SpaceX is about to do the unthinkable.

On Sunday morning, the company plans to launch a doomed Falcon 9 rocket from Cape Canaveral, Florida, with a brand-new spaceship for NASA, called Crew Dragon, perched on top.

The 230-foot-tall vehicle is expected to heave itself off the ground between 8 a.m. and 12 p.m. ET, but then suddenly shut down its engines about 84 seconds into flight. At that point, the Falcon 9 will be traveling nearly twice the speed of sound some 13 miles above Earth's surface.

What comes next for the rocket will be catastrophic. Within seconds of cutting its engines, aerodynamic forces will throttle the uncontrolled, tube-shaped body and rip it to pieces. Inside, huge tanks full of liquid oxygen and RP-1 kerosene propellant will rip open so a large explosion and fireball is almost a given.

But if all goes according to plan, the Crew Dragon will escape to safety moments after the failure begins.

Such a scenario is one of an astronaut's worst nightmares, but NASA is excited to get on with the flight. That's because the spectacle is part of a highly orchestrated, human-free, and strenuous test of the Crew Dragon's launch escape or abort system.

If the empty spaceship flies away to safety and splashes down in the Atlantic Ocean, as planned, SpaceX will be a penultimate step closer to launching astronauts its first-ever human passengers who are part of NASA's Commercial Crew Program.

"We are purposely failing a launch vehicle to make sure that our abort system on the spacecraft that we'll be flying for our crews works," Kathy Lueders, the manager of the agency's program, said during a televised press briefing on Friday. "This is a very important test."

Nine astronauts will fly the first four crewed missions inside SpaceX and Boeing's new spaceships for NASA, called Crew Dragon and CST-100 Starliner, respectively. NASA via AP

More than the safety of SpaceX's launch system for astronauts is riding on the in-flight abort test. In fact, NASA's ability to launch astronauts from American soil at all partly depends on it.

In July 2011, NASA retired its space shuttle fleet without a new American ship to get astronauts to and from orbit from the International Space Station a $150 billion, football field-size laboratory that orbits Earth. Since that time, the agency has had no practical choice but to buy tickets aboard Russia's Soyuz spacecraft for astronauts, to the tune of about $80 million per seat today.

The first crewed flights of NASA's commercial program were supposed to start taking off around 2015. But neither SpaceX nor Boeing, which is also part of the agency's program, have not yet completed rigorous mandatory testing required to launch astronauts.

"Most of us are just way past ready for this to happen. It has taken a lot longer than anybody thought," Wayne Hale, an aerospace engineering consultant and retired NASA space shuttle program manager, told Business Insider. "This year we really need to do it. It really needs to be done."

Saturday's test is the next-to-last step toward that goal, which is why it's so crucial that everything go right.

"The number-one most important thing is we launch them safely," Benji Reed, SpaceX's director of crew mission management, said during NASA's briefing at Kennedy Space Center on Friday.

Hale said that "everybody hopes at this stage that success is the outcome." But he added that in-flight abort tests are not only rare only a handful of them have been done since the Apollo moon program in the 1960s but also "a very difficult situation" where "many things can go wrong."

SpaceX has had trouble with its parachutes, for example, though Hale noted that tweaking and testing has apparently resolved those difficulties. Meanwhile, Boeing also saw a parachute deployment hiccup with its CST-100 Starliner spacecraft due to an incorrect rigging. A clock error on the Starliner also caused Boeing's first uncrewed launch of the vehicle toward the space station to veer wildly off-course.

SpaceX performs a parachute test for its Crew Dragon spaceship, which is designed to ferry NASA astronauts to and from space. NASA

Benji said the Crew Dragon is pre-programmed to detach itself from the Falcon 9 rocket "at the right point in time" if anything goes wrong.

"We're looking for anything that's off-nominal," he told Business Insider.

In the case of Sunday's test, the rocket will shut down while the vehicle is moving through extreme, though not maximum, forces in the atmosphere what Lueders described as "a stressing test" for the entire system, and one that SpaceX ultimately chose over less trying and expensive ones.

"Getting this test behind us is a huge milestone," she said. (The launch was originally scheduled for Saturday, but NASA and SpaceX delayed it due to worsening weather conditions.)

Shortly after detaching from the rocket on Saturday, Reed said Crew Dragon should fire its SuperDraco escape engines for about 10 seconds. That should be enough to put many miles between the doomed rocket and the spaceship.

"We expect there to be some sort of ignition, and probably a fireball of some kind. Whether I would call it an explosion that you would see from the ground? I don't know," Reed said of the rocket. "We'll have to see what actually happens."

As the rocket breaks up, Crew Dragon will coast to an altitude of about 25 miles, shed its aerodynamic "trunk" (which serves as dead weight), and begin to fall toward Earth, according to a SpaceX animation on YouTube (below). The plummeting capsule will then use clusters of small rocket engines, called reaction-control thrusters, to right itself at high speed. The goal is to keep the gumdrop-shaped base facing down and its parachute pods pointed up.

About 4 minutes and 30 seconds after launch, two small drogue shoots will pop out of the capsule's top to stabilize its fall. Four enormous main parachutes will deploy about a minute later and dramatically slow down the vehicle. A little while later about nine minutes total into the mission the Crew Dragon is supposed to splash down about 20 miles offshore in the Atlantic Ocean, where SpaceX recovery crews on boats should be ready and waiting to recover it.

SpaceX and NASA will then review all of the data they collect from the safety test and see if it matches their predictive computer models. That process could take months, and smaller tests may be required afterward.

Assuming the abort test is a success, SpaceX will be poised to fly its first-ever humans NASA astronauts Bob Behnken and Doug Hurley on a demonstration mission called Demo-2. (In March 2019, the company launched an uncrewed Crew Dragon to the space station and back on a mission called Demo-1.)

"The main objective of this test is to show that we can carry the astronauts safely away from the rocket in case anything's going wrong," Reed said.

This story has been updated with new information. It was originally published on January 17, 2019.

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SpaceX's next rocket launch is doomed, and that's great for astronauts - Business Insider