... but Hurricane Isaias threatens their ocean splashdown

NASA astronauts Doug Hurley and Bob Behnken are due to return to Earth this weekend, but a storm headed for Florida may keep them in space a while longer.

• SpaceX has NASA’s approval to land the company’s first space mission carrying people, called Demo-2, back on Earth.
• But the ocean splashdown of two NASA astronauts aboard SpaceX’s Crew Dragon ship may need to wait for Hurricane Isaias to clear out.
• Astronauts Bob Behnken and Doug Hurley can’t land until at least two out of seven planned landing sites have good weather conditions.
• NASA is monitoring the situation and said Behnken, Hurley, and their spaceship can stay in orbit for at least another two months, if necessary.

NASA astronauts Bob Behnken and Doug Hurley, who made spaceflight history on May 30 by becoming the first people to launch to orbit aboard a SpaceX vehicle, may see their weekend homecoming plans thrown to the wind.

After docking SpaceX’s Crew Dragon “Endeavour” ship to the International Space Station and spending two months there, the men are preparing to undock on Saturday. They’re due back on Earth on Sunday around 2:42 p.m. ET.

NASA is overseeing SpaceX’s experimental mission, called Demo-2. On Wednesday, the agency gave the company a “go” to proceed with its landing plans. But Hurricane Isaias could force the astronauts to stay in orbit a while longer.

The cyclone has already hit Puerto Rico as a tropical storm with high winds and flash-floods, leaving hundreds of thousands without power. It later developed into a Category 1 hurricane, with sustained winds of 75 mph.

Isaias’ current path would bring dangerous weather to several potential landing sites by Sunday afternoon – the planned time for the astronauts’ splashdown.

“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.”

“We cannot wait to get Bob Behnken and Doug Hurley back to Earth. But of course we have some weather pending,” Jim Bridenstine, NASA’s administrator, said during a press briefing on Wednesday.

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

SpaceX’s Crew Dragon is guided by four parachutes as it splashes down in the Atlantic Ocean about 200 miles off Florida’s east coast on March 8, 2019, after returning from the International Space Station on the Demo-1 mission.

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

The storm could affect several landing areas just as Endeavour is supposed to reenter Earth’s atmosphere, deploy its parachutes, 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. Given current conditions, mission managers are hoping to land Demo-2 in the Gulf of Mexico near Panama City, a NASA spokesperson said.

“This mission will be a bit unusual as timelines will be in flux quite a bit up until undocking as we finalise landing locations,” the agency spokesperson told Business Insider in an email on Friday.

Panama City is second-westernmost location of the seven options. As of Friday morning, the National Hurricane Centre does not project that tropical-storm-force winds will affect the area.

A July 31 map shows NASA and SpaceX’s landing zones for the Crew Dragon Demo-2 mission amid the estimated path and conditions of Hurricane Isaias. Panama City is indicated with a red arrow. The outer-edge green shows a 5-10% chance of sustained tropical s

Depending on how large the storm grows and how nasty weather conditions become, mission managers may scrub 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.

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 can share life support and last 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.

Susie Neilson contributed reporting for this story.

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