We describe the High Energy Telescopes (HETs), which are part of the IMPACT investigation for the STEREO mission (Principal Investigator: Janet Luhmann, University of California at Berkeley). The two STEREO spacecraft were launched from Cape Canaveral, FL on October 25, 2006. High energy electrons (~ 0.7 -6 MeV) and nuclei from hydrogen to iron (~ 13 – 200 MeV/nucleon) are detected by the HETs, one on each spacecraft. Observations from one pass through the Earth’s magnetosphere and from four X-class solar events in December, 2006 are presented to illustrate the capabilities of the HETs. The HET observations are also compared with observations from other spacecraft. The event of December 13th was the first Ground Level Event in almost two years. We will compare the elemental composition of this event with that of the previous Ground Level Event on January 20, 2005.

This work was supported by NASA (at Caltech and JPL under contract NAS5-00133 and grant NAG5-12929).

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 103-106