sevenperforce

Higher combustion completion and higher chamber pressures both increase net efficiency and Isp, but from a fuel consumption standpoint it's not like anything is getting dumped overboard in ORSC or FRSC (in comparison to GG or CCTO, where something IS getting dumped overboard or injected into the exhaust).

The article wasn't entirely correct; from a fuel consumption standpoint, an ORSC or FRSC engine is just as efficient. However, the preburner must be oversized in order to run both oxygen and fuel turbopumps, and using the same driveshaft runs into seal issues. You also have mixture problems, and you can't run chamber pressure nearly as high as a FFSC because you're running split.

My thoughts exactly. When I saw the news of the divorce I thought "Oh no, now he might not have enough money for BO" and then I laughed.

On Blue Origin and Jeff Bezos: No Superheroes: Why it shouldn’t be so easy to applaud Jeff Bezos

AFAIK Elon initially guessed the green flash was "a bit of copper from the chamber" and then eventually confirmed it was "because we vaporized some copper" but brazing was my own speculation.

Well to be fair that was my guess. I mean I think I was right, but still.

On the one hand, not having a separate production line for MVacs is definitely savings...but still.

SS is way cheaper than Lithium-aluminum alloy, but 38 engines vs 10? It's like crack. Also, Elon says he has a copy of Ignition! on his bedside table.

Not an extensible nozzle a la Centaur. Also, this is incredible: Elon says that the 270 bar is without deep cryo propellants. The screenshot he posted was an actual snap of the pressure vs time; time is the x-axis in seconds. 11 second fire.

Not at all. It's definitely still "crew payload module for the chomper" but with the the "chomper door" problem eliminated by detaching the chomper door altogether and making the escape portion of the crew payload (the "Dragon 3") integrate with the vehicle OML.

Notionally, the contingency abort vehicle would be mated to the remainder of the cabin module in much the same way that Dream Chaser was to mate to the top of an Atlas V or to the ISS: through the tail. Other connections, like the external hydraulic loops and prop feed lines, would have standard breakaway valves. The abort vehicle would contain head pressure bottles topped by the main system loops to fuel RCS (for nominal mission use) and hot-gas meth-ox thrusters for escape, ignited in the same way as the Raptors. 300 m/s should be enough. If the forward canards double as wings, they can cock back for stability and then use thrusters or splashdown for landing.

Another view: I wonder...if we imagine ripping that giant hatch off entirely? The "crew Starship" would comprise a standard cargo LV with a drop-in hab and crew vehicle, with no other modifications to the OML. A vehicle could be validated for crew launch by multiple cargo launches and then "retired" back to cargo service only once a certain number of crew launches were completed. With that kind of volume, I wonder if a wider (8-9 meter) Dream Chaser style crew vehicle, mounted inside that space, would be workable. Somewhere between Dream Chaser and a truncated version of the lenticular Apollo design. The forward canards of Starship could even be incorporated as the wings of the escape capsule for passive stability at abort.

That's the problem -- how to create an escape capsule that still works in nominal entry.

Back of the envelope says the shuttle had a cross-sectional area of 346 square meters while Starship will cross-section at around 460 square meters without counting any portion of the articulated wings. The new Starship will be lighter than the 2017 IAC version due to use of stainless. Starship will be positively balloon-like compared to the famous flying brick. Shuttle's wings were actually far too good at providing lift; they developed so much lift that they would have pushed the vehicle to coast into a higher altitude where lower speeds would stall them out. Hence the strict 40-degree AoA and the infamous S-curves. The shuttle's wings were sized for glide, approach, and landing, not entry. Starship will have a higher angle of attack, meaning it will decelerate more before hitting the thicker part of the atmosphere. Its airbrakes are are for controlling vehicle attitude; contribution to drag is just a bonus.

That's Raptor. They have no reason to test Merlins that long at this point. And nearly 4 minutes? That's a full mission-representative Starhopper burn. Starhopper is staying under 5 km so that's the sort of burn length we would expect for a full-duration mission.

I suppose I can do some math... The above numbers are nice because they give us two data points for two variants of the same system. For the crew variant, 2400 tonnes mass at staging and 450 tonnes dry, using only Vacuum Isp, gives 6267 m/s; for the tanker variant, 2590 tonnes wet and 470 tonnes "dry" gives 6389 m/s. The difference of 122 m/s is attributable to the lower staging velocity for the heavier payload, relative to the first stage. If we use the guiding assumption that staging velocity is going to be about the same (realistically, SpaceX wants staging at as high a velocity as the first stage can efficiently RTLS from, so it will be the same across designs), then 6.2-6.3 km/s is a good estimate of expected dV on Starship. I suppose this could be used to nail down the parameters of the 2017 IAC version, which in turn would speak to the #DearMoon version, which in turn would give us a new Starship estimate.

The biconic entry is what really makes an escape capsule a challenging thing. In a way, it's the same problem the Shuttle had. Every launch vehicle with capsule LES has had the crew cabin ensconced neatly atop the launch vehicle, with clean separation baked right into the design. You can't do that quite so easily with a biconic-entry vehicle, because you are no longer following an otherwise-nominal separation; rather, you have to cut a plane across the heat shield. The only other option is to have your escape capsule buried inside the outer mold line of the vehicle nose, requiring purposed explosives to shred the vehicle skin in order to achieve clean separation. Of course, the former option--putting a seam in the heat shield--is nothing new; the Shuttle and Buran did it neatly with landing gear, as did at least few different capsules that had hatches passing through the shield. It's just not a good option for an actively-cooled heat shield like the one proposed for Starship. You'd need to use detcord to clean-cut circumferentially around the ventral mold line, and then you're dealing with a LOT of excess weight, so you'd be better off going with the "blow the nose to shreds and blast off" approach. I wonder if the placement of the forward actuating fins can be adjusted back so that the forward section of the cabin could separate straight up, taking the fins with them to provide passive aerodynamic stability. Locate some head-pressure tanks inside the cabin area (used in nominal missions to pump the mains) and connect them to hot-gas thrusters for separation boost. Then glide to a landing on skids, or something. That's an option that allows ejection on predetermined seam lines without any additional explosives. Ejection at a diagonal is a possibility, of course. It's just harder from the standpoint of passive aerodynamic stability, and you REALLY have to shred the entire outer skin.

I am kicking around the idea of combining ejection seats with what would in essence be a solid, pressurized roll cage. Titanium or hardened steel with external crumple zones and passive, single-use TPS. Ejection seats for landing mishap or a pad abort; in any other envelope you depend on the armored cabin to protect you from vehicle breakup and then you eject at a safe altitude a la Vostok 1. You run into mold line issues with respect to TPS. The Starship's active heat shield is part of the outer mold line and so cannot easily make the crew capsule a serially-mounted stage. It would be neat if you could find a way to utilize the upper canards. I don't know, though. Too complex, and you end up with a module that could very well need its own LES. Well, 130 is not as many as we might think when flying full-reuse, but I'm thinking seriously about what alternative LES options might be out there.

I don't think we will see a crew of 100 on it any time soon, but LES capacity for up to 20 crew is probably a safe bet. You don't want to be limited to only 7-10 people when you have that kind of mass budget. Do you embed a Dragon analogue inside the larger cabin and use detcord to shred the Starship's outer mold line in an abort, or do you integrate the escape capsule into the outer mold line? Does the escape pod have an internal heat shield or does the external heat shield have a shear point? How do you keep the escape vehicle aerodynamically stable during a pad or Max-Q abort? One thing learned from Challenger is that a hardened cabin is surprisingly good at keeping crew safe in an RUD as long as it doesn't take a direct breaching hit from a structural member. Kind of hard to rig chutes that would deploy successfully in that kind of situation.

In the 2016 ITS variant, they specified that the crewed interplanetary ITS would have a dry mass of 150 tonnes and the tanker (which presumably could also be adapted for cargo) would have a dry mass of 90 tonnes. Quoted payload to LEO (presumably with cargo variant) was 300 tonnes. Thus, when we have the IAC 2017 version at a "dry mass" of 85 tonnes and a payload of 150 tonnes, we don't know if the 150 tonnes is the payload for the cargo variant (with a dry mass lower than 85 tonnes) or if 85 is the cargo variant, and the 150 tonnes represents the 85-tonne vehicle plus a crew cabin of unspecified mass.

So here's a question. Let's say that the Starship absolutely positively does need an LES. What's the safest, cleanest, lowest-mass way of doing it?

Yeah, dry mass goes down with SS even though it is denser, because it is stronger. Similar to replacing aluminum with titanium, etc. Dry mass estimation is complete guesswork at this point, though. It was also never clear in the 2017 IAC version whether the "85 tonnes dry plus 150 payload" was for a cargo launcher or for the crewed/interplanetary version. Dry mass also goes down because you don't need a bunch of PICA-X.

Yep I just realized that. Durrr, there go my calculations. Though now it can potentially tell us something about Starship. 170 metric tonnes times 7 engines comes to 1.19 kilotonnes, significantly less than the 1.34 kilotonnes of the 2017 IAC version. And that's with a 1:1 TWR, which is obviously not workable (but that's where Elon is going to put the numbers, because eternal optimism, and because the engines can run harder). The 2017 model had an estimated dry mass of 85 tonnes and "typical ascent payload" of 150 tonnes, meaning 6.5 km/s of dV. Payload to LEO already dropped once from 150 tonnes to 100 tonnes between the 2017 IAC and the 2018 #DearMoon presentation; that was when they were still looking at composite. However, that is most likely the result of swapping vacuum Raptors out in favor of SL Raptors. I haven't seen a solid estimate on vacuum Isp for SL Raptors, but it's probably in the 355 s range, which gives almost the same amount of dV. For Super Heavy's 31 engines, we're looking at a stack GLOW of 4.4 kilotonnes at a liftoff TWR of 1.2 or thereabouts. Subtracting Starship gives 3,200 tonnes for Super Heavy, which is actually greater than the 2017 IAC numbers. It may be more nimble off the pad than I imagined, or that may be part of a more radical redesign, or potentially he wasn't thinking about the implications of what he was saying.

A full-flow staged-combustion engine cannot use film-cooling for the combustion chamber because it preburns both propellants prior to injection. From a perspective of diameter alone, the Raptor's nozzle is not nearly large enough to support a vacuum-optimized expansion ratio. Thus, no flow separation. Heuristic views of the nozzle suggest that it may be a convergence-based altitude-compensating curve. So you'd have internal flow separation stabilized by higher pressures around the rim. Also, recall that this is not yet full thrust. "Frag"....what a guy.

If this holds (which, let's face it, is not terribly likely given SpaceX's naming convention track record), I guess we'll see usage like this: "Tune in tomorrow on our YouTube channel to see the inaugural launch of Starship Heart of Gold on its journey to Mars." "Ten minutes to launch, and Starship is completing LOX loading, along with its Super Heavy booster." "T minus sixty seconds. Starship is on internal power." "Starship with Super Heavy, go for launch." "Starship Heart of Gold has cleared the tower." "We have just received confirmation that Starship has passed through Max-Q, the point of maximum dynamic pressure on the Starship and its Super Heavy booster." "In just under twenty seconds from now, Starship will separate from its Super Heavy booster as the latter's engines shut down and continue into orbit." "Starship's main engines are throttling down on their boost into orbit. Meanwhile, the Super Heavy booster that lifted Starship to the edge of space is about to perform its entry burn on the way back to Cape Canaveral." "We have confirmation of a good engine cutoff and a good nominal parking orbit for Starship Heart of Gold! Stand by for the initiation of Super Heavy's landing burn." "Super Heavy has touched down after successfully launching Starship Heart of Gold! Ground crew, prepare for Starship tanker launch at 0600 hours." I can get behind that. Just not under it.