I think the chances of the SpaceX mission around the Moon going ahead on schedule in 2018 is tiny. But on the remote chance it does happen, I would not fly on that mission, if you paid me a billion dollars. The problem is that they have to rely on hardware that is hardly tested in space at all. First, they will have plenty of tests of their current Dragon, but it is only rated for re-entry from LEO (Low Earth Orbit). It is over-engineered so its heatshield could withstand a re-entry from the Moon, but it's not rated for that. The larger Dragon 2 has a thick enough aeroshell to handle the much higher speed of re-entry into the Earth’s atmosphere from the Moon with plenty of margin to spare. But it has its first flight in 2018, and this would probably be its third flight.

Also, they won't be able to use the Falcon 9 “full thrust”. This can launch a Dragon 2 to LEO and is what they would use for its first crewed flight to the ISS, but it's not powerful enough to launch a Dragon 2 around the Moon. So they have to depend on the Falcon Heavy to launch this second crewed mission, a rocket that will fly for the first time perhaps in late 2017. I don't know how many Falcon Heavy flights there will be before the last quarter of 2018, they didn't say, but it can't be that many.

So, though it would be not the first flight of a Dragon 2 , it would be one of the early flights, probably the third such (manned or unmanned). Also the first crewed flight on a Falcon Heavy, if they do it on that timetable. Also it would follow soon after the first ever SpaceX crewed flight into space, earlier the same year. This would be their second ever crewed flight and the first test of the combination of a Dragon 2 on the Falcon Heavy, and they send it around the Moon!

For SpaceX fans, just to say, I'm quite critical in this article but it has an up beat ending. It's not my aim to discourage SpaceX in their human spaceflight ambitions :). Rather the aim is to encourage them to do it safely.

SpaceX Dragon 2 which will fly for the first time in 2018, a major upgrade from the existing Dragon. If they do send humans around the Moon in 2018, then that will be after one unmanned flight of this spacecraft to the ISS, one short crewed flight to the ISS, then next time it goes around the Moon on a one week long flight with paying passengers. with no "lifeboat". And they are committed to go around the Moon with no possibility to abort soon as they leave the vicinity of Earth.

Their unmanned rockets have blown up once each year for the last two years (Sept 1, 2016 and June 28, 2015). If one of the early flights of the Falcon Heavy blows up, then that will delay things a lot and surely lead to questions of passenger safety.

They are also using a fueling procedure where they load the fuel after the astronauts are on board - something never done before with passengers, and there is some concern that it is less safe. The rocket can explode while the fuel is being loaded, and that’s what happened to one of their rockets last year (the explosion on Sept 1, 2016). If the fuel is already on board before the passengers, you have removed one of the risks that could happen. The passengers might be able to escape if the rocket explodes on the launchpad with them on board. SpaceX have a system that should do that, which also should be triggered automatically in the case of an explosion like that - but it is itself one more thing that could go wrong, and so far never tested with humans on board. If the first crewed flight to the ISS blows up, even if the crew survive in the escape capsule, that would surely again lead to questions of passenger safety and delay things.

This is an essential part of their rocket design because they use fuel that has to be kept very cold (to increase its density for a higher performance). They can’t keep the fuel this cold for long after it is loaded. This makes it impossible to load the fuel hours in advance before the crew.

But if neither of those things happen, it doesn't show that it is safe. As Richard Feynman wrote about the Challenger disaster:

"The argument that the same risk was flown before without failure is often accepted as an argument for the safety of accepting it again. Because of this, obvious weaknesses are accepted again and again, sometimes without a sufficiently serious attempt to remedy them..."

In this case, loading the fuel after the passengers seems like a risky approach, and perhaps his remark is therefore relevant to it. Even if they get several launches without incident using this procedure, it doesn't prove that it is now safe. The FAA needs to keep a careful eye on this just as it should have done with Challenger.

They are also depending on a life support system working for a week in space which has only ever been tested for that long on the ground. And there is no way to abort the mission back to Earth. This is the worst thing about it for me. If they have an Apollo 13 style failure of life support on the way out, then they will have to make do with whatever they have in their spaceship to try to fix it. SpaceX have had issues with quality control of their parts, so I think it’s not impossible that a vital part of their life support system fails in some way. If the carbon dioxide scrubbers stop working, for instance, the carbon dioxide build up would kill the crew on those time scales. Apollo 13 were able to use the attached lunar module as a “lifeboat”, but they will have no lifeboat.

There is no problem with life support going wrong in LEO, not minor things like the CO2 scrubbers not working, as you can just abort back to Earth within a few hours of noticing the problem. But on this mission it could easily be several days before you can return. Such a tragedy would unfold very slowly. And there would be absolutely nothing that anyone on Earth could do about it except give them advice.

Here is a "future fake news" story to dramatize it, maybe help it seem more real, as something like this could actually happen.

If they do this, I wouldn’t fly on it if you paid me a billion dollars for the ride. But I expect it will be delayed and delayed, as happens so often with SpaceX.

Also the FAA will need to approve it for safety, and it doesn’t seem very safe, at least, not as they have outlined it. I don’t think it is “bluffing” but it is hugely optimistic, that they will be able to achieve so many ground breaking innovations so quickly, and that nothing will go wrong with any of them, and that they will all be completed on timetable and be passed as safe for flight. They often claim that they will be able to do things many years before they actually do. For instance they claimed the Falcon Heavy would be ready some years ago (first they said 2011, then late 2013 to 2014) and it is still not ready.

Everything is in the timing.

HOW COULD THEY MAKE HUMAN SPACEFLIGHT MUCH SAFER?

So far this article has been quite critical of SpaceX's human spaceflight. But I didn't write this to discourage them - that's the last thing on my mind. Rather, it’s to encourage safe human flight.

I just think that it is important to focus on safety for human missions in space. Elon Musk’s “fun but dangerous” spaceflights will seem less “fun” after the first crash that kills everyone on board, and he may begin to get some flak at that point. That was him talking about a Mars mission, but it’s clear he thinks of this mission as dangerous too. The BBC quotes him as saying that the “tourists”

"are entering this with their eyes open, knowing that there is some risk here. They're certainly not naive, and we'll do everything we can to minimise that risk, but it's not zero."

So what else could they do to make it safer? Well they have a brilliant approach, that they plan to use the same pressurized cabin for payloads to the ISS that require a pressurized cabin, and for human flight. But they lose a lot of that advantage by continually changing their designs.

So my first suggestion is to not be in such a rush to send humans into space. They have a great design now, the Dragon 2. Once they have it flight ready - well every time they fly it to deliver cargo, they make a profit. So what’s the rush to send humans?

They have a big advantage here over the Space Shuttle which had to have humans on board even for the first mission. So why not just sign off on the design and keep to the same design without constant tweaks? Just fix what needs to be fixed when issues turn up. And the same with the rocket. Do all the tweaks you like with unmanned rockets and spaceships. But once you are ready for humans, then finalize the design of both the rocket and the spaceship, and keep them “as is” for long enough to make sure the humans fly in a spaceship that is essentially the same one you tested many times already in uncrewed missions.

Also, to keep a careful watch on loading fuel after cargo for any signs of possible issues, whether it blows up on the launchpad or not. It’s important not to get complacent after several successful launches with no problems with the system as happened with Challenger. Successful launches, even many of them, do not prove safety for human space flight by themselves.

My second suggestion is that if they want to send tourists around the Moon - why not do one week missions to LEO first? I’m sure many would pay good money for that. End each mission with a one day visit to the ISS perhaps - and pick up parcels to return to Earth. Okay it’s going to be a small space to live in for a week, but then it would be for a flight around the Moon too, and you have the vast vistas of the Earth and of space outside your windows.

If Virgin Galactica hope to make money from selling sub-orbital hops, surely SpaceX can make it from selling a week in weightlessness in LEO. Far far safer. If anything goes wrong they can be back on Earth in hours.

It's risky enough going into space as it is, without making it even more risky than it is already by missing out steps that could make the missions safer. This “step by step” approach may get us further in the long run even if it seems slower to start with.

I say this as someone who is keen on humans returning to the Moon. But - humans safely on the Moon!

See also my answer to What are your opinions on the SpaceX ‘tourist flight around-the-Moon’ in 2018? which also has cites for the various facts and figures here.