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IAC-04-IAF-M.5.08
SATELLITE NETWORKS USING MID-ALTITUDE ELLIPTICAL
ORBIT CONSTELLATION «MOLNIYA-ZOND»
Doniants V. N.
«ZOND-HOLDING», Molodogvardeiskaia Str., 2 Bld.2, Moscow, 121467, Russian Federation
Phone: 7-095-955-9600; Fax: 7-095-955-9602
Email: victord@zond.ru
Ulybyshev Yu. P.
Rocket-Space Corp. «ENERGIA», Lenin Str.4A, Korolev, Moscow Region, 141070, Russian Federation
Phone: 7-095-513-6406; Fax: 7-095-513-6138
Email: yuri.ulybyshev@rsce.ru
Zemskov E.F.
Rocket-Space Corp. «ENERGIA», Lenin Str.4A, Korolev, Moscow Region, 141070, Russian Federation
Phone: 7-095-513-8849; Fax: 7-095-513-8620
Email: evgeny.zemskov@rsce.ru
ABSTRACT
Geometric and statistical analysis of satellite networks using the mid-altitude elliptical orbit constellation
MOLNIYA-ZOND and a set of ground stations is considered. The space segment consists six satellites
placed in two orbital planes at elliptical 4-hours orbit with critical inclination and apogee in the North
hemisphere. Elliptical orbit satellite constellations can provide a more intensive coverage of high latitudes
and North Pole areas (such as the Russia, Canada, and North Europe) than can circular orbit
constellations, with fewer satellite at a lower total cost system. New geometric analysis method for
satellite networks based on common mappings of ground station visibility conditions and a satellite
constellation in a two-dimensional space is proposed. The dimensions of the space are the longitude of
ascending node and time. The visibility conditions mapping for a ground station is an area and the map of
the satellite constellation is a moving grid. Interference with geostationary satellites belt also discussed.
Problems of satellite network connectedness for the MOLNIYA-ZOND constellation are considered.
Results of communication network statistical simulation for several scenarios from a simple type "user-
satellite-user" to transcontinental communication are presented. A data for universal space platform
VICTORIA, which was developed in the Rocket-Space Corporation ENERGIA and can be use for the
MOLNIYA-ZOND project, is presented.
INTRODUCTION
The use of satellite constellations in elliptical
orbits providing continuous visibility of a
latitude band is preferable for regional satellite
communication systems oriented to middle
and/or polar geographic regions for one of the
Earth hemispheres. The first was the MOLNIYA
system developed at 1960-s in the Soviet
Union[1]. A special feature of the orbits for such
systems, starting from the MOLNIYA, is a use
of the critical inclination (i = 63.4°) and placing
its perigee in a hemisphere, opposite to the
communication regions.
The paper is a continuation of authors' previous
studies[2-4] (in which was presented a
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constellation design method, coverage analysis,
optimization of constellation deployment and an
estimation of navigation possibilities for the
MOLNIYA-ZOND satellite communication
system) and included an analysis of dynamical
satellite networks using ground stations(GSs). A
data for universal space platform(USP)
VICTORIA, which was developed in the
Rocket-Space Corporation ENERGIA and can
be use for the MOLNIYA-ZOND project, is
presented.
1. MOLNIYA-ZOND SATELLITE SYSTEM
Well-known symmetric satellite constellations
for circular orbits which was introduced
independently by Mozhaev[5] and Walker[6].
Similar idea is also applicable for elliptical
orbits [7]. In this case, the satellite constellation
contains a total of N = PxS satellites with S
satellites evenly distributed in time in each of P
orbit planes which are uniformly distributed
around the equator at interval of 2π/P. All of the
satellite orbits are assumed to be at the same
inclination, semi-major axis, eccentricity and
argument of perigee. Within each orbit plane,
the S satellites are uniformly distributed at
intervals of T/S, where T is orbit period. We
define phase shift in a constellation as a time
shift between perigee passing of the satellites of
adjacent orbit planes.
The MOLNIYA-ZOND system will be used 6
operational satellites in elliptical orbits with
period T ~ 3h59m, eccentricity e = 0.461,
altitudes of the perigee and apogee hπ=500 km
and hα=12300 km, respectively[2]. The satellites
are arranged in two orbital planes with an
angular distance between ascending nodes of ∆λ
= π. For every orbit plane, the time shifts of
satellites perigee passing are equal to ∆T = T/3.
Phase shift of satellite positions in different
planes ∆T*=0.
The communication of users in the system is
provided through a «user-satellite-ground
station.» chain. It is assumed that required
minimum elevation angles in the chain make up
for the users α ≥ 25° and GSsα ≥ 10°.
The orbital parameters of the constellation
practically excluded the influence of second Van
Allen radiation belt (altitudes of ~13000...19000
km) and its work area is predominantly outside
of the first Van Allen radiation belt (altitudes of
~2000...9000 km).
The satellite constellations for continuous
coverage have considerably differing
characteristics of visibility and respectively
communication conditions for different
geographical latitudes. One of the main property
of the satellite constellations for continuous
communication is a multiplicity of coverage, i.e.
a guaranteed number of satellites being at any
moment in the visibility zone of a user or ground
station (See Fig. 1). Within a range of longitudes
25°-90° n.l. the constellation provides
guaranteed single continuous coverage (α ≥
25°). For double coverage, ranges of latitudes
make up ~ 75° - 90° n. l. (α ≥ 25°) and, for α ≥
10°, it is ~ 60° - 90° n. l.
Fig. 1: Multiplicity of continuous coverage for the
MOLNIYA-ZOND constellation
For the near-polar regions triple coverage takes
place in ~65% of the time and quadruple
coverage in ~30%. A geographic map of the
guaranteed elevation angles for continuous
coverage is presented in Fig. 2. As shown the
constellation is provided the continuous
coverage with α ≥ 25° for latitudes more than
25° n.l. and no less than α ≥ 40° for latitudes
more than 40° n.l.
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Fig. 2: Geographic map of elevation angles for the MOLNIYA-ZOND constellation
2. SATELLITE COMMUNICATION
NETWORKS
2.1. User communication through
satellites
In a simple case, users can be connected with
each other if the users are located in the footprint
of a satellite from the satellite constellation. It is
possible for the satellite constellations with at
least single redundancy coverage. However, the
maximal distance allowable between two users
depends on the activity of coverage, i.e. on the
users' latitudes[8]. Examples of such areas for
users located in Halifax (latitude 45° n.l.,
Canada) and Reykjavik (latitude of 64° n.l.,
Iceland) are shown in Figs. 3-4, respectively. Fig. 3: Area of communication through satellites
for a user in Halifax
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Fig. 4: Area of communication through satellites
for a user in Reykjavik
It should be noted that the areas for the users
with same latitude can be presented by
corresponding longitude shift.
2.2. Connectedness of ground station
network
Suppose that there is a satellite with all known
orbit parameters except the right ascension of
ascending node and location along orbit. There
is a nonmoving in inertial space user (for the
continuous coverage, the Earth rotation can be
neglected). Let us consider a two dimensional
space with dimensions - longitude of ascending
node and time. For a time no more than several
orbit periods, the orbit precession can be
neglected in the following analysis. The motion
of the satellite in the space represented by a
straight line that is parallel to the time-axis. In
order hand, the visibility conditions for the user
or GS can be depicted in this space as an area
that included all of the positions (i.e. the
longitude and time ) of the satellite for which
meet the visibility conditions.
Further, in the two dimensional space a satellite
constellation may be presented as a moving grid
(see Fig. 5). The satellites are the grid nodes. For
each orbit plane, they are placed at same vertical
line spacing along time-axis of T/S. The spacing
between adjacent vertical lines (i.e. adjacent
orbit planes) is 2π/P. The slope of grid lines
between adjacent planes is corresponded to a
phase shift.
Fig. 5: Map of a satellite constellation and
visibility area
For continuos visibility of a satellite from the
constellation, it is need the continuos presence
of at least one node of the grid inside of the
visibility area. Similar reasonings can be also
applicable to an analysis continuous link
between a pair of GSs. In this case, at least one
node should be belongs to intersection of the
corresponding visibility areas. An example for a
pair of GSs located in Moscow and Norilsk is
shown in Fig.6.
Fig. 6: Visibility areas for GSs and grid
for the MOLNIYA-ZOND constellation
Time
Longitude
Visibility
area
T/S
2/S
π
Phase shift
Satellites
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In the same place a part of the grid for the
MOLNIYA-ZOND constellation is also
depicted. As shown at any time there is at least
one satellite in joint visibility area of the GSs.
For analysis and computation can be used
methods of computational geometry[9].
Statistical distribution of the links - probabilities
for number the joint visibility satellites and
distribution of the duration for visibility
intervals are pictured in Fig. 7. As shown, the
duration of continuous link through one satellite
is no less than one hour for ~ 80% of the time.
Fig. 7: Link statistics for GSs in Moscow and
Norilsk
By similar ways can be designed a network of
GSs with continuous connectedness.
2.3. Geometric interference with
geostationary belt
For non-geostationary satellite communication
systems, in principle, a radio-interference with a
geostationary systems is possible. In general
case, the analysis of the problem is very
complex and included more aspects. It are
constellation geometry, GSs locations,
frequency bands to transmit and receive, antenna
characteristics, etc. We consider only geometric
behavior of possible interference the
MOLNIYA-ZOND ground stations with the belt
of geostationary satellites. More particularly it is
an estimation of probability when the line-of-
sight to the two satellites (a MOLNIYA-ZOND
satellite and a geostationary satellite) as seen
from the GS are within a given keep-out angular
radius (~5o). The possible interference for the
GS will be a cone centered on the direction to
the geostationary satellite if the operating in the
same or very nearby frequency band. The
possible zones of lines-of-sight near to
geostationary belt for GSs with latitudes of 45°
and 55° n.l. are shown in Figs.8-9 (green color)
vs longitude of the GS and time at interval of
one orbit period. The probabilities are ~5.1%
and ~7.9%, respectively. However, the
MOLNIYA-ZOND constellation has a coverage
redundance. Therefore, in most these cases, the
GSs have been the additionally the visibility of
at least one satellite at a position, which does not
interfere with geostationary belt. The
probabilities for non-fulfilment of these
conditions (see Figs. 8-9, red color) are no more
than ~1.6% and 0.1%, respectively.
Fig. 8: Zones of possible interference for GS at
latitude 45 deg
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Fig. 9: Zones of possible interferencefor GS at
latitude 45 deg
Thus the MOLNIYA-ZOND ground stations
could operate practically without an interference
with geostationary systems.
2.4. Service area
Based on the previous considerations was
constructed a possible GSs network for the
communication at most part of the North
hemisphere. The GSs are located in the Russia
(Moscow, Norilsk, Khabarovsk) and Canada
(Vancouver, Halifax). The service area (with
excluding of geostationary belt interference) is
presented in Fig.10.
Fig. 10: Service area for the MOLNIYA-ZOND system
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It is shown that this area is slightly differ from
coverage area (see Fig. 2). Statistical
characteristics for transcontinental link between
Moscow and Vancouver - distributions for
number of accesses and the duration of
continuous accesses are presented in Fig.11. The
duration of continuous link without of hand-over
is no less than half hour for ~60% of the time.
Fig. 11: Statistics of link between Moscow and
Vancouver
3. SATELLITE COMMUNICATION
SYSTEM
3.1. Major features
The “Molniya-Zond” system is being developed
for provision of mobile personal communication
on the territory of Russian Federation (latitude
band φ ≈ 410 – 800 n.l.) using of a elliptical orbit
satellite constellation N = 2x3. Basic
requirement to the system is provision of
following services:
• duplex telephone communication;
• E-mail;
• paidging communication;
• determination of user’s coordinates by
request.
The system should provide simultaneously up to
3500 users communication channels by
2.4 kbit/s.
3.2. Universal space platform VICTORIA
The universal space platform VICTORIA, a
space-proven platform for a wide range service,
was developed by Rocket-Space Corporation
ENERGIA. Based on this USP was produced
the communication satellites YAMAL-100 and
YAMAL-200. Now three satellites of the
YAMAL series functioned at the geostationary
orbit. Now the ENERGIA designed new
communication and remote sensing satellites
based on this platform. The use of the
VICTORIA for the MOLNIYA-ZOND system
is studied.
The key of the VICTORIA building is
providing a set of standard, experimental and
in-flight validated modules and subsystems
for designers [10, see also
http://www.energia.ru/english/energia/usp/usp.h
tml ). In a sense, it is a principle near to well-
known "Lego" idea, i.e. a combination of
modules from the set for a satellite with specific
purpose.
Fig. 12: Major modules of universal
space platform VICTORIA
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An example of a mid-size satellite based on the
USP VICTORIA is shown in Fig. 13.
Fig. 13: Mid-size satellite based on the
VICTORIA platform
REFERENCES
1. Cherniavski G.M., Bartenev V.A., Orbits of
communication satellites, Moscow, Sviaz,
1978, 240 pp. (in Russian).
2. Donianz V.N., Ulybyshev Y.P., "Elliptic
Orbit Constellations for Regional
Communucation and Molniya-Zond Satellite
Constellation", 53rd Int. Astronautical
Congress, Houston (USA), Oct .10-19,
2002, paper IAC-02-M.4.05.
3. Ulybyshev Y.P., Donianz V.N.,"Dynamic
Communication Networks Using Satellite
Constellations and Ground Stations", 53rd
Int. Astronautical Congress, Houston
(USA), Oct .10-19, 2002, paper IAC-02-
M.4.07.
4. Ulybyshev Y.P., Donianz V.N., "Satellite
Communication System «Molniya-Zond»
Using Mid-altitude Elliptic Orbit
Constellation", 54th International
Astronautical Congress of the International
Astronautical Federation, Bremen
(Germany), 2-8 Oct. 2003, paper IAC-03-
M.2.05.
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Continuous Earth Coverage and
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Coverage", Journal of the British
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9. Berg M., Computational Geometry:
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Springer-Verlag, 2000. - 367 pp.
10. Semenov Y., Legostaev V., Vovk.A.,
Zemskov E., et all "Results of Small
Spacecraft Design Based on Multipurpose
Platform VIKTORIYA", IV International
Conference & Exhibition Small Satellites.
New Technologies, Miniaturization,
Efficient Applications in the 21st Century,
Korolev (Moscow Region, Russia). May 31
- June 4, 2004, Paper.III.18