RU2367910C1 - Method for building of orbit-based functional addition to global navigation system - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: invention is related to satellite navigation and may be used to build orbit-based functional addition to global navigation satellite system (GLONASS). Substance of method consists in the fact that on board of low-orbit spacecraft navigation equipment of user is installed, which is used to receive navigation messages, as well as additional equipment used to receive signals of on-air television of ground stationary television radio stations, bearing frequencies of two or more television channels are separated, on the basis of which Doppler shift of bearing frequencies is detected, orbit parametres are detected, calculating ephemerids of spacecraft, and navigation messages are formed in accordance with specified structure of navigation message, then radio navigation signals are broadcasted in direction of navigation information consumer location.

EFFECT: higher reliability of navigation detections of navigation information consumers performed with the help of GLONASS, due to increase of orbit-based navigation message sources number.

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Description

There is a method of building a ground-based functional complement to the global navigation satellite system (GNSS), based on the placement on the earth's surface of additional analog radio stations of the on-board radio equipment of GNSS navigation spacecraft, while forming navigation messages in accordance with the structure of the GNSS navigation message, emitting radio navigation signals in the direction of the location of consumers of navigation information [1, p.203].

The disadvantage of this method is that the territory of the earth's surface on which the navigation message emitted by one terrestrial radio station can be received is relatively small, since the radio waves used to transmit the navigation message propagate in direct line of sight from the antenna emitter. Therefore, when implementing this method of constructing a functional supplement to cover a large territory, it is necessary to install a large number of ground-based transmitters.

There is also a known method of constructing a functional complement to orbital-based GNSS, based on the launch of two spacecraft into highly elliptical orbits with an apogee of 47 ÷ 50 thousand km and a perigee of 25 ÷ 22 thousand km [2, p. 7-15]. To implement the method, the following set of actions is carried out: two spacecraft are placed in highly elliptical orbits; measure the current navigation parameters of the orbits of the spacecraft of the functional complement using ground-based measuring instruments; transmit the measured parameters to the center of the ground control complex; determine the parameters of the orbit and calculate the ephemeris of each satellite of the functional complement in the ground control complex; transmit ephemeris aboard the NCA; generating navigation messages in accordance with a given GNSS message structure; broadcast radio navigation signals in the direction of the location of consumers of navigation information. A system of 20 spacecraft, including two spacecraft in such highly elliptical orbits and 18 full-time GLONASS spacecraft, is equivalent to a system of 24 full-time spacecraft GLONASS. A sign characterizing such a way of constructing a functional complement is the placement of the spacecraft in highly elliptical, and not in traditional, circumcircular orbits. Such an action ensures that at least four spacecraft are located in the radio visibility zone of surface consumers of navigation information with a smaller total number of the entire spacecraft orbital grouping.

The disadvantages of the method are: firstly, the fact that the launch to highly elliptical orbits of two spacecraft requires a significant expenditure of resources in excess of the cost of resources to launch to the regular orbits of the GNSS; secondly, the use of orbits that are different from the orbits of GNSS full-time spacecraft leads to the need for time-consuming additional studies to determine patterns of navigation measurements of orbits that provide the required accuracy in calculating ephemeris information. In addition, the flight of a spacecraft of a functional complement in a highly elliptical orbit leads to the need to control the orientation of the spacecraft and the radiation pattern of the antenna emitting a navigation message, which complicates the control technology for the use of such spacecraft.

The technical result achieved by the invention is to increase the reliability of navigation definitions of consumers of navigation information performed using GNSS, by increasing the number of sources of navigation messages orbital-based. The invention, in addition, provides the expansion of the field of application of low-orbit spacecraft (SC), not specifically designed to solve the problems of terrestrial consumers, as well as high operational efficiency of the use of the SC of a functional complement due to the absence of the need for the resources of the ground-based complex to calculate the ephemeris information necessary for operation KA functional complement.

The basis of the invention is the task of determining the orbit parameters of a low-orbit spacecraft in autonomous flight using signals from terrestrial stationary television radio stations emitted during television broadcasting, with an error not exceeding the error of the orbit parameters of the standard GNSS NS.

The essence of the invention lies in the fact that to achieve the above technical results, in the method of constructing a functional complement of orbital-based navigation to a global navigation satellite system aboard a low-orbit spacecraft, the intended purpose of which is not related to the task of broadcasting navigation messages for consumers of satellite navigation information, is placed navigation equipment GNSS consumer through which navigation messages are received, and additional the equipment with which terrestrial stationary television radio stations receive terrestrial television signals, select the carrier frequencies of two or more television channels, determine the Doppler shift of the carrier frequencies, determine the orbit parameters, calculate the ephemeris of the spacecraft, generate navigation messages in accordance with the structure of the GNSS navigation message, broadcast radio navigation signals in the direction of the location of consumers of navigation information.

The essential features characterizing the invention and providing a technical result.

1. The inclusion in the composition of the onboard equipment of a low-orbit spacecraft, which is not properly designed for solving navigation problems by surface consumers of GNSS information, additional equipment, providing an extension of the scope of its functional application.

2. The following set of sequential actions for the formation of the navigation message KA functional additions:

- reception of broadcast television signals;

- Measurement of the current navigation parameters of the orbit by the signals of terrestrial television;

- determination of the parameters of the orbit of the spacecraft of the functional complement by the current navigation parameters measured by television signals;

- Reception of navigation messages of GNSS NSA;

- Calculation of the ephemeris KA functional additions;

- the formation of the navigation messages of the spacecraft of the functional complement and the sequence of radio navigation signals;

- broadcast of radio navigation signals in the direction of the location of consumers of navigation information.

Existing methods for constructing a functional complement to GNSS are based on the deployment of ground-based or orbital-based technical systems designed specifically for the formation of a navigation message and its broadcasting in the direction of the location of consumers. To implement the existing methods for constructing a functional complement, resources are required not only for the placement of technical systems of the functional complement, but also for the operation of such technical systems. So, in the case of applying the method of constructing a functional complement in highly elliptical orbits [2, pp. 7-15], the set of actions carried out to calculate the ephemeris of such spacecraft and the formation of navigation messages is provided to remain the same as with the existing regular set of actions performed for calculation of ephemeris and the formation of navigation messages of regular GNSS NS.

In the claimed method, additional costs for the deployment of technical systems designed for the formation and broadcast of navigation messages are not required, since low-orbit spacecraft can be used as carriers of technical systems of functional complement, placed in orbits for solving problems of space communications, remote sensing of the Earth, geodesic and meteorological providing. For such spacecraft, the task of generating and broadcasting radio navigation signals is not a regular one. When installing additional navigation equipment on board such spacecraft and using television signals to determine the parameters of the orbits, the resources of the ground-based control complex are not required to solve the problems of calculating the ephemeris information of the spacecraft designed to build a GNSS functional supplement. Thus, a high operational efficiency of the application of the spacecraft of the functional supplement is achieved.

The justification of the feasibility of the method of constructing a functional supplement is: firstly, to justify the possibility of autonomous determination of the spacecraft’s orbit by on-board equipment using television signals with an error not exceeding the error in determining the orbits of GNSS navigation spacecraft; secondly, in substantiating the possibility of forming a navigation message on board a spacecraft functional message based on the information contained in the received navigation message of the GNSS spacecraft and the orbit parameters calculated from television signals.

The prerequisites for the possibility of using television signals to measure the current navigation parameters of the orbit with the high accuracy necessary to determine the parameters of the orbit of a functional satellite are the following characteristics of the broadcast television network [3, p.240, 251]:

a) radio broadcasting stations have a high radiation power, and an extensive network of radio stations with known emitter coordinates has been created in the territory of the Russian Federation, which currently includes about 350 radio stations with a power of 5 to 50 kW;

b) television signals are highly stable carrier frequencies of the image.

In the proposed method, the radial speed of its movement relative to the television radio station is used as the current navigation parameter for calculating the ephemeris of the spacecraft of the functional supplement. The error in measuring the radial velocity V _R from the television broadcasting signals with the unrequited method of measuring the radial speed of movement relative to the television radio station is estimated by the formula [4, p.155]

where C, ΔC is the speed of light and the error of its determination;

f _0KA , Δf _0KA - frequency and frequency deviation of the reference generator of the spacecraft from the nominal value;

f ₀ , Δf ₀ - frequency and frequency deviation of the reference generator of a television radio station from the nominal value;

Δf _∂ is the instrumental error in measuring the Doppler frequency shift.

Suppose that reference frequency generators are installed on a television radio station and satellite, for which the characteristics of the relative instability of the reference frequency generators are close: Δf ₀ / f ₀ ≈Δf _0KA / f _0KA This assumption does not violate the rigor of the analysis, but allows to reduce the presentation of the analysis results. Given that V _R << C, as well as the uncertainty of the signs of the frequency deviation from the nominal value (Δf ₀ / f ₀ = ± | Δf ₀ / f ₀ |) and the instrumental measurement error (Δf _∂ = ± | Δf _∂ |), the equation to estimate the error of measuring the radial velocity, we will present in the form

We write the estimate of the variance of the radial velocity measurement in the form

- дисперсия погрешности измерения скорости света;Where

- variance of the error in measuring the speed of light;

- дисперсия отклонения частоты эталонных генераторов от номинального значения;

- variance of the deviation of the frequency of the reference generators from the nominal value;

- дисперсия инструментальной погрешности измерения доплеровского смещения частоты.

- the variance of the instrumental error in measuring the Doppler frequency shift.

The first terms in (1), (2) are caused by inaccuracy of information about the propagation velocity of radio waves. The relative error of the speed of light is estimated by the expression

where ΔC ₀ is the relative error of the speed of light in vacuum;

ΔC _tr , ΔC _ion - deviations of the speed of light from the nominal value due to the action of the troposphere and ionosphere, respectively.

The relative error of the speed of light in vacuum is ΔС ₀ / С≈3 · 10 ^-9 . Therefore, the contribution of ΔС ₀ to the estimation of the error in measuring the radial velocity is negligible. The error in the tropospheric measurement of radial velocity is small [5]; to solve the problems of spacecraft navigation, it can be neglected. Since television signals are broadcast in different frequency ranges, in order to eliminate the error in determining the radial velocity due to the influence of the ionosphere, in accordance with the proposed method, the Doppler shift of the carrier frequencies of the image of two television channels is measured and the two-frequency method of accounting for the ionospheric error is applied. Therefore, the error of the first term in expressions (1), (2) can be neglected.

где

- дисперсия долговременной нестабильности;

дисперсия кратковременной нестабильности. Для исключения ошибки, обусловленной долговременной нестабильностью эталона частоты, в соответствии с предложенным способом применяют псевдодоплеровский метод навигации.The second term (1), (2) is due to the instability of the reference frequency generators. Frequency instability is characterized by the ratio of its deviation from the nominal value to the nominal frequency and consists of short-term and long-term frequency instability. The frequency dispersion can be represented as

Where

- dispersion of long-term instability;

dispersion of short-term instability. To eliminate errors caused by long-term instability of the frequency standard, in accordance with the proposed method, the pseudo-Doppler navigation method is used.

In accordance with the requirements for television transmitters established by GOST 20532-83, when the television transmitters operate in the exact offset of the carrier frequencies, the carrier frequency of the television channel may deviate from the nominal value on a daily time interval of ± 1 Hz, and within one month ± 100 Hz [ 6, p. 8].

To determine the parameters of the orbit, it is sufficient to conduct sessions of measuring the radial velocity of the spacecraft lasting one minute. At such intervals, under the regime of the exact offset of the carrier frequencies, the relative short-term instability of the frequency standards of television transmitters broadcasting decimeter-wave radio waves will be 10 ^-11 -10 ^-12 .

Ensuring the relative frequency stability of the airborne standard 10 ^-11 ÷ 10 ^-12 over an interval of several minutes is achieved using modern frequency standards that are produced commercially [7, p.6].

Thus, the error in measuring the radial velocity caused by the second term of expressions (1), (2) depends on the short-term instability of the ground and airborne frequency standards, and at Δf ₀ / f ₀ = 10 ^{-11 it} will be 0.006 m / s, and at Δf ₀ / f ₀ = 10 ^-12 - 0.0006 m / s.

The potential measurement error of the Doppler frequency shift of the received signal is estimated by the dispersion according to the expression [7, p.103]

where d is the distance between the television radio station and the spacecraft;

k = 1.37 · 10 ^-23 W / (K Hz) is the Boltzmann constant;

T _W - equivalent noise temperature (Kelvin);

Δt _ISM - the duration of the measurement interval;

Δf _∂t - Doppler frequency shift in the interval Δt _ISM ;

δ _P is a coefficient characterizing the radiation power of a television radio station in free space;

P is the power of a television radio station.

In the methodology for assessing the potential accuracy of radial velocity measurements published in [8, p. 103], the duration of the measurement interval is

Δt _meas = 1 s. For low-orbit spacecraft with such a measurement interval, the Doppler shift of the carrier frequency 12 of the television channel will be Δf _∂t ≤50 Hz. The measurement error of real equipment is higher than potential. The increase in error is due to the properties of the equipment of the receiving and measuring tract. Suppose that on-board equipment allows measurements to be made with an error that is not more than 10 times higher than the potential, and random measurement errors are distributed according to the normal law. Then, with a probability of 0.95, the instrumental error in measuring the radial velocity does not exceed the values of σ _∂ <20σ _{∂-potential} .

From the radiation patterns of television antennas, it follows that about 10% of the power of television radio stations is radiated into free space [9, p. 273], so in expression (3) we take δ _P = 0.1.

Thus, the instrumental error in measuring the radial velocity of a spacecraft at a distance d <1500 km from a television radio station using a signal of 12 television channels at an equivalent noise temperature T _w = 300K, δ _P = 0.1, P = 25 kW will be 0.0001 m / s . We estimate the error in measuring the radial velocity by summing the terms of expression (1), and when Δf ₀ / f ₀ = 10 ^-12 , d = 1500 km, T _w = 300K, δ _P = 0.1, P = 25 kW, it does not will exceed 0.001 m / s. This error value corresponds to the error of ground-based measuring tools used to measure the orbit parameters of the standard GNSS NS.

The determination of the orbit parameters from the measured values of the radial velocity is carried out by the methods described in [9, p.145-185]. At the same time, since the error in measuring the current navigation parameters of low-orbit spacecraft from the broadcast signals corresponds to the error in the standard means for measuring the orbit parameters of the GNSS satellite, the error in determining the orbit of the functional supplement satellite corresponds to the error in determining the parameters of the GNSS satellite orbit.

The task of forming a navigation message on board the spacecraft of a functional supplement is to determine the necessary data transmitted by each GNSS spacecraft. The data contain operational and non-operational information [10, p.325-336].

The task of generating operational information of the navigation message of the spacecraft of the functional supplement consists in calculating the spacecraft ephemeris according to the orbit parameters determined by the television signals. The calculation of the ephemeris is carried out using the methods for predicting the trajectory of the orbital motion described in [9, p.186-197].

The GNSS monitoring and control subsystem adjusts the GNSS spacecraft timeline to provide a unified UTC (SU) system time scale according to the ground-based time standard [10, p.290-292]. The refinement of the onboard time scale of the spacecraft of the functional supplement is performed on the basis of the information contained in the GNSS navigation message and the calculated parameters of the orbit of the spacecraft of the functional supplement. Moreover, to determine the time in the UTC (SU) scale on board the spacecraft of the functional supplement, the relation

where t _{UTS (SU)} is the time in the UTC (SU) scale on board the GNSS spacecraft at the time it emits a navigation message received on board the functional supplement;

x ₀ , y ₀ , z ₀ coordinates of the GNSS satellite, the navigation message of which is received on board the functional supplement satellite;

x ₁ , y ₁ , z ₁ - coordinates of the spacecraft of the functional supplement at the time of receiving the navigation message, calculated by the current navigation parameters, measured by television signals.

To clarify the time of the spacecraft of a functional supplement, a navigation message of such a GNSS spacecraft is used, in which the age of the operational information, which is the time interval that has passed since its calculation, is of the least importance. This is due to the fact that the age of operational information is proportional to the magnitude of the departure of the GNSS spacecraft onboard time scale from the ground standard scale.

Non-operational information contains the ephemeris almanac of the entire orbital group of the GNSS spacecraft, and therefore, additional calculations are not required to form a navigation message aboard the spacecraft. Non-operational information contained in the navigation message received on board is suitable for forming a portion of the navigation message of the spacecraft of a functional supplement containing non-operational information.

A block diagram of a device for implementing the proposed method is presented in the drawing.

The device comprises a receiving antenna 1, a high-frequency amplifier 2, band-pass filters 3 and 4, a frequency band switch for television channels 5, a signal mixer 6, a reference frequency switch for television channels 7, frequency factors 8, 9 and 16, a high stability reference frequency generator 10, low frequency amplifier 11, frequency meter 12, on-board computer 13, receiving antenna 14, GNSS navigation information consumer equipment 15, encoder 17, transmitting antenna 18.

In this case, the first output of the high-frequency amplifier 2 is connected to the input of the band-pass filter 3, the second output of the high-frequency amplifier 2 is connected to the input of the band-pass filter 4, the first input of the switch of the frequency ranges of the television channels 5 is connected to the first output of the calculator 13, the second input of the switch of the frequency ranges of the television channels 5 is connected to a band-pass filter 3, the third input of the frequency band switch of the television channels 5 is connected to the band-pass filter 4, the first input of the signal mixer 6 is connected to the band-pass filter 5, and in the second input is connected to the output of the reference frequency switch 7, the first input of the switch 7 is connected to the factor 8, the second input of the switch 7 is connected to the factor 9, the third input of the switch 7 is connected to the first output of the calculator 13, the first output of the generator 10 is connected to the factor 8, the second output the generator 10 is connected to the multiplier 9, the third output of the generator 10 is connected to the multiplier 16, the second output of the calculator 13 is connected to the first input of the encoder 17, the second input of the encoder 17 is connected to the input of the multiplier 16.

The device operates as follows. Antenna 1 receives a television signal, which amplifies high-frequency amplifier 2 and supplies a signal to bandpass filters 3 and 4, which limit the frequency band of the television signal to the frequency range in which the carrier frequencies of the two television channels are located, taking into account the Doppler frequency shift. The frequency band switch of the television channels 5 by a signal from the first output of the on-board computer 13 connects the output of the switch to the first or second input of the switch 5. The signal from the output of the switch 7 is fed to the first input of the signal mixer 6.

The reference frequency generator 10 generates a reference signal of high stability frequency, which is fed to the inputs of the factors 8 and 9. The multiplier 8 generates a reference frequency signal of one television channel, and the multiplier 9 generates a reference frequency signal of another television channel, which respectively arrive at the first and second inputs of the switch reference frequencies 7. The switch reference frequencies 7 on a signal from the first output of the on-board computer 13 connects the output of the switch with the first or second input of the switch 7. The signal from the output of the switch 7 enters the torus to the second input signal of the mixer 6.

The signal from the output of the frequency band switch of the television channels 5 is fed to the first input of the signal mixer 6 and mixed with the signal of the reference carrier frequency of high stability of the television signal supplied to the second input of the mixer 6. The mixer 6 emits low-frequency oscillations of the Doppler spectrum, which, after amplification in the amplifier 11, arrive at the frequency meter 12, which measures the Doppler shift of the carrier frequency of the television signal. The receiving antenna 14 receives a GNSS navigation message, from which the navigation information consumer equipment 15 extracts overhead information necessary for generating a functional supplement satellite navigation message. On-board computer 13 performs the following actions:

- determines the radial speed of the spacecraft relative to the television radio station by measuring the Doppler shift of the carrier frequency of the television signal;

- determines the parameters of the orbit by the values of the radial speed of movement;

- calculates the ephemeris of the functional complement;

- generates a navigation message, subject to subsequent broadcast on-board equipment.

The input of the multiplier 16 receives the signal of the reference frequency of the navigation message from the third output of the reference frequency generator 10. The multiplier 16 generates a signal of the reference frequency of the navigation message. The signal from the second output of the calculator 13 is fed to the first input of the encoder 17, the second input of which is the signal of the reference frequency of the navigation message. The encoder 17 encodes the signal of the reference frequency according to the generated navigation message. The radio navigation signal generated by the encoder 17 is fed to the antenna 18 and is broadcast in the direction of consumers of navigation information.

Literature

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Claims (1)

A method of constructing a functional complement of orbital-based navigation to global navigation satellite systems (GNSS), characterized in that on board a low-orbit spacecraft, the intended purpose of which is not related to the task of broadcasting navigation messages to consumers of satellite navigation information, they place GNSS consumer navigation equipment, with which receive a navigation message, and additional equipment with which they receive signals of terrestrial television Directions of terrestrial stationary television radio stations, allocate the carrier frequencies of two or more television channels, on the basis of which the Doppler shift of the carrier frequencies is determined, orbit parameters are determined, spacecraft ephemeris are calculated, navigation messages are generated in accordance with the GNSS navigation message structure, broadcast radio navigation signals in the direction of location consumers of navigation information.

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