- Stabilized ground tracks used in the Salyut/Mir program
- Stabilized ground tracks in the US-P (EORSAT) and US-A (RORSAT) programs

Orbits with repeating ground tracks play a great role in space systems engineering. Ground tracks that repeat according to a certain pattern have important applications in remote sensing missions, reconnaissance missions, and to provide multiple opportunities for rendezvous and docking with an orbiting vehicle.

For example, the orbit of Salyut-3 at the time of Soyuz-14 and -15 launches to it was such that it repeated every 63 revolutions, i.e. almost every four days. The nodal period at such occasion was 89.85 minutes. The same was true for Soyuz-21 when it was launched towards Salyut-5. Soyuz-23 and -24 were launched when the period was nearer 89.55 minutes, which corresponds to a ground track that repeats every 79 revolutions.

A general theory can be developed to calculate such orbits. The repeating pattern is determined by four parameters:

- N = the integer number of orbits per day upon which the pattern is based
- M = the number of revolutions from the base revolution on the initial day that denotes the revolution with which the ground track shall be matched on the day when the repeating pattern shall occur.
- Q = ground track is synchronized after this number of days.
- i = the inclination.

However, these points in the diagram can be connected with curves for periods with the same N and M parameters, but with varying values of Q. This is shown below where some of the orbital periods used by Salyut missions have been marked with red rings.

The figure below shows the
orbital period of Salyut-4 during 1975. The launches of Soyuz craft destined
for Salyut are marked, including the launch failure called the "April 5
anomaly". All Soyuz launches except the unmanned Soyuz-20 took place at
a period very close to 91.35 minutes.

The US-A spacecraft maintained
an orbit at i = 65^{o} and a nodal period of 89.65 min, which corresponds
to an average altitude of 255 km. This turns out to be an orbit with the
parameters (N,M,Q)=(**16, -1, 7**) which corresponds to a ground track
that repeats every 111 orbits, i.e. weekly. the graph below shows how Kosmos-1249,
a US-A spacecraft. launched in March 1981, was maneuvered extensively
to keep its nodal period extremely close to 89.65 minutes.

The US-P spacecraft are still
in use and they have operated in pairs in widely separated orbital planes.
However, they have always maintained orbits with a well defined repeating
pattern. These spacecraft use an orbit at i = 65^{o} and a nodal
period of 93.30 min, which corresponds to an average altitude of 434 km.
This turns out to be an orbit with the parameters (N,M,Q)=(**15, 1, 4**)
which corresponds to a ground track that repeats every 61 orbits.

A simple Visual Basic program to design orbits with different repeating patterns can be found here.