On Thursday evening, without any advance notice, SpaceX tweeted that is had signed the world’s "first private passenger to fly around the Moon aboard our BFR launch vehicle." Moreover, the company promised to reveal "who's flying and why" on Monday, September 17. The announcement will take place at the company's headquarters in Hawthorne, Calif.

There were only two other clues—tweets from Elon Musk himself. Was the rendering of the Big Falcon Spaceship in SpaceX's tweet new? Yes, Musk said. And was he the passenger? In response to this, the founder of SpaceX simply tweeted a Japanese flag emoji. This would seem to be a strong clue that the passenger is from Japan. Or maybe Musk was enjoying the epic Seven Samurai movie at that moment.

By announcing this on Thursday, and waiting four days to provide more details, the company has set off a big guessing game as to who will fly. Of course that is an interesting question, but we have many other questions that we'd like to see answered before that. We've included some of those questions below, along with some wild and (slightly) informed guesses. Musk even answered one of them for us.

Q. When will this flight take place?

It was only last year, in February, that SpaceX announced its intention to send two private individuals around the Moon by the end of 2018 aboard a Falcon Heavy rocket and Dragon spacecraft. That date seemed unrealistic almost from the beginning, not least because the company was already struggling then to meet a 2018 deadline to fly astronauts to the International Space Station. (That will now happen no sooner than April, 2019). Musk since scrapped the lunar flyby via Falcon Heavy, saying it would be better to do such a mission via the Big Falcon Rocket (BFR) and its second stage spaceship (BFS). So it really depends when those vehicles will be ready.

Q. When will the BFR and BFS be ready?

That's a great question. Last September, when discussing the BFR and BFS at an international conference, Musk said SpaceX has a goal of sending two BFS launched on a BFR to Mars in 2022. At the time, Musk quipped, "That’s not a typo, although it is aspirational." The BFS is a far more complicated version than the Dragon spacecraft, which has a crew complement of at most seven astronauts for a few days in space, not dozens or more people for weeks or months.

One data point we have is that SpaceX conducted its pad abort test for the Dragon crew spacecraft in May, 2015. It will take at least four years from that time to launch humans into space aboard the crewed Dragon, and the Dragon spacecraft was fully funded by NASA. The company's president and chief executive officer, Gwynne Shotwell, said last week that she believes SpaceX will be “hopping” the BFS late next year in Brownsville, Texas. (This would seem to be a more simple exercise than a full-on pad abort test). Therefore we can probably safely assume that it will take a minimum of four years between "hops" of the BFS and actual spaceflights. That gets us from "late" 2019 to "late" 2023.

As for the rocket, or BFR, we have no idea. The only real data point we have is that Musk unveiled the Falcon Heavy rocket in April 2011, and it flew seven years later. If we count 2016 as the moment when Musk unveiled the BFR, that gets us to 2023 for the rocket's readiness.

So in conclusion, from these two data points, we can probably safely assume the BFR and BFS—which would easily be the most complex rocket and spacecraft ever built—will not be ready before the end of 2023. And a lot would have to go right. A lot.

Q. When will SpaceX say it is flying the mission?

We have two guesses. We think, from sources, that the company is targeting an internal date of 2024 or earlier. One potential date to target publicly might be December, 2022. This would be the 50th anniversary of the last human mission to the Moon, Apollo 17. This flight, carrying Gene Cernan, Ronald Evans, and Harrison Schmitt, landed back on Earth on December 19, 1972. Humans haven't returned to deep space since, so there is symbolic power there. Such a date would also "beat" NASA's own deep space architecture, the Space Launch System rocket and Orion spacecraft, to a human lunar orbit mission by at least a year.

Q. When do you think it will happen?

We have no doubt that SpaceX has the technical chops to build such a rocket and spacecraft. After all, they went from a rocket with a single engine to one with 27 engines in a little more than nine years. They're a smart bunch. But technical wizardry doesn't happen without funding. And these new vehicles will be expensive. At a minimum, development costs are probably in the neighborhood of $5 billion, and likely several multiples of that.

Q. So how will SpaceX pay for it?

That's the biggest question we have. We don't know. SpaceX is profitable, but even at 20 missions a year at $60 million, it probably is only meeting payroll expenses for a company of more than 7,000 people. So it is reasonable to assume that the company has been able to do a lot of the really cool developmental things it has done because it received multi-billion dollar contracts from NASA for its commercial cargo and crew programs. These helped lead to things like rockets landing on drone ships.

So where does the BFR money come from? NASA isn't paying, at least for now. The US military, through its Launch Services Agreement program, may pay some development costs, but that wouldn't begin to cover the BFR or BFS. (Asked Thursday night how SpaceX would pay for this, Musk said, "Revenue from launching commercial satellites, transport of crew & cargo to ISS and Starlink. Also, advance payment by prospective BFR customers, like this one." Starlink is the company's plan to deploy satellite Internet. Reasonably, it seems at least a few years away from delivering a significant profit.

Q. Come on, man. Is any of this realistic?

Until Musk answers the funding question definitively, we have a hard time putting too much stock into timelines. Therefore, when we know SpaceX has the funding to pay for this, we will consider the human mission around the Moon realistic.

Q. So who is going?

We don't know. According to Forbes, there are 34 Japan-born billionaires in the world. It could be any of them. Or it could be a wealthy sheikh. Or it could be a rich American. We don't know. Also, it seems like there would be many people on the spacecraft, because conceptually the BFS is a big vehicle. So will the first person basically be inviting others to join him or her?

We're eager to find out, but then again, who is flying is not our biggest question. That's how we get from here—concept drawings of the BFR and BFS and some basic hardware—to the actual vehicles themselves.

Q Anything else you can tell us?

Not really. We understand that the announcement caught some SpaceX employees off guard. We've also heard that the company leaders are taking this program very seriously. All in all, it also kind of feels as though we've seen this rodeo before, with the 2017 announcement of the Falcon Heavy Moon mission. We hope for a different outcome this time.