A TALE OF THREE ROCKETS

How many rocket engines does it take to lift off on your way to the moon? Five? Thirty? Thirty-three? This is the tale of three very different booster rockets, all of them designed to send humans to the moon, and only one of which has ever flown with complete success. These are NASA’s Saturn V of the late 1960s and early 1970s, the Soviet Union’s N1 of the same era, and SpaceX’s Starship of the present day.

Here are the three boosters, all rendered in the same scale.

Let’s take each in turn.

SATURN V

In most respects, the Saturn V is one of the most successful rockets of all time. It never failed in any of its flights, either test or operational, and it delivered nine crews of three astronauts each to the vicinity of the moon, and America’s first space station Skylab into Earth orbit. It was a monumental achievement.

The hardest part of getting into space—at least the part requiring the most energy—is getting the entire vehicle off the ground, through the region of maximum dynamic pressure called Max Q, where the combination of speed and atmospheric resistance exerts the greatest stress, and to an altitude of about 40 miles. This means the first stage of a booster is necessarily the most powerful and most massive. It has to lift the entire rocket, including itself.

The first stage of the Saturn V used five F-1 engines. The F-1 remains the most powerful single combustion chamber liquid-propellant rocket engine ever developed. All together, that first stage produced 7.5 million pounds of thrust.

N1

In the 1960s the U.S. and the Soviet Union were locked in a competition for national prestige by their achievements in space. The Soviets definitely began in the lead, not only putting the first human in space (Yuri Gagarin), but putting him into orbit and not just the up and down ballistic trajectories of America’s first two astronauts, Alan Shepard and Gus Grissom. They also launched the first woman, put the first two simultaneously orbiting crewed spacecraft in orbit, flew the first multi-person spacecraft, and carried out the first space walk.

But it wasn’t until three years after President John F. Kennedy declared the American intention to reach the moon before the end of the decade that Soviet political leadership committed to the same goal.

Even then, the Soviet space program was not under unitary control of an organization like NASA. It was a military program with competing centers and designers, and the rockets were ICBMs designed to deliver nuclear weapons, not ones intended solely for human exploration.

To be fair, this was also true of the early American boosters. The Redstone and Atlas of the Mercury program and the Titan of the Gemini years were all initially built to carry bombs. But the Saturn was built specifically to go to the moon.

The intrigues and clashing personalities of the Soviet space program read like a Tolstoy novel, or maybe more like Dostoevsky. Rather than trying to sort all that out, I’m going to focus on the doomed attempt to build a rocket capable of carrying Soviet cosmonauts to the moon—the N1.

The N1 first stage used 30 NK-15 engines, which all together produced 10.2 million pounds of thrust.

How well did that work? Not very well.

Four times the N1 lifted off. Four times it failed to last long enough for first stage separation. The second launch barely cleared the tower before it leaned over and fell back onto the launch pad, destroying it in a massive explosion that sent debris flying miles away.

There were several issues having to do with rushed timelines and limited testing, but the complex plumbing required to feed 30 engines was fragile. The stresses induced in a launch proved to be too much to handle.

STARSHIP SUPER HEAVY

If 30 engines didn’t work out fifty years ago, why is SpaceX going with 33 in its Super Heavy booster? In a word: computers.

The N1 failed because 30 engines were too many to be able to fire, throttle, and steer at the same time. The failure of one engine could cause a cascade of destruction and destroy the entire vehicle, even if not all engines were needed to reach orbit.

Sensors and computers can quickly detect and shut down a problematic engine in 2023, allowing the booster to continue on its path.

The Super Heavy has lifted off twice with its Starship upper stage attached. Its first launch in April 2023 had three engines failing during liftoff, with at least three more engines shutting down during the flight. The rocket was destroyed four minutes into the flight when it went out of control before the first stage separated.

In the second flight in November 2023, all 33 engines of the first stage were fired full duration. Starship and Super Heavy passed through hot staging, but the booster was lost shortly after initiating its flip maneuver and boostback burn. The Starship second stage had its flight termination system activated around the time of engine cutoff, after having continued powered flight until more than eight minutes after launch and reaching over 80 percent of orbital speed. (Description from SpaceX.)

The problems revealed in these launches seem solvable, and SpaceX’s strategy of using clusters of smaller rockets seems sound. Its thrust of 17.1 million pounds, once it is fully operational, will make it the most powerful rocket ever to fly.