sevenperforce

He said they would do dewar tanks for orbital ops to prevent boiloff but those will presumably be separate from the hot-gas bottles. Those legs scare me for even earthbound concrete-pad landings, let alone lunar or interplanetary ops.

I agree. I understand where their resources are being placed, but it was annoying to not have better renders of some of the critical areas, like the heat shield. It wouldn't have been too hard to add a honeycomb texture. Also, I think Elon mentioned once before that with the properties of stainless, they might be able to get away with only putting heat shielding on the very hottest parts of the windward side, so it may not even be over 10,000 tiles. I thought there were 21,000 tiles on the Shuttle but I just saw another source that said over 31,000. I believe the majority had to be removed, inspected, and reaffixed every flight. These definitely would not need to be removed and might not even need to be inspected individually. A lot of titanium, yes, but at least they don't have to do anything between flights. I'm disappointed by the renders. I think a lot of these details (like where the header tanks are) just aren't there. At least they appear to have abandoned the "land on launch clamps" nonsense. The narrow stance for Superheavy isn't a problem, I don't think. With hot-gas thrusters both fore and aft (Falcon 9 has only forward cold-gas) and multiple gimbaled engines for landing, plus a LOT of aft weight (the legs, for example, will probably weigh more proportionally than on Falcon 9), I don't see any trouble landing Superheavy. Starship is a problem. With payload up top and fewer engines in the back and those ginormous fins and that narrow, narrow stance...egads. They definitely need hot gas thrusters for days. It's a very kerbal thing, of course: if you lack control at some critical flight envelope, just throw on some more Vernors and be done with it. Speaking of which, the "turn and burn" approach makes more sense. I appreciated that he explained that. The engines only gimbal to 15%, so the flip adds horizontal velocity, which must be canceled before landing. You could correct this by using the control surfaces to orient almost nose-down before initiating the flip but that would end up accelerating you toward the ground, which you also do not want. I think I have a better idea how to pull this off in KSP, too. I am surprised they did not ever try a subscale demonstrator with SuperDracos or something.

I think they just don't have space for them to gimbal. If there was a vacuum Raptor failure, I think they'd just use the SL engines instead. SL Raptors have such a high chamber pressure that underexpansion losses aren't too bad. Ideally, you'd want a single gimballing vacuum Raptor in the center, so you could perform single-engine vacuum burns as efficiently as possible. The engines on the outside would be the SL raptors and they could gimbal in through the CoM or in parallel. But they didn't really have space for that, and putting the SL cluster at the center also allows for up to a double-engine-out landing, where the SL Raptor gimbals through the CoM alone and can still touch down safely.

I would say that if we're being technical, the control surfaces never leave aerodynamic stall. The body stays in a hypersonic lift state for most of entry, right up until the final "drop" from 20 km or so. But of course your point is right. I am surprised they have not yet gone to a cargo-bay approach, keeping the header tanks and other stuff in the nose as with the current model and doing a cylindrical payload section, including for the manned version. The hot-gas thrusters are pretty cool, though. I wonder -- if they put the meth and ox bottles up front, would the hot-gas thrusters be strong enough (and oriented properly) to provide abort capability for the crew cabin? One thing he didn't discuss in connection to the hot-gas thrusters is that the meth and ox bottles can be refueled with a simple pump from tap-off of the tank pressurant or from thermal vaporization of main-tank props. They seem to have wholly abandoned transpiration cooling plans, but I wonder if they might revisit a regenerative cooling approach. Weld piping along the stagnation path of the hypersonic flow and pipe cryo methane and LOX through to vaporize and thus sap heat. You need to vaporize props to keep the hot-gas thruster bottles full, after all. With similar channels on the leeward side, you could even use this system in space for power generation on orbit. Pipe liquid methane through the sunward side to vaporize and run a generator; pipe the methane gas through the leeward side to condense. Solar power without solar panels.

Yeah, that was interesting, though they tested some on the last cargo Dragon, and they attached some to Hopper (presumably for vibration, acoustics, etc). I can understand that the substrate (steel) can take higher temps, but you have to wonder about any adhesive used, strikes me that would perhaps be the limiting factor. That said, X-37 has some thinner ceramic tiles as I understand it. The ceramic/glass tiles will be bolted on, not glued on as with the Shuttle. As you know, the primary concern for the Shuttle tiles was foam strikes, because of the idiotic choice to sling the orbiter alongside a giant tank covered in icy flaky insulation rather than putting the crew vehicle on top where it belonged. But the adhesive was also problematic, and it was something like two man-years of work just for tile maintenance between each flight. Adhesive failure (caused during early flights because engineers would spit in the glue to make it easier to work with) resulted in multiple tile loss every flight. Not all the tiles were different shapes, but most were. Not only will Starship lack any problems with foam strikes, but it will also take fewer, larger tiles that are almost all approximately the same size. Because they will be bolted on, rather than glued, it will be easier to replace and inspect. As shown by this image of the way they were affixed on Starhopper, they will simply be affixed by transplanar bolts: Presumably the bolts will run to nuts welded onto Starship's outer skin. THAT will be a lot of work. By pixel counting, each of those tiles is roughly 31.5 cm across horizontally, or 863 cm2. A 50-meter-high, 9-meter-wide vehicle has a cross-section on one side of 834 square meters, not counting the Plasma Deflector Shields or Squid Fins. Let's round up to 1000 square meters to account for those control surfaces. So we're looking at roughly 11,600 tiles. Maintenance on 11,600 identical bolted-on tiles should be easier than the Shuttle's 21,000 varying-geometry glued-on tiles. Welding on the 35,000 nuts will be a pain for sure, though. My guess is that the size of the tiles is as large as they can get while still ensuring that the loss of any single tile will not be catastrophic. It's particularly significant that bolting the tiles on will make it impossible to have a "zipper" failure, which was always a dramatic concern for the Shuttle. I suspect they are still iterating leg design. The current legs on Mk1 are simply steel I-beams enclosed inside those little tack-welded fairings; they're definitely not retractable or extendable. We may see them swap these out for this version before it flies, or we may see them jack it up and add crush cores underneath and then fly. Elon definitely made it seem like the chances of Mk1 or Mk2 ever going to orbit are very low, so I wouldn't expect to ever see thermal tiles coating this particular vehicle, although the "belly band" may be a place where we see them test the tile attachments. Landing legs will likely be identical on both windward and leeward for Mk1 and Mk2. With Mk3 and Mk4, which will have full heat shields, we'll see a different shape on the windward side to minimize sharp edges. They may go with fixed-column legs on the windward side (as shown in current renders) and fold-down or push-out legs to leeward, just to give a little extra stability. It was interesting that Elon said he wanted to try and skip the entry burn for Superheavy, as planned for New Glenn. With 301 stainless it should be easier to buff up the base. I don't know what I think about those legs, though.

I would have to look closely at the fission products of various uranium or plutonium reactor designs in order to get an idea of how lightweight the barrier metal would need to be. It is a shame that there is no antonym of "dense" other than "lightweight" which is really an antonym of "heavy".

They are lifting the nose cap into place right now. Am I the only one rather extremely concerned about the tipping moment on those little legs? The ground spread is even smaller than on the 2017 IAC version.

If you have molten uranium and molten hafnium/molybdenum in the same cylinder being centrifuged, the higher density of the uranium will force it to the edge while the barrier metal will "float" in an inner cylindrical layer. Same temperature. The uranium will heat the non-radioactive barrier metal; the barrier metal will heat the hydrogen. I probably should have done a mockup.

Yep. Of course if SpaceX was allowed to build Dragon 2 in the middle of a field it might have been flying crew for two years now......

Does anyone have eyes on legs yet?

In the zoomed view, it almost looks like the fairing might slide down some distance over the base.

Lowering. Looks like there are people who are going to be stuck inside....

It is lifting. Nearly level with the top of the tank half now.

Is it just me or does it look like the "slot" for the Squid Fin actuators is on the windward side?

Better to have horizontal intake fans that can be ducted downward for ground operations, lift off that way, and then reorient the duct for forward acceleration once airborne.

You know, it just occurred to me – why do we need to have the “shell” be solid at all? Build an actively-cooled cylindrical thrust chamber with a layer of uranium enclosing a layer of a less-dense, non-radioactive metal like hafnium or molybdenum, hollow in the center. Withdraw the control rods or add the reflectors (or however you want to do it) and let it start to heat up, while centrifuging the whole affair. Eventually, the uranium will melt. Then the hafnium will melt. However, because uranium is so much denser than hafnium, they will remain separated by the centrifugal forces and thus the uranium will never be in direct contact with the propellant flow through the center. The reactor can run all the way up to the boiling point of uranium metal (7100 C) with all the heat going by direct thermal transfer straight into the hydrogen propellant. Critically, the propellant never touches the uranium and so there is no significant radioactivity in the exhaust, just like with a solid-core NERVA or a graphite pebble-bed. Ve2 ∝ Rgas*Tc and we know that a bare-metal liquid core at 3000 K has a specific impulse of around 1600, so this design would be able to push up to a specific impulse of 2500 seconds. Assuming you can get off the ground (a LOX-afterburner, water injection, and/or ejector shroud come to mind), you can reach LEO with margin to spare and a 32% fuel fraction.

They have tack-welded the chines on the windward side of the starboard aft fin. This is a battleship version. Way heavier than it needs to be. And it can still get to an orbit and return, even if it's not a useful orbit. That's what prototypes are for.

When hydrolox is burned at stoichiometric ratio, it burns notably (though not vastly) hotter than the maximum operating temperature of the SSME. The lower temperature used in the SSME did help keep the engine cooler and reduce stresses, but the primary reason for the lower temperature was to add more hydrogen to the propellant flow. By adding more LOX, the engine could have burned hotter (with additional, though not prohibitive, active cooling), but pushing less hydrogen at higher temperature would have resulted in lower bulk specific impulse than pushing more hydrogen at lower temperature.

They plugged the dorsal hole in Starship overnight: Looks like a connector for fueling, potentially?

Remember that SL raptors have a significantly-increased vacuum thrust. It's not 330 s all the way up.

A solid-casing molten core NTR has the same operating temperature as a vapor core rocket but it's heavier. Most liquid-core designs, however, do not have solid casings. Rather, the molten fuel is centrifuged to keep it inside the thrust chamber while the liquid hydrogen is pumped through and heated by direct contact with the fuel. The outside of the chamber is actively cooled. This allows a much higher operating temperature than a gooey pebble bed or solid-casing molten-core rocket, but you do end up with uranium in your exhaust, which is generally not desired.

You're right -- there aren't many advantages for a vapor core over a molten core, and the limit is the melting point of the case. There are, however, a few advantages. A vapor-core rocket uses uranium hexafluoride gas, which can be more easily removed for reprocessing than liquid. It's also lightweight in comparison to a molten-core NTR. As Project Rho explains, the benefit of building a vapor core is learning how to build a nuclear lightbulb, which is where the real magic happens.

So those triangular things were definitely the transitional element from the top of the wing to the raceway. They are longer on one side than the other. Although it is not yet light in Texas, you can see that at least one of them was installed last night. Starship isn't meant to reach orbit without the booster. This is still an orbital prototype, even if it will initially be flown without the booster and thus suborbitally. It's as if they had used Columbia rather than Enterprise for the initial Shuttle flight tests.

A rather large challenge for SSTOs is always going to be re-entry and landing. How do you get back down? How do you land? Using a very large VTOL intake fan is a large weight penalty, but if it obviates the need for wings, wheels, or landing burn propellant, then maybe it's a good trade-off. If that same intake fan can be used to force air through rocket ducts to add thrust at liftoff and reduce the need for bigger/heavier engines, all the better. But remember that an intake fan, even one pointing into the airstream, is only going to be useful from Mach 0 to Mach 2 or so (it's useful beyond, but only marginally). And you need to make Mach 25 to hit orbit. Simply using a ducted rocket engine is going to give you many of the same advantages and a much greater useful envelope. Why make it a saucer? Is there some particular purpose, like volume concerns?

The amount of thrust that can be provided by a fan scales as a function of the area of the fan. Intake fans work best when they are facing the airstream. Their efficiency, however, drops rapidly with Mach number. Once you are above Mach 1.5 you are better off relying on ram effect. You've got it flipped. You want to use methane as your launch fuel because it is denser and will provide better T/W; you want to use liquid hydrogen to finish your ascent and provide all your burns in vacuum. An ideal nuclear SSTO would lift off pushing water or hydrazine through the engine, transition to RP-1 once well in motion, transition to methane during the final boost out of the atmosphere, and finish the flight on hydrogen. That way you have constant volumetric flow but a mass flow that decreases as your need for thrust decreases, and a specific impulse that increases as it becomes more important. Of course the tankage for this is stupidly difficult so that wouldn't work well for those reasons. Another good option is to have a constant-flow liquid-hydrogen NTR with a LOX afterburner and drop tanks for the LOX. At liftoff, you inject LOX into the engine bell downstream of the throat to boost your thrust tremendously and to prevent overexpansion and flow separation. This gives you a higher T/W ratio than what is standard for NTRs. You decrease the LOX flow as you ascend to match the desired expansion ratio, and then you eventually drop your LOX tanks (they will have a high ballistic coefficient and can be chuted down into the ocean for reuse) and proceed to orbit on hydrogen alone.