developed by the Belgian Science Policy and consisting of a database
on Earth observation satellites (technical characteristics, application
fields...), and their products and applications.
Remote Sensing Center Resources
developed by the university of Wisconsin-Madison provides the characteristics
of the passed, current and future Earth observation satellites,
as well as the possibility of visualizing in real-time the location
of more than 500 satellites.
and well structured, this site developed by The Tech Museum of Innovation
in the USA is a good general introduction.