The MAGSAT spacecraft was launched on October 30, 1979, into a twilight, sun-synchronous, orbit with inclination 96.76¿, perigee 352 km and apogee 561 km. The Cesium vapor scalar and fluxgate vector magnetometers together measured the field magnitude to better than 2 nanotesla (nT) and each component to better than 6nT. Two star cameras, a high-accuracy sun sensor and a pitch axis gyro provided the 10--20 arc-second attitude measurements necessary to achieve this accuracy. The magnetometers were located at the end of a boom to eliminate the effect of spacecraft fields. An optical system measured the attitude of the vector magnetometer and sun sensor (at the end of the boom) relative to the star cameras (on the main spacecraft). The data are available in several formats from the National Space Science Data Center and are undergoing analysis by a team of investigators.