Before NASA decided to launch Apollo on the Saturn V rocket, the agency considered a larger rocket called Nova. The necessary launch vehicle for the heavier Direct Ascent mission profile, this mind-blowingly large rocket was never built.

The Saturn V was massive. Standing 363 feet (110 meters) tall with a 33-foot (10 m) diameter, it delivered 7.5 million pounds (3.4 million kilograms) of thrust at the moment of launch. This three-stage rocket had five F-1 engines in its first stage, five J-2 engines powering its second stage, and a single J-2 engine on its third stage.

Nova was conceived as both taller and wider than the Saturn V, and almost twice as powerful. Its first stage was powered by eight F-1 engines, each of which could deliver 1.5 million pounds (680,000 kg) of thrust — bringing the rocket’s total power to a whopping 12 million pounds (5.4 million kg) of thrust at launch.

The second stage was powered by four liquid-hydrogen M-1 engines that could produce an additional 4.8 million pounds (2.2 million kg) of thrust. The third and final stage was akin to the Saturn V’s — it had one J-2 engine, whose 200,000 pounds (90,000 kg) of thrust could send a heavy payload to the Moon.