Four astronauts are hoping that Friday is the day that they’ll get to head to the International Space Station.

They were all ready to go on Wednesday after putting on their spacesuits and boarding their SpaceX spacecraft atop a Falcon 9 rocket at NASA’s Kennedy Space Center in Florida. But with less than 45 minutes left in the countdown, SpaceX called off the launch. Mission controllers were unable to solve a hydraulic issue with a clamp arm that holds the rocket before it launches.

The weather along the launch path looked iffy on Thursday so Friday is the next chance for them to get off the ground.

Friday’s flight is a routine rotation of crew on the space station, but it is garnering extra attention because it will at last allow the return to Earth of Suni Williams and Butch Wilmore, two NASA astronauts whose brief scheduled visit to the space station last June was unexpectedly stretched to more than nine months (and at least two extra days after Wednesday’s scrubbed flight).

Here’s other information about the mission, which is named Crew-10 because it is the 10th such mission by SpaceX ferrying crew to and from the space station.

When is the launch and how can I watch it?

The four astronauts — two from NASA, one from Japan and one from Russia — are scheduled to launch at 7:03 p.m. Eastern time.

NASA is broadcasting coverage of the launch starting at 3 p.m., which you can watch in the player above. At the launchpad, the astronauts are now strapped in and are performing prelaunch checks. The side hatch was closed at about 4:50 p.m.

Forecasts call for 95 percent chance of favorable weather.

A backup launch opportunity is available on Saturday at 6:41 p.m., but the weather will not be as promising. It will be windy with only a 50 percent chance of favorable conditions.

Who is going to space on Crew-10?

Anne McClain of NASA is the commander of Crew-10, and Nichole Ayers of NASA is the pilot. The other two crew members are Takuya Onishi of JAXA, the Japanese space agency, and Kirill Peskov of Roscosmos, the Russian space agency.

This will be the first spaceflight for Ms. Ayers and Mr. Peskov and the second spaceflight for Ms. McClain and Mr. Onishi.

Will Suni Williams and Butch Wilmore be rescued after getting stranded in orbit?

Sort of.

Not really.

The spacecraft that will bring back Suni Williams and Butch Wilmore has been docked at the space station since late September and could have returned to Earth at any time.

Ms. Williams and Mr. Wilmore launched to the space station in June last year for a test flight of Starliner, an astronaut capsule built under a NASA contract by Boeing. Because of propulsion problems, NASA officials decided that Ms. Williams and Mr. Wilmore would not return to Earth in Starliner. In early September, the spacecraft undocked from the space station, re-entered the atmosphere and landed in New Mexico without any problems.

Just as when an airline scrambles to rebook passengers after a flight is canceled, NASA had to find seats on a ride home for Ms. Williams and Mr. Wilmore.

The next spaceflight was Crew-9, which lifted off a couple of weeks after Starliner left the space station without anyone aboard. Two astronauts assigned to the flight were bumped off, leaving two seats in the SpaceX Crew Dragon capsule for Ms. Williams and Mr. Wilmore on the return trip.

Thus, the Crew-9 capsule could have brought back the two astronauts any time after that, but that would have left the space station understaffed, affecting scientific experiments, operations and maintenance.

NASA and SpaceX could have rushed the Crew-10 mission to launch earlier, but NASA officials decided it was best for Ms. Williams and Mr. Wilmore to join the space station crew and keep the planned schedule for Crew-10.

When will Williams and Wilmore return to Earth?

If Crew-10 launches today, it will dock at the space late on Saturday.

The astronauts of Crew-9 and Crew-10 will overlap for a few days at the space station. About four days after Crew-10 launches, Ms. Williams and Mr. Wilmore — along with Nick Hague of NASA and Alexander Gorbunov, the two astronauts who arrived with Crew-9 — will climb aboard their spacecraft and head home, perhaps as soon as March 19.

Their stay could be extended again if there is bad weather at the possible splashdown sites off the coast of Florida.

What have the astronauts said about their extended stay?

In an interview last month published on Friday, Michael Barbaro, the host of “The Daily,” asked the astronauts, “So, if not stuck, exactly how do you describe this scenario you find yourselves in?”

“That’s a great question,” Mr. Wilmore said. “I would say it’s work. It’s wonderful enjoyment. It’s been fun. It’s been trying at times, no doubt. But stranded? No. Stuck? No. Abandoned? No.”

This was the third trip to space for both Ms. Williams, 59, and Mr. Wilmore, 62, and they realize it might be their last one. “We’re heading home,” Ms. Williams said. “And it makes you really want to enjoy every bit of your time that you have up here.”

Michael Barbaro contributed reporting.