Double probe boom for electric field measurements in the ionosphere
These two booms equipped with one probe each are used to do electric field measurement at an altitude of 200-700 km. The voltage difference divided by the distance gives the electric field in the direction of the booms. Using two such boom systems, oriented perpendicular to each other and separated along the axis of the spinning rocket, one can measure the electric fields in all three dimensions. The boom system above you was most likely flown on the sounding rocket S10 that was launched from Esrange in 1974.
Space and Plasma Physics have since the 60s up until today contributed to about 40 sounding rockets, most of them carrying double probes for electric field measurements developed here at KTH.