Getting Ready for the Third Science Flight of SUNRISE

SUNRISE is a balloon-borne, stratospheric solar observatory dedicated to the investigation of the structure and dynamics of the Sun's magnetic field and its interaction with convective plasma flows and waves. The previous science flights of SUNRISE in 2009 and 2013 have led to many new scientific results, so far described in around 90 refereed publications. This success has shown the huge potential of the SUNRISE concept and the recovery of the largely intact payload offers the opportunity for a third flight.The scientific instrumentation of SUNRISE 3 will have extended capabilities in particular to measure magnetic fields, plasma velocities and temperatures with increased sensitivity and over a larger height range in the solar atmosphere, from the convectively dominated photosphere up to the still poorly understood chromosphere. The latter is the key interaction region between magnetic field, waves and radiation and plays a central role in transporting energy to the outer layers of the solar atmosphere including the corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters with slit-scanning and context imaging with slitjaw cameras. The SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich near-UV range between 300 nm and 430 nm which is poorly accessible from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter (SCIP) will sample 2 spectral windows in the near-infrared, containing many spectral lines highly sensitive to magnetic fields at different formation heights. In addition to the two new instruments the Imaging Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and spectro-polarimeter flown on both previous missions, will be upgraded to IMaX+, enhancing its cadence and giving access to 2 spectral lines in the visible spectral range. All three instruments will allow investigating both the photosphere and the chromosphere and will ideally complement each other in terms of sensitivity, height coverage and resolution.A new gondola with a sophisticated attitude control system including roll damping will provide improved pointing/tracking performance. Upgraded image stabilization with higher bandwidth will further reduce residual jitter, maximizing the quality of the science data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für Sonnensystemforschung together with the Spanish SUNRISE consortium, the Johns Hopkins University Applied Physics Laboratory, USA, the German Kiepenheuer Institut für Sonnenphysik, the National Astronomical Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA).