English: In response to a NASA request for instrument proposals, Dr. Phil Christensen developed the idea of TES. His experience as a graduate student at UCLA exposed him to Mars exploration. It was there that he worked with data from the Infrared Thermal Mapper. The IRTM was a more primitive version of TES that flew on the two Viking orbiters in 1976. In 1983, when NASA called for instruments to fly on board the planned Mars Observer spacecraft, Phil answered with the TES concept. He assembled many of the same IRTM engineers from the Hughes Santa Barbara Research Center (SBRC), to help design and build TES. A team of scientists also was recruited by Phil to help guide the process. One of these scientists, Dr. Hugh Kieffer, was the principal investigator for the IRTM instrument.