From the `Tracking and Data Relay Satellite System (TDRSS)` option on Celestrak's NORAD Two-Line Element Sets [Current Data TLE page][1] I've compiled current TLE inclinations for "on line" TDRS spacecraft:

    Spacecraft     inc(degs)
    TDRS 3          14.4405
    TDRS 5          14.5306
    TDRS 6          14.0861
    TDRS 7          15.0545
    TDRS 8           7.9573
    TDRS 9           5.8274
    TDRS 10          5.5187
    TDRS 11          5.0141
    TDRS 12          5.6613

While not included (yet) on that page, according to this [answer][2] TDRS-13 has entered into service, and can still be found in Celestrak:

    TDRS 13          6.7494

While these satellites are in [geosynchronous orbits][4], they would not be considered [geostationary orbits][3]; their large inclinations result in [analemma][5]-shaped ground tracks, and the antennas of TDRS ground-segment stations would need to trace their daily, nearly North-South movement in order to remain in contact.

This is probably not a big deal, considering the attention and resources already necessary to maintain this critical segment of so many ongoing missions.

But I am curious about the inclinations themselves. There is a cluster (TDRS-3 through TDRS-7) between 14 and 15 degrees, and another (TDRS-9 through TDRS-13) between 5 and 6 degrees. The newest member TDRS-13 is and has been close to 7 degrees for a while now, and TDRS-8 is near 8 degrees.

Are these inclinations specified, station-kept and optimial in some way, or do they reflect non-station-kept "inclination creep" that is a natural phenomenon for circular orbits at this distance, or is there another way to uderstand this distribution in TDRS inclinations? 

[![TDRS-13 ground track][13]][12]

**above:** Screen shot of TDRS-13 analemma-shaped ground track from [N2Y0][14].

  [1]: https://www.celestrak.com/NORAD/elements/
  [2]: https://space.stackexchange.com/a/26268/12102
  [3]: https://en.wikipedia.org/wiki/Geostationary_orbit
  [4]: https://en.wikipedia.org/wiki/Geosynchronous_orbit
  [5]: https://en.wikipedia.org/wiki/Analemma
  [12]: https://i.sstatic.net/4mJhZ.png
  [13]: https://i.sstatic.net/4mJhZm.png
  [14]: http://www.n2yo.com/?s=42915