A number of radio tomography schemes of the ionosphere and near-space environment (Earth's magnetosphere, plasmasphere, and protonosphere) are analyzed by utilizing multisatellite systems. A new approach to space-time tomography is proposed. It is shown that application of high orbital systems of Global Positioning System and Global Navigation Satellite System type with ground-based receivers is promising in the case of space-time tomography. Computer simulation results showed the possibility of realizing radio tomography of the near-space environment with the help of some multisatellite systems.¿ 1997 American Geophysical Union