Editor's Note, May 27, 2020: Due to poor weather conditions, the SpaceX shuttle launch slated for this afternoon has been postponed to Saturday, May 30. The launch would have been the first to blast off from United States soil in nine years.

The last space shuttle flight launched on July 8, 2011, from Kennedy Space Center’s Launchpad 39A. Since the shuttle’s return to Earth 11 days later, NASA astronauts have flown to the International Space Station on Soyuz rockets, managed by Russia.

NASA astronauts Robert Behnken and Douglas Hurley will fly on the SpaceX Crew Dragon spacecraft, set to launch on a Falcon 9 rocket at 3:22 p.m. on May 30. After about 24 hours, the Crew Dragon will autonomously dock with the International Space Station (ISS), where Behnken and Hurley will join the three astronauts currently onboard.

The mission was initially scheduled to last only two weeks, per the New York Times’ Kenneth Chang. But the Crew Dragon spacecraft could stay in orbit for up to 110 days, and NASA says in a statement that “the specific mission duration will be determined once on station based on the readiness of the next commercial crew launch.”

The launch will be the first crewed flight, and final test flight, of the SpaceX system. The Associated Press’s Marcia Dunn reports that Dragon capsules have been carrying cargo to the space station since 2012, and in March 2019, SpaceX performed a successful test of the Crew Dragon spacecraft’s ability to autonomously connect with the ISS. A second Crew Dragon was destroyed during an abort engine test last April, causing a delay.

With the abort engine issue fixed, and a successful in-flight abort test this past January, the Crew Dragon is ready for lift off. Because it’s a test flight, the astronauts will put the spacecraft through its paces. Before joining NASA, Hurley was a Marine Corps fighter pilot and test pilot and Behnken was a flight test engineer, and both have flown on two space shuttle missions each. During the flight to the ISS, they will test the spacecraft’s control systems and maneuvering thrusters, and conduct more tests once the Crew Dragon is docked.

The astronauts’ exact mission hasn’t yet been specified, but they will join the Expedition 63 crew conducting research. The New York Times reports that in February, Hurley shared that the pair was training to use the space station’s robotics and conduct spacewalks.

The mission is considered an essential project, so preparations at NASA and SpaceX are continuing despite criticism. The launch itself will require hundreds of employees at NASA and SpaceX, who will work in shifts and wear personal protective equipment when necessary to reduce the chances of spreading COVID-19, Neel Patel reports for the Technology Review.

“I’m not sure risking so many lives to launch two people to the same place we’ve been going for 20 years should be prioritized,” former NASA deputy administrator Lori Garver told Marina Koren at the Atlantic. “The harm is being done now because keeping the [launch] date means everyone is working now.”

But others support the mission as essential to reduce NASA’s reliance on Russian rocket launches, because upkeep of the ISS requires constant attention, and because a successful launch from U.S. soil could offer a morale boost to the country amid the COVID-19 pandemic, per the Atlantic.

In addition to SpaceX’s system, NASA has also funded a crew capsule in development by Boeing. The capsule, called Starliner, is delayed after a failed test flight last December when the spacecraft entered the wrong orbit, missing the ISS, and software errors were discovered that would have destroyed it during re-entry into Earth’s atmosphere. Boeing plans to repeat the uncrewed test later this year.

Looking ahead, NASA is in negotiations for at least one more seat on a Soyuz mission. NASA has also already announced the next Crew Dragon mission—on its first operational mission—bringing four astronauts, three from the U.S. and one from Japan’s space agency, to the space station.