Three SRS-2000 gyroscopes was used in BETTII project. Here are some excerpts from the article on Attitude Control System for a Balloon Based Telescope BETTII:
The BETTII payload is an 8-meter long boom interferometer, using a double-Fourier Michelson interferometer, to obtain far-infrared spectra of young stars in clustered star formation regions. BETTII provides a high angular resolution which will allow us to gather data on spectral energy distributions of individual deeply embedded protostars forming in dense clusters and distinguish between multiple embedded sources.
The three SRS-2000 gyroscopes used to measure the angular velocity, using Sagnac model, which offer high precision and have very low angular random walk, thus adding little noise to each measurement. These gyroscopes are exceptionally good, if we integrate the gyroscope angular velocity measurement to obtain a position estimate, the estimation error we
would make after one hour of integration would have a standard deviation of 2 arcseconds. The bandwidth is 50Hz but they can be read up to 2kHz. Additionally, built-in thermal regulators maintain the temperature within a certain range in order to maintain precision when operating at different temperatures.
The three gyroscopes were mounted in an orthogonal configuration, however because the mount could not be orthogonal to the arcsecond level we had to apply a rotation matrix in the software in order to make the measurements perfectly orthogonal. By doing this cross correlations between different axes velocity measurements are avoided. Otherwise, that would have affected the pointing estimation.
Full article on Attitude Control System for a Balloon Based Telescope BETTII you can find here or spiedigitallibrary.org/conference-proceedings-of-spie