Why does SpaceX's historic astronaut flight for NASA have two commanders?

SpaceX's historic crewed mission to space has … two commanders?

Over the weekend, veteran NASA astronauts Bob Behnken and Doug Hurley made history as they launched into space on a SpaceX Crew Dragon capsule as part of the company's Demo-2 test flight, the first crewed flight to orbit to launch from the U.S.  since NASA's space shuttle program ended in 2011. The Demo-2 mission launched from NASA's Kennedy Space Center in Florida on Saturday (May 30) and reached the International Space Station 19 hours later with a smooth docking.

But, while most human spaceflight missions have one commander, Demo-2 has two. For this mission, Hurley serves as the Crew Dragon's spacecraft commander and Behnken as joint operations commander. 

Related: SpaceX's historic Demo-2 astronaut mission: Full coverage

In his role as joint operations commander, Behnken's specific responsibilities include reaching and docking with the space station. Hurley, on the other hand, is responsible for the Crew Dragon capsule, now officially named Endeavour, launch, landing and recovery. 

The astronauts also share a number of responsibilities and will work together with NASA astronaut Chris Cassidy, helping out with now that Behnken and Hurley have joined Cassidy aboard the space station. They may even take part in some spacewalks outside the station to upgrade its solar array batteries among other maintenance work.

The astronauts will spend anywhere from approximately one to four months aboard the space station working with and helping out Cassidy. The purpose of this mission was to demonstrate the capabilities of the Crew Dragon capsule  — to make sure it can safely ferry human passengers to (and from) the space station. 

With the success of this mission, SpaceX aims to launch Crew-1, the first operational astronaut flight for NASA later this year. Currently, NASA hopes to launch Crew-1 Aug. 30, NASA Administrator Jim Bridenstine has said. 

• How SpaceX's Crew Dragon Demo-2 mission will work in 13 steps 
•  SpaceX will make history with NASA astronaut launch next week
•  In photos: SpaceX's historic Demo-2 test flight with astronauts 

Follow Chelsea Gohd on Twitter @chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.

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