Author Topic: The fascinating problem of the starship landing legs  (Read 383788 times)

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #20 on: 12/04/2020 05:49 pm »
Love this topic and all the cool ideas emerging from the community. I had posted a much more complex versions in another thread awhile back but wanted to massively simplify. I think no matter what happens the legs will have to be internal to the skirt (as to reduce the heat shield complexity) and in Elon speak needs to be ultra simple. I'm also dubious about the flaps having enough strength to take the loads? 

So this design tries to use simple industrial springs for the auto leveling. Clearly this design would need actuators to retract but would love to know what you all think. This is an extremely rough sketch but I think you can get the basic design conceit from it

Offline DusanC

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Re: The fascinating problem of the starship landing legs
« Reply #21 on: 12/04/2020 05:53 pm »
IMHO currently most probable solution are 6 New Shepard style legs, 3 windward, 3 leeward, flush with OML, as long as the SS skirt.

https://www.blueorigin.com/assets/BlueOrigin_NewShepard_LandedBooster.jpg

Offline Lars-J

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Re: The fascinating problem of the starship landing legs
« Reply #22 on: 12/04/2020 05:55 pm »
Love this topic and all the cool ideas emerging from the community. I had posted a much more complex versions in another thread awhile back but wanted to massively simplify. I think no matter what happens the legs will have to be internal to the skirt (as to reduce the heat shield complexity) and in Elon speak needs to be ultra simple. I'm also dubious about the flaps having enough strength to take the loads? 

So this design tries to use simple industrial springs for the auto leveling. Clearly this design would need actuators to retract but would love to know what you all think. This is an extremely rough sketch but I think you can get the basic design conceit from it

That is cool but too Rube-golberg-y, IMO. Keep in mind that these legs need to be structurally very strong AND have a decently sized footprint pad to spread the load on the Moon or Mars. Your legs are like stilettos heels for elephants. ;)
« Last Edit: 12/04/2020 05:55 pm by Lars-J »

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #23 on: 12/04/2020 05:59 pm »
IMHO currently most probable solution are 6 New Shepard style legs, 3 windward, 3 leeward, flush with OML, as long as the SS skirt.

https://www.blueorigin.com/assets/BlueOrigin_NewShepard_LandedBooster.jpg

Minus a heat shield of hexagonal tiles whose integrity is essential to mission success I'd have to agree. However if memory serves there were significant concerns even with the Space Shuttle that the landing gear doors and fuel line doors were a concern and potential LOC risk? That's the primary reason I will be surprised if any solution that requires external pods or complex tile placement will end up being the solution.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #24 on: 12/04/2020 06:04 pm »
Love this topic and all the cool ideas emerging from the community. I had posted a much more complex versions in another thread awhile back but wanted to massively simplify. I think no matter what happens the legs will have to be internal to the skirt (as to reduce the heat shield complexity) and in Elon speak needs to be ultra simple. I'm also dubious about the flaps having enough strength to take the loads? 

So this design tries to use simple industrial springs for the auto leveling. Clearly this design would need actuators to retract but would love to know what you all think. This is an extremely rough sketch but I think you can get the basic design conceit from it

That is cool but too Rube-golberg-y, IMO. Keep in mind that these legs need to be structurally very strong AND have a decently sized footprint pad to spread the load on the Moon or Mars. Your legs are like stilettos heels for elephants. ;)

Couldn't agree more, but like I said this is a rough sketch of the design conceit around deployment. Look at it more as trying solve the spatial problem than an actual loads based solution. Even initial napkin designs have to have the heavy loads analysis and trades done to determine if it's feasible. I'd love to know if from a structure and loads perspective it is a non starter and why.

Meaning is it worth beefing up the legs? Redesigning how they attach to the skirt structure? Would springs be enough? Initially I actually had the legs separate for a total of 12 contact points but brought them together thinking that would increase strength.
« Last Edit: 12/04/2020 06:08 pm by Pheogh »

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #25 on: 12/04/2020 06:06 pm »
Love this topic and all the cool ideas emerging from the community. I had posted a much more complex versions in another thread awhile back but wanted to massively simplify. I think no matter what happens the legs will have to be internal to the skirt (as to reduce the heat shield complexity) and in Elon speak needs to be ultra simple. I'm also dubious about the flaps having enough strength to take the loads? 

So this design tries to use simple industrial springs for the auto leveling. Clearly this design would need actuators to retract but would love to know what you all think. This is an extremely rough sketch but I think you can get the basic design conceit from it

Yeah something like this would be nice. I think the torsion forces at the bottom of the skirt would be too high to be feasible, though. The legs need to be oriented with their major supporting structure aligned as closely as possible with the longitudinal axis of the ship. It's a shame that they can't just use the F9 landing leg system...the footprint is enormous, the mechanism is relatively simple, etc.

I have to say, the 6 stubby foldout mechanism they have implemented currently feels like the right answer, on paper, but it doesn't account for the randomness of real field work quite as much as I feel it should/could.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #26 on: 12/04/2020 06:13 pm »
Well if you guys think my simplified design was Rube-Goldbergy check out my initial design pass  ::) Hahahahha.

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #27 on: 12/04/2020 06:17 pm »
Hey everyone. New here. Been enjoying the YouTube livestreams since the beginning. So fun.

Ever since the prototype landing legs had their go with sn5 and sn6, I've been absolutely fascinated by the problem space of how to optimize the landing system:
Maximizing footprint...
Minimizing mass...
Maximizing robustness...
How to compromise optimally between these three factors?

As many of us probably do, I have opinions...

I don't know exactly how the attachment system works, so I guess I'm about to find out, but I threw 6 renders into this post that demonstrate 2 iterations of what I think would be the best options.

Both work under the assumption that the aft flap wings should contain two of the legs, and that the flaps should be reopened just prior to touchdown (when aerodynamic forces have been reduced to negligible levels, the engines have fired up, and the flare has been completed). My reasoning for this: The flaps have a wide footprint, and are very strong compared to the aft skirt. Both use a windward and leeward leg that extend just prior to touchdown in a manner similar to F9's legs do. The windward leg is heatshielded by a shroud that protects its entire length. The flap legs retract into the flaps so that they are protected by the already-extant heatshields. 

The engines are rotated radially by 30 degrees to make space in the skirt; a strong flanged mounting system for the leeward and windward leg deployment pistons would then have room to be installed.

I'd love to talk shop about it with anyone who's interested  :D

Neat, a fellow raven :)  welcome to NasaSpaceFlight :)

Something similar was posted on twitter a few days ago, and commented on by Elon, I think your variant has more merit though

Quote
https://twitter.com/ErcXspace/status/1334237562823725056

Quote
    Here is my weird Starship Leg Design, 2 deployable inside the skirt and 2 inside the flaps. All self levelling. (Really rushed the modelling part on this one, please excuse me) pic.twitter.com/Tkuip3neFw
    — Erc X (@ErcXspace) December 2, 2020

https://twitter.com/elonmusk/status/1334321901783511041
Quote
    Not bad
    — Elon Musk (@elonmusk) December 3, 2020

Nice, Raven's FTW!

I just saw this tweet yesterday and redrafted it to see what was going on. The problem I ran into was that the footprint is too small when the wings are folded like that. The ship wants to fall over backwards because the wingtips actually lie inside the skirt along the lateral axis.

Another concern I had was that yaw forces acting on the wingtips would simply be too great on the actuator/hinge mechanism. That's why I chose to extend the major axis of the landing legs from the root of the wing, instead. It's also worth noting that the actuator jack is fully extended when the wings are extended, providing the greatest mechanical advantage for structural rigidity.
I'm pretty sure the wings have to be open at touchdown for these sorts of solution to really work, structurally speaking.
« Last Edit: 12/04/2020 06:35 pm by Corvus Corax »

Offline DusanC

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Re: The fascinating problem of the starship landing legs
« Reply #28 on: 12/04/2020 06:29 pm »
IMHO currently most probable solution are 6 New Shepard style legs, 3 windward, 3 leeward, flush with OML, as long as the SS skirt.

https://www.blueorigin.com/assets/BlueOrigin_NewShepard_LandedBooster.jpg

Minus a heat shield of hexagonal tiles whose integrity is essential to mission success I'd have to agree. However if memory serves there were significant concerns even with the Space Shuttle that the landing gear doors and fuel line doors were a concern and potential LOC risk? That's the primary reason I will be surprised if any solution that requires external pods or complex tile placement will end up being the solution.
Same tiles, same placement pattern and no external pods. Flush with outer mold line. Tiles would remain on the external part of the leg. Like Dreamchaser front skid.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #29 on: 12/04/2020 07:08 pm »
So maybe something more like this?... a hybrid... So the short stubbies take the longitudinal loads and the extenders only have to deal with the horizontal loads trying to tip the vehicle over on uneven surfaces.

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #30 on: 12/04/2020 07:12 pm »
So maybe something more like this?... a hybrid... So the short stubbies take the longitudinal loads and the extenders only have to deal with the horizontal loads trying to tip the vehicle over on uneven surfaces.

Perhaps. But remember that there is a whole booster beneath the starship on the way up. There needs to be a flush hardpoint attachment down there, so you have to keep it flat/clean :/

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #31 on: 12/04/2020 07:19 pm »
Pre-deployment... Pretty flush and of course just a napkin sketch, but looks feasible to me.

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #32 on: 12/04/2020 07:21 pm »
IMHO currently most probable solution are 6 New Shepard style legs, 3 windward, 3 leeward, flush with OML, as long as the SS skirt.

https://www.blueorigin.com/assets/BlueOrigin_NewShepard_LandedBooster.jpg

Minus a heat shield of hexagonal tiles whose integrity is essential to mission success I'd have to agree. However if memory serves there were significant concerns even with the Space Shuttle that the landing gear doors and fuel line doors were a concern and potential LOC risk? That's the primary reason I will be surprised if any solution that requires external pods or complex tile placement will end up being the solution.
Same tiles, same placement pattern and no external pods. Flush with outer mold line. Tiles would remain on the external part of the leg. Like Dreamchaser front skid.

I strongly agree about the windward tiles peeling off of the main face on deployment like that. If any sort of external leg is implemented, then that's more or less a must.

The takeaway I get from the New Shepard landing system is that it proves just how spindly of an assembly you can get away with. This is why I'm so intrigued by the in-wing leg approach. It's highly consolidated; sharing as much of the existing structure as is possible. It doesn't take much to get the structure up to the required strength, apparently, so why not consolidate?

Offline WH2OPaddler

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Re: The fascinating problem of the starship landing legs
« Reply #33 on: 12/04/2020 07:34 pm »
As I understand it, Luna Starship will fly to the moon on one-way missions. There, the aft engines aren't used, so damage to any of the 6 standard engine bells during landing and/or settling may be acceptable. That is not the case for Mars, unless of course those missions will be one-way trips as well (which kind of defeats its re-usability aspect).

In most of the cases being presented here, it's presumed that Mars' surface will support the weight of Starship with little settling. I also get the sense that debris impingement is not considered an issue (landing tests on unprepared surfaces need to confirm this life-critical proposition, preferably multiple times). And while I fully understand the concern with weight, landing a high aspect ratio vehicle on stubby little legs with mere feet of separation between the ground and its engines strikes me as a bad idea. Landing gear are another in a long line of life-critical design features that, given the designs being discussed, I would not trust with my life.

IMO there needs to be: A) sufficient ground clearance to provide a low probability of engine damage due debris impacts; B) a landing gear contact circle wide enough to guarantee stability on all likely-to-be-encountered surfaces, and C) feet with a combined surface area that matches or exceeds the compressability of those anticipated landing surfaces. Bottom line: If there's a place for out-of-the-box over-design, landing gear design is it. Fly to the moon, land there, and afterward give consideration to possible weight reductions. Ditto that approach for Mars.

Personally, I think Blue Origin is on right track for landing gear. Ad Astra.
David Boyle, Author, Window In Time & Colonizing Mars, Part 1 - Getting There

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #34 on: 12/04/2020 07:39 pm »
IMHO currently most probable solution are 6 New Shepard style legs, 3 windward, 3 leeward, flush with OML, as long as the SS skirt.

https://www.blueorigin.com/assets/BlueOrigin_NewShepard_LandedBooster.jpg

Minus a heat shield of hexagonal tiles whose integrity is essential to mission success I'd have to agree. However if memory serves there were significant concerns even with the Space Shuttle that the landing gear doors and fuel line doors were a concern and potential LOC risk? That's the primary reason I will be surprised if any solution that requires external pods or complex tile placement will end up being the solution.
Same tiles, same placement pattern and no external pods. Flush with outer mold line. Tiles would remain on the external part of the leg. Like Dreamchaser front skid.

I strongly agree about the windward tiles peeling off of the main face on deployment like that. If any sort of external leg is implemented, then that's more or less a must.

The takeaway I get from the New Shepard landing system is that it proves just how spindly of an assembly you can get away with. This is why I'm so intrigued by the in-wing leg approach. It's highly consolidated; sharing as much of the existing structure as is possible. It doesn't take much to get the structure up to the required strength, apparently, so why not consolidate?

Totally agree on several of your points. The integrated wing design is an interesting development but I do share the load concerns others have mentioned. I just keep seeing that Tweet from Elon about the trades they are working, and others where he has mentioned the best solution is keeping it all internal to the skirt. The other thing that keeps rattling about in my brain is his quote about the best design is no design and the best part is no part.

Not that any of these solutions will avoid that entirely but I think he is trying to say "k.i.s.s." The other thing to consider is that I can't imagine a complete skirt redesign at this point which is what the leg extending from skirt solution would require not to mention the heat shield impacts we have already covered.

Either way I absolutely love all the various ideas and would love to keep seeing more. Regretting right now I didn't hold out in mechanical engineering long enough to learn about load paths and have some understanding of the digital tools to test out all the stresses of various designs.

The last big question is when we will actually see some ideas emerging from the SpaceX team. I would imagine it won't become mission critical until Starships start falling over and as long as they are landing on improved pads.

Offline daveglo

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Re: The fascinating problem of the starship landing legs
« Reply #35 on: 12/04/2020 07:40 pm »
Pre-deployment... Pretty flush and of course just a napkin sketch, but looks feasible to me.
Pretty creative!  How would you handle the need to provide some resilience to the design?  Some kind of feature to allow for uneven loading & surfaces?

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #36 on: 12/04/2020 07:51 pm »
Pre-deployment... Pretty flush and of course just a napkin sketch, but looks feasible to me.
Pretty creative!  How would you handle the need to provide some resilience to the design?  Some kind of feature to allow for uneven loading & surfaces?

This is my concern, as well. There would be a tremendous leverage force on the skirt from the extended arm. Methinx it may buckle under the load :/

Offline adrianwyard

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Re: The fascinating problem of the starship landing legs
« Reply #37 on: 12/04/2020 07:55 pm »
Yep. A challenge for all legs is handling any residual horizontal velocity (and/or crushing movement in the soil as weight is applied.) ISTM New Shepard style legs would not handle this well as there is no give horizontally. Contrast this with the F9 leg design that is braced to horizontal loads and its foot 'bumps' that can slide somewhat.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #38 on: 12/04/2020 07:56 pm »
Pre-deployment... Pretty flush and of course just a napkin sketch, but looks feasible to me.
Pretty creative!  How would you handle the need to provide some resilience to the design?  Some kind of feature to allow for uneven loading & surfaces?

The back of the napkin notion is that those pink industrial springs or dampeners (placeholders) would be able to absorb the difference and then perhaps some kind of sensor would lock them when the craft detected it was level.  Those kind of systems are way beyond my abilities, but ultimately there is going to have to be some kind of active dampening that is then able to lock its self or come to some kind of stable state? Does anyone on here know how the LM legs worked? Were they active or passive?

Sorry for the roughness of this concept I just hashed it out last night and have been progressively realizing some of its shortfalls.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #39 on: 12/04/2020 07:57 pm »
Yep. A challenge for all legs is handling any residual horizontal velocity (and/or crushing movement in the soil as weight is applied.) ISTM New Shepard style legs would not handle this well as there is no give horizontally. Contrast this with the F9 leg design that is braced to horizontal loads and its foot 'bumps' that can slide somewhat.

Wondering if you saw my crazy concept from farther up in the thread trying to fold F9 legs into the base of Starship?

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