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I know I might get an answer like "the sky is not the limit"...

But considering the actual state of the art of modern satellites ADC systems. Haven't we reached a "maximum" yet? Or are there still a lot of improvements which have to be made? What is being worked on for the moment? What are some major difficulties engineers developing those systems are facing nowadays?

What are some mission failures caused by the ADCS (Attitude Determination and Control Systems)?

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    $\begingroup$ We're right at the beginning of the glorious path of ion RCS engines, and frictionless magnetic bearings still need to enter usage in reaction wheels. $\endgroup$
    – SF.
    Jan 28, 2016 at 1:08
  • $\begingroup$ I'd say magnetorquers (en.wikipedia.org/wiki/Magnetorquer) are another technology that is being worked upon and will probably improve reliability and reduce propellant load for low-earth-orbit satellites in the future. (Just an opinion though, so I'll leave this as a comment.) $\endgroup$
    – Andy
    Jan 28, 2016 at 13:20
  • $\begingroup$ Roughly along the lines of Feynman's There's Plenty of Room at the Bottom (here or here) there is probably room for innovation for satellites 1U and smaller. Low power, high reliability, small volume, low cost, long life... Not necessarily re-inventing the wheel (pardon the pun) algorithmically, but making small stuff work well is more than shrinking the designs of the large stuff. $\endgroup$
    – uhoh
    Jan 29, 2016 at 9:00

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The major improvements in ADCS are caused when there are failed components, and one has to work around these limitations. For instance, Kepler has only 2 functioning reaction wheels, when it originally required 3. Advances in ADCS have allowed it to retain some stability utilizing the 2, using the Sun as a third force. Hubble used similar technology as well, for broken reaction wheels, until they were replaced in a Shuttle servicing mission.

The basics are already known, as you stated, and in fact, have been known for some time. There are refinements to further improve the systems, but the algorithms are known.

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  • $\begingroup$ Using Kepler as an example is inappropriate. The reaction wheels lasted far longer than the mission was planned for. This wasn't a case of component reliability as much of an issue of the mission being extended so much until something broke. Also the algorithms are not fully "known". We certainly know about several algorithms, but it is still an active area of research. A new version of QuEST comes out all the time and ever more variations of Kalman filters are used on satellites. Because ADCS is non-linear, a globally optimal solution has yet to proven. $\endgroup$
    – Knudsen Number
    Mar 15, 2019 at 15:48
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A lot of research is going into sub-arc-second pointing accuracy to allow the next generation of telescopes after JWST to do even more impressive feats. NASA in the 2019 SBIR is soliciting calls for tech development in this area. (Check S3.04) https://sbir.nasa.gov/solicit/61545/detail?data=ch9

A lot of the research here, basically comes down to dumping reaction wheels as the choice for control because reaction wheels are terribly mechanically noisy. I have seen proposals for EP to be used as a low noise replacement.

Jitter stability is the other area I can think of off the top of my head.

As far as problems go, dealing with noise is generally the biggest problem.

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