START (Spacecraft Technology and Advanced Reentry Test) was a United States Air Force program to experiment with lifting bodies, which began after the cancellation of the Dyna-Soar project. It began in 1960 using subscale models of the X-20 Dyna-Soar to test materials, and continued with the ASSET and PRIME suborbital tests of subscale lifting body designs and B-52 drop tests of the X-24A and X-24B lifting bodies into the 1970s.