I just read in Satnews Daily that:
A 3U CubeSat funded by NASA and led by the University of Colorado’s Laboratory for Atmospheric and Space Physics, MinXSS requires precision pointing to carry out its scientific objectives. Integrating an array of high-performance miniaturized space sensors and actuators, including BCT’s Nano Star Tracker and Micro Reaction Wheels, the XACT unit provides state-of-the-art attitude control for small spacecraft like MinXSS. On-orbit telemetry from the XACT unit and independent spacecraft instrumentation indicates 1-sigma cross-axis pointing error better than 8 arcseconds, which is less than the width of the Empire State Building as viewed from Los Angeles. (my emphasis)
8 arcseconds is only about 0.002 degrees! Of course a "big sat" like a major telescope with high magnification (or high precision) can do much better, I thought that in general 1U to 3U cubesats were in the 0.1 to 10 degree range - mostly determined by a balance between cost and requirements.
Is this some kind of record for a 3U cubesat?
note: the MinXSS (and this and ArXiv) generally points at the sun to measure low energy X-ray spectra. So when it is making measurements it is not rotating with respect to the stars, as an earth-pointing spacecraft would have to do.
edit: I figured out where the need for high pointing accuracy might come from.
above: GIF made from frames of the video AR1226 M2.5 Flare and CME, June 7, 2011 05:00-13:00 AIA 211/193/171 Composite
The X-ray detector inside the Amptek X123 (and here) is a single silicon PIN diode, about 500 microns thick, with areas between 6 and 25 square millimeters shown as standard on the website. An optional pinhole collimator is also available.
The collimator is actually two pinholes spaced about 37 millimeters apart, and they come standard down to 25 microns in diameter. So it's possible that the FWHM could be of the order of 0.04 degrees configured off-the-shelf, and even narrower if a larger distance between pinholes was chosen. They may be able to point at the corona or a CME specifically and record a soft X-ray spectrum.