SpaceX plans to send humans around the moon in 2018. Can they pull it off?

Two private citizens have booked a trip around the moon scheduled for 2018, according to a SpaceX announcement Monday afternoon. 

Yes, you read that right. The commercial spaceflight company that has yet to fly any crewed missions into space plans to send two non-astronauts beyond Earth's orbit next year. Is that really possible?

"My guess is that 2020 is more realistic," Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, says in a phone interview with The Christian Science Monitor. 

There's still a lot that has to be done before the space tourists can depart on their adventure. First, the equipment needs to be tested.

According to SpaceX's announcement, the two space travelers will ride in the company's Crew Dragon spacecraft, or version 2 of its current Dragon capsule that carries supplies to the International Space Station. But the Crew Dragon isn't scheduled for an initial uncrewed test flight until later this year, with the goal of launching its first crewed test flight by mid-2018.

And the rocket that Crew Dragon is supposed to fly atop, Falcon Heavy, hasn't been tested yet either. It's due for a test launch this summer.

It's not impossible to shoot the SpaceX craft around the moon and back on that timeline, Dr. McDowell says, but one small delay could throw it all off. And there are always delays, he says.

SpaceX has been criticized before for failing to leave room for such delays in its "punishing schedule," as Scott Pace, a former NASA official and director of the Space Policy Institute at George Washington University, put it in an interview with The New York Times in September 2016.

This criticism came after one of SpaceX's semi-reusable rockets exploded during a routine test. Dr. Pace expressed concern that people working for the company might be run ragged by the demands, leading to human errors.

That's a significant concern when talking about sending millions of dollars of equipment up to the International Space Station, but the stakes become much higher with humans, especially non-astronaut humans, on board.

The lunar mission isn't the only major SpaceX mission set for 2018. The company aims to send an uncrewed spacecraft to Mars the same year as part of its long-term goal of colonizing the Red Planet.

Having a circumlunar piloted flight by 2020 would be "an impressive achievement," McDowell says.

That's not to say it won't happen, he says. "SpaceX has a great record of doing exactly what they say they're going to do but always several years later than they said they were going to do it. So I have full confidence that this will happen, but on 'Elon time'," McDowell says, referring to SpaceX's chief executive officer and founder Elon Musk.

The passengers' trip would take about a week and they would travel about 300,000 to 400,000 miles, The Verge reported. The spacecraft would zoom by the surface of the moon, fly out farther into deep space, and then loop back to Earth. 

This would be the first time ever that space tourists fly beyond Earth's orbit, McDowell says.  American businessman Dennis Tito, was the first private citizen to buy a ticket to the great unknown. On April 28, 2001, he flew aboard a Russian Soyuz spacecraft to the International Space Station.

SpaceX isn't the only spaceflight organization considering a flight to the moon. NASA, too, has been considering a next generation rocket, the Space Launch System (SLS), to send a capsule on a trip around the moon. 

Although the path would be similar, NASA's capsule would not contain people and the goal would be for it to fly in 2019. 

If SpaceX can meet the goal of sending a crewed capsule around the moon in 2018, beating NASA, McDowell points out, this could change the dialogue at the space agency from whether to build their own vessels or just to pay SpaceX for a ride.