Everything SpaceX Had To Get Right For Crew Dragon's Splashdown

• SpaceX and NASA's Crew Demo-2 mission is officially a success after the safe return of the Crew Dragon capsule and the astronauts inside.

• Elon Musk has said that this was the most nerve-racking part of the entire mission.

• High speeds and temperatures make it extremely dangerous to reenter Earth's atmosphere and splash down safely.
• Here's everything that had to go right in order to bring Bob Behnken and Doug Hurley home.

Following is a transcript of the video.

Abby Tang: Moving at about 28,000 kilometers per hour through temperatures of up to 3,500 degrees Fahrenheit, SpaceX Crew Dragon capsule and the astronauts inside safely reentered Earth's atmosphere on August 2nd.

NASA: Welcome back to planet Earth and thanks for flying SpaceX.

Abby Tang: The world nervously watched the historic launch, the first from US soil in almost a decade on May 30th, 2020. But it's this landing that Elon Musk most feared. Here's what had to go right in order to bring Bob Behnken and Doug Hurley home.

There are two main reasons why reentry is the most dangerous part of the mission. Extreme speed and temperature. SpaceX and NASA had to think about these factors in three key ways. The first pain point was finding the precise angle for reentry. Not steep enough, the Crew Dragon would have bounced right off the atmosphere and back into orbit. Too sharp or too fast and the astronauts could have faced fatal gravitational forces and the spacecraft could have caused enough drag to break up and disintegrate. Then even at the correct angle, moving at about 25 times the speed of sound through the atmosphere, creates extreme friction, which produces superheated plasma. A heat shield has to deflect and absorb the energy created by the plasma.

At 3,500 degrees, the shield gets hot enough to glow, but Musk said "due to the Crew Dragon's asymmetric design, "the craft could have over-rotated during reentry "and diverted plasma into launch escape pods on the side." If that happened, the ship could have overheated in some parts or started wobbling, causing the crew to lose control. The plasma caused a six minute communications blackout between the Crew Dragon and Earth.

NASA: Dragon SpaceX, comm check.

Abby Tang: So if anything went wrong in that moment, remote control would have been impossible. In 2019, auditor's listed parachute problems as a key risk to NASA's commercial crew program. And the physics turbulence, a space capsule parachute goes through is one of the most difficult calculations for researchers. SpaceX and NASA had to design a completely new system for the Crew Dragon. After multiple versions and dozens of tests, the Mark three design was approved. Even so Musk's worry was that they might not deploy correctly or that the system would guide the Crew Dragon to the wrong splashdown location. All of these risks were assessed and calculated six ways to Sunday as Musk told aviation week, but they could never be fully done away with.

NASA estimated that there was a one in 276 chance of this mission being fatal, but both Behnken and Hurley told us they were comfortable with those odds. Luckily that bet paid off. We can officially call this historic mission a success. And SpaceX is set to fly the same Crew Dragon back into space with four astronauts in spring of 2021.