SpaceX is landing 2 NASA astronauts off the Florida coast even though Hurricane Isaias threatened several Florida splashdown locations

• SpaceX is about to return its first crewed space mission, called Demo-2, and land it on Sunday afternoon.
• Hurricane Isaias complicated original plans to return two NASA astronauts to Earth aboard SpaceX's Crew Dragon spaceship in the Atlantic Ocean.
• Elon Musk's aerospace company will now try to splash down NASA astronauts Bob Behnken and Doug Hurley in the Gulf of Mexico.
• Two out of seven total landing sites near Florida must have good weather conditions.

Update: SpaceX has successfully landed NASA astronauts Bob Behnken and Doug Hurley back on Earth. For the latest, visit our live coverage page with streaming video commentary from NASA TV.

Astronauts Bob Behnken and Doug Hurley are about to return to Earth and wrap up an historic space mission for both NASA and SpaceX.

Behnken and Hurley launched to orbit aboard SpaceX's Crew Dragon vehicle on May 30, then docked the spaceship (which they named "Endeavour") to the International Space Station. Their experimental mission, called Demo-2, is the first with humans ever launched by SpaceX, founded by Elon Musk. It also represents a new era of commercially developed and operated space vehicles started by NASA almost 10 years ago.

But before the mission can succeed, the crew must safely land.

After a two-month stay in orbit, the men climbed back into the Crew Dragon capsule and undocked from the ISS on Saturday at 7:34 p.m. ET.

The capsule is now preparing for a fiery fall back to Earth, scheduled for 2:48 p.m. ET on Sunday. (You can watch NASA TV's continuous live-streaming coverage at the end of this story.)

NASA is overseeing SpaceX's experimental mission. On Wednesday, the agency gave the company an initial "go" to proceed with its landing plans. If it affected enough splashdown sites, Hurricane Isaias could have forced the astronauts to stay in orbit a while longer.

But the sites NASA picked in the Gulf of Mexico remain unaffected, and the astronauts are set to land off the coast of Pensacola, Florida. Recovery crews are waiting to recover the astronauts with boats, airplanes, and helicopters.

As of 12:55 p.m., NASA mission controllers reported the weather was calm and the seas were smooth.

"It looks like glass. It's awesome," one mission controller said on NASA's live feed.

The ship had successfully fired its thrusters to push itself into a deorbit path as of Sunday at 2:08 p.m. ET.

"We cannot wait to get Bob Behnken and Doug Hurley back to Earth," Jim Bridenstine, NASA's administrator, said during a press briefing on Wednesday, noting the agency would continue to watch the weather.

Crew Dragon can't land if there's rain, lightning, big waves, or winds exceeding 10 mph

Isaias became a named tropical storm on Wednesday night, when its wind speeds exceeded 39 mph. It reached hurricane status the next day, when sustained winds reached 75 mph.

The storm affected several landing areas just as Endeavour prepared to reenter Earth's atmosphere and splash into the Atlantic Ocean or Gulf of Mexico.

Three of the seven landing zones that SpaceX and NASA prescribed for the test mission, called Demo-2, lie within the "cone of probability" for the storm's path. Those splashdown sites (shown below) are located in the Atlantic Ocean off the coasts of Cape Canaveral, Daytona, and Jacksonville. Mission managers instead chose sites in the Gulf of Mexico near Pensacola or, as a backup option, Panama City.

"This mission will be a bit unusual as timelines will be in flux quite a bit up until undocking as we finalize landing locations," a NASA spokesperson told Business Insider in an email on Friday.

Pensacola is the-westernmost location of the seven options, and Panama City is the second-westernmost.

"We won't leave the space station without some good landing opportunities in front of us," Behnken told reporters from the ISS on Friday morning, adding that NASA and SpaceX are keeping him and Hurley informed. "The lion's share that work happens on their end. We don't control the weather, and we know we can stay up here longer."

If weather conditions had become nasty, mission managers may have scrubbed the undocking and landing attempt. Steep waves, rain, lightning, low clouds, poor visibility (for helicopters to fly the astronauts from a SpaceX recovery boat back to land), or even winds stronger than about 10 mph can trigger a "no-go" decision.

"We're going to watch the weather very carefully," Steve Stich, the manager of NASA's Commercial Crew Program, said on Wednesday.

NASA and SpaceX gave the final "go" for undocking on Saturday evening.

Behnken and Hurley could have stayed in orbit another 2 months, if needed

Once the astronauts undock, they have to land within about three days because the spaceship only has enough water and lithium hydroxide — which scrubs carbon dioxide from the air — to last Behnken and Hurley for that long, Stich said.

While docked to the ISS, though, Endeavour could have shared life support and lasted much longer. The vehicle has been in space for more than 60 days, but this version of Crew Dragon is designed to last about 120 days due to its solar-panel design, Stich said. In theory, that gives SpaceX and NASA opportunities through most of September to safely get Behnken and Hurley back home.

"We know we can stay up here longer," Behnken told reporters during a briefing on Friday morning. "There's more chow and I know the space station program's got more work that we can do."

Stich noted SpaceX and NASA can make a call as late as an hour before undocking to delay the whole sequence and try again another day.

"If the weather's looking bad that day, we're not even going to try to undock," Stich said. "The beauty of this vehicle is we can stay docked to the space station."

As part of the process to approve a landing, NASA and SpaceX used a robotic arm to survey Crew Dragon's heat shield, which must withstand temperatures of of to 3,500 degrees Fahrenheit during atmospheric reentry, for damage by space debris.

"There were no areas on the vehicle that were any concern for entry," Stich said.

NASA TV is streaming around-the-clock coverage of the astronauts' attempt to return to Earth. You can watch the agency's broadcast via the YouTube feed below.

Susie Neilson contributed reporting.

This story was originally published July 29, 2020. It has been updated with new information.

Do you have a story or inside information to share about the spaceflight industry? Send Dave Mosher an email at dmosher+tips@businessinsider.com or a Twitter direct message at @davemosher. More secure communication options are listed here.