Orbital Traffic Management for Non-GEO Systems
- Paper number
IAC-06-B3.5.06
- Author
Mr. John Draim, United States
- Coauthor
Dr. Paul J. Cefola, Massachussets Institute of Technology (MIT), United States
- Year
2006
- Abstract
Abstract: The operation of various multiple-satellite constellations in non-GEO space creates risks falling into two major categories. First, there is the risk of physical collisions between satellites. Although statistically small, this risk is not to be ignored- as the case of the French Cerise satellite has shown. Secondly, and of much greater practical concern, is the problem of electronic interference occurring when two satellites and a ground station approach colinearity. Such interference can be either up-link or down-link. At the present time, the regulatory bodies generally assign different frequencies to the different licensed non-GEO systems. For GEO systems (manly of the FSS type), frequency re-use is made possible by longitudinal separation of satellites into two- or three-degree slots spaced around the equator. An apt analogy for the GEO arrangement would be to cars parked along a curbing, separated by white spacing lines. In the case of non-GEO satellites that will never appear stationary in space, a means of achieving physical separation is not immediately apparent. However, the authors have shown that an ordered system of elliptical-orbit satellites can be designed to appear to observers on the ground as a slowly moving grid that maintains almost constant inter-satellite separation both in-track and cross-track. Now, the analogy is to a multi-lane superhighway, wherein all cars maintain separation both transversely (by lanes) and in-track (by drivers maintaining a decent interval from cars in front). Another important advantage of using elliptical orbits, in such a system of systems, is the ease with which they can be de-orbited- thus removing the danger of expired satellites colliding with those that are still active. An earlier study describes such a system that provides 2880 ‘equivalent slots’, using slowly moving 8-hr elliptical satellites. Even this number could be increased, through using either (a) a different frequency for left leaning and right-leaning elliptical satellites, (b) using different codes in CDMA for the right-leaning and the left-leaning satellites, or (c) using a different signal polarization.. Depending on the mission or application, arrays of 3-. 4-, 4.8-, 6-, 8- 12-, and 18-hour periods may prove optimal, with interference protection provided by signal polarization, frequency separation, or CDMA techniques. Repeat cycles other than one-day are possible, with orbits per day equal to any rational fraction. A thorough study of gains achievable through international non-GEO orbital array standardization is highly recommended.
- Abstract document
- Manuscript document
IAC-06-B3.5.06.pdf (🔒 authorized access only).
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