T' Doppler Shift from Giant Leap Rocketry, Inc. Ya scallywag! T' Doppler Shift is 2.6" in diameter with 54mm motor mount. It includes a light-weight version o' t' Acme fin canister, makin' this rocket a very stable and high-performance machine. It features t' all-new "Fin"-ders --- which are stylish fairings that cover t' gap betwixt t' fins and t' body.