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:

    COSPAR       NORAD    Launched       Spacecraft   current inc(degs)
    1988-091B    19548    1988-09-29     TDRS 3          14.4405
    1991-054B    21639    1991-08-02     TDRS 5          14.5306
    1993-003B    22314    1993-01-13     TDRS 6          14.0861
    1995-035B    23613    1995-07-13     TDRS 7          15.0545
    2000-034A    26388    2000-06-30     TDRS 8           7.9573
    2002-055A    27566    2002-03-08     TDRS 9           5.8274
    2002-055A    27566    2002-12-05     TDRS 10          5.5187
    2013-004A    39070    2013-01-31     TDRS 11          5.0141
    2014-004A    39504    2014-01-24     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:

    2017-047A    42915    2017-08-18     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.

**Question:** Are these inclinations specified, station-kept and optimal in some way, or do they simply 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? 

**note:** I understand that without station keeping, inclination will increase. But I'm looking for more of an answer than "It might be...". Considering that TDRS-13 *started at almost 7 degrees* suggests that it might be more than just an intrinsic lack of North-South station-keeping ability. 

[![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