Loss of life, injury and huge economic losses are incurred annually due to irregular and insufficient sea–state information. Figures indicate that, each year, the marine insurance industry pays out over $2 billion in claims for weather–related accidents, while bad weather causes one ship of over 500 t to sink somewhere on the globe every week. Accurate knowledge of local ocean conditions is therefore crucial in providing forecasts and early warnings of severe weather conditions. Space–borne systems, particularly satellites, provide the ideal platform for global monitoring of sea conditions via altimetric measurements. As an alternative to active altimetry, another concept is passively receiving reflected signals from the Global Positioning System (GPS) and other Global Navigation Satellite System (GNSS) satellites. This concept was first developed by Dr Manuel Martin–Neira at ESA–ESTEC. ESA9s Passive Reflectometry and Interferometry System makes use of GPS/GNSS signals from satellites and their reflection off the ocean surface to derive oceanic properties such as surface height, significant wave height, wind speed and wind direction. Surrey Satellite Technology Ltd are proposing a nanosatellite demonstration mission to ascertain the feasibility of the GPS ocean reflectometry concept.