sevenperforce

TEA-TEB was used for the dev Raptor, but the production raptor will use vapor ignition, probably with a couple of redundant spark ignitors. Vaporization of RP-1 to LEL is nearly impossible (that's why it's safer than petrol), but methane vaporizes easily and ignites readily. For example, any gas stove. So the engine can restart as many times as it wants, no ignition fluid required. Top off props and go.

And now I have a new craft project to do with my kids.

There's an old trope that's not entirely true but makes for relatively stimulating dinner conversation: Question: What part of the Space Shuttle launch vehicle is based on an animal's body part? Answer: The solid rocket boosters. NASA's SRBs remain the most powerful single rocket engines ever launched. The only question: why weren't they any larger? The SRBs were built out of segments that were each 3.71 meters in diameter. This diameter was chosen because it was the largest diameter that could be transported by rail through tunnels in the United States. Rail tunnels were built with just over 3.71 meters of clearance based on a 1.44 meter rail track width. US rail tracks were standardized at 1.44 meters in 1886 based on an 1845 British decision to standardize rail tracks at this width. The 1.44m rail width was designed to be just larger than the standard axles at the time, which were build to fit the existing ruts in roads around the country. Those roads were build by the Romans, who brought Roman wagons north from the European continent. Roman standard axles were based around chariots at the Circus Maximus and it was the widest axle that could be behind a two-horse chariot and not have wheel-to-wheel contact at the starting line. So the size of the Space Shuttle solid rocket boosters are dependent on the width of two horse's butts. Yeah, $5M/fairing is a nice chunk of change, but if cost for recovery is too much then sunk cost fallacy.

What is Mr. Steven's gross displacement, anyway?

I am sure that they will tear down the first recovered Falcon Heavy core for thorough inspection, just like they did with the first Block 5.

Of note -- methane pyrolysis takes place through a chain, as fusions yield successively ethylene, acetylene, and then finally carbon-carbon. While this takes place quickly, it is enough of a delay that total pyrolysis will happen well out away from the vehicle surface. We are talking about the return trip, right?

The atmosphere will be shock-compressed and undergo compressive heating. Some of that heat will mercifully be used up disassociating the nitrogen and oxygen into plasma. The rest will radiate away as a blackbody from the plasma in every direction. Radiation incident on the vehicle will heat the vehicle. Forcing methane through tiny pores accomplishes two things: first, it provides a heat sink to carry thermal energy away from the vehicle; second, it blocks some portion of the radiation incident on the vehicle. If the methane does pyrolize appreciably, that's a good thing, because carbon black is almost completely opaque to radiation and will pick up more than methane gas alone. Heh! Wasn't trying to snark; I was just saying that whoever that guy is, he's right.

"Someone on NSF" is correct.

Will the test launch carry crash test dummies to evaluate loads? The StarShip+SuperHeavy combo has taken this to the next level by using a single engine design for both stages. This was driven by reuse, to be sure---vacuum engines take up too much space, are too hard to cool, and are useless to land---but it also means a massively simplified production line. What's the closest we've ever come to getting a working transpiration-cooled active heat shield? Definitely insulating foam. On Elon time, which means fall at the earliest. The hopper is, as others have said, just a flying testbed for the engines. They want to test for a lot of things: pogo, turbine spin-up rates, throttle cycling, gimbal authority, and so forth. This is about validating the simulated aspects of the model before they start flying the full-size version. The fairing is much higher than it needs to be for aerodynamic and element protection purposes---the cylindrical portion is completely unnecessary---so I suspect that the sizing is intended to approximate the CoM of the larger vehicle so that they can get meaningful data from pitch correction on descent.

Foam hit the tiles on every launch. It was just a thing that happened. Slinging a crew vehicle alongside a launch stack rather than placing it properly on top was always going to be a risk. Columbia could have been saved, in theory, if the Shuttle had been designed from the ground up with an ejectable cabin containing closed-loop ECLSS and an integral single-use heat shield. But getting such a system to work properly would have introduced other failure modes. The chutes alone would have been a nightmare.

Incidentally I do not see any ducting for wiring, etc running through the rocket internally. They can slap it to the side, sure, but I somehow doubt they would. The fairing has legitimate purpose -- first, to protect avionics, fuel lines, and so forth from the elements; second, to give a nice draggy element for later tests. They will want to test engine-out landings at high drop rates; at some point they are likely to do an ascent, then either cut engines or throttle them way down to pick up speed. Having the fairing up top will help keep it radial-out.

I am sure they still need to slap the avionics package somewhere on top of that upper bulkhead, under the cone. Then they could fly it without the fairing, but the avionics would get wet. They may also be running RCS out through the sides of the fairing. Don't know if those holes are for fuel lines. Also don't know if they have built the ten-tonne-class hot-gas thrusters yet. They can fly without RCS easily enough (I don't believe the original Grasshopper had cold-gas thrusters) but they will probably want them at some point. They could also bolt nitrogen bottles to the top of that bulkhead and just run cold-gas thrusters through the holes as a stopgap. With the fairing being so easily removable (and, now, replaceable) I can see them doing some incremental upgrades as they fly.

My guess is that the "heat shield test" is really just them heating up a panel of steel on one side and then using a camera to measure radiative cooling on the other side. Alternately, they very well may have fabricated a laminated steel shield with (empty) cooling channels and they are testing its radiative and reradiative properties.

Probably a much poorer dynamic range than human eyes. Yeah, seeing artificial lights on Earth was clearly artistic license. I'm not sure about stars. If I was far, far better at math than I am (or had a few hours to devote to it), I could take the cross-sectional volume of Earth's atmosphere tangent to the lunar-facing disc and solve the Rayleigh cross-sectional scattering equation to determine the scattering angle and attenuation for visible-spectrum light at the lunar distance. This would give apparent magnitude of scattered solar insolation which would tell you how many stars would be visible.

Is it just me or is that a heat shield? Just you. That's the upper bulkhead. Which means we know that my first cutaway from yesterday was broadly correct: Should be able to firm up those internal dimensions nicely now.

I agree; single-pass, no circulation. I wonder what the radiative absorption properties of liquid and gaseous methane are like. You have an outer skin (the one with pores) that receives primarily radiative heating from shock-compressed air during entry. That skin heats and radiates in every direction, heating the inner skin. The inner skin is also heated by conduction at the contact points. The inner skin will likely also cool radiatively, sending radiation back into the tank itself. If liquid methane is fairly transparent to radiative heat but gaseous methane is more opaque, then the CH4 transpiring through the pores will be able to absorb both radiative heat from the shock-compressed air AND radiative heat from the outer layer of skin as the gas blows away. After a little digging, it looks like gaseous methane has a generally high transmission spectrum but has absorption peaks at 3500 nm and 7600 nm. Blackbody radiation at 1200C peaks at 2000 nm. Flexibility on that bulkhead is so cool to see.

I do not believe any blue will be visible at all. Here's a diagram. Scales are way off, obviously, but the scattering angle is also amplified so it works the same way: At (A), the moon is fully illuminated. At (B), we see part of the earth's shadow cast on the moon, but it is so bright that it washes out our ability to see red light cast on the moon. A lunar observer standing exactly on the terminator would see the sun blindingly bright at the edge of the Earth's disc. At (C), the moon is fully within the scattering-only region. The ring of atmosphere appears red because the light which is scattered at a low angle is roughly 20 times brighter than the blue diffuse sky radiation (skyshine has an intensity of 5% that of sunlight). Satellites, even geostationary ones, pass through the black triangle of total shadow and thus never would be able to observe the entire atmosphere at once, though there is a chance that geostationary satellites would be able to see a small ring-section of Earth's atmosphere glowing red for a longer time shortly after local sunset or just before local sunrise. At sunrise or sunset, we are able to get scattering from the light directly above us before the sun's direct rays reach us, which mixes things up. From the moon, you wouldn't see any of that; you'd only see the red light.

Primary cause of color in lunar eclipses is differential Rayleigh scattering. ISS and weather satellites don't get far enough from Earth to pick up atmospheric scattering at any point other than local sunrise and local sunset. 100% incorrect. It's not at all the color of the standard sky; it's red. That's why the lunar surface turns red. Rayleigh scattering scatters higher-energy photons at a higher angle than lower-energy photons. Example: White light, a broad spectrum of photons, enters the gem from the right. Blue photons are scattered in every direction, causing the entire gem to appear broadly blue in color, while red-orange light is not significantly scattered and instead passes through (with some refraction) to cast an orange glow. It's the same with the sky. The sky scatters blue photons, which makes the sky look blue, but the sun looks orange when you look at the light it casts on the ground. When it comes to a lunar eclipse, the Earth occludes ALL sunlight except for what is scattered, and almost all light is scattered at such a high angle that it cannot reach the moon. The only light that is scattered at a low enough angle to reach the moon is red, which is why the moon turns red in a lunar eclipse.

Is that realtime? I wonder if the motion of the satellite taking the imagery had anything to do with the appearance. At the height of totality, the atmospheric distortion could well be low enough that it would be much dimmer. During a solar eclipse you could see the moon's shadow cast on earth much more clearly than from, say, the Space Station. There wouldn't be a terrific light show or anything, but the sense of movement would be much more visible...watching your own shadow track across the Earth would let you sense your own movement through space. A glowing red ring in the sky might still be in the cards if you were looking while the moon was at the very center of the Earth's umbra. The NASA animation clearly showed too broad a dynamic range. No way any part of the Earth would be visible against that much of the sun's disc. But I played around with contrast and saturation to try and get a closer approximation of what it WOULD look like and I think it's closer: So a notably red ring is possible, I think.

I'm a little worried about steel's susceptibility to stress corrosion cracking. I worked in fuel transportation safety and steel pipelines are ridiculously vulnerable to SCC. Micrometeoroids may prove an easier problem with steel than with composite. Notes from Apollo indicate that they felt impact vulnerability was far lower with steel pressure vessels, though there was no other description. Of particular importance is the possibility that the double-wall design could act as a Whipple shield, thoroughly insulating the tanks from damage in all but the largest impact events. If so, I could see SpaceX deciding to do the double-wall etched design across the entire skin of the vehicle, even the leeward side, when building man-rated Starships (as opposed to tankers and cargo launchers). Obligatory: YES this would actually be a thing, I love it.

Even if they had moored it to actual sunk posts, the posts or D-rings could still have broken. They really needed guy wires for an object this size.

I'm sure there's a joke about deflated male egos and/or <<a certain blue pill>> in here somewhere. It blew over because it wasn't tied down. They had it tied to some weights. Not to anything actually fixed. REALLY stupid.

This one will not go suborbital -- unlikely to break 5 km. No need to go suborbital because they don't have the systems to test entry and descent anyway. But yeah, it potentially has a LOT of dV. My upper tank size was an upper bound, but if we assume that the upper bulkhead is mounted flush with those triangular supports rather than at the top of the base, that shaves off 72 cubic meters of volume. Let's round it up to 80 to account for volume displaced by the supports themselves. That puts a lower bound on upper-tank size at 361 cubic meters or 412 tonnes. At 3:8 (less generous from this perspective than @RedKraken) you get total prop mass of 520. With my dry mass that gives 7.1 km/s dV; with @RedKraken's it's 8.5 km/s.

For some reason I was thinking that the upper tank would be methane and the lower tank would be LOX (I guess I was thinking in terms of tailfirst stability on landing) but that's completely wrong. Upper tank (which will bathe those triangular members) is LOX, as with Falcon 9 S1 and S2; lower tank is methane. If mixture ratio is 3.8:1 and LOX is 2.4x as dense as liquid methane, then the volumetric ratio should be 1.58:1, which makes sense. That being said, the values above give a volumetric ratio of almost 3:1, which is twice what it should be. When I just measured and calculated, I got 264 cubic meters for the lower tank and only 441 cubic meters for the upper tank (9.76 in the lower tube + 43.85 for each 9x2 spherical cap + 343.5 for the central cylinder) which comes to a volumetric ratio of 1.67:1 which is within 6% of where it should be, which is pretty bloody close for a pixel-count from a blurry drone shot. Upper tank will hold slightly less propellant because it has those triangular supports in it, which brings it even closer to perfect. This would translate to an upper-bound fuel mass of 111 tonnes and an oxidizer mass (sticking with the 3.8:1 mixture ratio) of 421 tonnes for a total propellant mass of 531 tonnes. If we guess the hopper at around 75 tonnes dry, that gives us a GLOW of 606 tonnes. Three Raptors produce 611 tonnes of thrust. At a SL Raptor isp of 330 s, that's 6.76 km/s of dV.