Inclination is the angle between an orbit and the Equator as the satellite travels northward. For polar orbits, the inclination is 90°. Orbits with lower inclinations do not travel over the poles, spending more time at lower latitudes.

Altitude of a satellite its distance measured over sea level, and determines its orbital velocity

Phase shifts capture the relative placement of satellites in a constellation. Successive orbital planes cross the Equator at different points, e.g. the orbits in Fig. 1. If phase shifted uniformly, 30 orbital planes would have a separation of 12° between successive planes. Each orbital plane can carry many satellites, e.g., if each plane carries 20 satellites, successive satellites in a plane would be separated by 18°.

A Satellite Network(SN) consists of two components:

1. the space segment: this is a constellation of satellites interconnected with inter-satellite links (ISLs), and
2. the ground segment: this includes a number of terrestrial ground stations(GSTs) that form bidirectional communication links with the constellation, called ground-to-satellite links (GSLs). GSTs are a terrestrial radio station designed for communication with satellites, which may be located either on the Earth’s surface, or in its atmosphere. They are points of presence with multiple antennas capable of tracking many satellites simultaneously and are also connected to the ground fiber network. A typical end-to-end connection through an SN may consist of terrestrial connectivity between GSTs and terrestrial end-points, up and down GST-satellite connections, and potentially several ISLs.

SpaceX has launched 60 satellites into the first orbital plane of their Starlink network. However, the satellites are not the final version; these satellites have phased-array antennas, but lack laser-based inter-satellite links (ISLs) that others have simulated [1, 4]. An alternative to ISLs is to relay between satellites via a ground station[7].

Original plans for the first phase of Starlink involved:

1. 1600 satellites,
2. 32 orbital planes
3. 50 equally spaced satellites per plane
4. Inclines at 53°from the equator
5. Altitude of 1100 km.

This original design was well suited to ISLs[4], with distances between satellites in the same plane being similar to those between neighboring planes, permitting a relatively “square” mesh of laser links to be formed. This research[4] concluded that it should indeed be possible to use such a constellation to achieve lower latencies than optical fiber, so long as the endpoints were more than roughly a thousand kilometers apart.

In November 2018 SpaceX filed revised plans with the FCC.

Revised LEO constellation:

1. lowers the altitude of the satellites to 550km,
2. uses fewer orbital planes (24 rather than 32)
3. increases the number of satellites per plane from 50 to 66.
4. the orbital inclination of 53°remained unchanged.

Basically, SpaceX keeps the total number of satellites roughly the same. In the revised constellation neighboring satellites in the same orbital plane are much closer to each other than to the corresponding satellite in the next orbital plane. Using ISLs in this first phase might be difficult: the technology is in its infancy[7], and it is likely that the laser-links were simply not ready in time.