Satellite-based radio echo sounding technique is of interest to the Earth science community over Antarctica and Greenland, as well as to the planetary science community for exploring subsurface structures of Mars and Europa.  Pioneered by the Mars exploration community using MARSIS radar on board the Mars Express mission, such a technique has demonstrated ice sounding capability down to a few kilometers.  This paper presents an overview of ESA's activities in the areas of Earth Observation and Planetary Exploration for preparing future satellite-based sounding missions.  These activities include: (a) establishing observational requirements; (b) understanding VHF/UHF wave, propagation and scattering within the subsurface medium; (c) designing radar payloads and satellite systems; (d) developing data processing algorithms for enhancing resolution and sensitivity.  The BIOMASS P-band Synthetic Aperture Radar (SAR) mission, a candidate among the ESA's future Earth Explorer missions, represents a unique opportunity for exploring ice-sheet sounding of Antarctica and Greenland from space.