This paper reports a development and demonstration of inflatable extension boom in the experiments of the ISAS/JAXA sounding rocket, S-520-25. The inflatable extension boom developed by the authors is the longest in ones with conductive part to work as an electrode for collection of electrons surrounding the rocket. S-520-25 sounding rocket was launched in August 31, 2010, and 5 experiments including an extension of the inflatable boom were conducted. The inflatable extension boom and its system worked very well with no problem to form 4-m-long electrode in space.
