The Delta L, Thor-Delta L, or Thrust-Augmented Long Tank Thor-Delta was a US expendable launch system used to launch the Pioneer E and TETR satellites in 1969 (failed) and HEOS satellite in 1972. It was a member of the Delta family of rockets.The Delta L was a three-stage rocket. The first stage was a Long Tank Thor, a stretched version of the Thor missile, augmented by three Castor-2 solid rocket boosters. The second stage was the Delta E.