Can BFS land on the Moon and return? No aerobraking, no ISRU resources to refuel on the surface for return, but much less delta-V than going to Mars. Landing legs are there, though the engines may be overpowered and require some clever "hover-slam" burn. In general, BFR is not being designed for Moon landings, but - is it capable of them?
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1$\begingroup$ "BFR is not designed for moon landings"--I'm not so sure about that. I remember in a presentation, the BFR system was advertised to handle orbit, the Moon, Mars, and beyond. SpaceX has also released promotional pictures of the BFR system on the Moon and I'm pretty sure that we'll see a BFR moon base and moon landing before the Martian equivalent as it's just such a good trial run. $\endgroup$– DragongeekSep 24, 2018 at 10:54
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$\begingroup$ "BFR is not being designed for Moon landings" – I think you mean BFS here? BFS is designed to land on any surface in the solar system. So, no liquid or gas planets, but anything with a surface is fair game. That's the reason why SpaceX went for propulsive landing, because not all interesting destinations (including the moon) have an atmosphere. Even Falcon 9, which is not intended to leave Earth has propulsive landing in order to gain experience with it as preparation for BFS. $\endgroup$– Jörg W MittagSep 25, 2018 at 8:17
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$\begingroup$ @JörgWMittag: I meant BFR as the entire system: BFS, its booster, and the fuel carriers. BFS alone likely wouldn't cross the Karman line, and after reaching orbit it doesn't have enough fuel to go anywhere meaningful, needing to wait for orbital refueling. $\endgroup$– SF.Sep 25, 2018 at 8:33
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There are two parts to this question. (1) does a refueled BFS have the delta-V budget to get from LEO to the surface of the moon and back to Earth intercept (2) can the control systems, landing legs, etc. handle a soft landing on the Moon.
Re (1) the answer is (as usual) implict in the diagram in this question. The delta-V required is about 8.7 km/s. This year-old chart suggests that this is achievable witha payload of perhaps 25 tons. If some (most) of the payload is to be left on the Moon then this will increase somewhat. So, on the face of it, this is OK.
This discussion suggests that it might be helpful to do some refueling in a higher orbit in order to carry a larger payload. That means more tanker launches, since each one carries less, but it might offer a way to get a large payload to the Moon.
Re (2) one raptor has a full thrust around 2MN and the mass of a BFS with payload and return fuel is going to be something around 200 tons, one engine will provide about 1 Earth gravity of acceleration. Even throttled down it will be too much to hover (though OK for Mars, unsurprisingly enough), but SpaceX do seem to have nailed the problem of landing under those conditions with the F9. Another problem is uneven ground. So far they have only landed on smooth steel or concrete surfaces, but with their Mars ambitions they will need to solve that one anyway.
So, in conclusion, yes, it can, although even fully refueled the payload is significantly reduced.
If we're going to be doing this a lot, it would make sense to design a dedicates lunar orbit to lunar surface shuttle vehicle. There is no real point in taking your Earth return fuel, your heatshield and most of your engines down and up a 1.6 km/s gravity well, rather than leaving them in orbit.
answered Sep 24, 2018 at 9:27
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$\begingroup$ I was primarily thinking of it as a dress rehearsal before Mars trip. Much closer to go, much easier to abort and go back home (or send a rescue craft) if something goes wrong. $\endgroup$– SF.Sep 24, 2018 at 9:39
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$\begingroup$ Much harder in terms of delta-V though, because you can't aerobrake and you can't make propellant in situ. I suppose you could land a few disposable fuel tankers ahead of the manned ship. $\endgroup$ Sep 24, 2018 at 9:40
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$\begingroup$ ... but there's not much point in taking your earth launch and return vehicle away from LEO $\endgroup$– user20636Sep 24, 2018 at 9:54
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3$\begingroup$ They already have a ship in the Atlantic Ocean and one in the Pacific Ocean. The solution is obvious, put a third ship in the Sea of Tranquility. $\endgroup$– uhohSep 24, 2018 at 16:18
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2$\begingroup$ @JCRM, without the heatshield you would need an extra 4.1 km/s to slow down into LEO on the return from lunar orbit. A dedicated space only craft is still something to consider, but it is by no means a done deal. $\endgroup$– LexSep 24, 2018 at 22:07