sevenperforce

The orbit to which SLS can presently send Orion is precisely as useful as the orbit to which Delta IV Heavy sent Orion. Which is, to say, not at all. And what is SLS ready to be used for? Launching an all-up lunar surface sortie? Oh, wait, it doesn't have the capacity to do that. Launching a moon lander? Oh, wait, it doesn't have the launch cadence to do that. For SLS to do anything useful, it needs to be supported by commercial "replacements" to do everything it can't do. Which means we need to tackle those "deceptively large amounts of development" with or without SLS. The amount of "development" required to make SLS useful is arguably less than the amount of "development" it would take to order an expendable Starship to assume the role of the Ares V in a Constellation-style mission architecture. You could even slap Orion on top; there's plenty of margin. Don't bother man-rating it; just send crew up in Dragon.

The bios for each member of their "team" are just.....wow.

I have two I wrote for NASA/ULA and one I'm writing for Astrobotics/ULA so come at me bro

Uh, no. I'm going. I'm definitely going. That is now my plan. I'm going. Offer me a space on a lunar free-return in Starship? Hell yes; I'm in. I don't actually know anyone who is better at explaining science and spaceflight and the wonders of the universe than me. Nye, Tyson, and everyone else included.

That's the same image I used.

Wait, that can't work. The vacuum Rutherford only pushes 24 kN while the render (even at 4.2 m) puts the upper stage at around 89 tonnes. You'd need 10 vacuum Rutherfords to even get a TWR as high as the (very low thrust) Centaur. I think this is just a bad render.

Aren't all nine lit together from pad plumbing, to make the onboard TEA-TEB reservoir smaller? They've never lit two outboard engines alone without first lighting the center engine to give them gimbal control during startup transients. I wonder if they wrote the code to attempt a two-engine relight and hoverslam if the center engine fails to restart for a single-engine landing burn. That's the only time they'd have sufficient propellant margin.

They say they are doing kerolox. Electric pumps don't scale up well, due to battery weight. Yep, the Soyuz-TMA re-entry module is just three tonnes.

Someone pointed out that while RocketLab claims Electron has a 4.5-meter fairing, it also claims the overall rocket is 40 meters long, which would make the diameter as shown just 4.2 meters. Maybe the 4.5-meter fairing is aspirational? I also made a scaling error on Superheavy which has been corrected. At a tank diameter of 4.2 meters, the total propellant load of Neutron (both stages) shrinks to just 405 tonnes, which drops the GLOW to around 446 tonnes, which makes a little more sense. To match Falcon 9's TWR off the pad with just four engines, Neutron would need to develop 1500 kN engines. Which is still pretty significant. Of course, I doubt Neutron will be as sporty off the pad as Falcon 9, but still.

Correct me if I'm wrong, but I would think that successful restart of each engine is a single failure point for Falcon 9 recovery regardless of mission profile. If they are doing a three-engine burn it's because they don't have enough margins for a single-engine burn, so a failure of either outboard engine means they don't have the thrust they need. If they are doing a single-engine burn then they only restart the center engine, and if it fails to restart they're screwed anyway. The reason they always light the center engine first is to avoid bad juju during startup. This isn't like KSP where the engine roars to 100% the instant you stage; they have to spin up the turbopump and then start pouring in TEA-TEB and wait for a full, good ignition. There are timing variations (which, again, is why they lost the first Falcon Heavy core when the center engine took too long to start and they ran out of TEA-TEB for the other two engines). If they tried to light all three engines at once (or, worse, tried to light only the two outboard engines), then one of the outboard engines could reach full throttle before the other engine(s) had ignited, producing a massive amount of off-center thrust. Lighting the center engine first ensures that they have gimbal control alive and operating during startup transients. The impression I received from the explanation was that hot gas recirculation during the ascent caused a burn-through of the engine boot and triggered a commanded shutdown of that engine, resulting in the other 8 engines completing the ascent at higher throttle. When they attempted the restart for the entry burn, the damaged boot caused a thrust shortfall on that engine which was ultimately unrecoverable.

"Images courtesy of Kerbal Space Program"

A couple of added notes.... That helps explain why 8 tonnes seemed so low -- that's the reusable payload. Same ballpark as Falcon 9.

So let's talk about Neutron. Here's that comparison I know you all want.... They put the fairing diameter at 4.5 meters and their images show the fairing as being slightly smaller than the body of the rocket, but the rocket skin is probably a touch thicker than the fairing anyway so I'll just say 4.5 meters all the way down. It definitely looks like they are going with stainless steel construction aping Starship, which is fascinating. By pixel count, I'm getting the following height measurements: Stage 1 (total): 28.2 m Stage 1 (tankage): 25 m Interstage: 3.5 m Stage 2 (total): 7.3 m Stage 2 (tankage): 5.8 m I'm also getting a first-stage engine bell diameter of 1.4 m, though I don't really put much stock in that because it's the easiest thing to render. Assuming common bulkheads and nearly-flat spherical caps, that gives us an estimated volume of 397 cubic meters on the first stage and 92 cubic meters on the second stage. I doubt they'll be doing densified propellant, so with a bulk density of roughly 1.02 tonnes per cubic meter, that's a propellant load of 405 tonnes on the first stage and 94 tonnes on the second stage. Given stainless steel construction at a much smaller size than Starship, I'm going to ballpark a propellant mass fraction of about 92%, giving us a first stage dry mass of roughly 32 tonnes and a second stage dry mass of roughly 7.5 tonnes. With an 8-tonne payload, this would give it a GLOW of 546.5 tonnes, almost exactly the same as Falcon 9. In the render, the vehicle diameter is 323% the engine bell diameter. You can fit seven engines into a circle at 300% but there's no room for gimbal. Looking at that render closely, I'm actually thinking this is a four-engine first stage, perhaps with a central Rutherford engine for the landing burn like the LinkSpace design. This would mean the engines would need to have a SL thrust of around 1800 kN each. There's no way engines that size could fit in that tiny interstage with a properly-sized expansion nozzle, so I suspect they will do a pair of vacuum Rutherfords for the upper stage.

Yep. They were probably already throttling down the first-stage engines at that point so shutting down the bad one and throttling the others back up a little was likely easy enough. If this had happened earlier in the first-stage burn, they likely wouldn't have had enough propellant to even attempt an entry burn. With an engine-out in a nine-engine cluster in KSP, you'd probably need to shut down the opposite engine to balance thrust (even with Vectors) but I'm guessing Falcon 9 is able to keep eight engines burning since its TVC PID programming is much smarter than the SAS in KSP.

Yep. And with lower thrust due to the engine-out on ascent, the ascent burn probably took longer and cost a little more propellant, leaving it with even lower margins. Otherwise perhaps it would have attempted a single-engine entry burn. I just realized that given the core landing failure on FH1, the tipover on FH2, the core landing failure on FH3, and the intentional expenditure of the core for the upcoming FH4, it will be NET October of this year before we even have a chance to see a recovered FH core. That one is 6.35 tonnes to GTO so it should have no trouble reusing all three cores just as it did for FH2.

Same here.

All nine engines are lit on the pad using TEA-TEB plumbed from the ground. Only three specific engines are plumbed to the onboard reservoir of TEA-TEB needed for in-flight restart. When the first Falcon Heavy launch failed to land the core, it was because the onboard TEA-TEB reservoir ran dry just after restarting the core engine for the second time, meaning there was not enough remaining for the other two engines to relight. They fixed this in subsequent Falcon Heavy flights by making the core's reservoir bigger. So this is the problem. If Falcon 9 had lost one of the other four six engines on ascent, it would have been okay, but since it lost one of the intended landing engines, it was stuck. It can't choose other engines to relight because they aren't plumbed with TEA-TEB. I'm guessing they went ahead and tried to force a restart of the engine that previously shut down and its burn-through got worse. Starship, of course, won't have this problem because all of the Raptor engines use their own internal spark igniter and can relight at any time, independent of any other engine or system.

Well, if they design their own capsule then they already have multiple options for the service module engine and RCS thrusters -- Rutherford, Curies, or HyperCurie. But I suspect you'd want to get a stable orbit on the first two stages alone. Very crude render, but nbd. With no aero control surfaces, I wonder if they will try to build on the Electron heritage and use supersonic chutes to ensure good pointing and help reduce the necessary landing propellant. You have to have pretty precise targeting for a platform landing, though.

Yes, trying to trap one single hydrogen atom inside a buckyball certainly wouldn’t get you very far. It doesn’t matter how energetic your propellant is if you have an effective tankage mass ratio of 720:1. I’m more thinking about what could be theoretically possible on the very edge, regardless of whether we have any clue about how to actually pull it off. For example, what if we messed around with ionization? An atom (or even molecule) trapped inside a fullerine remains in place due to the quantum degeneracy pressure of fermion exclusion; the electron lattice of the fullerine is dense enough that the molecule cannot simply float through. What if we were to ionize a bunch of hydrogen atoms and trap their electron inside a carbon nanotube? The carbon nanotube would become negatively charged, attracting the free protons, but the protons would repel each other which would prevent them from entering. Once decomposition starts; this gives you both the ~4.3 eV from each pair of hydrogen atoms, but also the whopping 13.6 eV of ionization energy from each individual atom. If you were able to do this in a carbon nanotube lattice at even 25% hydrogen by weight, you’d end up with a propellant specific energy of 380 kJ per gram.

The way I'm reading it, they are abandoning IVF.

One of my physics professors was one of the first to really analyze the ionization behavior of endohedral fullerenes -- atoms trapped inside buckminsterfullerene: I wonder if it would be possible to trap monatomic hydrogen inside a fullerene-like molecular structure (it could be sphere, a toroid, or a continuous hollow web) in such a way that the hydrogen atoms could not react with each other, for whatever reason? Molecular hydrogen has an anomalously long bond length: about 1.8 angstroms, roughly twice as long as a covalent O-H or N-H bond. I believe molecular hydrogen is on the order of 7 angstroms from end to end. If you could place monatomic hydrogen inside a molecular substructure too dense to allow bonds to form, you could cram it very very full of the stuff.

Yes, I believe so -- 11k seconds wouldn't mean continuous.

Wow. It looks like SLS may never be the largest operating launch vehicle, if Elon can do an all-up Starship flight by the end of this year.

Well this is definitely not to scale. Centaur III is roughly 3 meters across. The two RL10C-1-1s on Centaur V ARE bigger than the RL10C-1 on Centaur III, but only slightly (157 cm dia vs 145 cm dia). Also I wasn't aware of this but it seems ACES has been entirely canceled. https://spacenews.com/ula-studying-long-term-upgrades-to-vulcan/

How much time do they need?