Enlarge /. Crew Dragon will withdraw from the International Space Station on Saturday.
On Saturday evening, the spacecraft Crew Dragon with NASA astronauts Doug Hurley and Bob Behnken called Dragonship Endeavor was docked by the International Space Station to begin its journey home.
The undocking was done after NASA and SpaceX decided that the spacecraft on Sunday from the Florida Panhandle in the Gulf of Mexico would find a calm sea and light winds off the coast. This is the first water landing for a US spacecraft since 1975 when an Apollo capsule sprayed in the Pacific after the Apollo Soyuz test project. The landing is scheduled for 2:48 p.m. ET (6:40 p.m. UTC). A last call to the weather will be made on Sunday.
After Endeavor moves away from the "Keep Out Sphere" surrounding the space station, it will make room between itself and the rotating laboratory before further engine burns are carried out. This will prepare the spaceship for combustion in orbit on Sunday, about 50 minutes before hosing down. When asked what he and Behnken would spend most of their last night in space, Hurley quipped at a press conference with reporters this week: "Sleeping."
Most of us would probably find it difficult to sleep in space the night before a historic water landing. But Hurley and Behnken are professionals, both with almost two decades of careers as astronauts. And that's a good thing, because there are definitely some risks before tomorrow's landing.
Although NASA and SpaceX have pushed Dragon and its four main parachutes through all kinds of tests, this version of the Dragon spacecraft has only been tested once throughout the landing process – during the Demo 1 mission in March 2019.
One problem concerns the asymmetrical design of the Dragon backshell, in which eight SuperDraco engines are embedded in four engine housings. Since the four engine capsules protrude from the sides of the spacecraft, Dragon's shape is not uniform about its axis of rotation. This asymmetry could theoretically cause Dragon to roll into the Earth's atmosphere as it re-enters.
To take this into account, SpaceX and NASA have performed more than 1,000 computer simulations that model the shape of the dragon and its path through the atmosphere. Because of the warming, aerodynamic stability, and atmospheric turbulence, the simulations and resulting analysis are fairly complex, but SpaceX engineers believe they understand the process – they believe Dragon will be up to the challenge. And of course a Crew Dragon vehicle performed well when it re-entered last March.
NASA and SpaceX have a lot to do with this mission. With the safe return of Hurley and Behken to Earth, the space agency Dragon can put it into operation and fly four complements from four astronauts to the station from autumn this year. And SpaceX plans to reuse this special capsule for an operational mission in early 2021.
The space agency plans to continuously document the mission until Sunday afternoon:
The Demo 2 mission returns to Earth.