Digression - Orbit Mechanics!
By way of a digression lets look at some orbit mechanics! This figure shows a generalised
orbit... remember Kepler from school! The planet is at one focus... orbiting body sweeps out
equal areas in equal time... define apogee, perigee, period, inclination mention stability
Orbit Mechanics (2)
- Geostationary (GSO/GEO) - 36,000 km / 24 hour period / <5° inclination
- Geosynchronous (GSO/GEO) - as stationary but higher inclination
- Low Earth Orbit - <2,000 km / 80 - 130 minutes period
- Medium (Intermediate) Earth Orbit - 2,000 km - 10,000 km / 130 minutes - 6 hours
Here are the main classes of orbit...
Orbit Mechanics (3)
- Inclined Highly Elliptical (HEO)
- Sub- and super-synchronous
-Combine orbits into "constellations"
- groups of orbits to provide global or regional coverage
- key to defining service characteristics
...and here are a few more! The CONSTELLATION puts a number of satellites together to
provide a COVERAGE.
Concept (6) - Network Configuration
-There is no "typical" S-PCN configuration
-Some things to be considered:
- routing in space or on the ground (ISLs?)
- integrated into terrestrial network / overlay / stand-alone?
- gateway distribution... politically difficult!
We'll not try and answer these now but will look at specific proposals...
Let's touch on the network configuration. This is complex and could be an entire lecture in
itself! Mention some key considerations. (slide)
We'll focus on three specific examples
Bear in mind some of the key issues:
- NGSO vs. Super-GEO
- CDMA vs. TDMA
- ISL vs. non-ISL