With NASA’s Orion Abort-System Test, Americans Just Took a Small (and Very Big) Step Closer to the Moon

It was a modest little rocket scheduled to make a modest little flight, and yet an awful lot of people showed up at Cape Canaveral before dawn this morning to watch it happen. They had good reason to be there. With the flight, America’s planned return to the moon by 2024 moved a small but critical step closer.

Easily the most harrowing part of the next lunar flight will be the first, when astronauts climb into their Orion spacecraft at the top of a rocket 36 stories tall, sloshing with more than 5 million pounds of fuel, and ground controllers effectively set it all on fire. If things work as they should, the fire will be precisely controlled, producing a thrust that will exceed 7.5 million lbs. and sending the crew on a fast climb to space. But there’s no guarantee that things will go as they should and the wrong kind of accident would be utterly unsurvivable. If the Apollo program’s Saturn V moon rocket had blown up just after liftoff, it would have produced the largest human-generated non-nuclear explosion in history.

Keeping the astronauts alive thus means equipping the rocket with a system that can detect the signs of an imminent explosion and instantly blast the spacecraft up and away from the doomed rocket, allowing the crew to make a safe parachute descent into the ocean. Testing that system was the reason the modest little rocket was sent on its modest little flight today.

Ignition was planned for 7:00 a.m. E.T., less than half an hour after sunrise. From the safe remove of a viewing stand atop a concrete bunker—that happened to serve as the firing room next to the pad from which John Glenn was launched in 1962—the test rocket was barely visible, more than 2.1 miles away. That was partly because the rocket measured just 93 ft. from ground to tip, or about a quarter of the height of NASA’s planned Space Launch System rocket, which is being built by prime contractor Boeing and is set for its first uncrewed test flight in 2022. (Lockheed Martin is the prime contractor for Orion.) The much smaller nine-story test stack consisted of a booster with a dummy version of the Orion spacecraft, designed to match the actual Orion’s weight, 22,000 lbs. On top of the Orion was a spire-like escape tower.

This version of the multi-use booster was originally designed for a far less friendly purpose, serving as the upper stage of a Peacekeeper nuclear missile. It uses rubbery solid fuel, and can’t be throttled up or down, or even be shut off once it’s lit. It simply burns until it’s exhausted.

For today’s test, there was only enough fuel on board to allow the booster to burn for 55 seconds, but even then, 100,000 lbs. of additional dead weight had to be added as ballast to keep it from flying too fast or too high. “The rocket is pretty sporty,” said NASA test manager Jenny Devolites at a press event the day before the launch.

It showed that sportiness when the engine was lit, and the rocket leapt off the pad, accelerating to 800 mph and climbing to 31,000 ft., about the altitude at which commercial airlines fly, trailing a long white plume behind it. As it reached the end of its 55-second burn time, a signal was sent to four smaller launch-abort engines arrayed around the tower at the top of the rocket. Within milliseconds they fired, producing 400,000 lbs. of additional thrust, pulling the dummy Orion away from the booster, accelerating it to Mach 1.3, or about 1,000 mph, and an altitude of 45,000 ft. At the top of that parabola, additional steering rockets fired to flip the Orion to a proper descent orientation. The escape tower, its job then done, was then jettisoned.

For everything happening off of Earth all in one place, sign up for the weekly TIME Space newsletter.

None of that would have been pleasant had humans been on board. The escape rockets would subject the crew to a sudden load of 7 g’s, meaning that a 150 lb. astronaut would feel a weight of 1,050 lbs. The reorientation of the Orion would also mean a somersault ride and a lot of swinging side to side. “The 7 g’s is what’s going to get your attention the quickest,” said astronaut Randy Bresnik at the Monday press conference, “but it’s a very short duration.”

In a real emergency, things would quickly settle down, when parachutes would deploy, depositing the crew gently in the Atlantic just off the Florida coast. NASA has already tested the parachutes, so in this case, the dummy Orion was left to make a death plunge into the ocean, striking the water at 300 mph, less than three minutes after it left the pad, sending up a huge water spout visible more than three miles away on shore, then sinking out of sight forever. But it died having succeeded in the work it was built to do. The abort test, lasting only minutes, was declared a success.

As early as 2024, there will be a real Orion with four astronauts on board, and Americans will be flying moonward again. The stakes that day will be mortal; the brief flight flown today will allow the still unnamed astronauts to face those risks with far more confidence.