1、330 RW. ITU-R S.743-1 RECOMMENDATION ITU-R S.743-1 THE COORDINATION BETWEEN SATELLITE NETWORKS USING SLIGHTLY INCLINED GEOSTATIONARY-SATELLITE ORBITS (CSOS) AND BETWEEN SUCH NETWORKS AND SATELLITE NETWORKS USING NON-INCLINED GSO SATELLITES (Question ITU-R 5 114) ( 1992- 1994) The IT Radiocommunicati
2、on Assembly, considering that the definition of a geostationary satellite in the Radio Regulations (RR No. 181) has no indication for a a) maximum value of the angle of inclination of the orbit of a geostationary satellite; b) tends to be the limiting factor of a geostationary space stations life; c
3、) that station-keeping fuel on geostationary space stations constitutes an appreciable portion of in-orbit mass and that North-South station-keeping consumes up to 90% of the total fuel; d) than about 0.9“ of orbit change per year, and the inclination will never exceed the natural limit of 15“; that
4、, in the absence of North-South station-keeping, the orbit of a geostationary satellite is subject to no more e) that, on the other hand, the absence of North-South station-keeping may require additional equipment at the earth stations, such as angular tracking, polarization tracking and for digital
5、 transmissions also, larger size elastic buffers and more complex synchronization methods; f) that the Second Session of the World Administrative Radio Conference on the Use of the Geostationary-Satellite Orbit and on the Planning of Space Services Utilizing It (Geneva, 1988) (WARC ORB-88) considere
6、d the matter of coordinating slightly inclined geostationary satellite networks, and referred action to the ex-IFRB and the ex-CCIR; g) that the ex-IFRB requested the ex-CCIR to study the related problems: - the technical aspects of coordination between geostationary satellites and those in inclined
7、 geostationary orbits; the technical aspects of coordination between satellites in inclined geostationary orbits; - that there appears to be no intrinsic limitation on the coordination of satellite networks using slightly inclined h) geostationary orbits; j) inclined geostationary-satellite orbits,
8、that the data required by RR Appendices 3 and 4 (WARC ORB-88) include the effects of using slightly noting that a) inclined orbit, will be equal to or greater than that between two geostationary-satellite networks (near O“ inclination); b) under Co-coverage conditions, the isolation between two geos
9、tationary-satellite networks using slightly inclined orbits may be either less, or greater, than that between two geostationary-satellite networks near O“ inclination, depending on the relative nodal phase; c) under Co-coverage conditions, the isolation between two closely spaced geostationary-satel
10、lite networks with frequency re-use by dual linear orthogonal polarization, one or both of which use a slightly inclined orbit, may be less than two geostationary-satellite networks, depending on the relative nodal phase; under Co-coverage conditions, the isolation between geostationary-satellite ne
11、tworks with one using a slightly d) under non co-coverage conditions, between two geostationary-satellite networks, one or both of which use slightly inclined orbits, the isolation may be less. or greater, than that between two geostationary-satellite networks, depending on a nuniber of factors in a
12、ddition to the relative nodal phase, U 4855232 0521655 434 I . ,* . . W 4855232 0523b5b 370 Rec. ITU-R S.743-1 331 recommends 1. that the coordination of geostationary-satellite networks using slightly inclined geostationary-satellite orbits be performed in accordance with the RR that apply to geost
13、ationary-satellite networks based upon the minimum separation between the satellites concerned; 2. that in bands shared with terrestrial services the inclination limit for the application of 0 1 may need to be determined by the inter-service sharing considerations (see Note 1); in other bands 0 1 ma
14、y be applied up to the natural inclination limit for satellites launched initially into a geostationary or near-geostationary orbit if N/S station-keeping manoeuvres are not undertaken; 3. slightly inclined geostationary orbits, the information given in Annex 1 should be utilized; that for interfere
15、nce considerations involving the coordination of geostationary-satellite networks using 4. used to minimize any deleterious effects (see 5 5 of Annex 1); that the relative nodal phase between the orbits be adjusted if practicable, and/or other measures should be 5. Note I - Recommendation ITU-R SF.1
16、008 deals with possible use by space stations in the fixed-satellite service of orbits slightly inclined with respect to the geostationary-satellite orbit in bands shared with the fixed service. that the following Note should be regarded as part of the Recommendation. ANNEX 1 1. Introduction The inf
17、ormation contained in this Annex should be used in connection with the coordination of satellite networks using slightly inclined geostationary-satellite orbits (GSO) and between such networks and other satellite networks using non-inclined GSO satellites. During slightly inclined GSO operation, the
18、re are basically three factors which affect the interference between two satellite networks. These are: - - - the exocentric angular separation between the coverage areas of the networks as seen from either satellite; the exocentric angular width of the coverage areas as seen from either satellite;
19、the topocentric angular spacing between the satellites as seen from an earth station of either network. These factors cause the net antenna discrimination (earth station and satellite antenna) between the two networks to vary in time. In cases where satellite networks have a common service area (Co-
20、coverage networks), the earth-station antenna is the basic element providing discrimination between the networks. Where satellite networks have separate service areas (non Co-coverage networks), both the earth station and satellite antenna contribute to the discrimination between the networks. 2. Ge
21、ometric considerations The geocentric angle, pg, between two slightly inclined geostationary satellites with latitudes (y1 and y2) and longitudes (pl and a a 0; 3 c3 a -1 3 -2 -3 -4 -5 -6 -7 -8 -9 m The results in Figs. 9-12 show that the net discrimination between a slightly inclined geostationary
22、orbit satellite network and a geostationary-satellite network is greatly impacted by the relative positions of the coverage areas of the two networks. In some cases (see Fig. 12), the net discrimination is practically always greater than nominally achieved if the two networks were geostationary. The
23、se are the cases where the impact of the satellite antenna discrimination is negligible. In some other cases, where the impact of the satellite antenna is significant, there is a loss of the net discrimination (compared to nominal) for a certain period of time during the day. The magnitude of the lo
24、ss and its duration are functions of the inclination, satellite spacing and the width of the coverage area. However, it should be emphasized that, due to the choice of point A on the satellite antenna pattern (see Fig. 7) the above results represent the “worst case“. In many cases, the relative posi
25、tions of satellite network coverage areas will be such that the motion of the coverage area due to the slightly inclined orbit operation will have a negligible effect on the net discrimination between the two networks. In these cases, the variation of the overall discrimination will be determined by
26、 the discrimination of the earth-station antenna, which for this case (one slightly inclined geostationary and one geostationary network) is always equal to or greater than nominal. Further studies are needed for the cases involving two slightly inclined geostationary orbit satellite networks. Rec.
27、ITU-R S.743-1 339 26 24 22 20 18 16 14 12 10 8 6 4 2 O -2 -4 -6 -8 - 10 - 12 - 14 - 16 FIGURE 9 Relative net discrimination as a function of time O 2 4 6 8 10 12 14 16 18 20 22 24 Time from ascending node of satellite No. 1 (h) I I I l r I I I I I I I I I I I I I I I I I I l inclination: 3“ ( 1; 9“
28、( ) Beam position: 1 1 1; 3.0“ I.)(- (-I Check point: Satellite beam diameter: 1.5“ 340 26 24 22 20 18 16 14 2. 12 = 4855232 052l1665 383 Rec. ITU-R S.743-1 FiGURE 10 Relative net discrimination as a function of time I I I 1 I I I I I I I I - 14 - 16 I I I I 1 I I l I I I O 2 4 6 8 10 12 14 16 18 20
29、 22 24 Time from ascending node of satellite No. 1 (h) Inclination: 3“ ( 1; 9“ ( 1 Beam position: 2 Satellite beam diameter: Check point: - 4855212 0521bbb 21T 26 24 22 20 18 h 16 c 12 G 10 c8 E .s 4 .; -2 5 14 O m f U -2 go 0 Lu 2 -6 - -4 -8 - 10 - 12 - 14 - 16 Rec. ITU-R S.743-1 34 1 FIGURE II Rel
30、ative net discrimination as a function of time r I 1 I I I I I I I I 1 t I I I 1 ! 1 I I I I I I O 2 4 6 8 10 i2 14 16 18 20 22 24 Time from ascending node of satellite No. 1 (h) Incl i nation: 3“ ( 1; 9“ ( Beam position: 3 Satellite beam diameter: Check point: );3.0“ )i Y- (- ni I 342 - I - - - - -
31、 - - - I I I I I I I I l I I 26 24 22 20 18 16 14 12 10 8 6 4 2 O -2 -4 -6 -8 - 10 - 12 - 14 - 16 4855212 0523667 156 Rec. ITU-R S.743-1 FIGURE i2 Relative net discrimination as a function of time Inclination: 3“ ( 9“ ( 1 Beam position: 3 Satellite beam diameter: 1.5“ Check point: D 12 5. Control of
32、 nodal phasing In the previous sections, it was shown that the loss of the earth-station antenna discrimination becomes significant when nodal phase difference between two neighbouring satellites approaches 270“. However, it is possible at moderate cost in station-keeping fuel to prevent the occurre
33、nce of worst orbital phasing of two neighbouring satellites through controlling the orbital nodes, a form of second order station-keeping. Figure 13 shows, in the lower pair of curves, the yearly requirements in terms of orbital velocity changes AV for a satellite subject to tight North-South statio
34、n-keeping (curve A) and for one subject to maintenance of its orbital node at 90“ right ascension (curve B). The velocity changes, which are proportional to the amount of station-keeping fuel needed to produce them, become equal after about 9 years. When considering total cumulative fuel requirement
35、s for the two modes of operation, node phasing would require the same amount of fuel as North-South station-keeping only after i6 years (upper curve pair). For a 7 year satellite operation with no North-South station-keeping, the maintenance of a node at 90“ right ascension would use only half as mu
36、ch fuel as full North-South station-keeping. In practice, it will not be necessary to maintain a node at 90“ right ascension - what is needed is a node correction which prevents the occurrence of the worst case interference geometry. How much fuel wil! be required depends, infer alia, on the differe
37、nce in the inclination of the satellites; in favourable situations no node control may be needed even though the satellites of two potentially interfering networks may both be in slightly inclined geostationary orbits. 4855232 0521bb Rec. ITU-R S.743-1 750 600 450 h v L. Q 300 150 O FiGRE 13 Yearly
38、(lower curve pair) and cumlative AVrequPemens i 8 I 8 I A 343 O 5 IO 15 20 Year from start of no N-S station-keeping N-S station-keeping tr $3 - Node control 6. Coordination considerations From the previous analyses there appears to be no intrinsic limitation on the coordination of networks using ci
39、rcular slightly inclined geostationary orbits. In the case of a geostationary network and a network using a slightly inclined geostationary orbit, the isolation between the networks will be equal to or greater than it would be in the case of the two geostationary-satellite networks under Co-coverage
40、 conditions. Thus, coordination will be the same as if both networks were geostationary. If both satellite networks use slightly inclined geostationary orbits, some decrease in isolation as compared to the isolation between geostationary-satellite networks might occur under the most unfavourable nod
41、al phasing of the satellites and under Co-coverage conditions. However, this can be determined and accounted for in coordination. Under non Co-coverage conditions, satellite antenna discrimination is involved and this adds complexity in terms of estimation of interference effects. These effects can
42、also be determined and accounted for in the coordination proces s. 12 4855232 O523669 T29 344 Rec. ITU-R S.743-1 However, there is the case where coordination was achieved on the basis of essentially O“ inclination but at some later date the inclination is allowed to increase. It would appear that i
43、n most practical cases, the increase in interference would not be significant, i.e. the probability that all conditions are simultaneously present for worst-case interference is considered to be quite small. Hence, in most such cases, there will be no need to re-coordinate a network previously coord
44、inated as geostationary and planning to suspend North-South station-keeping with other geostationary networks. While, generally, the inclined orbit operation of a networks satellite is supportable on the basis of inter-network coordination agreements that assume the networks satellite to be geostati
45、onary, there may be some circumstances where geostationary inter-network coordination agreements provide insufficient protection for inclined geostationary orbit operation. Thus, there is a need to determine the conditions for which geostationary inter-network coordination agreements would not suffice to prevent unacceptable inter-network interference from occurring when one or more networks commence inclined geostationary orbit operation.
