On July 16, 1969, a towering Saturn 5 rocket sat on Pad 39A at NASA’s Kennedy Space Center in Florida. At 9:32 a.m., the five enormous F-1 engines of its first stage ignited, expelling orange flame, dark smoke and 7.5 million pounds of thrust to lift the three astronauts of Apollo 11 into space. Buzz Aldrin and Neil Armstrong set foot on the moon four days later.

Today, at that same launchpad, technicians working for SpaceX, Elon Musk’s upstart rocket company, are preparing for the maiden flight of what is by most measures the world’s most powerful rocket since the Saturn 5. The Falcon Heavy will be able to carry more than 140,000 pounds to low-Earth orbit, or more than twice as much as current competing rockets.

Aboard the demonstration flight, which may take off in the weeks ahead (sign up for The Times Space Calendar to be notified of the date), will be a whimsical, cross-promotional payload for Mr. Musk — a cherry red Roadster built by his other business, the electric carmaker Tesla. The car would travel around the sun in endless ellipses that extended as far out as Mars’ orbit.