* NASA on Saturday gave SpaceX a "go" to undock the company's first crewed space mission, called Demo-2, and land it on Sunday evening.
* Hurricane Isaias complicated original plans to return two astronauts to Earth aboard SpaceX's Crew Dragon spaceship in the Atlantic Ocean.
* Elon Musk's aerospace company may 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, and NASA has until about 5 p.m. ET on Saturday to call off the undocking.
* Should the weather worsen, NASA and SpaceX can try again a day later or some other date over the next two months.
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Astronauts Bob Behnken and Doug Hurley have a "go" to return to Earth this weekend 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 are preparing to undock from the ISS on Saturday at 7:34 p.m. ET. If that procedure goes well, they're due back to Earth on Sunday around 2:41 p.m. ET. (NASA TV's continuous live-streaming coverage, which you can watch at the end of this story, kicks off Saturday around 5:15 p.m. ET.)
NASA is overseeing SpaceX's experimental mission. On Wednesday, the agency gave the company an initial "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 at least 75 mph. Isaias' current path threatens to 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."
However, in a blog post published on Saturday afternoon, NASA announced that the astronauts had a "go" to proceed with landing.
"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.
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. Recovery crews will be waiting to recover astronauts with boats, airplanes, and helicopters.
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 Pensacola or, as a backup option, Panama City, NASA said on Saturday.
"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. As of Saturday afternoon, the National Hurricane Center does not project that tropical-storm-force winds will affect the area.
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.
Given the intense preparatory work required to prepare Crew Dragon for its return, NASA and SpaceX have until about 5 p.m. ET to make the final call for undocking, the space agency said.
Behnken and Hurley can stay 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 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.
NASA TV will stream around-the-clock coverage of the astronauts' attempt to return to Earth starting around 5:15 p.m. ET on Saturday, August 1. 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.
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