sevenperforce

Is that for berthing only, or for docking as well?

It's about managing mitigatable risk and maximizing benign failure modes. Complete loss of power on a transpacific flight is not a mitigatable risk; if that happens, everyone is sharkbait whether they have parachutes or not. It's the same as a large meteor impact on orbit; there's no way to survive it, so there's no sense trying to mitigate it. You also don't need to mitigate benign failure modes. A 747 with loss of power on landing is a big emergency to be sure, but it has a nominal recovery mode: land deadstick. Thus, no need to mitigate. Loss of power on landing in a BFS is not at all benign, but you CAN mitigate it with an abort capsule and chutes. Only if maximizing the comsat market lowers access prices by orders of magnitude.

Funny thought... Imagine a future where cryptocurrency becomes far bigger than it is now, but where the interception of communication makes transferring cryptocurrency highly difficult, and AI-aided hacking becomes a huge problem. You could have Mars cryptomining centers where you would HAVE to have people on hand, because the cryptomines would be completely unplugged from outside communication. People would visit the site, transfer mined currency from the mine to a flash drive, and then put the flash drives on Earth return rockets. Now THAT would be a reason for a Mars colony. And there's no money in that, yet.

Forced air cooling is possible on Mars. Not on the moon.

Still better than what has happened on/around OCISLY and JRTI.

I have yet to come up with a single role for people that cannot be better handled with telepresence. Anyway, a polar lunar station might still not be as good of a heat sink as Mars. Atmospheric cooling > lithocooling.

That's the problem.

Aircraft have engine failure abort modes on landing. It's called "glide".

Update: additional (paywalled) discussion indicated that 50-kN methalox thrusters, likely the ones intended for RCS on New Glenn, wold be used for the actual landing. The BE-3 cannot throttle deeply enough for moon landings. The 4.5-tonne payload would only be enabled by SLS; smaller rockets would have the BE-3 performing part or all of the TLI burn. So we are likely looking at a hydrolox BE-3 crasher stage with as many pressure-fed methalox thrusters as needed for the desired payload.

It's the image supplied by BO but it doesn't tell us much. Blue Moon is supposed to be able to drop 4.5 tonnes on the surface of the moon and presumably uses a BE-3 architecture. They talk about delivering it with NG or SLS, which means it's probably not intended to go from LLO to the lunar surface, but rather to go from TLI to the lunar surface. To be useful, it needs to be able to target the poles as well. We're probably talking about 3.5 km/s or a little more. Let's say 3.8 km/s, to allow for extended hover on landing. The BE-3 is combustion tap-off, so it is necessarily less efficient than an expander-cycle (RL-10) or staged-combustion (SSME) hydrolox engine, and is probably more comparable to a GG cycle like the RS-68. A vacuum-expanded nozzle will give it a better isp, likely in the 420-s range. 420 s and 3.8 km/s means a prop fraction of 60.3%. A vacuum-expanded BE-3 would have a thrust of 500 kN or so. 500 kN gets you far more thrust than a 5-tonne-payload-class moon lander would ever need. Assuming a TWR of around 50 for the BE-3 and a hydrolox tank mass fraction of around 20, we're talking about around 10.5 tonnes of wet mass plus 4.5 tonnes of payload and a vehicle dry mass of about 1.5 tonnes. Note that the BE-3 uses expendable pyros for ignition so it is not a candidate for cislunar reuse.

Landing LES for a propulsively-landed vehicle is just a bit more complicated than the standard pad abort or Max-Q abort. Passive aerodynamic stability is a big problem. Abort systems are supposed to be fire-and-forget; you don't want to be depending on gimbal or differential thrust for stability during an abort. If you're dropping through the atmosphere at Mach 1.5, your aerodynamic profile will be exactly opposite of what it would be going at the same speed in the other direction. Standard LES assumes you are already pointed in the right direction.

Sitting duck? As in, it would be targeted by antisat weapons? That's unlikely. Nuclear point defense these days is not really a question of repelling an extinction-level nuclear assault by a symmetric superpower, but of protecting native targets from a rogue state with a small rocket and a cheap nuke on top. Cough, DPRK. You only need a few satellites. Plenty of time, and 3-4 satellites means you have at least two sats with eyes on DPRK around the clock. Beam angle shouldn't be as much of a problem in space as it would be for something like the YAL-1.

Bingo. That being said, I would love to be proven wrong. Agreed. So would someplace with better insolation. Like a sun-sync orbit. I was thinking heat rejection. Iceland has become a prime cryptocurrency hub because it's cold, and you need a heat sink for running big servers. Mars is the only place close enough to the sun that solar power is viable but that still supplies a constantly cold atmosphere for heat rejection. You might be able to do better with a sun-synch satellite with a ginormous radiator array, but radiators can only get you so far.

Mars would be a good place to mine cryptocurrency.

My preferred nuclear point defense approach is to put a few megawatt chemical lasers in an inclined, eccentric orbit so that you have line-of-sight to your probable ICBM flight paths at all time.

Space is hard. Landing on Earth is easy. We've been surviving falls with parachutes for centuries.

The BFS will have autogenous pressurization, which will tend to make the fireball a good bit bigger. In any case, it's not something I'd like to chute down into. The point is that the launch escape system will need to be able to not only arrest downward momentum at the BFS's terminal velocity, but reverse it; otherwise it won't be able to get any sideways motion.

The main concern I have here is clearance. As with a pad abort, your escape motor needs to be able to push the vehicle clear of the ensuing fireball. We've all seen the landing failures of Falcon 9 first stages; the BFS would be bigger, and autogenously pressurized, so you're talking about what would essentially be a giant fuel-air bomb. Successfully pulling away from the doomed ship doesn't do you much good if you chute down into a firestorm.

This exact method is used in point defense (think Iron Dome but scaled up) against cruise missiles. The anti-missile missile sends up a warhead that is packed with high explosive and a bunch of tungsten cubes about an inch wide. The explosive causes the tungsten cubes to spread out into a nice big cloud; it just takes one or two tungsten impacts to shred the incoming missile. ICBMs are coming in much faster, from much higher altitude, and must be intercepted much higher, so this isn't quite as effective for ICBMs.

Man-rate that SOB and let's do this!

I said higher-energy storables, not higher-energy hypergolics. Peroxide isn't exactly storable. I suppose the other solution is storable cryogens. Is Blue Moon supposed to be based on BE-3?

They need a bit extra, given that they have to cancel their downward velocity AND boost clear of the ensuing fireball.

We need higher-energy storables with orbital propellant transfer. Or something like that. Otherwise, sending a new multistage lander for every single mission is going to get really pricey, really fast, no matter how cheap our launches are.

Until rapid and reusable orbital rockets become commonplace, all launches will be bespoke.

Someone upthread mentioned the inanity of the scene in G.I. Joe where the Arctic icepack is smashed with explosives and suddenly the ice floes begin sinking through the water like great boulders and destroying the Cobra submarine base. Which is pretty bad. But, just a few minutes later, a ballistic missile is fired from the base. With two warheads -- one aimed for Moscow, and the other for Washington, DC. Because hey, that makes sense. Then again, the missile is about twice the size of a Saturn V, so I suppose it has all the dV it could ever want. But then the hero proceeds to jump into a hypersonic fighter jet and chase down both missiles. Separately. First the one going to Moscow, because it's "closer". Then, after shooting down that warhead, it turns around and flies to Washington DC and shoots down THAT one. Oh, and to top it off, the jet doesn't actually have a control for its weapons. Its weapons are voice-activated.