sevenperforce

Seeing it with the wings folded back like that is just pure beauty. This angle shows how the wings are blended into the rest of the body. There should be a very significant negative stagnation behind those chines which will tend to promote passive aerodynamic stability. Yeah, I've thought of this too -- the current fold-out design on the windward side, but F9-style or ITS-style on the lee side. Just as I suspected when I saw the original failure:

Previously, word of Elon was that they would do a dual-bell. However given the visible flow separation, it appears they didn't do a dual bell design at all (if they did, the flow separation would occur at the discontinuity) and instead they have simply truncated the bell just below the point of flow separation. Less efficient at sea level than the altitude-compensating nozzle of the RS-25, but more efficient in vacuum.

Lovely discussion points on pentaborane-9 from this and other sources: "Problems with this fuel include its toxicity and its characteristic of bursting into flame on contact with the air." "...reacts violently with some fire suppressants, notably with water." "Its acute toxicity is comparable to some nerve agents." "It is difficult to extinguish a pentaborane fire. Structural firefighting clothing will NOT provide adequate protection." "In humans, minor intoxication has been reported to cause various central nervous system (CNS) symptoms, some of which are dizziness, drowsiness, blurred vision, fatigue, muscle spasms, hallucinations, memory loss, behavioral changes, poor judgment, lethargy, confusion, inability to concentrate, headache, nausea, vomiting, and feelings of constriction in the chest." "With severe intoxication...spasms, convulsions, agitation, hallucinations, hepatitis, destruction of skeletal muscle, coma, and death." "In case of spillage ignition, the area should be deluged with water. The water will not extinguish the fire but is of value in cooling surrounding equipment and facilities." "In conclusion, the best way to decontaminate a spill area is ignition of the pentaborane." "We find as a matter of law...that the release of pentaborane creates problems of uniqueness and magnitude and constitutes an unnecessary, extraordinarily and inherently dangerous hazard."

Sometimes I just marvel that Glushko designed a version of the RD-270 which would have run on PENTABORANE and pushed 340 s AT SEA LEVEL. Now THAT would have been just beyond.

Oh my god this is beautiful. The glorious Mach diamonds. The roar. The utter power of the biggest vacuum engine ever constructed. THEY BUILT A VACUUM ENGINE THAT CAN BE TESTED AT SEA LEVEL. Seriously this is freaking amazing.

Exactly. My somewhat-informed materials science take: Ductile yield strength and fracture propagation in cold-rolled steel are extremely well-understood. Weld failures, on the other hand, are dependent on many, many difficult-to-predict variables. In order for their digital models to accurately predict the vehicle's response to transitive stresses, they needed to be sure that their welds were substantially stronger than the bare steel, in all failure modes. If they are certain that the bare steel will fail before their welds do, then their computer modeling is much simpler and much more accurate. What we see here is that ductile failure and fracture propagation took place entirely within the bare steel regions, preferentially along areas where the bare steel was stressed (but not by the welds themselves). It's particularly notable when you see the torn steel on the left with a fracture that passed across the weld without traveling down it.

I agree with @RealKerbal3x: we need to measure everything in gas mileage times pressure.

Yep, I'm pretty sure that's exactly what they were going for.

Maybe, but now that I think about it, I am not entirely sure that the forward canards give enough pitch authority. It would be hard to pitch up unless the rear fins were much smaller, in which case you'd lose that roll damping.

Oh, I don't short. I hold about 50% of my inventory and swing-trade the rest on 2-3 day cycles. I am usually pretty good at selling high and buying low but I definitely picked the wrong approach on Monday.

Educated guess about where we go from here: Pressure test with thrust simulator Nose cone completion Raptor mating 3x Static fire 1 Nose cone mating Static fire 2 Flight It makes sense they would pressure test and do the first static fire before mating the nose cone -- less chance of damage if things go south.

Right, it's unrealistic. We will not get colonies on the moon or Mars without Starship or a similar vehicle operating at high capacity. But it's much more realistic than supposing we could get anywhere close to constructing those colonies within ten years. It's still the easy part.

In the first two designs -- the 12m 2016 ITS and the 9m 2017 MBR -- the vehicle would have had no forward canards and would have used aft split flaps for pitch and roll. Roll would couple with yaw, but that could be handled by RCS, and overall yaw authority would also use RCS while using the aft flaps to maintain constant AoA. The vehicle would be flying at such a high AoA that longitudinal yaw would basically just be rotation around the prograde axis, which is undamped and therefore wouldn't require much expenditure of propellant (as opposed to altering pitch, which would require constant propellant expenditure to fight against the airstream). This would have worked well enough for Earth and Martian entry, actually (see for example the Russian Kliper concept), but terminal descent was very challenging, and it would have been even more challenging to make a descent and landing profile that would work reliably on both Earth and on Mars. That's why they added the forward canards/flaps/squidfins. With both fore and aft control surfaces, there's a much broader range of allowable entry modes and more control during terminal guidance. This, also, is why they had to move the header LOX tank from inside the main LOX tank (original design) to the nose: the forward canards would have made the front end too draggy and not heavy enough, inducing tailspins or total loss of control. IT'S SO FLUFFY From viewing, it looked like a circumferential weld failure WITHOUT stress fracture propagation, which I believe is the best of all possible failure modes.

I made the wrong damn bet on $TSLA yesterday -- good god.

A little look at how having all four flaps allow for multiplanar control authority: If you were to only have the forward fins actuated and have the aft fins fixed, then yaw and roll would be coupled: you couldn't yaw in one direction without rolling in that direction too.

Oh, blowing it up would be out of the question. The goal is to nudge it out of the impact zone. The hypo specified an interstellar object. Not sure how we'd have ten years lead time for something like that, but if we did, we're talking about rather high velocities. The Chicxulub impactor did enough damage to render the Earth uninhabitable for humans as we exist today and it was less than 80 km in diameter with an impact velocity of around 20 km/s. An interstellar impactor would have an impact velocity of easily up to 50 km/s or higher, meaning that it could mass only 1/4 the size of the Chicxulub impactor and delivery the same-size punch. Definitely not a large planetoid.

If you want to make it an interesting hypo, then say something like this: "Assume the existence of stable, self-supporting bases on both the moon and Mars, capable of accepting the majority of human life between the two of them. Assume further that you are restricted to current technology in actually getting humans to the off-world bases. How do you do it in ten years?" Because building a stable off-world colony is the work of a century, not a decade.

I don't think you'd want to mess with engine start transients during the flip recovery and terminal descent. I've thought about this a lot, actually, and I think it's a potential failure mode hedge. If you have only two actuated control surfaces and one of them locks up, you're screwed. If you have four, then you can lose one and compensate with the other three. It also allows broader control range for different entries. Remember that the ship which goes to Mars needs to be able to return to Earth. The Earth return is also going to be the highest-energy entry, so you want the most data on it. Therefore you want the Mars return to use the same EDL mode as your basic ship so you get the most data. That also means your Mars EDL needs to be incorporated in the same system. EDIT: Moreover, if you only have two forward canards, yaw is strongly coupled with roll and so you will have very little yaw authority. Honestly, yaw is challenging to control even with four actuated surfaces.

Tsar Bomba and the B41 were technically 4.5-stage devices: (boosted) fission primary for the first 1.5 stages, fusion secondary, fusion tertiary, and optional fission(able) tamper. Both the two-stage W56 (MUCH smaller) and the B41 had a yield to weight ratio of approximately 5 kt/kg, although declassified documents suggest even potentially higher (and cleaner) yields. But whether you build a multistage device or just clustered smaller warheads, using that yield to weight ratio suggests you could potentially fit up to one gigaton TNT yield equivalent on a SINGLE expendable Starship.

It looks like it has a reasonable degree of passive stability. My suspicion is that with the gimbal kick from those engines it can perform the tail flip even if the aft fins aren't fully folded. Just might take a little more thrust than normal.

Yep, exactly. There is no theoretical upper limit to the size of a multistage thermonuclear device. With just the US, Russia, and China working together we could easily build a dozen gigaton nukes. Throw in nuclear engineers from Israel, France, and the UK and we can probably double our output. Ten years is a long time, even when you're dealing with interstellar velocities. I would say we could launch the first interceptor in under 24 months and send backup interceptors every six months thereafter. Ten years is not enough time to develop off-world closed-loop life support for any significant segment of the human race, however. On the other hand, if you specify that you already HAVE closed-loop life support available (moon or Mars base, for example), the hypo becomes much more interesting.

They won't do this. I agree. It's really nontrivial and the amount of back-and-forth they've done suggests it's still unsolved. Yep, I agree. God, I'm excited.

e cannot be changed but π could be different in a non-Euclidean universe. Of course if you define π as "the ratio of a circle to its circumference in Euclidean space" then that's unchangeable, although only tautologically.

That's the whole problem with controlling fundamental constants. It has to be a local effect or you break the universe. If you can screw around with fundamental constants locally, then you simply make curvature of the distortion field arbitrarily great.