2 astronauts have been stuck in space for months. How they get back to Earth is the biggest safety decision in decades.

• Boeing's spaceship problems have left NASA uncertain about how to return two astronauts to Earth.
• The Boeing Starliner spaceship faced thruster problems and helium leaks, causing safety concerns.
• But bringing the astronauts back on SpaceX's Crew Dragon has its own safety risks.

Boeing's spaceship problems have put NASA in an extremely difficult position.

Two astronauts, Suni Williams and Butch Wilmore, have been stuck on the International Space Station for more than two months because of issues with the Boeing vehicle they flew there.

The Starliner spaceship had thruster issues and helium leakage as it approached the ISS. Since then, weeks of testing and troubleshooting haven't fully assuaged NASA's concerns, though assessment is still ongoing.

Now, NASA officials aren't sure what to do. They have two options — either send Williams and Wilmore home on Starliner, or wait and send them back on a SpaceX Crew Dragon spacecraft . Both options are risky.

The NASA officials who must make this call — ideally by the end of the month — are thinking back to the Space Shuttle Columbia disaster. Because of damage to one of the vehicle's wings, that shuttle disintegrated as it reentered the atmosphere in 2003, killing all seven astronauts on board.

That's why NASA's been assessing its options for Williams and Wilmore for weeks, running tests with a Boeing thruster on the ground, and is now convening multiple boards and decision-making bodies.

"We've got time, and it's a fairly major discussion," Ken Bowersox, the associate administrator of NASA's Space Operations Mission Directorate, said in a press briefing on Wednesday.

After all, this could be the agency's biggest safety decision in decades with two astronaut lives on the line.

The astronauts are at risk either way

NASA could send Williams and Wilmore back to Earth aboard Starliner, as they originally planned before the technical issues.

Boeing has expressed full confidence in the vehicle, but some NASA officials still worry they don't have enough certainty about how the thrusters would behave when it comes time for the spaceship to push itself into a fall back to Earth.

Alternatively, NASA could deploy the backup plan it's hatched with SpaceX . Williams and Wilmore could hitch a ride home with SpaceX's next astronaut crew, aboard the company's Crew Dragon spaceship. They wouldn't come home until February, but at least they would be on a ship with a yearslong record of safe flights.

There are risks to that plan, too. It would leave Williams and Wilmore without a reliable emergency evacuation plan for a few days.

That's because Starliner would have to undock and plunge back to Earth empty, making way for the new Crew Dragon ship. In the days between Starliner's departure and the new Dragon's arrival, the astronauts on the ISS would be relying on the single spaceship remaining on the station — another Crew Dragon — to evacuate them in case of an emergency.

Williams and Wilmore don't have spacesuits compatible with that ship. They won't have SpaceX spacesuits until the new Dragon arrives with them.

"There are some of our contingency situations that require suits, so we don't have full protection in those situations," Bowersox told BI during the press briefing. "Those are the types of things that raise the risk level and complicate our decision process."

Why NASA hasn't made a decision yet

So NASA is taking the time to run its data and options through three "technical authorities:" a chief engineer, a chief health and medical officer, and a chief of safety and mission assurance.

The agency has also brought in "new propulsion system experts" to give feedback, Bowersox said.

Once those various reviews are complete, the agency will complete a flight readiness review with representatives from across the agency and make its decision.

"I've been very hyper-focused lately on this concept of combating organizational silence. If you look at both, unfortunately, Challenger and Columbia, you can see cases where people had the right data or a valid position to put forward, but the environment just didn't allow it," Russ DeLoach, the chief of NASA's Office of Safety and Mission Assurance — the third technical authority — said in the briefing.

"I recognize that that may mean, at times, we don't move very fast," he added.

Willams' and Wilmore's mission, which is Starliner's first crewed test flight, was supposed to last about eight days, though that was the minimum mission length. There was always a possibility it would take longer than that.