What is a Walker constellation?
A Walker constellation is a standardised orbital configuration developed by British engineer John Walker in the 1970s that provides optimally symmetric coverage. It is described by three parameters: N (total satellites), P (number of orbital planes), and F (phasing factor, 0 ≤ F < P), written as N/P/F. All satellites share the same altitude and inclination; planes are equally spaced in right ascension, and satellites within each plane are evenly distributed.
Walker-Star vs. Walker-Delta
Walker-Star configurations use a 90° inclination (polar planes that cross both poles), optimal for high-latitude coverage. OneWeb uses a Walker-Star configuration at 1,200 km with 12 polar planes. Walker-Delta configurations use an inclination less than 90°, optimising coverage for mid-latitudes where most of the world's population lives. Starlink's initial shell uses a Walker-Delta configuration at 53° inclination. GPS uses a Walker-Delta pattern with 6 planes of 4 satellites at 55° inclination.
Why it matters
Walker's mathematical framework allows designers to analytically determine the minimum satellite count for continuous coverage of a given latitude band, without trial-and-error simulation. This makes it the industry standard starting point for constellation design, even when final constellations deviate slightly from the pure Walker geometry to accommodate ground station locations, launch constraints, or orbital maintenance requirements.