In the present paper, ENA energy spectra at the location at the SAC-B satellite are simulated by using AMPTE/CCE/CHEM ion distributions as originating source, with the purpose of analysing the SAC-B/ISENA response at different magnetic local times and latitudes. The shape of the ENA spectra simulated along different lines of sight on the equatorial plane is analysed to show that an instantaneous estimate of the global convection electric field will be possible with the ISENA data every few minutes. This unprecedented time resolution for the measurement of such a crucial parameter of the Earths magnetosphere will allow testing of many theories, like tail convection, pressure balance, global circuits, ring-current shielding, etc. ¿ American Geophysical Union 1996