ON A NEW THEORY OF THE GEOSTATIONARY SATELLITE MOTION AND ITS APPLICATIONSR. I. KiladzeAbastumani Astrophysical Observatory, Georgia (FSU) 1. INTRODUCTIONLaunching artificial Earth satellites into the geostationary orbits (GO) began about 40 years
ago. At the present time the geostationary satellites (GS) moving in a sharp resonance with
the Earth rotation have the most wide applications in resolving many practical problems,
mainly those related to the TVcommunications, intercontinental communication and military
purposes.
After expiration of its active period a GS becomes a passive object and is transferred
onto a higher or lower orbit in the neighbourhood of the GO. According to the statistics by
January 2005 there were 346 GS working in the GO and their total number was 1124.
Besides of observable objects there are ten thousand small fragments, smaller than 1 m
in size, which are small space debris (SD) moving in the vicinity of the GO. They are
accompanying every launch of the GS and are created as a result of the GS explosions.
According to the recent investigations the number of such explosions is 12; 2 of them
were the Russian GS (Ekran 2 and Ekran 4) and 10 were the U.S. “Transtages”. Maybe this
number is underestimated; therefore, in addition to elaboration of reliable methods for the
detection of explosions by direct observations, it is necessary to dispose of the program for
the search of all lost objects, and especially, of potentially dangerous ones for working GS.
These fragments are endangering the existence of the GS because of the possibility of
collisions. The number of small fragments is growing with time (their existence timespan in
the region of the GO is unlimited) and the probability of their collision with the SD grows.
Recent investigations of the evolution of 456 uncontrolled GS observed more than 1000 sharp
changes in their drift, which may be explained in terms of collisions with small SD [1].
The main problem of the GS motion control is still related to the cataloguing of all
observed small objects moving in the GO region.
For elaborating a model of choking up the GO region by the SD it is necessary to have a
reliable theory of the GS motion by which the available observations and orbital elements
might be represented on the long timespan. It is also necessary to compile the software for
calculation of the orbital evolution for hundreds of fragments in a short time.
2 THE THEORY OF A GEOSTATIONARY OBJECT MOTION2.1. Statement of the problemOur task was to construct a simple method to calculate the longperiod evolution of the real
GS orbits. The elaborated method, based on observations made on the timespan of 1000
through 2000 days with the mean square error σ in the range of 0°.025 through 0°.045, allows to represent the orbital evolution on the timespan of 7000 through 10000 days with an error
of 0°.1 – 0°.2.
The theory has been tested by means of representation of long series of TwoLine
Orbital Elements (TLE) of the NASA Goddard Space Flight Center and of the osculating
elements (OE) determined by us directly from astrometric observations [2].
The principal peculiarity of the motion of a GS is the exact 1:1 commensurability of its
mean daily orbital motion n with the Earth’s rotation velocity S_{1}. In the case of absence of
perturbations due to the nonsphericity of the Earth’s shape and to the lunisolar attraction, the
GS once launched at some geographical longitude would always rest there. However, under
the influence of ellipticity of the Earth’s equator, it begins to move like a pendulum near two
stable points of libration with longitudes 75°Å and 255°Å. Because of the asymmetry of
Earth’s equator the periods of the small oscillations around these points differ by 110 days,
being equal to 840 and 950 days, respectively.
To simplify the representation of such a motion Gedeon [3] has introduced a special
system of coordinates, called by him stroboscopic.
In this system instead of the continuous time the discrete timetimemoments are used
as the argument of the equations of motion separated by daily intervals, and the phase plane
of the stroboscopic longitude λ and drift dλ/dt is introduced in terms of orbital elements as
follows:
where M is the mean anomaly, Ω is the longitude of the ascending node, ω is the argument of
the perigee, S is the Greenwich sidereal time, Ω_{1} and ω_{1} are secular changes of the node and perigee longitudes.
In the stroboscopic system of coordinates, – in the case of an exact commensurability of
motions, – the central body and a satellite seem to be motionless, and in the case of an inexact
commensurability the satellite would seem to slowly move along a trajectory. Such a picture
may be observed if the system, “the Earth – a satellite”, is in the darkness, being periodically
illuminated by short lightflashes.
The stroboscopic system has properties of the inertial and noninertial (rotating)
coordinate systems. Introduction of this system essentially simplifies the equations describing
the longperiod motion of the GS, but results in a loss of the shortperiod oscillations.
To describe the GS motion A. Sochilina in 1985 has used the Laplace plane [4], being
first applied by H. Struve [5] to the satellite motion. It passes through the vernal equinox and
is inclined by some angle Λ (depending on the semimajor axis of an orbit) to the geoequator.
For the GS the angle Λ is equal to 7°.34188.
The physical meaning of the Laplace plane is the following. Due to the equatorial bulge
of the Earth a couple of forces are created which are trying to make the plane of the GS orbit
to coincide with that of the geoequator; as a result the plane of the orbit (in the case of
absence of other forces) precesses, being constantly inclined to the geoequator. On the other
hand the common attractions of the Moon and the Sun try to make this plane to coincide with
the ecliptic.
The resultant of these two couples of forces compels the GS orbit plane to precess by
the constant inclination to a plane lying between the geoequator and the ecliptic and called the
Laplace’s plane.
The choice of the Laplace plane gives some advantages over other planes of reference:
relative to it the inclination of orbit i changes (because of inclination of lunar orbit to ecliptic)
only in limits of ±0°.5 and the longitude of the node Ω and the perigee argument ω become practically linear functions of time. The resonance equation for the stroboscopic longitude λ also becomes simpler.
As a result the problem may be resolved by use of the first order theory with small
corrections for the second order only.
Usually the precision of some osculating orbital elements is not satisfactory, –
especially for the calculation of satellite’s drift dλ/dt – but the derivatives of λ with respect to
time may be improved by use of the data of preliminary orbits combined with the longperiod
motion theory.
In the process of work with the Catalog of improved orbital elements [6] in 1996 it was
pointed out that on the 1000day span some GS show considerable systematic differences in
the longitude (in some cases reaching several degrees) between observed “O” and calculated
“C” values.
After estimation of the theory accuracy R. Kiladze [7] assumed that these discrepancies
could result from accidental changes in dλ/dt which in their turn are caused by the collisions
with small particles.
2.2. Perturbation forcesPerturbations of the GS orbital elements may be found from the Lagrange equations. The
perturbing function due to the geopotential U, the lunisolar perturbations R_{L}, R_{S} and the radiation pressure R may be expressed in terms of orbital elements referred to the Laplace
plane [8]:
(1)
where GE is the gravitational constant, a_{e} , the mean equatorial radius of the Earth, G_{lm} = C_{lm} √1 S_{lm}, C_{lm}, S_{lm}, the geopotential parameters, E_{lmk}(Λ), D_{lkp}(i), the inclination functions and X_{l2p+q}^{l1,l2p}(e) , the Hansen coefficients calculated in [9], M, Ω, ω, e, i, a, the GS
orbital elements.
The perturbing function due to the Moon is expressed as follows:
(2)
where ε is the inclination of the ecliptic to the geoequator, Ω_{L}, ω_{L}, e_{L}, i_{L}, a_{L}, the orbital elements of the Moon.
One can obtain the perturbing function due to the Sun by changing the index L in (2) to the index S.
According to Kepler’s third law
The mean radiation pressure function is as follows:
(3)
where λ_{S} is longitude of the Sun, the ratio of the surface area to the mass expressed in cm^{2}/gr).
The equation for calculation of Λ may be obtained from the condition that the sum of
terms of perturbing functions U, R_{L}, R_{S}, with argument Ω, be equal to zero:
(4)
where are the mean motions of a satellite, the Moon and the Sun, respectively, expressed in radians per day:
At last, all resonance perturbations are accounted for by the differential equation for λ [2]:
(5)
where A_{lmkpq} is the function of a, e, i and of the geopotential parameters, λ_{lmkpq}, the phase angle depending on λ_{lm}, and the geopotential parameters C_{lm} = J_{lm}cosmλ_{lm}, S_{lm} = J_{lm}sinmλ_{lm}, LSP
meaning the lunisolar perturbations.
The solution of this equation is described in [10].
2.3. Integration of the equations of motionFor simplification sake let us write the equation (5) as follows:
(6)
where
(7)
Choosing the Laplace plane as the basic one for the coordinate system guarantees that
the change of coefficients À_{i}, m_{i}, φ^{i} and s_{i} in (6) with time is very slow (i.e. that they are almost constant).
If these coefficients and the longitude of node Ω are constants, in the case of absence of the lunisolar perturbations, the equation (6) allows for the first integral:
(8)
where Ñ_{1} is the integration constant, being analogous to the Jacobi’s constant in the restricted problem of three bodies and in such a case the problem can be solved in terms of the
quadrature:
(9)
(10)
The behavior of the function Π(λ) is shown on Fig.1. It is like the asymmetric double sinusoid with maximums and minimums of different heights.
Accordingly, depending on the value of parameter Ñ_{1}, the GS can move in accordance with one of the three modes– the simple libration around one from the two stable points 75°E
or 105°W, the compound libration (around both points), or in the mode of the circulation (the drift) around the Earth.
Fig.1. The function Π(λ).
Because of the smallness of dΩ/dt, the solution of equation (6) may be expressed in the form (8), if one considers Ñ_{1}, as a slowly changing function of time.
(11)
In such a case one can obtain the derivative of Ñ_{1} with respect to time: introducing a new variable of integration dλ instead of dt by means of (8) we get:
(12)
The exact calculation of the righthand side of the equation (12) is not feasible since the
dependence of variables C_{1} and Ω on λ is unknown; but, with an accuracy acceptable for practical applications, they may be considered on short time intervals as constants equal to the
average values of the quantities C_{1} and Ω, respectively.
The variability of C_{1} and inaccuracy of calculations by means of (10), connected with the variability of Ω with time, may be significantly diminished by introduction of the
oscillating system of coordinates, attached to the Π(λ) function.
On Fig. 2 different types of motion in the phase plane are schematically shown. If the
value of the drift is less then 0.3°/day, then the GS move in the mode of a libration around one
of the stable points with the amplitude depending on the initial longitude.
The GS having maximum amplitudes of libration may periodically change their motion
modes because of the lunisolar perturbations.
Fig 2. Different types of the GS motion in the phase plane “longitude λ vs. rate of drift dλ/dt”.
2.4. Formation of the intermediate orbit, the Lagrange’s equationsThe method for calculation of the longitude just described allows to calculate ephemerides for a majority of the GS for the time intervals of several years with quite satisfactory accuracy for observers.
Further improvement of the ephemerides accuracy is possible by improving the GS
orbital elements. For all this it is important to have the intermediate orbit which is maximally
close to the real one.
The solution of this problem is published in [11] and [12]. Keeping the main terms in
the righthand sides, the Lagrange equations for the 4 orbital elements e, i, ω and Ω, in terms
of the coordinates used, may be reduced to the form:
(13)
(14)
(15)
(16)
where
(17)
ω, i, Ω and e denote here the orbital elements (the argument of the latitude, the inclination, the longitude of the ascending node, and the eccentricity), ω_{L}, Ω_{L}, the argument of the latitude and the longitude of the node of the Moon on the ecliptic, respectively, λ_{S}, the longitude of the Sun. D stands here for the light pressure, k, A, m, x^{•}, Ω^{•}_{L} and R^{•} are considered as constants.
2.5. Solution of the Lagrange’s equation systemThe equation system (1316) is actually subdivided into two systems, each containing two
equations.
Multiplying equations (13) and (14) by expressions respectively, and summing them up, one can obtain the equation in complete derivatives with respect to time, allowing for the first integral:
(18)
Using the integral (18) the solution of system (13) and (14) may be received in the form
of the elliptic integral:
(19)
In order to resolve the system (15)(16) let us introduce new coordinates p and q by:
(20)
and also
(21)
where
(22)
Then the system (15)(16) becomes:
(23)
The solution of the linear system (23) isn’t difficult, because the free terms in the right
hand sides of these equations are the variables found from the equation of system (18)(19).
At last, by integrating the expression (21) the time can be calculated as the function of
variable τ:
(24)
The computer software compiled on the basis of the described solution of the problem
copes successfully with the task of the orbit construction and of following its evolution on the
timespan of tens of years for every known GS.
2.6. A new motion integral – the “Kren” integralIt is necessary to mark the scientific meaning of the first integral (18) obtained by integration
of the Lagrange equations. After the epoch of resolving the twobody problem by Newton, in
the scientific armory of celestial mechanics there appeared only a single first integral, i.e. that
of Jacobi found in XIX century.
By means of the integral (18) the inclination of the GS orbit to the Laplace plane is
given as the function of its longitude of the node and of the orientation parameters of the lunar
orbit.
Because the oscillations of the inclination of the GS orbit are described by (18), we
named this integral by the Russian word “Kren” (the tilt, the banking angle) and the constant
C_{2} by the Kren constant, respectively.
It is shown in [11] and [12] that in the general case the change of the value of C_{2} is not greater than C_{2}×10^{8}, i.e. C_{2} is practically constant. Consequently, (18) is always highly accurate.
Today the constants C_{1} and C_{2} are used for the identification of unknown GS discovered in the process of the sky surveillance with objects lost in the past. But with the science progress each of the known first integrals has found a new, sometimes unexpected application. We should expect that the Kren integral will not be an exception of this rule.
3. THE MODEL OF CHOKING THE NEIGHBORHOOD OF GEOSTATIONARY ORBIT BY FRAGMENTS OF EXPLODED SATELLITE3.1. Explosions on geostationary orbitsAs it was mentioned above the cosmic space developing is accompanied by the choking of it with different fragments following the satellite launches. This phenomenon has caused
anxiety since a long time, not only because of damage to working satellites by collisions, but
also due to the potential start of a cascade process of their destruction.
An especially tense situation is created on the GO zone, where the quantity of objects
inaccessible for observation because of their smallness is estimated as hundreds of thousands.
One of the sources of the GO choking are explosions of geostationary objects. From
time to time this information appears in the scientific literature [13, 14]. The explosion of only one satellite may generate several thousands of small fragments thrown out from the satellite with great or small velocities and remaining in the vicinity of the GO for a practically unlimited timespan. The velocity of the GS changes during this timespan by several m/s.
The drift of GS changes, therefore, more than by 0.05°/day.
Because of the smallness of these fragments they can be observed but with great
technical difficulties, and the ascertainment of the explosion of each single GS is, as a rule,
possible only by indirect methods, a long time after the event [15, 16].
The method of determination of the timetimemoments and of dynamic characteristics
of the explosion of an GS by using its orbital element changes is elaborated by the authors
[17, 18].
Today there are revealed 12 exploded GS by means of this method. Their real quantity
can be greater.
For these objects their designation numbers, the timetimemoments of the explosions
T_{0}, the orbital elements e, i, Ω, ω, λ and the drifts dλ/dt before and after the events are given in Table 1. The sharp change of the drift Δ(dλ/dt) given in the last column of Table 1 is considered as the principal indication of an explosion: if its value exceeds 0.1°/day, the event is considered to be an explosion.
The data about first 10 exploded objects are given in [18].
Table 1. The orbital elements of 12 exploded GS
(*) Orbital elements of GS 76023F and of its fragment GS 76023J. (**)In different sources this GS is designated in a various way. For GS 76023F we hadn’t the orbital elements before the explosion, therefore the
explosion timetimemoment is determined by establishing the identity of the object itself and
its fragment GS 76023J.
The check for correctness of the timetimemoment T_{0} of an explosion consists in identifying the GS positions in the threedimensional space as calculated by two orbital element systems (before and after the explosion). The mean discrepancy depends on the accuracy of the orbital elements used; for the TLE data it is about 12 km.
To get a clear view of the field of the space debris spreading after an explosion it is
useful to construct the manifold of orbits for the fragments in the framework of the twobody
problem for the spherically symmetrical explosion. The study of the orbital evolution allows
to determine the size and the shape of the region of motion of the fragments.
For determination of the shape of the space occupied by the fragments it is important to
know the ratio “Earth’s attraction/ the lunisolar attraction” and the radiation pressure. The orbital evolution of the fragments with a crosssection up to 40 m^{2}/kg has been studied by means of the numerical integration on the timespan of 100 yrs [19].
3.2. Determination of orbits of fragments generated after an explosionWe use the Cartesian system of coordinates with equator of date as a fundamental plane; Xaxis is directed to the point of equinox of date [20]; the position of the GS at the timetime
moment of an explosion t_{0} is defined by its radiusvector r_{0} and the vector of its velocity V_{0}. Suppose that at this timetimemoment all fragments are ejected with the velocity ΔV.
Fig. 3. Determination of the intersection point of orbits
On Fig. 3 the arc LL' represents the celestial equator. The arcs Ω_{0}S and ΩS are projections of orbits of the GS and of its fragment on the celestial sphere; S is their intersection point. By Ω_{0}, i_{0}, u_{0}, Ω, i and u are denoted the longitudes of nodes, the inclinations of orbits and the arguments of latitude of GS and its fragment, respectively; α and δ are the right ascension and declination of the point S.
The equations relating arcs of great circles (Fig. 3) to the orbital elements of the GS and
its fragment are given in [17].
For a symmetrical explosion the absolute value of ΔV is in limits of 1 – 250 m/sec depending on the fragment masses. The angle l is measured from the direction of the
transversal velocity of the GS from 0° to 360°, the angle φ is measured from its orbital plane
in limits of ±90°.
Small values of eccentricities are natural for the GS, and the ratio ΔV/V_{τ} is less than 1/12. Furthermore, one can use simple formulae [17] to estimate the change of the orbital parameter Δp and that of Δi and ΔΩ as well:
(25)
(26)
where ν_{0} is the true anomaly, ω_{0}, the perigee argument, e_{0}, the eccentricity, a_{0}, the semimajor axis, p_{0}, the orbit parameter, Ω_{0}, the longitude of the ascending node, i_{0}, the inclination of the GS orbit at the timetimemoment of an explosion.
In the process of investigation of the orbital evolution of the GS fragments it is
necessary for each of them to use its own Laplace plane, turning the coordinate system around
the Xaxis by the angle ΛΛ_{0}.
The data for the explosions of 9 objects and for their 5 fragments are given in Table 2
containing the value of ΔV, the longitude l relative to the GS transversal velocity and the latitude with respect to the orbital plane of the motion in the orbital system of coordinates,
the argument of latitude u_{0}, the geocentric distance r_{0} of the GS and the discrepancy Δr in distances expressed in km.
Table 2. Changes in velocities and directions of motion for exploded objects and differences
in distances Δr, calculated from data of Table 1
The detailed investigation of the GS 68081E explosion [13] shows that for the
fragments of 18 – 20 magnitude the average velocity change ΔV is 70km/sec. Furthermore, ΔV is about 250m/sec. for smaller particles which are invisible for optical instruments.
The example of calculation of the initial orbital elements of the fragments of the GS
76023F referred to their own Laplace planes for the ejection velocities of 250 km/sec, is
illustrated by the Table 3.
The Table 3 clearly shows that the inclination of the Laplace plane to the equator Λ
exceeds 12° for the fragments having the great negative drift. The total inclinations of the
orbits of small fragments to the equator, calculated as a sum of the orbit inclinations to the
Laplace plane and Λ, may reach 27° in the evolution process. For the GS moving in the
equatorial plane the relative velocities of such fragments may reach 1.5 km/sec.
It should be mentioned that at the timetimemoment of an explosion the longitude of
the ascending node of the GS 76023F orbit was 25°. In the case of the explosion at the
longitude of 180° the inclinations of the fragments’ orbits to the equator would reach 40°.
Table 3. Initial orbital elements of fragments generated by the explosion of the GS 76023F
for ΔV = 250 km/sec
76023F Transtage Ò(MJD)= 43060.2079
3.3. Model calculations of the orbital evolution of the fragments after an explosionThe problem of the study of the fragment dynamics is interesting from the point of view of
choosing the program of search for table (i.e. of 18 – 20 mag.) objects.
For this purpose let us investigate the evolution of an explosion point position in time
and space. Obviously, at the timetimemoment of the explosion the orbits of all fragments are
intersecting in this point.
For representation of the dynamics of fragments generated by the GS explosion by use
of the method described in [17] there were investigated the behavior of 32 GS fragments
ejected with the same velocities in different directions directed to the vertices and along the
sides of a rectilinear icosahedron (i.e. the polyhedron with 20 sides). Moreover, also the
model consisting of 300 fragments with the same ejection velocities was investigated.
For the timetimemoments of each GS explosion the initial orbits of their fragments
referred to the corresponding Laplace planes were constructed. It is postulated that at this
timetimemoment the modules of the vectors of fragment velocity changes are the same, not
exceeding 250 km/sec.
After this timetimemoment each fragment begins to move along its orbit intersecting
the orbital planes of other bodies, including the orbital plane of the paternal body because it
may be considered as the greatest fragment, – in the point of the explosion.
The inclination of the fragment orbit to the initial one is
(27)
where Δi is expressed in radians, V_{p} is the polar component of the total velocity of the fragment and V_{τ} is the tangential velocity of the GS.
Accordingly, the initial poles of all fragment orbits are displaced along the great circle
of the celestial sphere 90° from the point of explosion (Fig. 4).
On the other hand, the semimajor axes of the fragment orbits are differing from the
semimajor axis of the initial orbit by:
(28)
After an explosion the motion of each fragment is referred to its own Laplace plane.
Their poles are disposed along the great circle of the celestial sphere passing through the
celestial pole and initial pole of the relevant Laplace plane (Fig.4).
Fig. 4. The location of the poles of fragment orbits and of those of their Laplace planes just after the
explosion.
After the explosion the orbits of all fragments begin to precess around the poles of their
Laplace planes with different speeds. As a result, after some timeinterval these poles will be
located along the curve slightly differing from a great circle. Consequently, the corresponding
orbital planes intersect each other in almost the same line. We have called this phenomenon
the regularization of fragment orbits.
The problem concerned with calculation of the regularization timetimemoment (the
most favorable epoch for observations of the fragments) and its numerical description by
computation of spherical coordinates A and D of the intersection point of trajectories of the
fragments and their dispersion σ is studied in [18].
The evolution of the ensemble of 32 fragments ejected from the GS with velocity of 75
m/sec is studied on the basis the theory of motion [21 – 27] for all 12 events, described in
Table 1, over the timespan of 30,000 days (about 80 yrs).
The results of these calculations are given in Table 4 containing designations of the
exploded GS, the data for the most compact location of the intersection points of orbits of the fragments, the geocentric coordinates A, D of these points and the values of the average
deviations σ of the fragment trajectories from the intersection points.
Table 4. The timetimemoments, equatorial coordinates of points of orbits’ compact
intersection and dispersions for 12 fragments of the exploded GS
For an illustration, the behavior of the GS 68081E fragments on the time spans of 2000
days is shown in Fig. 5.
Fig. 5. The evolution of the poles of the GS 68081E fragments on the intervals of 2000 days.
It is seen from Fig.5 that the poles of the fragment orbits 2000 days after the explosion
occupy a significant area on the sky, but after 3899 days they are aligned along the great
circle. Subsequently they occupy again more and more area on the sky.
A majority of the GS investigated by us show the similar process of the orbit
regularization with other characteristic times.
In several cases (GS 66053J, 78113D), however, the process of the orbit regularization
is faintly presented.
Fig. 6. The evolution of the poles of the GS 66053J fragments on the time intervals of 3000 days.
As an example the orbital evolution of the GS 66053J fragments on the timeintervals of
3000 days is represented on Fig 6. The minimum of the dispersion is reached 9630 days later
after the explosion timetimemoment but it is so faintly presented that Fig.6 is hardly
differing from the picture of the stochastic distribution of the points on the plane.
The cases for other ejection velocities (250, 20 and 10 m/sec) of fragments are also
investigated but they don’t influence significantly the behavior of the GS fragment orbits: the
configurations on Figs. 5 and 6 are invariant with respect to the change of the fragment
ejection conditions, and only the scale of each Figure changes proportionally to ΔV.
3.4. Evolution of fragments’ orbits after explosionIt is clear from above that the regularization process of the GS fragment orbits is mainly
depending on the angles φ_{1} and φ_{2} represented on Fig. 4, i.e. the angles between the great circle passing through the poles of the initial orbit and the Laplace plane and the great circles
on which the poles of the orbits of fragments and their Laplace planes are located.
To clarify this dependence a numerical experiment has been made: it has been
calculated for each exploded GS what the orbital evolution would be if the explosion occurs
with some delay with respect to its real timetimemoment (i.e. if it would happen at another
point of the GS orbit).
Some results of this experiment are represented in Table 5. In the first column of Table
5 the differences of mean anomalies ΔM with the step of 30° (which corresponds to the
explosion delay of 2^{h}) are given, in other columns the timeintervals between the timetime
moments of explosions and those of regularizations and corresponding values of dispersions σ
for the intersection points of trajectories are given.
Table 5 shows that for each GS there are two values of ΔM (separated by approximately 180°); for them the values of σ reach minimum. These values are written in the bold type.
If the timetimemoments of the real explosions of the GS and the values of ΔM are known, it is easy to find that the GS whose right ascensions are about 9 or 21 hours at the
timetimemoment of the explosion are characterized by the minimal values of σ.
Table 5. The regularization models of the orbital planes for 12 exploded GS. The
configurations with minimal values of σ are written in the bold type.
The dynamics of this phenomenon are as follows.
At the timemoment of explosion of the GS all fragment orbits intersect each other in
two opposite points of the celestial sphere.
Because of perturbations their orbits change and, according to the initial conditions, the
intersection points of the visual fragment trajectories create two streams the centers of which
are lying apart by 180° in the longitude. After a sufficient time the fragments are intersecting
with the basic orbit practically at every point. If the ejection velocity of the fragments is 75
m/sec, the inclinations of their orbits don’t exceed 5°.
After several (about ten) years of the evolution the orbit planes intersect each other
nearly in one line, i. e. they have the common node.
Such ordered configuration exists during 2 – 4 years after which the orbital planes take
different orientations anew.
The values of σ as a function of time passed after the explosion and its delay for the GS 66053J and 73040B are shown on Figs. 7 and 8.
Fig.7. Dependence of σ on the time passed after the explosion and its delay for the GS 66053J
Fig. 8. Dependence of σ on the time passed after the explosion and its delay for the GS 73040B
Figure 7 shows that σ may reach minimum not only once, but every successive minimum always is less deep than previous one. This happens because the line of the poles of
the fragment orbits placed eventually becomes more and more different from the great circle
(Fig. 9).
Fig. 9. Displacement of the poles of the GS 68081E fragment orbits at the second minimum of σ, 19890 days after the explosion
The regularization phenomenon of the GS fragment orbits creates the most favorable
situation for observations of fragments near their common node which all of them pass once a
day.
From this affinity of the GS fragment orbits is founded the barrier method of search for
the fragments: in the years favorable for their detection (when σ has a minimum, according to
Table 4) the permanent observations in the vicinity of both nodes should be made as long as
possible. By monitoring the environments of these points (of the radius σ) during a day it is
possible to observe all fragments generated by an explosion of the same GS.
By the way, the small particles ejected by the explosion with great velocities spread
themselves along the GS orbit faster than those having the smaller relative velocities, the
evolution of which runs slower.
In Table 4 the geocentric values of the data (in particular those of σ) are given. When observing from the Earth’s surface the deviation of individual fragments from the common
center may grow because of the differential parallax. This effect of the vertical stretching
depends linearly on the ejection velocity by the explosion. For velocity of 75 m/sec it is equal
to 0°.83 sin z and 0°.89 sin z (where z is the zenith distance) for the upper and lower
directions, respectively.
At last, the studies of the evolution of fragment orbits show that in their intersection
points the distances between the orbits periodically become zero, which makes the favourable
conditions for collisions. As it is shown in [15, 16] many uncontrolled GS had repeated
collisions, the exploded objects being frequently met among them.
4. CONCLUSIONSFor elaboration of efficient precaution measures for safety of the controlled satellites in the
GO zone it is necessary to clear up primarily the real situation about the littering and to
process all orbital data in order to know the real quantity of explosions.
The new longperiod theory of the GS motion allows to analyze the observation data of
the uncontrolled objects for long timespans and to discover the accidental changes of orbits
depending on explosions or collisions with the space debris.
The model of creation of fragments for 12 exploded GS is constructed and their orbits’
evolution on the timespan of 80 yrs is investigated, the timemoments and dynamic
parameters of explosions being determined.
The maximal change of the inclination of fragment orbits (when the ejection velocity is
75 m/sec) is about ±5° depending on the argument of latitude and the location of the
explosion point on the GS orbit. In the process of the evolution the inclination of small
particle orbits to the geoequator may reach 40°. Such fragments are the most dangerous for
the Earth satellites, because they can provoke the cascade process of continuous
fragmentation [28, 29].
The search for the fragments becomes easier at time periods when the planes of the
fragment orbits intersect themselves in the same line. During this period all fragments once a
day pass two isolated points (the antipodes) on the sky.
Our results may be used for the organization of observations of the spreading area of the
smallsize debris using the groundbased instruments and for identification of the litter
sources as well.
The process of fillingup the cosmic space with the explosiongenerated fragments
depends on relative velocities ΔV: the velocities ΔV < 75 m/sec are typical for greater
fragments which intersect the initial orbit of the GS at two parts about 10° long, lying apart by
180°. When the distances between the orbits in the intersection points become zero, the
favorable conditions for collisions occur.
The smallsized debris with great velocities (about 250 m/sec) fills up the neighborhood
of the exploded GS and soon begin to intersect all orbits. Moreover, there are created objects
having masses of about 10 g and relative speeds of 11.5 km/sec. They can not only collide
with the GS but also can provoke the cascade process of fragmentation.
From this point of view also the process of permanent “burial” of the GS near the GO
(staying 200 – 300 km afar) which ceased to work, because the exploded GS can create
fragments with great orbital eccentricities and inclinations of order of 30°.
In order to have the permanent and reliable information about the choking of the GO
area it is necessary to put into operation more powerful means of groundbased technics for
observations, and also to launch a satellite, with a telescope aboard, in the environments of the
GO with the means for the permanent communication with the Earth.
REFERENCES
Ðàçìåùåí 20 äåêàáðÿ 2006.
