sevenperforce

When I buy a plane ticket, I'm buying a ride to my destination, not a slot on a particular plane. If the airline needs to switch out the plane or perform extra maintenance, that doesn't breach the contract. The difference, of course, is that my plane ticket is very time-sensitive and I expect to be compensated in some degree if there are extreme delays. Launch purchasers are much more understanding of departure delays, since it's the nature of the business.

We should do the math...if an empty tanker is placed in low lunar orbit, could a fully-loaded crew vehicle leaving from LEO (no eccentric-orbit refueling) reach LLO, dump its return/landing propellant in the tanker, land, ascend, and then refuel for the homeward journey? If they are really going to use orbital refueling for BLEO operations, they are going to need to be Scott-Manley-good at flying rendezvouses.

I can also see smoothly-sliding scales for mass costs in a way that adding a couple of COTS SRBs (I'm looking at you, ULA) could never achieve. Every tonne of payload costs about a tonne of propellant on LEO, so SpaceX can offer discounts for lower payloads (or charge a premium for more massive payloads) because any propellant it doesn't use can be offloaded to an LEO tanker for whatever the next big BLEO mission is. "You want your comsat to go up next week? Great. Up to 30 tonnes to LEO for $15M. If you want it to go to GTO, it's an extra $5M, and if you want direct to GEO it'll be $30M. Whatever margins we don't use, we'll dump into our LEO tanker anyway. Your bird is 12 tonnes? Oh, good; you qualify for a 25% flyweight discount. GEO it is, then. Next!"

Exactly. The way to disrupt a market is not "if you build it, they will come" but rather "meet current demand with added capacity". Fill the market while giving it room to grow. Big Dumb Boosters don't work because they depend on economies of scale. BFR is solvent on current demand but can also exploit whatever economies of scale arise in the process.

BFS will have a much better ballistic coefficient than even the Shuttle. I expect we see a small amount of ablation on each flight but nothing substantial. It's the reliability of landing that concerns me.

One thing I have always wanted to see is a TSTO with an upper stage that thrusts perpendicular to its long axis. By the time you get to staging, you're far enough out of the atmosphere that it's not going to cause any drag losses to pitch 90 degrees. Then you can have a low-impact biconic entry with supersonic retropropulsion and no need for a flip on landing, and engine-out or landing leg failure is typically survivable because you're already laying down on the ground. It requires linear aerospikes or some other funky engine arrangement, though. But damn if it wouldn't be a beauty. Bezos can go to the Moon on New Glenn. Musk could go to the Moon on Falcon Heavy, if he wanted to, though a Raptor-based lunar ship would be far more efficient for the same development effort. I know that SpaceX will never mix kerosene and methane, but a reusable methalox upper stage to drop onto F9 or FH would be SO stinking capable. I am thinking we will always see more refurb than a 747 or a CRJ. Best case we could hope for would be the sort of refurb that a B-2 or an SR-71 has.

Launch price/tonne is low, yes, but that's not the point. His model is that launch price is low, period, regardless of price per tonne. You only need a half-dozen flight articles to corner the market, and that's if it is just a tenth as rapidly-reusable as Musk claims. No, no. Cheaper per launch than Falcon 1. I have no doubt that SpaceX will eventually have a fully-reusable, TSTO, composite-body, Raptor-based launch vehicle operating in LEO. Beyond that, who knows? Is NG going to reuse the upper stage? I can't imagine that New Armstrong will actually be built. Something that much larger than Saturn V seems like crazy talk, even to me. I'm guessing they get F9B5 to five flights without refurb and ten flights before end of life. For their eventual methalox TSTO, I'm guessing 20 or 30 flights before refurb and 50 flights before EOL. But even that changes everything. One static fire will eliminate all the concerns that doomed N1. Then you have three times as many LOV failure modes. Conservatively.

The center of pressure is what worries me. Without a bunch of grid fins or something (which would be a pretty brute-force approach, and wouldn't really work with the biconic heat shield), I don't see the center of pressure going high enough for passive tail-first aerodynamic stability. And if the center of pressure WAS high enough for passive tail-first aerodynamic stability, I don't see how biconic entry would be possible. I know KSP without FAR isn't exactly a reliable aerodynamic model, but I've thus-far been unable to build any BFS clone that isn't either a nose-first lawn dart or tailspins on entry. And that's with very cheaty fuel-pumping.

BFR is actually a good deal more straightforward than Falcon Heavy. More engines, sure, but they are all mounted on a single thrust plate so there is no differential torque to worry about. Jury is still out on "landing on the launch pad".

No way. Where'd you see that? I think there's a pretty good chance of seeing a subscale composite vehicle powered by at least one production SL Raptor doing grasshopper tests by mid-2019. Maybe even suborbital entry tests. I wouldn't expect to see the full-size version until early 2020. The nerd in me (okay, let's be fair, the nerd in me IS me) would really like to see a true SSTO, albeit one with zero payload, using crossfed parallel boosters to achieve desired payload. In other words, "This is an SSTO. It can go to orbit and come back and land, but it can't carry any payload. But it can carry 10 tonnes of payload to LEO for each parallel crossfed RTLS booster you strap on. And it has room for 6." But since even that wouldn't necessarily permit airplane-like operations...the BFR architecture is probably better. It's a valid concern. The DC-X tests didn't have big tail fins to deal with. The Falcon 9/H boosters have a very low center of mass, so they automatically orient themselves engine-first. But the only way I see the BFS being able to orient itself tail-first is if it does an aerodynamic pitch-up followed by an RCS-controlled stall, which strikes me as rather risky idea. It would not perform an entry burn, no. Thermal stresses for typical LEO entry would actually be lower than for the Shuttle, since it carries its own tanks and thus has a much greater surface area for its mass. The Shuttle would have done far better with a single composite heat shield than those horrible tiles. The tiles were a political thing.

Well that stinketh.

Exactly. The Enterprise doesn't take off and land from Earth every time it comes by, after all.

What about something like a Mk2 cockpit, with egress in the rear, between escape engines, and a heat shield underneath? Not right on top, but along the dorsal side just aft of the nose.

Mars EDL is a one-time affair, for the most part, and you cannot very well abort in that event. BFR/BFS is supposed to be used many, many times in LEO, and if you have the capacity to include abort and don't use it, you're running an entirely unacceptable risk of LOC.

Well, if it is REALLY as cheap as Musk thinks it will be, then they'll surely want to use it for crew launches instead of Falcon 9. A lunar version would need abort for Earth EDL from cislunar space. The dubiousness of the Shuttle abort modes (and the two Shuttle LOCVs) are why I raised the question of abort on BFS.

That was my thought. Trouble is that BFS's re-entry profile is highly dependent on its OML. How do you integrate a Dragon 2 + trunk with the BFS OML, still allowing it to enter normally, while ensuring it can do a successful abort, while also allowing crew to move freely out of the capsule and into the rest of the ship?

Dammit!

Same size, not too dissimilar dV, either (LM has more energetic propellant but less of it, because hydrogen is denser fluffier than methane). One goes from Martian orbit to the surface of Mars and back; the other goes from Earth orbit to the surface of Mars or from the surface of Mars to the surface of Earth. 40 cabins. You could cram 4 people in each for a short hopper flight, so 160 people. For interplanetary missions, yes. But god help us if we are planning on sending 160 people from Earth to LEO in one flight.

Well, don't players already have the power to deny other players from interacting with them? After all, unless you're completely out of dV, it's pretty darn easy to dodge another player's, erm, advances.

Without mods, spacecraft traveling at high relative velocities will clip through each other without colliding. But yeah, that would be a fun part of multiplayer.

I'm sure there's some libration, just as with our moon, though probably less.

I agree, the lack of the LES is an issue, second stage problems and landings will be an total loss. I would use an pretty simple LES, not much of an heat shield, not able to deorbit, chance of fail in the late stage is pretty low, if you reach orbit you send an rescue mission. During reentry I don't think LES is very useful i think, trying to separate during deorbit will be very hard in any case. Now landing is dangerous and here an LES would be very useful. I definitely agree with having an ascent/landing capsule separate from the larger crew compartment, for the same reason that you wear an IVA suit during ascent and entry. I don't ever see orbital launches being a shirtsleeve environment. The trouble with a rescue mission is that if you're going to do a rescue, then your escape pod needs to have its own robust onboard RCS system for docking, and that's tricky. Might be cheaper, mass-wise, to just go with a heat shield. I'm having trouble coming up with a good placement that integrates with the rest of the craft but can still leave the rest of the craft in a hurry if need be. Mr Steven is the only netted recovery ship so far, but I'm sure they'll still chute it down to the water and recover it. They are, however, trying to save the booster.

My guess is that splashdown is splashy enough to spray water all over the sensitive insides.

What exciting gameplay do you anticipate when passing suspiciously close to another player's vehicle with a relative velocity of 7 km/s? You asked "What immersion is lost by sharing SoI locations?" Nothing is lost by sharing them, except for the ability to timewarp independently.

Well, the whitepaper doesn't list a dry mass, but it has the thing powered by six restartable RL-10 engines, so if you want an ascent TWR of 2:1 on Mars then you'd expect a takeoff mass of around 88.9 tonnes. They budget 780 m/s for EDL, so you'd expect a fully-loaded mass of 106 tonnes. You could put a BFS tanker into LMO pretty easily. Get two fully-loaded BFSs into LEO, have them both burn in parallel toward Mars until the apoapse is at the edge of the Earth's SOI, then have them dock, transfer propellant from one to the other, and then have one complete the TMI while the other returns to Earth. The one that heads to Mars can aerocapture and circularize with little expenditure of propellant.