On May 27, NASA astronauts Bob Behnken and Doug Hurley are expected to become the first humans to ride a Dragon. The two astronauts will catch a ride to the International Space Station in SpaceX’s Crew Dragon capsule as part of the Demo-2 mission, the final test before NASA officially certifies the vehicle for human spaceflight. It will be the first time in nine years that NASA astronauts have launched to space from the US—and the only time they’ve ever flown on a commercial rocket.
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SpaceX has spent more than a decade preparing for this mission, and the company has had its fair share of setbacks. They’ve had parachutes fail and test capsules explode, but each of these failures helped the company make its crew capsule even safer than before. The Demo-2 mission signals that NASA officials believe the Crew Dragon is finally reliable enough to safely carry humans to and from orbit. Still, Demo-2 is a test flight—so what happens if something goes wrong?
Like the Russian Soyuz capsule that has ferried all astronauts to the space station for the past decade, SpaceX’s Crew Dragon is equipped with an abort system that can punt astronauts to safety if anything happens before, during, or after launch. But the devil is in the details, which is why NASA and SpaceX have spent a lot of time going over different abort scenarios for every imaginable contingency. WIRED spoke with current and former astronauts and NASA’s flight director for the mission to learn how they prepared for the unexpected. (SpaceX representatives did not respond to a request for comment.)
Pad Abort
About 3 hours before liftoff, Behnken and Hurley will roll up to the launch pad in a white Tesla. They’ll take an elevator to the top of the launch tower, walk down the end of the crew access arm, pop the hatch on the Crew Dragon, and climb inside. At that point, they’ll begin a series of system checks that determine whether everything is go for launch. A critical part of this process is arming Crew Dragon’s abort system.
There are three ways to trigger the capsule’s abort system once it’s turned on. The crew can pull a handle inside the spacecraft; mission control can send a remote command to the spacecraft; or the craft itself can automatically start the sequence if it detects a problem in the rocket. This will cause the eight small SuperDraco rocket engines on the capsule to fire and lift it away from the rocket.
A pad abort is mostly to protect astronauts from the risk of an explosion during the 45 minutes that the rocket is being loaded with propellant. A pad explosion has only happened once before in SpaceX history; in 2016, the company lost a Falcon 9 rocket and its satellite payload during fueling. “SpaceX has since done modifications to their design to help mitigate that,” says Zeb Scoville, NASA’s flight director for the Demo-2 mission. “But that’s exactly the kind of scenario a pad abort protects against.”
Still, it’s a brutal event for a spacecraft’s occupants. In a matter of seconds, the capsule goes from a standstill to rocketing skyward at about 350 mph. During the abort, the astronauts experience forces more than four times stronger than gravity, ascending about a mile and a half before the capsule splashes down in the Atlantic Ocean under parachute. It’s an extreme maneuver for extreme emergencies.
If the astronauts need to be evacuated in less dire situations, they can catch a ride to the ground on a zipline attached to the tower. For example, if the launch gets called off after the rocket is fueled, the normal process is to keep the astronauts in the capsule until the fuel is drained. Then they can come down the tower the same way they went up. But if there’s a problem draining the propellant, it’s important to get the crew away from the live rocket ASAP so the problem can be fixed. It doesn’t make sense to put the astronauts at risk by doing an abort, so instead they use the zipline to make their quick getaway.
In-Flight Abort
The Crew Dragon’s abort system stays armed for its entire journey into space. After liftoff, Scoville says that the decision to abort is made by the Crew Dragon’s software, because anything that goes wrong will happen in a fraction of a second. “You can’t count on the response time of a flight controller or crew to take those actions,” he says.
The computers on Crew Dragon are watching for things like unexpected changes in acceleration or any deviation from the expected flight path. NASA divides the rocket’s ascent into seven “stages of abort.” Each phase of the launch has different parameters that would trigger an abort and protocols for how the capsule would be controlled. It’s a delicate balancing act—the abort system must work every time it’s needed, but it can’t be so sensitive that it triggers when everything is going fine. Scoville says that getting the parameters right required running thousands of computer simulations that throw random parameter changes at the capsule’s computers to see how they would respond.
The most dicey part of the launch occurs in the second abort stage. This is the point of peak aerodynamic stress known as “max q,” which occurs about a minute and a half after launch. The rocket is moving at about 1,500 mph and all the aerodynamic pressure experienced by the capsule during max q makes it the worst possible time to abort. But it’s also the period during a launch when things are most likely to go wrong.
In January, SpaceX successfully conducted an uncrewed in-flight abort test to prove that the Crew Dragon could still pull away from the rocket if something went wrong during max q. As the rocket entered max q, SpaceX mission control killed its engines. The capsule automatically registered that something was wrong, fired its SuperDraco engines, and pulled away from the Falcon 9 rocket as it exploded in the air. The capsule kept coasting into the stratosphere before beginning its descent to Earth and splashing down in the Atlantic Ocean under parachute.
An in-flight abort is every astronaut’s worst nightmare. They’ve only happened a couple of times in the history of spaceflight, but NASA spends a lot of time preparing its crews just in case. “Ninety-five percent of the training we do is focused on the things that we can anticipate but we hope never happen,” says NASA astronaut Nick Hague, who survived an in-flight abort during a mission to the space station in 2018. It was the first crewed abort in 35 years.
About two minutes into the flight, Hague says the Russian Soyuz capsule started shaking violently side to side, an alarm sounded, and a big red caution light started flashing. By the time he registered what was happening, the rocket had already disintegrated and the automated Soyuz abort system had boosted them to safety. It’s hard to imagine a more stressful situation, but Hague says there wasn’t enough time during the emergency to be scared. “You’re focused like a laser on the task and trying to diagnose your situation to see if there’s anything you need to be responding to,” says Hague. “You know your best chance of survival is to execute this procedure flawlessly.”
In most cases, an in-flight abort means the mission is over. If it happens during Demo-2, the capsule will splash down in the Atlantic, where it will be recovered by Task Force 45, a detachment of Space Force troops specially trained to rescue astronauts. The 150 troops will be strategically stationed along the rocket’s flight path on the East Coast of the US and in Hawaii in case something goes wrong once the capsule is in orbit. But if the abort is triggered in the last few seconds of the rocket’s upper stage engine burn, it’s also possible for Behnken and Hurley to abort to orbit. If the capsule is still in good condition and there’s enough propellant left over after the abort to orbit, Scoville says it’s possible that they could continue on to the space station.
Abort in Space
If everything goes well during the launch, Behnken and Hurley will spend nearly a full day in orbit playing catch-up with the International Space Station. During that time they’ll be focused on running tests to demonstrate that the capsule can do everything it’s supposed to. But if something goes wrong, they’ll also have the option of returning to Earth early.
There are several events that might cause Behnken and Hurley to abort a mission once they’re already in orbit. These range from depressurization to a cabin fire, both of which have occurred on previous crewed missions. In fact, depressurization was the cause of the only deaths known to have occurred in space. In 1971, three cosmonauts returning from a mission to the Salyut 1 space station were killed after a pressure valve in the capsule failed and the cabin turned into a vacuum within seconds.
The Crew Dragon has multiple lines of defense against this kind of disaster. In the event of a small leak caused by a faulty component or impact from space debris, the capsule can pump more oxygen and nitrogen into the cabin to maintain pressure until the crew either returns to Earth or arrives at the space station. But if the breach is too large to plug with more gas, Behnken and Hurley’s flight suits can be pressurized and fed oxygen, effectively turning the suits into single-occupant spacecraft. Depending on where they’re at in the mission, it’s possible they could continue on to the space station even if the cabin is a total vacuum.
“The suit is kind of like an escape system, and is designed to be used only if you’re having a very bad day,” says Garrett Reisman, a former NASA astronaut who also spent several years as the director of SpaceX’s crew operations. “It’s nice to know it’s there, but you hope you never have to use it for its intended purpose.”
If NASA decides to abort a mission once Behnken and Hurley are in space, they’ll trigger the capsule to perform a deorbit burn that pushes it back into the atmosphere. At that point, drag will start to take effect and pull the spacecraft back toward terra firma. If it’s a dire situation, NASA might choose to deorbit the capsule immediately, even if it means landing in the middle of the Pacific Ocean.
Otherwise, mission control will take the time to evaluate the best emergency landing location based on weather and the location of rescue teams. Behnken and Hurley have enough food, water, and oxygen for four days on orbit, so there’s no reason to rush unless the situation demands it. “More often than not, when you feel that you’re rushed, you need to slow down to avoid making a mistake and driving yourself into a difficult situation,” Scoville says.
Assuming all goes well during the flight, Behnken and Hurley will spend up to three and a half months living and working on the space station. Once they’re ready to return home, they’ll board the Crew Dragon for another day-long journey back to Earth. The plan is for the capsule to splash down off the Florida coast, where it will be recovered by SpaceX’s GO Navigator ship. When it comes to human spaceflight, the best abort scenario is the one that never happens.
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