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18 minutes ago, Elthy said:

Maybe those are large flaps that fold outwards (hinge on the skirt). Those large, flat areas should be easier to shield from reentry than more prominent/protruding thinner legs like on the old renders.

I would hinge the leading edge, let it pop out 10-20 deg. with a telescoping, shockabsorbing 'leg' inside (= much wider base).

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1 minute ago, JIMMY_the_DOG said:

What's the difference between ITS and starship?

ITS was going to be 12 meters, carbon-fiber, with no wings, and primarily intended for Martian colonization.

Of course they had no budget for this and so they scaled back and built Starship. Originally designed to be carbon-fiber with PICA-X heat shielding as well, they switched to stainless steel and ceramic tiles because it works better and is a lot cheaper and easier to build. They added the flaperons to control attitude. Unlike ITS, Starship has valid use cases for LEO and cislunar activities.

Here's the image from the 2016 IAC showing those giant landing legs:

 

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4 hours ago, RealKerbal3x said:

the damage caused the propellants to ignite about 8 minutes later and boom.

That's 8 minutes longer than I expected given the earlier abort!

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4 hours ago, JoeSchmuckatelli said:

That landing sequence is not quite what I would expect - there is a lot of lateral movement for something so heavy.

It's fairly empty when it's only about to land. Large movement is what I expected. Plus they fired all three engines right from when it was parallel to the ground, and had only the engine thrust mostly to maneuver.

53 minutes ago, sevenperforce said:

If they had, there would be vertical crumple damage around the mouth of the engine bell.

That's only 1 engine out of 3... Touching might've been light on the forces since the side walls are still supporting some weight.

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4 hours ago, sevenperforce said:

What are we thinking in terms of actual mechanism?

My best guess is that when the legs failed to lock out properly, it came down hard on the engine bells and damaged the thrust puck. The impact probably ruptured the methane downcomer, allowing the remaining liquid methane from the methane header tank to mix with residuals in the main oxygen tank. The oxygen tank was basically a fuel-air bomb. Of course, no big deal...until the fire outside the skirt made its way underneath and up to the thrust puck. And then, kablooey.

If you go back about 5 or 10 or whatever pages, you'll see that I pointed out that the fire suppression system tailed off and ended. (Either they shut it off or they ran out of stored water.) Everything sat there for about another 5 seconds, then BOOM!

I still strongly suspect that there was an ongoing fire the entire time inside the engine compartment. But all that water was cooling everything down. Once that ended, temperatures rose inside and something failed. Whatever it was only needed the the fuel/air ratio to reach the right (ie. explosive) ratio, and then it exploded.

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5 hours ago, JoeSchmuckatelli said:

That landing sequence is not quite what I would expect - there is a lot of lateral movement for something so heavy.  I would have expected every frame to be moved up one spot with the final frame before landing being directly above the landed photo. 

Keep in mind that they have a really tough problem.

Their aerodynamic control authority only works when they are sideways. As soon as they start the flip, they are committed to 100% propulsive control. And like with any Kerbal suicide burn, that's a thing with very little margin. Burn too long and you run out of fuel and crash. Burn too much and you start going up. Burn too little or too late and you crash.

At least with Falcon the grid fins keep working almost all the way down to landing (although they lose control authority as the velocity decreases).

I think Starship is always going to be fundamentally locked into this almost-no-margin "do or die" pradigm. It's one reason I tend to wonder if it will ever actually be safe enough for people.

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Regarding the leg failure, does anyone know what the mechanism is? Hydraulic, I presume? Do they mechanically lock, or is that also hydraulic (if they are deployed hydraulically)?

What else is hydraulic? Engine gimbal?

Is there a chance the system had a transient pressure drop because of the change to a 3 engine flip, then rotating the 2 shut down out of the way, vs 2 dropping to 1, and somehow the deployment or locking was not to spec?

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e6zg1k89c2l61.png

This is an image from Maezawa's facebook page (apparently, I found it on reddit). It shows the landing legs a little bit more clearly, though I still can't tell whether they're F9-style flip-out legs or ITS-esque feet.

Just now, tater said:

Regarding the leg failure, does anyone know what the mechanism is? Hydraulic, I presume? Do they mechanically lock, or is that also hydraulic (if they are deployed hydraulically)?

What else is hydraulic? Engine gimbal?

Is there a chance the system had a transient pressure drop because of the change to a 3 engine flip, then rotating the 2 shut down out of the way, vs 2 dropping to 1, and somehow the deployment or locking was not to spec?

I vaguely remember reading at some point that they were mainly extended via gravity. I don't really know.

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9 minutes ago, RealKerbal3x said:

This is an image from Maezawa's facebook page (apparently, I found it on reddit). It shows the landing legs a little bit more clearly, though I still can't tell whether they're F9-style flip-out legs or ITS-esque feet.

They can flip out to leeward, no problem.

The "center" engine for the flip is the +Z engine, right?

      O
O        O

The top one when falling horizontally.  That top side is the leeward side, and as it flips, the leeward side then is lower WRT the ground than the windward side, as it burns to reduce the flip overcorrect.

So far, so good. It seems like if it contacts any legs first, they would be on the leeward side.

If the legs flipped down on that side—as "outrigger" legs, the belly legs could come down closer to the skirt line. It's asymmetrical, but I'm not sure that's a problem.

Edited by tater
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1 hour ago, mikegarrison said:

At least with Falcon the grid fins keep working almost all the way down to landing (although they lose control authority as the velocity decreases).

How much below terminal do the grid fins keep Falcon? 

 

Would a pair of pop-out fins perpendicular to the forward fins (even if merely passive) help with the final moments once flipped? 

 

Nvm - that would screw with the weight /COM

 

Rotatable fins? 

Edited by JoeSchmuckatelli
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Just now, JoeSchmuckatelli said:

How much below terminal do the grid fins keep Falcon? 

 

Would a pair of pop-out fins perpendicular to the forward fins (even if merely passive) help with the final moments once flipped? 

I've got no idea what the answer is to either of those questions, and I'm not going to just guess and pretend I know.

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3 minutes ago, mikegarrison said:

I've got no idea what the answer is to either of those questions, and I'm not going to just guess and pretend I know.

Yeah - as I think about it, once they're lighting the rockets, they really don't need some other aerodynamic system trying to compete.  Certainly would not help on moon or Mars 

 

I strike the question 

Edited by JoeSchmuckatelli
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1 hour ago, RealKerbal3x said:

e6zg1k89c2l61.png

This is an image from Maezawa's facebook page (apparently, I found it on reddit). It shows the landing legs a little bit more clearly, though I still can't tell whether they're F9-style flip-out legs or ITS-esque feet.

They're the same shape on the lee side and the windward side, so presumably they have a common design. The only way for the windward version to get out of the shielded fairing would be to extend downward first. So clearly they cannot be hinged at the skirt as with the F9 legs. 

So they may extend down and then out like the ITS legs. Or, they may extend down and then out, similar to the legs on New Shepard. 

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2 hours ago, mikegarrison said:

Burn too much and you start going up.

Also keep in mind that Starship can hover on a single engine, maybe two, so it’s not a full-on suicide burn. They are, however, very propellant limited right now, AFAIK these SNs cannot lift off with full tanks, no VacRaps, so that itself also greatly lowers their margins. The whole system will probably work better as, well, a whole system, including...

 

1 hour ago, JoeSchmuckatelli said:

Would a pair of pop-out fins perpendicular to the forward fins (even if merely passive) help with the final moments once flipped? 

We haven’t heard anything for a while, other than it’s been temporarily back-burnered, but SpaceX did/does have plans for hot-gas methalox RCS thrusters, which would greatly help with control during the flip. Now, hot-gas thrusters, a greater fuel load at landing ignition, and a whole bunch more flights to tweak the interactions of all of the above, now that the general concept has been proven, and things will look a lot less squirrelly. 

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1 hour ago, sevenperforce said:

They're the same shape on the lee side and the windward side, so presumably they have a common design. The only way for the windward version to get out of the shielded fairing would be to extend downward first. So clearly they cannot be hinged at the skirt as with the F9 legs. 

Not exactly. The belly side shows a single bulge across the whole bottom, vs two smaller ones to leeward.

(or did in the other new renders up thread)

Strike that, I swore they did, but I might have been doing a side by side with the old renders the other night, they look the same now.

Meanwhile in Starbase, TX, apparently SN11 heads to the pad Monday.

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1 hour ago, tater said:

Not exactly. The belly side shows a single bulge across the whole bottom, vs two smaller ones to leeward.

(or did in the other new renders up thread)

Strike that, I swore they did, but I might have been doing a side by side with the old renders the other night, they look the same now.

Some good notional renders from Twitter:

The fold-out legs a la Falcon 9 would be the simplest, sure, but they're also simply not possible because that would involve (a) a seam in the heat shield, and (b) the entire vehicle resting on the freaking heat shield tiles. 

His pop-out legs a la New Shepard are also a nonstarter because of the heat shield seam issue and because of load paths.

So the straight-down solution seems straightforward. It's also the most capable of auto-leveling and shock absorption.

ITS-style legs that descend straight down and then fold outward are another possibility.

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16 minutes ago, sevenperforce said:

The fold-out legs a la Falcon 9 would be the simplest, sure, but they're also simply not possible because that would involve (a) a seam in the heat shield, and (b) the entire vehicle resting on the freaking heat shield tiles. 

Those all have a seam (unless one is a cut-away diagram). The only way not to is the ITS style. It's not a problem to do F9 type if they don't have to be symmetric windward/leeward (leeward F9, others not).

Quote

His pop-out legs a la New Shepard are also a nonstarter because of the heat shield seam issue and because of load paths.

Yeah.

Quote

So the straight-down solution seems straightforward. It's also the most capable of auto-leveling and shock absorption.

This one:

Evq6voXWYAU4mcM?format=jpg

Still has a seam, though. Or is that supposed to be a cut away diagram the the gear are sliding underneath the cover?

Quote

ITS-style legs that descend straight down and then fold outward are another possibility.

Seems like a better idea, particularly if it can get a better stance on rough terrain.

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20 minutes ago, tater said:

This one:

Evq6voXWYAU4mcM?format=jpg

Still has a seam, though. Or is that supposed to be a cut away diagram the the gear are sliding underneath the cover?

I think this is the leeward view. The heat shield would cover the leg completely. 

20 minutes ago, tater said:

Seems like a better idea, particularly if it can get a better stance on rough terrain.

In three dimensions, there might be room to do something interesting. Two pistons that descend vertically and one that protrudes through the skirt (perhaps from the thrust puck) to the furthest extent of the foot.

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