ESTADIUS: A DAYTIME ACCURATE ATTITUDE ESTIMATION SYSTEM FOR STRATOSPHERIC BALLOONS, BASED ON GYRO-STELLAR MEASUREMENT

ESTADIUS is an autonomous, accurate and daytime attitude estimation system, for stratospheric balloons that require a high level of attitude measurement and stability. The system has been developed by CNES. ESTADIUS is based on star sensor and gyrometer data fusion within an extended Kalman filter. The star sensor is composed of a 16 MPixels visible-CCD camera and large aperture optics (135mm, f/1.8, FOV = 10 degrees x15 degrees) which provides very accurate stars measurements due to very low pixel angular size. This also allows detecting stars against a high sky background. The gyrometer is a FOG, with a performance class of 0.01 degrees/h. The system is adapted to work down to an altitude of similar to 25km, even with high cinematic conditions. Key elements of ESTADIUS are: daytime conditions use (as well as night time), autonomy (automatic recognition of constellations), high angular rate robustness (a few deg/s thanks to the high performance of attitude propagation), stray-light robustness (thanks to a high performance baffle), high accuracy (<1", 1 sigma). Four stratospheric qualification flights were very successfully performed in 2010/2011 and 2013/2014 in Kiruna (Sweden) and Timmins (Canada). ESTADIUS will allow long stratospheric flights with a unique attitude estimation system avoiding the restriction of the night/day conditions at launch. The first operational flight of ESTADIUS will be in 2015 for the PILOT scientific missions (led by IRAP and CNES in France). Further balloon missions such as CIDRE will use the system. ESTADIUS is probably the first autonomous, large FOV, daytime stellar attitude measurement system. This paper details the technical features and in-flight results.