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Are you people not aware that the FAA was just put through the wringer by Congress and the press for not being rigorous enough at independently doing their own safety analysis work?

This is a really bad time for somebody to ask the FAA to sign off on stuff, especially if they just say, "trust us, we're the experts, we know what we're doing".

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26 minutes ago, mikegarrison said:

Are you people not aware that the FAA was just put through the wringer by Congress and the press for not being rigorous enough at independently doing their own safety analysis work?

This is a really bad time for somebody to ask the FAA to sign off on stuff, especially if they just say, "trust us, we're the experts, we know what we're doing".

Very good point, I hadn’t correlated how badly they were stung by the 737MAX debacle with being asked to approve an experimental rocket vehicle for flight

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1 minute ago, StrandedonEarth said:

Very good point, I hadn’t correlated how badly they were stung by the 737MAX debacle with being asked to approve an experimental rocket vehicle for flight

Bureaucracy works like the old fable of Happy Jack.

Take contextual lesson learned from last failure, and apply it to new unrelated problem.

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1 hour ago, Wjolcz said:

I'm planning to make something like this in KSP

I made a Starship (sort of...) replica in KSP when Breaking Ground released. Actuated fins, landing legs on the lower fins, etc. Found two BIG flaws with this design: the first one is landing on actuated fin-legs. They are attached to the main body by hinges. These hinges are the weakest link. There was a LOT of stress put on those two poor hinges from all that Starship weight. Sometimes they just fell off. Other times they bent horribly. This might translate to IRL Starship, those actuated hinges need to survive the landing and then support 100+ tons, possibly twice that with cargo and people, and not break. If one hinge fails, then the entire thing will likely fall and explode hilariously. Happened more than once to my KSP Starship. I think that fin-legs are a major failure mode.

Second flaw is that it just doesn't want to make the final flip reliably. I had to add airbrakes to the bow to make it happen.

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5 minutes ago, sh1pman said:

This might translate to IRL Starship, those actuated hinges need to survive the landing and then support 100+ tons, possibly twice that with cargo and people, and not break. If one hinge fails, then the entire thing will likely fall and explode hilariously. Happened more than once to my KSP Starship. I think that fin-legs are a major failure mode.

IRL, flight vehicles landing on hinged landing gear is pretty much standard.

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Posted (edited)
16 minutes ago, mikegarrison said:

IRL, flight vehicles landing on hinged landing gear is pretty much standard.

Sure, but in my experience it was the torque that screwed things up. When Starship is standing on the ground, its mass is concentrated in the center, while the three legs are some distance distance away from center. This caused the fins to bend outwards, somtimes even to fall off from the stress. IRL landing gear on aircraft is usually located under the mass that it is supporting, so there shouldn't be any outward force. Provided the wing structure is sturdy enough, of course.

I not 100% sure in any of that, though, I'm not an aero engineer. Maybe in KSP hinges are super-weak or something.

Edited by sh1pman

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Landing gear is usually the strongest (and heaviest) individual part of a vehicle. It's not really the kind of thing KSP is good at modeling.

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@sh1pman All I can think of is this-

six_words.png

KSP is lacks so many elements of real world physics and even on the things it does have, it either does it poorly or does it unreliably. It has some good factors (orbit, burns, etc). But the point here being- don't simulate anything in KSP and make a judgement call for reality.

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4 minutes ago, ZooNamedGames said:

@sh1pman All I can think of is this-

six_words.png

KSP is lacks so many elements of real world physics and even on the things it does have, it either does it poorly or does it unreliably. It has some good factors (orbit, burns, etc). But the point here being- don't simulate anything in KSP and make a judgement call for reality.

That’s why I said it *might* translate to IRL Starship - because I’m well aware of this particular xkcd piece. I first learned about KSP from it, actually.

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15 minutes ago, sh1pman said:

That’s why I said it *might* translate to IRL Starship - because I’m well aware of this particular xkcd piece. I first learned about KSP from it, actually.

Me too!

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3 hours ago, sh1pman said:

Sure, but in my experience it was the torque that screwed things up. When Starship is standing on the ground, its mass is concentrated in the center, while the three legs are some distance distance away from center. This caused the fins to bend outwards, somtimes even to fall off from the stress. IRL landing gear on aircraft is usually located under the mass that it is supporting, so there shouldn't be any outward force. Provided the wing structure is sturdy enough, of course.

I not 100% sure in any of that, though, I'm not an aero engineer. Maybe in KSP hinges are super-weak or something.

The hinges on starship is 90 degree to the landing stress they can also flex a bit. the outward bend is absorbed by internal bracing, you might remember the triangle inside the hopper tank. 

Airplane landing legs are way more complex as they has to fold up. On large and heavy planes you tend to have to fold the wheel boggy at bottom to 

KSP hinges are weak  

2 hours ago, ZooNamedGames said:

@sh1pman All I can think of is this-

six_words.png

KSP is lacks so many elements of real world physics and even on the things it does have, it either does it poorly or does it unreliably. It has some good factors (orbit, burns, etc). But the point here being- don't simulate anything in KSP and make a judgement call for reality.

Funny as that looks like an Jupiter gravity assist to get an close flyby of the sun, this works just as well both in KSP and real world. 
Yes in KSP you don't have to worry about radiation from Jool nor the cold and lack of sunlight out there while an RTG would have issue close to the sun. 

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9 hours ago, Wjolcz said:

I'm still wondering how will they transport the fully assembled rockets and starships? They can't just lay them horizontally, can they? And transporting it horizontally will be quite a challenge.

Potentially relevant:

 

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4 hours ago, sh1pman said:

If one hinge fails, then the entire thing will likely fall and explode hilariously.

(Don't know a math sign for "A is_better_than B")

So, 6 > 4

Spoiler

landing-gear.jpg

 

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More legs is heavier, so that's an arbitrary assessment of "better".

Five legs is the minimum that can tolerate one failure on a reasonably flat surface.

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Posted (edited)
5 hours ago, RCgothic said:

More legs is heavier, so that's an arbitrary assessment of "better".

More legs are thinner, so not so heavier. But if 1 of 6 breaks, other 5 will stay.

1 / 5 = 144° gap, 1 / 6 = 120° gap.

Only 6.

8 are worse, but not because heavier, but because too thinner (remember Knipkamp chassis).

Edited by kerbiloid

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SpaceX appears to be beginning construction of the first Super Heavy prototype at their Florida site, alongside the Mk1 Starship that is being built there. As the Teslarati article notes, there are enough steel rings to build Starship Mk1 to about 120% of its planned height, so these new rings are probably segments of Super Heavy, or maybe another Starship.

Cocoa-orbital-Starship-prototype-progress-073119-Twitter-@flying_briann-4-segment-tracking-1024x457.jpg

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6 hours ago, Xd the great said:

Are they going to fly it over?

The twitter thread linked goes into more detail on what the twitter user believes is going to happen.  As a quick TL;DR though, she thinks they'll be taking it from the construction area on the green path on the bottom (State Rd. 528; there is currently evidence of this in the twitter thread.  Power companies currently working on burying overhead power lines so they won't be an obstruction; could be coincidence or not...) and then offloading it onto a barge at Port Canaveral.  From there it'll be placed on a barge and floated North (the purple path) on the barge to the turn basin at the launch complex (which has within the last year received refurbishment/maintenance to handle a "renewed need").  From there, it'll be removed from the barge in the turn basin and rolled the rest of the way to LC39-A using the light blue/cyan path that connects to the turn basin in the north and LC39-A.

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7 hours ago, RCgothic said:

More legs is heavier, so that's an arbitrary assessment of "better".

Five legs is the minimum that can tolerate one failure on a reasonably flat surface.

Each leg has to be able to bear a certain minimum peak force onset regardless of the number of legs, since we must presume that the vehicle will not descend in a perfectly vertical state. One leg makes first contact with the ground.

This places a minimum strength constraint on each leg and therefore requires a minimum weight for each leg. Therefore, increasing the number of legs for stability reasons will not reduce the mass of each individual leg and will increase the overall dry mass significantly.

Three legs are best.

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1 hour ago, Ignath said:

The twitter thread linked goes into more detail on what the twitter user believes is going to happen.  As a quick TL;DR though, she thinks they'll be taking it from the construction area on the green path on the bottom (State Rd. 528; there is currently evidence of this in the twitter thread.  Power companies currently working on burying overhead power lines so they won't be an obstruction; could be coincidence or not...) and then offloading it onto a barge at Port Canaveral.  From there it'll be placed on a barge and floated North (the purple path) on the barge to the turn basin at the launch complex (which has within the last year received refurbishment/maintenance to handle a "renewed need").  From there, it'll be removed from the barge in the turn basin and rolled the rest of the way to LC39-A using the light blue/cyan path that connects to the turn basin in the north and LC39-A.

Aww man, I wanted a quarter of Americans to look up at the sky and see a Starship flying and landing. That would have been good PR.

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49 minutes ago, Xd the great said:

Aww man, I wanted a quarter of Americans to look up at the sky and see a Starship flying and landing. That would have been good PR.

So did I.

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Posted (edited)
1 hour ago, sevenperforce said:

Each leg has to be able to bear a certain minimum peak force onset regardless of the number of legs, since we must presume that the vehicle will not descend in a perfectly vertical state. One leg makes first contact with the ground.

If you stop the engine before touchdown, and the ship falls down from some height.

Otherwise, if you're assisting with a landing engine, the first leg touches the ground, starts retracting (as anyway they must be retractable), then next one, then next one, and when all legs are in contact, you shutdown the engine.
The ship sits, the springs inside the legs get compressed, all legs are partially retracted.
Then you adjust every leg to make the ship stand vertically.

Especially when the ship is high, like Starship or LK-700, not low like LEM or AV-8B, and a crew is onboard.

If your ship has 3 legs and lands falls on 1, it will likely bounce with the landed leg and overturn between any two, unless they are very long.

So,

1 hour ago, sevenperforce said:

Three legs are best.

Yes, and 3 backup ones in between, expanded simultaneously just in case, lol.

P.S.
Btw, what is current statistics of Falcon landing? (crashes/landing attempts, ignoring splashes and single-use stages)
I.e. what is current probability of successful landing attempt?

Edited by kerbiloid

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1 hour ago, sevenperforce said:

Each leg has to be able to bear a certain minimum peak force onset regardless of the number of legs, since we must presume that the vehicle will not descend in a perfectly vertical state. One leg makes first contact with the ground.

This places a minimum strength constraint on each leg and therefore requires a minimum weight for each leg. Therefore, increasing the number of legs for stability reasons will not reduce the mass of each individual leg and will increase the overall dry mass significantly.

Three legs are best.

Add that more legs will not easy let you use the fins as legs and that you need complex legs who folds out. 
The legs/ fins has one realistic failure mode, that is then they are used as fins. Once you have angled them outward they are safe. 
Unlike most landing gear the hinges is 90 degree to the landing force, mechanical the hinge is just an bolt who hold the leg in position, much easier to make strong than the upper triangle who absorb the compression at top of legs or the part of the engine trust structure who the bottom will be connected to. 

The forward fin is much more of an single source fail

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Posted (edited)
8 minutes ago, magnemoe said:

Add that more legs will not easy let you use the fins as legs

Attach 6 finlegs to the Falcon. What's the difference?

8 minutes ago, magnemoe said:

mechanical the hinge is just an bolt who hold the leg in position

And we can see how the Falcon bounced off. Unlikely these simple legs are enough good for a crew.

Edited by kerbiloid

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RE the leg hinge structural question:  front end loaders are articulated with a hinge right under the cab.  The largest ones have operating weights north of 250t and payload ratings (what they're rated to lift) well over 50t.  That's a lot of force on a hunger and you never hear of them folding in half.  Granted there's a bit of a weight disparity, but SpaceX has a much longer hinge to play with giving them better leverage against the forces at play.

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