sevenperforce

Tidally locked. It's tidally locked, but its orbit around Jupiter is eccentric enough that it has substantial deformation over its 3.5-day orbit.

The only way two players can "meet" and be able to interact is if they rendezvous and match orbits. If they're in matching orbits, they can interact under my solution. The only problem is that you cannot meaningfully plan a rendezvous with a vehicle on an escape trajectory through their SOI, but that is a very rare instance.

Both the ITS and the BFR expected to use the upper stage as a launch escape system, in the IAC presentations. That's not a great idea; you're depending on turbopumps to spin up instantly and all the engines to come to full throttle fast enough to escape an exploding booster with a TWR barely over 1. More importantly, there's no LES for an upper-stage problem, like CRS-7/AMOS-6, and there's no abort mode on landing. Still has a low abort TWR and no contingency for a lot of other possible failures. What happens if you have a leak in your LOX header tank? What if there's MMOD damage to one of the winglets? What if a landing leg fails? Obviously, no launch abort system is going to help you on Mars or on the Moon...but for LEO operations, you want the ability to abort safely at any point from takeoff to touchdown. You don't want another Challenger (some part of the booster coming loose and hitting the orbiter and causing it to break up) and you don't want another Columbia (some sort of heat shield damage causing vehicle breakup during entry). Without a lifeboat escape, both remain issues for BFS.

A thought... I'm sure most of us are not so blinded by the His Muskiness to think that BFS will be allowed to fly crew without a launch escape system capable of zero-zero launch/landing abort. Certainly not for NASA. What's the most mass-efficient, fool-proof method to give a crew of 7 a failsafe abort mode that ensures LOV cannot become LOC?

Except that it’s still cheaper to fly with minimal payload. This discussion should probably be moved to the SpaceX thread, but... What would the most mass-conservative way to add crew-carrying capacity to BFS with 0-0 L/L abort and lifeboat capability?

I'm unclear on why you feel this is necessary. What in gameplay is lost by not sharing SOI locations?

Well, to be fair, those numbers were meaningless. But I agree with the rest of what you said. Unless SpaceX beats them to it. And, probably, gets it there faster. Falcon Heavy expendable can put 7.88 tonnes on a Hohman transfer to Jupiter, assuming an LEO exit burn of 6.3 km/s. How heavy is Europa Clipper without the lander and add-ons?

Ah, so not so much sorcery after all.

My impression is that you assume that all we want is a glorified shared save. With respect to the relative locations of SOIs, each player has their own game timeline preserved, so that they can still warp to maneuvers, etc. The vast majority of all player-to-player interactions occur when both craft are on closed orbits inside the same SOI. Thus, by limiting player-to-player interaction to those situations, we can allow virtually all player-to-player interactions you'd ever want, with only a handful of exceptions. My point is that there is no real reason at all for players to share the locations of SOIs.

Oh, I was just being overly enthusiastic, since to date we only heard of one entering successfully on each mission.

BOTH!!?? BOTH! WHAT IS THIS SORCERY!?!?

If the program had been started after the Shuttle got canned, with the sole requirement being "reuse mothballed STS parts" and no Congressional meddling, they could have saved a metric ton of money by doing a drop-tank or drop-engine SSTO crew vehicle, capable of being retrofit for SHL. If there was ever an engine for SSTO, other than Raptor, it would be the SSME. Fixed that for you. Specifically, it had a special tapering nozzle design to prevent flow separation at sea level but maintain high expansion at vacuum; the nozzle was regeneratively cooled using liquid hydrogen, it preburned both the LOX and the LH2, it used both high-pressure and low-pressure turbopumps, it had dual-redundant MECs, it had a separate hydrogen coolant loop for the combustion chamber, it used a ten-tank helium gas system for actuating all valves and purging the engine, and it had a 10.5+/- degree gimbal range along two axes using a titanium alloy gimbal assembly which also served as the thrust transfer mechanism. And with all that, it managed a vacuum ISP within 4% of the highest-isp hydrolox engine flying, the RL10.

Exactly. You don't understand it. That was my point before, but you insisted you did understand it. You still have not explained how there was any contradiction in what I wrote. Probably because you cannot, since there is no contradiction. There is only one kind of interaction that would be prevented by the timewarp system, and I explained why, and why it would be a very unlikely occurrence. Your lack of desire to understand a very robust solution does not give my solution issues.

Most likely thing I would anticipate would be algae-like mats which can exploit mechanical forces to sustain themselves. Big long tendril vines stretching up from the seafloor. Eyes are not entirely out of the question; hydrothermal vents might produce enough light to be detectable, producing selection pressure for rudimentary eyes.

A couple of problems. First of all, the RS-25 only has 1 second higher SL isp than the RS-68A. If you're using the vacuum isp of both engines, then you have to factor in far higher pressure losses for the RS-25 than for the RS-68A. Second, you only need 2 RS-68As on an SLS-sized core to deliver almost the same amount of thrust as four RS-25s, so your dry mass estimate for the RS-68 calculation was probably too high. If you add a third RS-68A, then your launch TWR jumps significantly and you have lower gravity drag than with four RS-25s. Not saying the RS-68A is a better engine than the RS-25; just saying those numbers might be a bit misleading. Shuttle-C would have been a great idea, had they continued flying the Shuttle and wanted to keep all the facilities identical. But it is a good thing they ended the Shuttle program. If NASA had been REALLY serious about reusing off-the-shelf Shuttle hardware, there were two very good options: Build a Shuttle-Derived Atlas, using three SSMEs at launch with two on a jettisonable skirt, and a smaller version of the ET. The sustainer SSME completes orbital insertion minus a few hundred m/s, and the Orion's own service module provides circularization. Orion could have been used for flying crew to the ISS. For cargo flights, remove the skirt and add SRBs and an ICPS-esque upper stage. For BLEO flights of Orion, send up Orion first, and then send up a cargo mission but without payload, and dock the ICPS to Orion for the LEO exit burn. Catch the jettisonable skirt with a chute and a helicopter and/or chute the SRBs down, if it's cost-effective. Build a Shuttle-derived ROMBUS, using one or two SSMEs on the core and 4-6 jettisonable tanks, again using the Orion's SM for circularization. Chute the tanks down for recovery if it's cost-effective. For cargo missions, replace 2 or more of the tanks with SRBs, using the exact same core attachment points, and fly as above. Either option would have gotten a man-rated vehicle flying in under 3 years, using the exact same SRBs and SSMEs. They are talking about capabilities that SLS does not have. EM-1 could be done, with crewed Orion, using what -- one RTLS Falcon 9 and two partially-expended Falcon Heavies? EM-2's PPE delivery mission could be done with a single reusable F9 launch plus a single recoverable Falcon Heavy. The crewed component of EM-2 is meaningless if replaced with a crewed EM-1, since there are no plans to dock Orion to the PPE during EM-2.

You're simply wrong. What do you imagine is the contradiction in saying that the solution only allows player-to-player interactions on closed orbits within SOIs? That is what it allows. Since virtually all possible player-to-player interactions occur on closed orbits within SOIs, the solution is fine for 99% of multiplayer situations. Work-arounds could be found for the handful of exceptions.

They would have been better off building a drop-tank SSTO out of an SSME. I haven't done the math, but my gut says you could put an Orion into orbit on a single SSME if you used ROMBUS-style drop tanks and gave Orion a Dragon-2-style LES package that would double as the OMS. Probably cheaper than ARES 1, too.

How many RTLS failures has Falcon 9 had? Because, see, the whole landing thing is still experimental, and they are using flight articles to test the limits of their launch and recovery system. So, yes, successful landing failures are expected. But they've got the RTLS business down. If you think everyone who's excited about BFR thinks BFR will fly crew without 0-0 LES, you're nuttier than the people who think it will fly people to Mars in 2024 and fly commercial P2P even earlier. BFR has plenty of margin to have an earth-launch crew version with a full capsule lifeboat with 0-0 LES. Of course, with multi-engine-out landing capability, we may see crewed flights from or to Earth without LES after a few hundred single-engine landings. Well, sure, it will work, and it probably won't kill anybody. But work for what? It's a bridge to nowhere. Wow. Seriously? Damn.

Both cannot be true. Which one is false? Well, you could always take a look at the very next sentence: "The only exception would be interplanetary intercepts." As I explain, this system works (every player is free to timewarp independently) because only allows player-to-player interactions when both craft are in closed orbits in the same SOI. The only player-to-player interactions not allowed would be interplanetary intercepts. Also explained above. And even there, you could have work-arounds. I explained up-thread that you'd need a collision rule for docking, because you don't want two people controlling the same craft at the same time. You'd need one person to give up active control; if two ships were docked in this fashion, the docked craft would be placed inside the universe of the person in active control, while the other person would only be passively watching. Swap control, and the craft switches back to the universe of the the other person. Undock (again, through some established system), and both players regain control of their vessels. So the work-around for an interplanetary intercept: if Player A has a cycler and Player B is trying to rendezvous with it, then Player A would need a probe in LKO that Player B could dock with, passively, so that Player B's intercept ship would then be placed inside Player A's universe. Player A could then rendezvous with it normally. Or, perhaps, Player A could temporarily cede control of his cycler to Player B, so that it would pop up in Player B's universe and he could complete the rendezvous.

It's not going appreciably faster than a first stage on re-entry. Most or all of the soot on a Falcon 9 first stage is the result of the retropropulsive burns; you can see this in some of the really clear RTLS videos. Plus, it's much much fluffier than a first stage so it starts decelerating much higher.

If you could pop a couple of airbags such that the whole thing was held out of the water, with a little water splashing up onto the outside but not the interior, would there be any damage?

I don't blame you. Yes, that's essentially the idea. The same problem arises for the positions of moons, too, so it's not so simple. Rather, the positions of bodies relative to their SOIs would not be shared at all. The only thing shared is the rotation of the central body and the locations of manmade craft. Each player is essentially playing their own game. Each player has his or her own set of on-rails planet positions, etc., that does not change, and you can timewarp to "fast-forward" the locations of all the on-rails bodies in the game. However, whenever your craft has a closed orbit with respect to its SOI (that is, it completes at least one orbit without crossing any SOI boundaries), it can see and interact with any other ships controlled by other players that also have closed orbits in the same SOI. If you have a closed orbit, you can "position warp" to another location along your closed orbit, without fastforwarding time at all. Since player-to-player interactions only occur when two players have closed orbits in the same SOI, every player is free to timewarp independently. This means that players would not necessarily see moons and planets at the same relative locations, but that's not a problem because if you both need to visit the same destination, you can both do separate transfer burns and arrive separately, timewarping as needed, until you both have closed orbits in that destination SOI and can interact. This allows virtually all player-to-player interactions you'd ever want, while preserving nearly-normal timewarp behavior without requiring any sort of "joint timewarp" agreements or workarounds. The only exception would be interplanetary intercepts; for example, if a one player was flying a cycler on a Kerbin swingby, a second player would not be able to directly rendezvous with it inside the Kerbin SOI. But those sorts of interactions are awfully rare, and players could work around this if the first player had a small probe in LKO.

Oddly, I see no chute at all. I guess they cut the chute just before/after impact so that the wind pulls the chute free of the fairing?

So close, so close. A bigger chute means more mass at launch, though I suppose it's not too terribly much. I want to see the video of the fairing in the water!

There's been a lot of speculation about this, but two ships is the most likely solution.