# Method for location of space vehicles

FIELD: cosmonautics, applicable in space activity - space exploration, exploration of the solar system, observation of the Earth from the space, at which it is necessary to determine the space co-ordinates of the space vehicles and the components of their flight velocity vectors.

SUBSTANCE: the method consists in the fact that in the intermediate orbit simultaneously with determination of the co-ordinates of the space vehicle (SV) at initial time moment t_{0} by signals of the Global Satellite Navigation Systems the determination and detection of radiations at least of three pulsars is carried out, and then in the process of further motion of the space vehicle determination of the increment of full phase ΔФ_{p}=Δϕ_{p}+2·π·N_{p} of periodic radiation of each pulsar is effected, the measurement of the signal phase of pulsar Δϕ_{p} is determined relative to the phase of the high-stability frequency standard of the space vehicle, and the resolution of phase ambiguity N_{p} is effected by count of sudden changes by 2·π of the measured phase during flight of the space vehicle - Δt=t-t_{0}; according to the performed measurements determined are the distances covered by the space vehicle during time Δt in the direction to each pulsar and the position of the space vehicle in the Cartesian coordinate system for the case when the number of pulsars equals three is determined from expression where D_{p} - the distance that is covered by the space vehicle in the direction to the p-th pulsar; Δt - the value of the difference of the phases between the signal of the p-th pulsar and the frequency standard of the space vehicle, measured at moment T_{p} - quantity of full periods of variation of the signal phase of the p-th pulsar during time Δϕ_{p}; N_{p} - column vector of the position of the space vehicle at moment Δt; - column vector of the space vehicle position at initial moment t_{0}; -column vector of estimates of space vehicle motions in the direction cosines determining the angular position of three pulsars.

EFFECT: provided high-accuracy determination of the space vehicle position practically at any distance from the Earth.

2 dwg

The invention relates to a space and can be used in the conduct of space activities - space, planets, solar system, Earth observations from space, etc. where it is necessary to determine the spatial coordinates of the SPACECRAFT) and the components of the vector of its velocity. In order to solve this problem, first and foremost, is the need to control the SPACECRAFT for its output in a given region of space with the required precision.

Given the ballistic nature of the motion of the SPACECRAFT and the limited capacity of the AC to perform maneuvers, for the calculation of the minimum control impacts on the SPACECRAFT must reasonably accurate knowledge of the parameters of its movement (coordinate vector and velocity vector) at a specific point in time. From the choice of method and its capabilities depend on the energy cost of maneuvering that for space missions are quite critical.

In many cases, the problem of determining the spatial coordinates need to decide autonomously, i.e. directly on Board the SPACECRAFT. This, in particular, allows control of the SPACECRAFT outside its visibility from the national territory or at very considerable distances from the Earth, for example, in the area of the geostationary orbit or interplanetary travel.

Still the La achieve this goal, different ways are used.

There is, for example, the ability to load on Board the spacecraft's radar. However, weight, cost and power consumption of the radar energy is considerable, which creates insurmountable restrictions for certain spacecraft.

You can also sight from the ground radar or theodolites and calculated to determine the orbit to determine the speed and the desired trajectory.

However, this leads to heavy dependence on the infrastructure of the earth and a large inaccuracies for the relative distances less than 20 km of Known means and methods of determining the location of the object (German Patent DE4019214, Gsaefe, Volker, G 01 11/14, 1991, Patent abstracts of Japan, vol.14, no 101 (P-1012) (4044) 23.02.1990, the Japan patent JP-A-1305312, Patent RU 2103202 C1, 64 G 1/24, 1998). However, the decision by Japan patent is not possible to accurately determine position coordinates of the object in the reference system and is practically limited to defining the distance between the fighter and the target specified in the German patent technical solution only allows to determine the distance between the object and the measuring device.

In addition, you can use the satellite system positioning GPS (Global Positioning System).

One of the most promising methods for the determination of coordinates in near-earth space, which can be used to determine the parameters of the magic cube MOV is I KA is the method used to build global navigation satellite systems (GNSS) type GLONASS (Russia), GPS (USA), etc.(L.1-5).

Based GNSS lies a permanent grouping navigation of space vehicles (NSV) with circular orbits at a height of ˜20000 km, the Number and placement of the NCA in orbits ensures that at any point on the earth's surface and near-earth space surveillance least four NSV. Navigation equipment NCA forms and constantly radiates in the direction of the Earth radio signals in the L-th frequency band. The relative stability of the emitted frequencies is provided rubidium, cesium, or hydrogen frequency standards and is of the order of 10^{-13}-10^{-14}. Radiated NSV radio frequency-modulated phase of a navigation radio signals containing:

- the ranging codes periodically repeating pseudorandom sequence (SRP), coherent with the emitted frequencies;

navigation frames containing information about the trajectory of the NCA and the current time.

Structure and characteristics of radiation NSV provide frequency (GLONASS) or code (GPS) separation of signals of different NSV, which allows them separate reception and processing.

For positioning in GNSS is used, p is EVDO-ranging (or differential-distance measuring method), uses the measurement of the delay between the moment of emission of the navigation signal and the moment of its acceptance by not less than four NSV.

The main advantages of GNSS include:

- continuity of service, i.e. the ability to determine the coordinates in almost any time;

- global, i.e. the opportunity to determine virtually any point on the Earth and near-earth space within the zone of action;

- autonomy, i.e. the ability to determine the coordinates in passive mode signals emitted by the NCA;

- openness, i.e. an unlimited number of users in the system.

At the same time, from the viewpoint coordinates determination KA, GNSS has several disadvantages.

The energy potential of onboard equipment and the shape of the pattern of onboard antennas NSV restricts the range of GNSS near-earth space, not exceeding a height of 3000 km

As the KA for this height decreases "geometric factor" of the system and decreases the number of simultaneously observed NCA, which determines the accuracy of the coordinates. At altitudes of more than 3000 km appear and gradually increase the time intervals at which the number of visible NSV is less than four, and GNSS does not provide continuity of service.

DL the determination of coordinates of a sufficiently high AC, you need to work on signals only those NSV, which are on the other unshaded side of the Earth and only at certain time intervals. The noise of the Earth, interference, as well as the reduction of the energy potential of the radio link can degrade the accuracy of measurements of the navigation signal and the impossibility of observation SPACECRAFT in the required time, which in turn affects the accuracy of determination of parameters of the motion of the SPACECRAFT.

When the position of the SPACECRAFT at altitudes near and large 20000 km and especially for high-orbit and interplanetary SPACECRAFT continuous high-precision coordinate determination using GNSS in General not possible.

The technical result of the invention is the provision of high-precision positioning of the spacecraft at virtually any distance from the Earth.

To achieve the specified result, it is proposed a method of determining the location of the SPACECRAFT (SC), which consists in the fact that the intermediate orbit simultaneously with the determination of the coordinates KAat the initial moment of time t_{0}the signals of Global Navigation Satellite Systems is the reception and detection of radiation not less than three pulsars, and then during the further motion of the SPACECRAFT is the definition of the growth in full phase Δf_{p}=ΔD5;
_{p}+2·π·N_{p}periodic radiation of each pulsar, the measurement of the phase signal of a pulsar Δϕ_{p}is determined by the relative phase high-stability reference oscillator KA, and the resolution of the phase ambiguity N_{p}is carried out by counting spikes on 2·π measured phase during the flight KA - Δt=t-t_{0}; on the conducted measurements are determined by the distance that the SPACECRAFT moved during Δt along the direction of each pulsar

and the position of the SPACECRAFT in the Cartesian coordinate system, for the case when the number of pulsars is three, will be determined from the expression

where D_{p}- the distance that the SPACECRAFT moved along the direction of the p-th pulsar during Δt;

C is the speed of light;

T_{p}the repetition period of the signal emitted by p-m pulsar;

Δϕ_{p}measured at time t the value of the phase difference between the signal p-th pulsar and the reference oscillator KA;

N_{p}- the number of complete periods of the phase change signal p-th pulsar during Δt;

- a column vector of the SPACECRAFT location at time t;

- a column vector of the SPACECRAFT location at the initial time t_{0};

- vector-Severiano move the SPACECRAFT in the direction of three pulsar;

matrix guides of the cosines of determining the angular position of the three pulsars.

Astronomical observations and the study of theory of formation and development of stars has allowed over the past few decades to obtain a sufficiently large amount of information about the number, location and characteristics of pulsating stars - pulsars.

Radiation of pulsars are recorded in radio, optical, x-ray and gamma frequency ranges. The pulse shape for the same pulsar in different ranges different, but the period of their constant repetition. The value of the repetition period for each individual pulsar (pulsar in the crab nebula has a period of T_{Crab}=33 MS pulsar PSR1509-58 has a period of T_{PSR1509}=150 MS, and the Vela pulsar - T_{Vela}=89 MS). The stability of the repetition rate of the pulses is very high and estimated to be 10^{-14}per year.

Currently, there are a sufficiently large number of pulsars. Telescope ROSAT cataloged 105924 pulsar in x-rays, the ATNF telescope has discovered more than 1,400 pulsars in radio range. Working directory pulsars contains 737 objects, of which 79 can be described as rather powerful. The most densely 27 known powerful x-ray pulsars are concentrated in the plane of galact the key, and the angular position of the currently known with an accuracy of ˜of 0.1 arcsec.

From the point of view of the observer, the signal emitted by the pulsar, in any frequency range can be represented as a periodic signal of the form

where T_{p}the repetition period of the signal emitted by the pulsar in the direction of the observer.

Fix at any arbitrary time t_{0}the initial phase φ_{0}received signal and generate a reference periodic signal S_{op}with a period of T_{p}and the initial phase φ_{0}.

Measuring at time t the phase difference between the received and reference signals can be recorded

where D_{p}- the distance at which the observer moved along the direction of the pulsar, during Δt=t-t_{0};

C is the speed of light;

N is the number of complete periods of the phase change during the flight.

The distance that the observer moved along the direction of the pulsar, during Δt is determined from the

To determine the position of the observer in any arbitrarily chosen Cartesian coordinate system {x, y, z} must measure no less than three different pulsars, the angular coordinates of which in wybran the second coordinate system is known.
Then, can be obtained three estimates D_{p1}D_{p2}D_{p3}respectively for the three known directions.

Ask for certainty, the direction of each of the three selected pulsars in a selected Cartesian coordinate system guides of the cosines of the {l_{i}, m_{i}n_{i}}, where l_{i}the cosine of the angle between the direction of the pulsar and the x-axis of the selected coordinate system, m_{i}and n_{i}the cosines of the angles between the axes y and z, respectively; i={1, 2, 3} is the sequence number of the pulsar.

Then the observer's position in a selected Cartesian coordinate system (figure 1) at time t_{0}+Δt can be determined from expressions

where- a column vector of the SPACECRAFT location at time t;

- a column vector of the SPACECRAFT location at the initial time t_{0};

- a column vector of estimates move the SPACECRAFT in the direction of pulsars;

matrix guides of the cosines.

To determine the value of N random nature of the motion of the SPACECRAFT or large enough intervals Δt use the following trick. Select the interval δt that satisfy the condition δt<T_{p}<Δt and at time t_{j}=t_{0}+j·δt for {j=0,1,2,3...} will measure 4
ϕ_{j}and if the condition Δϕ_{j}<Δϕ_{j-1}count the number of N_{j}=N_{j-1}+1. It is obvious that at time t=t_{0}+Δt estimate N_{j}will be equal to

The choice of initial time t_{about}measured by its ability to define the initial position vector of the observerat time t_{0}. In the General case such an opportunity, if the starting point is within range of any of the existing systems location (radar, navigation and so on)with the necessary technical capabilities.

For KA, the trajectory of which regardless of the destination apparatus usually begins at the intermediate near-circular orbit with an altitude ranging from 400 km to 2000 km, and further maneuvers and movement can begin at any point in the orbit, it seems reasonable to use one or more existing GNSS (GLONASS, GPS and so on).

Thus obtained coordinates of the SPACECRAFT at different points in time and, given the usually quite well-known law of motion, it is possible by known methods to calculate the parameters of the motion of the SPACECRAFT and to make a prediction of its position at the required time.

Conditional diagram illustrating described in the manual,
shown in figure 2. This diagram shows three channel, processing the signals from the three pulsars P_{1}, R_{2}and R_{3}each channel includes a detector signal of a pulsar, the synthesizer reference signal, the phase meter and counter periods. The keys To a_{2}and K_{3}depicted in the open position, which corresponds to the time interval on which the determination of the position of the AC is on the navigation GNSS receiver. At time t=t_{0}the keys To a_{2}and K_{3}locked, and the key K_{1}opens. In the evaluator coordinates stored initial position of the SPACECRAFT to determine the current position of the SPACECRAFT out of range of the vehicle. With the same time starts the measurement of the phase difference between the reference signal and the signal received from the pulsar, detecting and counting the number of jumps of phase N. To calculate the coordinates used in the evaluation phase Δϕ, a counter value N and the angular coordinates of the pulsar l, m, n. In the on-Board catalog of pulsars along with angular coordinates of pulsars also stores the parameters of its radiation, in particular for the period and form of radiation that can be used by the synthesizer to generate the reference signal.

The main advantages of the method include:

- global, i.e. the ability to determine the coordinates in almost any point on earth simple the of Christianity within the Solar system;

- invulnerability, i.e. the impossibility of interference with the positioning system on almost the entire range of flight KA;

- continuity of use, i.e. the opportunity to determine almost any time of the flight SPACECRAFT;

- autonomy, i.e. the ability to determine the coordinates in passive mode signals emitted by pulsars;

- openness, i.e. an unlimited number of KA, while simultaneously determining its location;

Literature

1. "Global satellite navigation system GLONASS". Ed. Vinaria, Ahipara, Vasoline, Moscow, IPGR, 1998, p.74-89 (prototype).

2. Wasallowed Satellite navigation and its applications", Moscow, ECO-TRENDS, 2003.

3. Wasallowed "satellite navigation Systems", Moscow, ECO-TRENDS, 2000.

4. The interface control document GPS ICD-200C-002, 25.9.97.

5. Global navigation satellite system GLONASS. The interface control document, Moscow, 1998.

The method of determining the location of the SPACECRAFT (SC), which consists in the fact that the intermediate orbit simultaneously with the determination of the coordinates KAat the initial moment of time t_{0}the signals of Global Navigation Satellite Systems is the reception and detection of radiation not less than three pulsars and then during the further motion of the SPACECRAFT is the definition of the growth in full phase Δ
F_{p}=Δϕ_{p}+2·π·N_{p}periodic radiation of each pulsar, the measurement of the phase signal of a pulsar Δϕ_{p}is determined by the relative phase high-stability reference oscillator KA, and the resolution of the phase ambiguity N_{p}is carried out by counting spikes on 2·π measured phase during the flight KA Δt=t-t_{0}; on the conducted measurements are determined by the distance that the SPACECRAFT moved during Δt along the direction of each pulsar

and the position of the SPACECRAFT in the Cartesian coordinate system for the case when the number of pulsars is three, is determined from the expression

where D_{p}- the distance that the SPACECRAFT moved along the direction of the p-th pulsar during Δt;

C is the speed of light;

T_{p}the repetition period of the signal emitted by p-m pulsar;

Δϕ_{p}measured at time t the value of the phase difference between the signal p-th pulsar and the reference oscillator KA;

N_{p}- the number of complete periods of the phase change signal p-th pulsar during Δt;

- a column vector of the SPACECRAFT location at time t;

- a column vector of the SPACECRAFT location in the beginning of the capacity t_{
0};

- a column vector of estimates move the SPACECRAFT in the direction of three pulsar;

matrix guides of the cosines of determining the angular position of the three pulsars.

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