Spaced-receiver analysis can be used to estimate the ionospheric zonal irregularity velocity. This involves first measuring the scintillation pattern velocity and then estimating the zonal irregularity velocity. A straightforward technique involving projection planes has been used to derive a relationship between the satellite position and velocity, the irregularities' position and velocity, and the scintillation pattern velocity. This relationship relies on the alignment of the irregularities along the field lines but is independent of the irregularity spectrum. When simplified, this relationship can be used to estimate the zonal irregularity velocity using either geostationary satellites or Global Positioning System (GPS) satellites. This estimation is straightforward but must be performed in a careful manner. An example of zonal irregularity velocity estimation using GPS satellites is presented. The average zonal irregularity velocity is estimated over a 3-week period in March 2002 at São Luís, Brazil (−3.59° dip angle). This hourly average velocity has been compared with the climatological radar observations from Jicamarca Observatory. The spaced-receiver zonal velocity agrees well (within ±8 m/s) with the radar's observations during postsunset hours.