sevenperforce

If it's one of the odd ones where they are putting 3 SSME at a slant, probably not. Maybe something with DIV tankage but with SSME on the bottom, and maybe a smaller DCSS... No, that was Shuttle-C, which was proposed in 1984 and mothballed in the early 90s but revived as the Shuttle-Derived HLV in 2009. The SDHLV actually would have been a reasonably good idea if we had needed expendable super heavy lift capabilities with Shuttle hardware. It would have been far more cost-effective than the Ares V: 89% of the LEO payload at 20% of the cost. However, we never really did need expendable super heavy lift after Constellation was canceled. Jupiter DIRECT would have taken a standard Shuttle stack, removed the Orbiter, and slapped adapters on the top and bottom of the external tank: a lower adapter to mount the three SSMEs and an upper adapter to mount Orion. Orion would have continued servicing the ISS all this time, using its service module to complete the orbital insertion and maneuver to the ISS. By now we would have had almost a decade of legacy experience with Orion. The concurrent evolution from the Jupiter-130 to the Jupiter-246 would have had significant heavy-lift capacity without the need to develop 5-segment SRBs.

Jupiter DIRECT. 'Nuff said.

I wish I could get Elon's attention to ask how the CH4 header tank is pressurized. There are three possibilities, really: Header tank pressed via main tank. Valves between header and main are closed at MECO Residual ullage in header provides inlet pressure for Raptor restart Valves between header and main opened immediately after restart Header tank pressed direct from Raptor via secondary line. Additional pressure to header from Raptor after valves between header and main are closed at MECO Residual ullage in header provides inlet pressure for Raptor restart Autogen press gas from Raptor maintains pressure after restart Header tank pressed by Raptor and by COPV via redundant lines. Additional pressure to header from COPV after valves between header and main are closed at MECO COPV line to header maintains ullage pressure after Raptor restart Autogen press gas from Raptor takes over once spun up I think the first possibility would definitely explain what we saw happen with SN8. There was just enough ullage in the header to restart Raptor, but with turbopump damage; the subsequent kick-flip produced enough inertia to maintain inlet pressure dynamically, but once the second engine shut down, the autogen press gas flowing into the main tank couldn't pressurize it fast enough to maintain pressure across the main-header valves. The second possibility would also explain it if the ullage pressure just wasn't sufficient to keep things operating until the autogen press gas started flowing. They could fix this by pressurizing the header tanks higher at MECO...I'm sure the header tank can handle 8-12 bar. I don't think Raptor will mind having a higher inlet pressure. The third possibility is clearly the safest but would require additional plumbing if they haven't already set it up that way.

I've been speculating a lot about the gas press system and COPVs, and I finally got livingjw to weigh in on the question over at the NSF forums. For those of you who aren't familiar, John is an extremely well-connected rocket scientist based in Florida who knows more than any one person fairly ought to. A couple of points: Autogen press gas needs to be piped straight from Raptor to the tanks at the highest temp possible, because the hotter the gas, the more space it will occupy and the lower ullage gas mass is required to maintain pressure. GCH4 and GOX COPVs are absolutely necessary. They supply the igniters, spin up the turbopumps at Raptor start/restart, and (eventually) will feed the hot-gas thrusters. They also provide ullage pressure to the header tanks prior to Raptor restart. For the COPV tanks, you want the GOX and GCH4 to be as cold as possible (without condensing) in order to store as much gas mass as possible, with pressure as high as possible, in tanks that are as light as possible. Because there's essentially unlimited heat in the preburner exhaust, the valves running from the regenerative coolant loop into the vaporization loop can be "throttled" to send more or less autogen press gas out. So there's a certain minimum amount running through a regulator straight to the tanks, and whatever is left would be passed through a coolant loop (probably using the CH4 downcomer) to reduce temperature before pushing into the COPVs. Here's a more detailed Raptor diagram that shows the hot press gas going out from vaporizing heat exchangers (in the fuel and oxidizer turbopump exhaust) to press the tanks, as well as the cold gas lines coming in from the COPVs. Not shown: the regulator that sends part of the hot gas into the tanks and the rest through a coolant loop and into the COPVs. This diagram suggests the use of helium for turbopump spinup but I believe John thinks they will use cold GOX and GCH4 for that. This makes sense to me as well. They will need GN2 to purge, though. Consumables, then, are GN2, LOX, and CH4. John pointed out that it's also possible to have a secondary vaporization line which sends the liquid methane and LOX through a shorter heat exchanger to vaporize only without superheating, and push this directly into the COPVs to avoid needing the coolant loop. I'm not sure which is more likely. He also argues that if you need to "restart" a Starship after a lengthy coast, you can have an electrical pump to send LOX and liquid methane directly into the COPVs and then use solar-powered electric resistance heaters to boil the contents and repress the COPVs. Very efficient, but I feel like incomplete vaporization might be a problem there, though. A faster method would be to use a dedicated burner and heat exchanger to produce warm GOX and GCH4 on demand. That's a good sign.

It distributes the force of the engines to the outer shell, which is the primary thing lifting the entire ship. So transitioning from engine thrust force to impact force would be natural.

The extension of the legs is limited by the clearance to the SL Raptor engine bells and their gimbal range. So trying to move anything else inside would seriously limit that. I don't think there's any harm in keeping the outer fairings; clearly this was contemplated by SpaceX early and so they've already done modeling for the heat shield and so forth. Once landed, the heel can indeed bear the entire weight of Starship. But the "feet" do more than just prevent tipover; they transfer the primary dynamic load of landing to the hydraulic pistons to the fairings. The heels only need to bear the static load. A member designed to bear a dynamic load requires much finer properties, and so this way the hydraulic pistons don't have to be actuated other than along the intended load-bearing vector. There would be minor refinements. Ultimately you'd have an intended design where the extended feet touch the ground first, transferring the dynamic load to the pistons like shock absorbers, and then coming to rest on the heels. Kind of like the way you land if you're jumping from a high place: you land on the balls of your feet and then come to rest on your heel. I would like to see a way to transfer the load to the thrust puck, since that's the way the rest of the ship is designed. Maybe something like this: However, this carries two problems. First, you're going to have a huge bending moment on the extending leg at its weakest point. Second, there's really no shock-absorbing role for the external pistons here, because the extending leg doesn't have free rotation. And you can't add freedom of rotation without screwing up the extending leg design.

So this is the top-down view of the header tank. Did...did the top just come off? Or does it fly like that?

Probably as wide as will fit, considering where they have to get clearance around the RVacs. They were inspired by this folding leg concept:

I was talking about the original bilateral-symmetry stainless steel renders, the ones currently on the SpaceX website. My proposal keeps the same outer mold line. Note also how there's space between each cargo bay and RVac for these "stiletto" legs to fold out. Let's see if it catches Elon's fancy.

Anything external only complicates TPS if you have to have a seam in the TPS. My model doesn't need a seam in the TPS. Okay, here you go. I think this would actually work. The "high heel" or "stiletto" has no hydraulics in it; just a spring and a crush core. The pistons on the outer fairings have hydraulics and crush cores. The only actuated part in the "stiletto" is the hinge itself. The pistons do all the auto-leveling and the springs in the "high heel" will compensate automatically. This design can handle coming down on one leg, on two legs, lateral velocity -- anything. Everything that contacts the ground is safely tucked up inside the skirt until it needs to be deployed. No seam in the heat shield.

I think I have an idea for how the foot could auto-level. Working on it now.

Kicking around some ideas for the Starship landing legs...what do y'all think of this? The internal legs rotate out just like the ones on SN5, SN6, SN8, and so forth. However, they are solid pieces of metal; no crush cores or auto-leveling elements. Each leg is paired with an external fairing like the ones shown in the renders on the SpaceX website. They contain a hydraulic piston with an internal crush core, just like the ones on the Falcon 9 first stage. This means that the most sensitive element -- those hydraulic pistons with crush cores -- doesn't have to rotate. The load path is split -- half against the base of the skirt, and half through the piston and fairing to the upper skirt. The hydraulic pistons can provide a degree of auto-leveling. The rotating joint is completely separate from the piston and so they can both be serviced/swapped out independently. Depending on how much internal clearance you have, the legs could even be much farther out...not as far out as Falcon 9, of course, but significant nonetheless.

I'm still seeing a 15-minute recycle. EDIT: Okay, yeah, that's a wrap.

Starship doesn't have enough dV for that. The Starlinks do. You can just dump the entire swarm in one eccentric orbit and they can all head off in different directions. You'd definitely need a separate bus.

I estimate the 260 kg spacecraft carries 33-60 kg of krypton, giving it 3600 m/s of dV. If it carried only hydrazine instead, it would have just 240 seconds of specific impulse which would give it 393 m/s of dV which is not nearly enough. Starlink is designed around its ion engine.

Dawn's three ion engines were gimbaled, which helped a little bit with attitude control and allowed for some assistance in unloading the reaction wheels. It carried 45.6 kg of hydrazine and it was nearly five times as heavy as a Starlink. So presumably a modified starlink with hydrazine thrusters for reaction wheel loading would only need around 10 kg of hydrazine. Or even less. I misspoke earlier -- the hydrazine thrusters were used for part of the orbital insertion at Vesta. It definitely needs the ion engine, though. The whole spacecraft is built around those engines. Nah, you wouldn't get any plane changes from the mothership. You'd simply use the mothership for the aerocapture into eccentric orbit, then release all the Starlinks so they could each do their own inclination changes independently.

Some amazing renders just to show how freaking huge Starship actually is...

Yes, absolutely. It would cost very little dV. Then aerobrake to circularize. MRO used aerobraking for circularization but it used its six large hydrazine monopropellant thrusters to provide all the dV for the initial eccentric orbital insertion burn. The Starlink satellites only have one ion engine. They have three reaction wheels. They would need chemical thrusters to unload the reaction wheels once they were out of LEO, though.

Yeah, the RCS was really only to unload Dawn's reaction wheels. The mission-ending failure happened when one of the reaction wheels seized and so it had to begin using RCS for pointing in that axis. Which, as I noted, is a problem for Starlink. Starlink uses a magnetic rod to unload reaction wheels, pushing against Earth's magnetosphere, but it can't do that outside of Earth orbit. Mars has no magnetic field. And I don't believe the sun's magnetic field is strong enough either...it's a lot stronger than Earth's, of course, but it's also a lot farther away. Earth's magnetic field drops from 0.5 Gauss at the surface to about 0.31 Gauss at an orbital altitude of 1,110 km, which is where the highest band of Starlink sats will operate. In contrast, even though the sun's magnetic field is twice as strong as Earth's at its surface, it drops to just over ten billionths of a Gauss at 1 AU, and even less at Mars. Well, the trick is the capture burn. To get from a Mars transfer orbit to a Mars capture orbit you need only 900 m/s...you need another 1400 m/s to circularize. There's no direct conversion from high-thrust to low-thrust transfers, but I know that if you're at EML-1, you can get a high-thrust transfer to GEO for 1,380 m/s and to LLO for 640 m/s. In contrast, a low-thrust transfer for those two maneuvers would cost you up to 1,750 m/s and up to 800 m/s, respectively. So if we assume the low-thrust penalty is on the order of 26%, that would mean a spiraling-out low-thrust capture at Mars would cost under 1,200 m/s, which is well within the capabilities of Starlink. Then it could circularize using successive aerobraking passes. If you do an aerocapture like this and enter a very eccentric Martian orbit, the cost of inclination changes to the individual Starlinks would be negligible. You could deliver a full constellation in a single mission.

Well that fracking sucks. Presumably a total loss. I suspect they will do a destructive cryo proof to see where it fails.

Love this render... A little more math... One thing I'm really curious to know is whether they were planning on a single-engine landing burn or a two-engine landing burn. My gut, even without doing maths, is that they were planning on a single-engine burn from the beginning, because that would give them the largest window for fine adjustments all the way down (hoverslams are hard). So the plan would be to use two engines to execute the flip, providing roll, yaw, and pitch control, and then shut down one engine as soon as roll was appropriately damped. Contributing support for this hypothesis: the engine that either flamed out or was shut down did so almost immediately after the flip was completed. In the view from beneath, you can really see how that engine damps roll and then immediately shuts down. Shutdown was almost exactly T+6:39.00, 1.33 seconds before my pixel-counting started (I needed the ground to come into view or it wouldn't have worked) and exactly 4 seconds before impact. The fire from the other engine was already green at this point, so we can assume it was already only providing a single gee of thrust. Thus we extrapolate back 1.33 seconds at 30.09 m/s to give us an altitude of 119.8 meters at the shutdown of that engine. Remember your kinematic equations: v2 = v02 + 2aΔx. So if you're 119.8 meters above the ground, dropping at -30.09 m/s, and you need to hit 0 m/s by the time you close that distance, what acceleration do you need? To counteract gravity and slow down Starship in a perfect suicide burn, the engines needed to produce 2.27 m/s2 plus the acceleration of gravity, or about 1.23 gees. That's not much thrust at all...clearly much less than would be expected if you were doing a two-engine suicide burn. Thus, I think we can safely conclude that they were intending a single-engine landing burn all the way down.

No, Dawn used ions at both Ceres and Vesta. However, their gravity wells are very shallow, and Dawn had already done a lot of the spiraling necessary to match orbit. Starlink sats could use aerobraking passes at Mars to circularize, but aerocapture would be a little more challenging. When you only have one pass you have to go hella low. Another issue with Starlink is that it has no way to unload its reaction wheels once it is out of Earth’s magnetosphere.

I could be wrong but I feel like that is the bottom end, where the downcomer attaches, and the downcomer simply sheared off entirely at the weld. Or it could be the top end. But if so, is it missing a cap? It wouldn't be much of a header tank if it was just open like that.

I did a careful pixel count of the entire descent from the first frame when the ground came into view, all the way down to impact, then converted to time and altitude based on measured pixel counts of the height of the rocket. Here's the raw data: Putting this into a scatter chart produces a pretty clear signal. It appears that for the last 2.5 seconds of flight, it was dropping toward the pad at an essentially constant speed, with the thrust of the dying engine exactly balancing the pull of gravity.

It's also entirely possible that they already have a separate autogenous press line running to the CH4 header tank and the valves remain closed the entire time after MECO, in which case it was a different problem. The more I think about it, the more I feel like the use of pressurant accumulator tanks will solve a lot of problems for Starship. They can feed the hot-gas thrusters directly and can provide full head pressure to the header tank even before Raptor relight. They'll need them for the landing engines on Lunar Starship, too, so why not just build them into the overall design?