ISS (Ionospheric Sounding Satellite) 1 and 2 were a pair of Japanese satellites, launched by NASDA (National Space Development Agency) and also known by their national name Ume ("plum"), that collected data on the ionosphere to aid in short-wave radio communication. Their instruments included an ionospheric sounder, a radio noise receiver, plasma measuring equipment, and an ion mass spectrometer. Both measured 3.9 by 0.8 meters and were launched by N-1 rockets from Tanegashima.