A study of LEO constellation with figure-of-eight shape ring network
- Paper number
IAC-06-B3.1.09
- Author
Dr. Ryutaro Suzuki, National Institute of Information and Communications Technology, Japan
- Year
2006
- Abstract
Many parameters have to be taken into account in designing a LEO satellite constellation including transmission delay, service coverage, minimum elevation angle, and the effects of space radiation. The constellation parameters were discussed by using a Walker Notation. The satellite orbit parameters were examined under conditions where at least two satellites were always visible from the user terminal to enable satellite diversity. The optimum inclination angle for the 2-pi constellation was directly derived from the spherical triangle formed by three adjacent satellites. Two groups of satellites in a 2-pi constellation system, i.e., ascending and descending, provide dual coverage of the earth’s surface. Therefore, the satellite diversity function installed in a ground terminal can be achieved by simply connecting an ascending and a descending satellite. The parameters to optimize the constellation for dual-satellite accessibility, which maximized the minimum elevation angle was discussed by focusing on the ascending satellite group. The parameter that minimizes the diameter of the circumscribed circle of the spherical triangle composed of two adjacent satellites in the same orbit and one adjacent satellite in an adjacent orbit should be evaluated. Then, the optimum inclination can be evaluated from the combination of the number of orbital planes, the number of satellites per orbital plane, and the phasing factor of the Walker notation. In order to improve the inter-satellite network performance, the bi-directional Manhattan Street Network (MSN) topology was discussed. The relational equations between constellation parameters to achieve a figure-of-eight shape MSN topology were evaluated. The figure-of-eight shape ring network may offer advantages with short connection delays in the north-south direction, and can be applied to regional connections under hierarchical control of the ISL network. Then the parameter sets with the optimum elevation angle which realize the bi-directional MSN topology were derived. In order to evaluate these parameters, the satellite altitude optimization was carried out by using the assumption of the minimum elevation condition for the user terminals. Then, the minimum elevation angle for the user terminal in the latitude area up to 70 degrees was assumed to be 20 degrees for the application of the mobile satellite communication. Finally, the single-satellite visibility and the dual-satellite visibility for optimized parameter sets were evaluated. The selected parameter sets of total number of satellites T, number of satellites in orbital plane P, phasing factor F, and orbit altitude H(km) (T/P/F/H) were (169/13/0/885), (132/11/-1/1100), (121/11/0/1110), (90/9/-1/1345), (81/9/0/1520, and (56/7/-1/1940). The single- and dual-satellite visibility for these parameter sets showed similar performance of the minimum elevation angle. However, the satellite orbit altitude was changed from 885 to 1940 km to compensate the minimum elevation performance. In case of the smaller number of the satellites, the orbit altitude should be higher to keep the minimum elevation angle higher. Then, other factors such as the launch cost of the satellites, increase of the propagation delay, or radiation hardness of the onboard devices should be discussed.
- Abstract document
- Manuscript document
IAC-06-B3.1.09.pdf (🔒 authorized access only).
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