The Apollo 8 astronauts were the first human beings to venture beyond low Earth orbit and visit another world. What was originally to have been an Earth-orbit checkout of the lunar lander became instead a race with the Soviets to become the first nation to orbit the Moon. The Apollo 8 crew rode inside the command module, with no lunar lander attached. They were the first astronauts to be launched by the giant Saturn V rocket, which had been launched only twice before. The booster worked perfectly, as did the SPS engines that had been tested on Apollo 7.