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"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. – Dragongeek Sep 24 '18 at 10:54
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"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. – Jörg W Mittag Sep 25 '18 at 08:17
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@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. – SF. Sep 25 '18 at 08:33
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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.
Steve Linton
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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. – SF. Sep 24 '18 at 09:39
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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. – Steve Linton Sep 24 '18 at 09:40
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... but there's not much point in taking your earth launch and return vehicle away from LEO – Sep 24 '18 at 09:54
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@JCRM: Thing is BFS is not just an Earth launch and return vehicle; far from it. It's meant as a Mars-bound vehicle, long term habitat (both space and Mars surface), and a fuel carrier (for orbital refueling of long-range BFS). Anyway, its first actual mission (beyond tests) is meant to be a tourist flight with a Moon flyby. – SF. Sep 24 '18 at 10:14
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@JCRM That's true. I did say "if we're going to be doing this a lot". SpaceX is picking a tradeoff between development costs and complexity on the one hand and efficiency of the ultimate system on the other. If the volume of business picks up enough, the tradeoff will move – Steve Linton Sep 24 '18 at 10:17
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@SF. The point was in response to the answerer's suggestion that a lunar orbit/surface be used. If one is optimising that 1.6 km/s then the 4.8 before it is also worth a good hard look. – Sep 24 '18 at 10:37
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3They 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. – uhoh Sep 24 '18 at 16:18
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2@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. – Lex Sep 24 '18 at 22:07
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The referenced delta V diagram is terrible. It does not take 4.8 km/s (4.1 km/s + 0.7 km/s) to get to lunar orbit. Translunar injection delta V from LEO ranges from 3.0 km/s to a bit over 3.2 km/s, depending on where the Moon is in its orbit, and lunar orbit insertion is about 1 km/s. It also doesn't take 1.6 km/s to get from LLO to the Moon's surface. It's more like 1 km/s, and about the same to return from the surface to LLO. Finally, transearth injection is about 1 km/s, totally about 7.1 km/s. – David Hammen Sep 26 '18 at 10:02
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@Lex - Make that about 3.1 km/s to slow down into LEO on return. It's translunar injection in reverse. – David Hammen Sep 26 '18 at 10:06