Image copyright SPACEX Image caption Artwork: The Dragon capsule was designed from the outset to be capable of carrying crew

Elon Musk, it seems, loves nothing more than to spin plates. When most of us might be looking to lighten the load, he's piling on the ambition.

The serial entrepreneur's latest gambit is to fly people around the Moon. Two wealthy individuals have apparently lodged significant deposits with his SpaceX company to make this journey.

We have no idea who they are, just that these space tourists include "nobody from Hollywood".

That Mr Musk should announce his intention to carry out a Moon loop should not really be a surprise; such a venture is on the natural path to deep-space exploration and colonisation - his stated end goals.

What does take the breath away is the timeline.

He's talking about doing this journey in late 2018, in hardware that has not yet even flown. That's Elon for you.

Image copyright SPACEX Image caption Artwork: The Falcon Heavy rocket should finally make a bow in the summer

For sure, his Falcon rockets have been working for some time now and the Dragon capsule has become something of an old hand at shuttling back and forth to the International Space Station (ISS). But the circumlunar project is another step on from robotic cargo runs to low-Earth orbit.

The Falcon Heavy, the much bigger rocket that will be needed, should make its debut this summer.

The crew version of Dragon, with its all-important life-support equipment, is targeted to make its maiden voyage at the end of 2017.

This will be an unmanned test outing; the first flight to the ISS with people aboard is slated for the spring of 2018.

That does not leave much time to configure and adapt systems for the longer, more arduous Moon mission.

Image copyright SPACEX Image caption Apollo 8 was the first mission to go around the back of the Moon

The Dragon may need to carry some extra propellants, oxygen, water, etc, to help sustain the required trajectory and the passengers. Communications at a distance would also have to be considered. But Mr Musk in his telecon with reporters on Monday said that major modifications to the Dragon or the Falcon would not be required. The journey is likely to last at least 6 to 7 days.

"Back in the Apollo days the outbound journey would usually take between two and three days and the same for the return journey, maybe about a one-week round trip once they leave the Earth," commented Jason Davis from the space advocacy group the Planetary Society.

"It is a little bit different than say putting an astronaut in low-Earth orbit on the International Space Station because your quick return to Earth is no longer an option.

"Once you fire that rocket and head towards the Moon, you can't turn around and go home so you are really kind of on your own for about a week with no-one to come and save you if there is a problem."

Mr Musk said his tourists understood the risks, and that they would receive "extensive training before going on the mission."

The entrepreneur added that the mission would be completed on autopilot. It's hard to imagine the ticketed passengers flying without also being accompanied by an astronaut of experience, and yet this seems to be what will happen. You might have thought that were there to be a problem, having someone aboard with intimate knowledge of the Dragon's workings could be really important.

It's a point picked up by retired Nasa astronaut Clayton Anderson in a BBC News interview: "I would tell [the tourists] to be ready for anything as best as possible.

"If you get on a flight from London to Washington DC, all you need to know is how to buckle your seatbelt and how to put an oxygen mask on your face before you put it on a child; how to find the emergency exit and how to use the bathroom.

"I hope for them it's that simple and that safe, but it remains to be seen. I would advise them to know as much as possible about any contingency activities that could happen and what their exact roles and responsibilities would be."

Media playback is unsupported on your device Media caption SpaceX says it will fly two private citizens around the moon next year

Of course, history tells us that everything in space "moves to the right". Timelines are rarely fixed. And SpaceX is not immune in this respect.

The Falcon Heavy is behind on its original schedule; like Musk, we all thought he'd be flying people to the ISS regularly by now; and his recently promised robotic Mars landing has just been pushed back two years. And don't forget the long list of satellite operators who've seen their launches delayed in the aftermath of two Falcon mishaps.

So, don't be surprised if this Moon loop also extends into the future. The really interesting sub-plot, however, is what this all means for the US space agency (Nasa).

It can be no coincidence that its leadership has announced that it will be looking to put people on the maiden flight of the agency’s huge new rocket, the Space Launch System, and its associated crew capsule, Orion.

These systems are currently due to fly in an unmanned test configuration late next year. A Nasa inquiry could now see a way to slip the mission to 2019 and make it a manned outing instead.

This would make for an intriguing comparison. You would have two missions launching almost at the same time, to both go around the Moon on what is termed a free-return trajectory, except one (SLS/Orion) would have cost considerably more to get to the launch pad than the other (Falcon Heavy/Dragon). It depends how you calculate it, but the difference is in the billions of dollars.

Image copyright BLUE ORIGIN Image caption Jeff Bezos is making steady progress with his plans

It is said that President Trump is looking very hard at how to expand commercial space activity during his administration. The Moon missions would give him considerable food for thought.

Publicly, both Musk and Nasa are on the same page. The agency, which has invested considerable sums in SpaceX, released a statement late on Monday saying that it commended "its industry partners for reaching higher".

Musk tweeted: “SpaceX could not do this without Nasa. Can't express enough appreciation”.

But the comparisons are inescapable. And this is a wave we are witnessing.

Jeff Bezos, the founder of Amazon, has been quietly acquiring space credentials through his impressive Blue Origin company. He is building a rocket to rival the Falcon Heavy that he calls New Glenn. He's even got one on the drawing board that's bigger still called New Armstrong.

The ambition is the same as SpaceX. So is the cost model. That is, to create something which is considerably cheaper than the public sector can deliver with its onerous oversight and its (politically driven) distributed manufacturing methods.

After all, it is in part the cost of access to space that has slowed the pace of exploration since the Apollo era.

(This article has been updated several times to incorporate new details and extend its scope).