From the first paragraph or two of https://en.wikipedia.org/wiki/History_of_SpaceX

> In August 2001, Musk shared a plenary talk with Mike Griffin at the fourth Mars Society convention where he announced his plans to send his greenhouse to Mars.[6] In October 2001, Musk travelled to Moscow with Jim Cantrell and Adeo Ressi to buy refurbished Dnepr ICBMs that could send the envisioned payloads into space.[7]

https://en.m.wikipedia.org/wiki/Dnepr_(rocket)