sevenperforce

This is why I still pine for Jupiter DIRECT. They could have done a much lighter Orion/MPCV to service the ISS with a service module large enough to fill the role of the OMS engines on the Shuttle. Same launch profile as the Shuttle (perhaps only with two SSMEs per launch), with the core ending up in an atmosphere-crossing orbit and the service module providing the remaining 300 m/s or so for LEO. Add an ICPS-sized second stage with everything else exactly the same, and Orion could co-manifest new modules to the ISS using the old Apollo flip-and-dock. Using an ICPS-sized second stage (and, again, NO other LV upgrades) and an upgraded heat shield, you can test a lunar free-return by using Orion's SM to complete TLI. With a slightly larger second stage and perhaps an extra SSME, you can use this Orion Lite with the upgraded heat shield as a minimal human taxi to NRHO. On a vehicle that's almost totally Shuttle-derived, without all the dev costs that SLS has incurred over the years.

Do you mean AJ-260?

They don't want to damage the pad. Remember there's no deluge system for sound suppression here. On that note -- I really do not understand how Elon could possibly think that they will be able to get away without a water deluge system on the orbital pad. For tests with BN2, sure? But for orbital flights we are talking about even more thrust than the Nova rocket (with eight F-1 engines). The Apollo 4 launch of the Saturn V without a sound suppression system seriously damaged Pad 39A. I can't imagine that the orbital pad will survive even a single unprotected Superheavy launch.

If SLS launches before Superheavy then it will briefly have the highest thrust of any rocket launched from US soil. SLS will be the highest-thrust hydrogen first stage ever (it's 22% higher-thrust than the Energia core). So I guess that's impressive, for what it's worth. And of course they do have the thrustiest boomsticks of all time, as pointed out by @tater and @wumpus and @RealKerbal3x. I suppose you could say that SLS has all the best parts but it's a situation where the whole is less than the sum of the parts. A hydrolox stage-and-a-half design is just an inherently crippling design.

Yeah, that's what I was going to say. Obviously the N1 didn't get very high but it certainly launched, and it made both Saturn V and the SLS look wimpy. The RL10C-3 is just 230 kg; four of those mass about half what the J-2 massed. I suspect @RCgothic meant that the wet mass of the S-IVB was lower than the wet mass of the EUS. The EUS is going to carry around 129 tonnes of propellant; the S-IVB only carried 109 tonnes of propellant. I suspected the Saturn V's second stage did much more to get the S-IVB nearly to orbit than the SLS core will do to get the EUS nearly to orbit. I don't know what the dV deficits are, though.

If we make it to Artemis 5. By 2026 I would be shocked if we don't have the fixed-thrust, non-gimbaled Raptors already operating. At 2.94 MN, those will be 53% more powerful than the proposed RS-25E.

Total first-stage thrust at liftoff: Falcon 9: 7.6 MN Delta IV Heavy: 9.42 MN New Glenn: 17.1 MN Falcon Heavy: 22.8 MN Long March 9: 24 MN Space Shuttle Stack: 30.3 MN Energia: 34.8 Saturn V: 35.1 MN SLS: 36.6 MN N1: 45.4 MN Superheavy: 76 MN I did not realize SLS will actually have more thrust at launch than the Saturn V. I also did not realize that Superheavy literally has more than twice the thrust of SLS. The equivalent of ten Falcon 9 boosters strapped together.

In August 2020, a Raptor on a test stand achieved 330 bar chamber pressure with thrust levels of 2.21 MN, at sea level. Maximum sea level thrust for the RS-25D at 109% power is 1.86 MN. So Raptor is already about 19% more powerful than the most powerful RS-25 configuration.

It's just insane to me that Raptor has significantly more thrust than the RS-25 in a package that is that much smaller. I've stood right next to the one they reconstructed at the Smithsonian and it feels like it should be closer to the thrust of an F-1 than to the thrust of Raptor. If you put a SL Raptor inside the RS-25's nozzle, it would only protrude by 28 cm. Then again, I suppose the RS-25 really isn't nearly as "large" as it looks since that is really a vacuum nozzle. Well that's horrifying.

It may be that going heavier than 13 tonnes all-up would run into problems for using the Dragon 2 system. Those four inline Draco thrusters will already have to do a half-hour insertion burn at NRHO. If they increased the mass much more, they would eventually have to start adding new inline thrusters, additional control thrusters, and do a complete avionics overhaul. Staying with 13 tonnes allows them to use exactly double the number of propellant tanks, with the exact same docking port and inline thruster configuration as Dragon 2. I feel like Dragon XL is really a stopgap to allow them to compete for Lunar Gateway operations until Starship is up and running. They didn't want to develop an entirely new vehicle. I don't see why they wouldn't pressure-test it. Even if BN2 has a wildly different thrust puck design or something, there would surely be some value in pressure-testing to validate the rest of the design. Unless I miss my guess this is already the single tallest liquid rocket stage ever constructed. It is definitely the first one anywhere near this size made of stainless steel. What kind of forces do you get with a structure that massive? Do you get resonance issues during cryo press? How do the stiffener rings hold up? I doubt they will ever fire it but I predict they will test transportation and they will do a nitrogen press test. If that goes smoothly they might do a cryo proof and then a destructive nitrogen test. I'm glad MK1 blew up. Those forward fins looked horrible.

I don't think so -- krypton thrusters are much flatter and concentric: These look more like star trackers, intended for navigation: I just can't imagine needing that many of them in that small of a space. Is it a berthing port or a docking port? It looks pretty clear to me that it's a docking port.

Interesting that it appears to have a Canadarm grapple target on the side for berthing but an LIDS/NDS-compliant docking port on the nose like Dragon 2. Does anyone have any idea what the three white boxes on the outside are supposed to be? Is that radar or coms? And what is that half-ring of six black cylinder things? Presumably they are sensors of some kind, probably star trackers, but why would you need that many of them in that kind of cluster? It looks like there are no aft thrusters so Dragon XL will have 12 Draco thrusters on its body plus the four inline thrusters around the docking port, just like Dragon 2. Dragon 1 had 18 thrusters. @Barzon said upthread that Anatoly Zak puts Dragon XL at 13 tonnes. I'm assuming that's the full mass with payload injected by FH onto TLI, including props and payload. Getting from TLI to NRHO efficiently requires a 180 m/s burn during the lunar slingshot and a 251 m/s insertion burn at NRHO. Those four inline docking port thrusters generate a combined 1.6 kN which is...............not a lot. The burn at flyby will take 24 minutes and burn 782 kg of propellant. The insertion burn will take a whopping 31 minutes and burn 1,013 kg of propellant. That's already significantly more propellant than the 1,388 kg carried by Crew Dragon. If we assume Dragon 2 needs another 350 m/s of dV or so for docking, orbital maneuvers, and disposal/deorbit, then we are looking at another 1,160 kg of propellant. If it can deliver around 5.5 tonnes to the Lunar Gateway then that puts its dry mass at around 3.5 tonnes. Dragon 1 had a dry mass of 4.2 tonnes but that included the heat shield. Given that the total amount of propellant Dragon XL needs is just slightly greater than double the propellant capacity of Dragon 2 (and my estimate of 350 m/s for disposal is probably generous), SpaceX may simply reuse the exact same propellant tanks as Dragon 2...just in pairs.

Aiming for an orbital flight with SN20 and BN3 by July 1? Insanity. But the good kind.

Is it possible to do an autogenous pressure-fed methalox expander cycle? E.g., you use part of the LOX to cool the chamber, allow it to expand, and then pipe it back to the LOX tank to maintain pressure. Same with CH4 but you use it to cool the bell instead. I don’t think that would work. But maybe? It seems like you wouldn’t be able to get a continuous pressure drop. If not, then maybe you split the autogen gas from the expander outlet...half is pushed through a low-temperature turbine and dumped downstream in the engine bell and half is pressed by the turbine and passed back to the tanks. It would not work for huge engines due to the inherent square-cube issues of the expander cycle but it could be good for small engines, like a lunar lander. The simplicity of pressure-fed engines and a low-temperature turbopump would be pretty reliable. Maybe they could even mix some TEA-TEB into the methane to bypass having an ignition system altogether. Then you could just have solar-powered resistance heaters to make sure your tanks are fully pressed, since they are autogenous and pressure-fed. You could refill the tanks as many times as needed.

@tater — is right, this shows the leeward side for the sake of detail. On the windward side, the footpad will be covered by the heat shield in the stowed position. I suppose the lee side could be covered by a stainless steel fairing if needed but I doubt it is needed. This whole design is intended to allow the footpad to slide down vertically, out from under the heat shield, and then rotate to meet the ground.

One of the most expensive software errors in history. The Ariane 5 re-used the code from the Ariane 4, which had a particular 16-bit variable set to represent the vehicle's pitch. Unfortunately, the Ariane 5's updated code used a 64-bit measurement for increased precision and they forgot to remove that part of the Ariane 4 code. Initially, the 64-bit measurement converted quite readily into the 16-bit variable, but at 37 seconds into flight the 16-bit variable overflowed, defaulting to a diagnostic value intended for pad checkouts. This sent a signal to the engines that the rocket was still perfectly vertical on the pad, and all three sets of engine gimbal actuators immediately tried to push the rocket "back" to its correct downrange pitch. Of course this just made the rocket pitch down toward the ground and aerodynamic forces ripped the stack apart 2 seconds later.

So this is the best leg design I've been able to come up with so far. It solves some of the biggest challenges overall: No seam in the heat shield, just a heat shield blister as depicted in the #dearMoon concept art No break, slot, or hole in the skirt Load path passes through the same skirt mounting points where it attaches to Superheavy Fully stable in the roll axis (no risk of buckling) Widest possible footpad area for landing on Martian (or even lunar) regolith Fairly minimal volume used inside skirt Fully self-leveling and shock-absorbing; can accommodate multiple piston failures All load-bearing actuators take purely vertical loads The only thing I'm unsure about is the actuation of the rotation. That actuation doesn't take any load (it can lock out like the current legs) and so the actuator can be extremely small; I'm just not quite sure where to put it. Spoiler for full-size image and legend.

The second burn. It was so short the bell didn't even glow. EDIT: Here's the burn. The startup appears to be longer than the burn itself. Incredibly precise. It's also really really cool to see that tiny chunk of ice suddenly break free under the acceleration, tumble down the engine bell, then get yeeted off into the cosmos by the exhaust plume.

No

That was the shortest MVac burn I’ve ever seen.

Ah, yes, I didn't think about the long gas flow path. But yeah if you do it that way you don't even have to cut the tiles. Just have them extend inward. You would simply omit tiles that were completely shrouded by the leg.

But why would you need the tiles underneath? If the outer part can be folded flush against the tank then it provides all the TPS for that region.

Starship needs to be able to come down on any of the three Raptors; that's the whole engine-out idea (and the reason they went from the 2017 IAC design with 2 SL Raptors to the present design with 3). Also, the offset center of mass with the tiles installed sits opposite the single dorsal engine, between the two ventral engines.

This was back when they were exploring transpiration cooling rather than the heat shield tiles, but the same principle applies for the leeward side. He's talking about re-entry, though. Not interplanetary transit. I don't think the weight offset from the tiles is significant.

If they fit tight enough to prevent gas entry then you don't need any heat shield underneath. I mean, I suppose that's the brute force solution. Use F9 legs covered in reinforced carbon-carbon instead of just the ablative black paint on the current F9 legs. They close flush to the stainless steel skin all the way around and you simply cut the tiles to wrap around them. Simple enough. You don't even need to bother with a bulge.