Towards the latter part of Korolev's life, he had been working on projects for reaching the planets Mars and Venus, and even had spacecraft ready to reach both. The United States was also working towards reaching these planets, so it was a race to see who would be successful. Korolev's two initial Mars probes suffered from engine failures, and the five probes the Soviet Union launched in hopes of reaching Venus all failed between 1961 and 1962, Korolev himself supervised the launches of all probes.