Navsat as reference satellite, remaining Navsat is as synergistic observation satellite, and the observation data of synergistic observation satellite wants reduction to reference satellite place.All synergistic observation satellites and reference satellite are carried out timing to same millisecond pulsar simultaneously and are observed, and respective original observed data are preserved.Simultaneously synergistic observation satellite and reference satellite complete the Doppler effect of original observation signal, special relativity effect and Shapiro according to respective Position And Velocity parameter and postpone to correct.After each timing has been observed, respective observation data has been sent to reference satellite by H_2O maser/communication link by each synergistic observation satellite.The not relative position measurement data between star in the same time utilizing inter-satellite link autonomous navigation system to provide by reference satellite, have carried out each synergistic observation satellite to the time delay at reference satellite place and have corrected.Time delay correct process as shown in Figure 3:

In t, i-th synergistic observation satellite relative to the position vector of reference satellite is in inertial space observe the direction vector of pulsar be then t is worked in coordination with satellite to the TOA measurement data time delay corrected value of reference satellite and is wherein c is the light velocity.Because i-th synergistic observation satellite is continually varying relative to the dynamic position vector of reference satellite, so the photon sequence time of arrival (toa that synergistic observation satellite i observes _ij) will correct accordingly one by one.Obtain one group of new observation sequence time of arrival, be namely equivalent to and the detector of collaborative satellite i is placed on the TOA observation sequence that reference satellite obtains.

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

After the observation waveform obtaining synthetic aperture timing recording geometry, first need to measure the clock correction of the spaceborne clock of reference satellite, measuring principle is as follows:

If observe the unit direction vector of millisecond pulsar in solar system geocentric coordinate system be (wherein be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of observed millisecond pulsar), 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), timing recording geometry in synthetic aperture observes the pulse arrival time obtained be toa _sat, the moment that the same pulse 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 formula, c is the light velocity, Δ t _cfor 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 completing the spaceborne clock clock correction of reference satellite, because satellite each in navigation constellation has completed relative time synchronously, therefore can calculate the clock correction of each satellite of navigation constellation and standard time TCB.Spaceborne for each Navsat clock is converted to clock correction relative to terrestrial time relative to the clock correction of TCB, and in the respective broadcast ephemeris of every satellite, clock error correction value is broadcast away, just can ensure that precision is served in navigation and the time service of user, namely complete the autonomous time synchronized of Navsat.

Below in conjunction with drawings and Examples, the present invention is further described.

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

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

The synthetic aperture observation of key point 1.X ray wave band.Namely on every satellite, carry an X-ray detector, multi-satellite carries out timing observation to same pulsar by the coordination of reference satellite simultaneously, and records respective observation data.After observation completes, respective observation data is sent to reference satellite by the link that communicates between every passing of satelline star/find range, reference satellite is after completing the time delay correction from the observation data of different satellite, all observation datas are carried out comprehensively, obtain the synthetic aperture timing observation data of reference satellite.Reach the X-ray detector load reducing Navsat, the technique effect shortening observation time, improve the autonomous timing tracking accuracy of Navsat and real-time.

Resolving of key point 2. reference satellite clock correction parameter.On the basis obtaining reference satellite synthetic aperture observation data, utilize suitable algorithm, calculate the clock correction of the spaceborne clock of reference satellite relative to the standard time.And utilize H_2O maser/communication link, what realize between other satellite carried clocks with the spaceborne clock of reference satellite is synchronous, and then realizes the autonomous time synchronized of navigation constellation.Reach the technique effect of Navsat constellation high-precision independent time synchronized.

Navsat is after sizing, and the equipment that every satellite carries is all the same.According to this feature, first the enforcement of technical solution of the present invention need to carry an X-ray detector on every satellite.When utilizing after other technology completes the autonomous measurement of Navsat position coordinates, utilize H_2O maser/communication link to coordinate other multi-satellite (collaborative satellite) by reference satellite and timing observation is carried out to previously selected X ray millisecond pulsar, namely X-ray detector is all pointed to measured pulse star by reference satellite and collaborative satellite, and records the x-ray photon time of arrival received separately.Simultaneously, the correction that all satellites participating in observation utilize respective position, speed, attitude parameter complete Doppler effect, special relativity effect, if the millisecond pulsar observed is in binary-star system, then also need to consider the change of pulsar around the apparent cycle caused by the revolution of binary-star system barycenter.After observation completes, observation data is sent to reference satellite by H_2O maser/communication link by each collaborative satellite.

The time delay that first reference satellite completes the observation data coming from different collaborative satellite corrects, time delay correct process as shown in Figure 3:

In t, i-th collaborative satellite relative to the position vector of reference satellite is in inertial space observe the direction vector of pulsar be then t is worked in coordination with satellite to the TOA measurement data time delay corrected value of reference satellite and is because i-th synergistic observation satellite is corded variations relative to the dynamic position vector of reference satellite, so the photon sequence time of arrival (toa that synergistic observation satellite i observes _ij) will correct accordingly one by one.Obtain one group of new observation sequence time of arrival, be namely equivalent to and the detector of collaborative satellite i is placed on the TOA observation sequence that reference satellite obtains.

After the TOA observation sequence time delay completed from collaborative satellite to reference satellite of all n synergistic observation satellite corrects, be just equivalent to and this n platform detector is all positioned over reference satellite place, and obtain respective TOA observation sequence.Add the observation sequence of reference satellite detector, just obtain the TOA observation sequence of n+1 separate detectors at reference satellite place, being superimposed by the observation sequence of this n+1 detector just to draw the equivalent observation sequence of synthetic aperture detector.

Compared with simple detector, the signal to noise ratio (S/N ratio) of observation signal through the superposition to n+1 sub-detector observation signal, can be promoted to original signal signal to noise ratio (S/N ratio) by synthetic aperture detector doubly.Namely for same pulsar, for obtaining the integrated pulse profile of same signal to noise ratio (S/N ratio), utilizing synthetic aperture observation technology, observation time can be foreshortened to original $\frac{1}{\sqrt{n+1}}.$

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

First, all synergistic observation satellites carry out timing observation to same millisecond pulsar under the coordination of reference satellite simultaneously, respective original observed data is preserved by every satellite, and completes the correction of the multinomial error source such as Doppler effect, special relativity effect according to the Position And Velocity parameter of satellite.After this has been observed, respective observation data has been sent to reference satellite by H_2O maser/communication link by each synergistic observation satellite.The not relative position measurement data between star in the same time utilizing inter-satellite link autonomous navigation system to provide by reference satellite, have carried out each collaborative satellite to the time delay at reference satellite place and have corrected.The observation waveform that overlap-add procedure just can obtain synthetic aperture timing recording geometry is carried out to each group of observation data completing time delay correction.

Obtaining clearly after pulse profile, first need to measure the clock correction of the spaceborne clock of reference satellite, measuring principle is as follows:

If observe the unit direction vector of pulsar be the solar system geocentric coordinate system position vector of Navsat when epoch of observation is the moment observing the pulse obtained arrive satellite is toa _sat, the moment that the same pulse obtained by 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 formula, c is the light velocity, Δ t _cfor 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 complete the measurement of solar system geocentric coordinate system position coordinates, therefore when ignoring measuring error, above formula right-hand member only has a unknown quantity Δ t _c.In theory, the measurement that timing observation just can complete the spaceborne clock clock correction of reference satellite is carried out to a millisecond pulsar, but in order to better eliminate observational error, also needs to carry out many millisecond pulsars repeatedly to observe, to improve accuracy of observation.After the measurement completing the spaceborne clock clock correction of reference satellite, because satellite each in navigation constellation has completed relative time synchronously, therefore can calculate the clock correction of each satellite of navigation constellation and standard time TCB.Spaceborne for each Navsat clock is converted to clock correction relative to TT (terrestrial time) relative to the clock correction of TCB, and in the respective broadcast ephemeris of every satellite, clock error correction value is broadcast away, just can ensure that precision is served in navigation and the time service of user, namely complete the autonomous time synchronized of Navsat.

Claims (1)

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

Step one, according to the ephemeris of each Navsat and the location parameter of millisecond pulsar, select the Navsat that a group can observe same millisecond pulsar simultaneously, and therefrom optional one as reference satellite, remaining Navsat is as synergistic observation satellite, and the observation data of synergistic observation satellite wants reduction to reference satellite place;

Step 2, all synergistic observation satellites and reference satellite are carried out timing to same millisecond pulsar simultaneously and are observed, and respective original observed data are preserved; Simultaneously synergistic observation satellite and reference satellite complete the Doppler effect of original observation signal, special relativity effect and Shapiro according to respective Position And Velocity parameter and postpone to correct;

Step 3, after each timing has been observed, respective observation data has been sent to reference satellite by each synergistic observation satellite;

Step 4, reference satellite utilizes not relative position measurement data between star in the same time, and carried out each synergistic observation satellite to the time delay at reference satellite place and corrected, concrete grammar is:

In t, i-th synergistic observation satellite relative to the position vector of reference satellite is in inertial space observe the unit direction vector of millisecond pulsar in solar system geocentric coordinate system be then t synergistic observation satellite to the TOA measurement data time delay corrected value of reference satellite is wherein c is the light velocity; Photon sequence toa time of arrival that synergistic observation satellite i observes _ijcorrect one by one, obtain one group of new observation sequence time of arrival, be namely equivalent to and the detector of collaborative satellite i is placed on the TOA observation sequence that reference satellite obtains;

Step 5, carries out overlap-add procedure to obtain the observation waveform of synthetic aperture timing recording geometry to each group of observation data completing time delay correction;

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

If observe the unit direction vector of millisecond pulsar in solar system geocentric coordinate system be wherein be respectively three coordinate components of unit direction vector in solar system geocentric coordinate system of observed millisecond pulsar, 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, timing recording geometry in synthetic aperture observes the pulse arrival time obtained be toa _sat, the moment that the same pulse obtained by the clock model prediction of this millisecond pulsar arrives solar system barycenter is toa _sSB, then observation equation is

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

In formula, Δ t _cfor 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, spaceborne for each Navsat clock is converted to clock correction relative to terrestrial time relative to the clock correction of TCB, and in the respective broadcast ephemeris of every satellite, clock error correction value is broadcast away, just can ensure that precision is served in navigation and the time service of user, namely complete the autonomous time synchronized of Navsat.