Author Topic: The fascinating problem of the starship landing legs  (Read 384060 times)

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #40 on: 12/04/2020 08:05 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 :/

Yeah mine as well. The main assumption I am making with this design is that it would be more efficient to work the structural trades instead of, again, breaking that heat shield in anyway. I just really believe (without an aerospace degree to support it) that breaking up the heat shield in anyway has got to be more challenging not only from a production standpoint but also from a fault path standpoint.

Just seems like working the loads internal to the skirt would be more feasible. Maybe it'll add some weight but if the design makes the manufacturing simpler I think that is worth it. As a Shuttle hugger it always killed me that one of the main problems was with the heat shield when it came to the reusability aspect.

Offline adrianwyard

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Re: The fascinating problem of the starship landing legs
« Reply #41 on: 12/04/2020 08:11 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?

I did (and Liked it accordingly!). The idea of bracing to the side of the vehicle once unfolded seems a good one and worth pursuing - although the TPS in the areas where it contacts would need to handle that somehow.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #42 on: 12/04/2020 08:28 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?

I did (and Liked it accordingly!). The idea of bracing to the side of the vehicle once unfolded seems a good one and worth pursuing - although the TPS in the areas where it contacts would need to handle that somehow.


I never really flushed that out but my thought was that there might be hard points at the top of those L brackets that could be thermally protected and supported internally. I seem to remember that there was a material that they used on the SR-71 and was considered for the Shuttle that is more robust and could take structural loads. In my mind we are talking about hopefully minimal points that would just allow the load path to continue into the internal structure/bracing but that most of the work would be done by the L bracket and not touch the tiles at all. Basically they would act like your fingers picking up a can. If that makes sense?

Offline _MECO

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Re: The fascinating problem of the starship landing legs
« Reply #43 on: 12/04/2020 08:56 pm »

I like this, but having the flap legs pivot down from the inside of the flap rather than the outside would give a much larger footprint overall. And if it were up to me I would just put two oversized Falcon 9 booster legs on the leeward side.

You wouldn't need any windward legs if you just fold the flap legs forward, giving you a respectable four-point footprint.

I tried folding the wings and using them as windward feet, but the footprint is just WAY too small in the Y-axis; the wings are too short to extend beyond the skirt...they're closer to the axis of the vacuum bell. The ship would fall over backwards :/

Otherwise, is this what you're talking about:

Maybe for replacing all windward legs with just flap legs, they could fold directly outward from the outside edge of each flap (rather than from the bottom). If ypu design it right you might not have to deal with movable heat shield sections, too.

Offline wes_wilson

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Re: The fascinating problem of the starship landing legs
« Reply #44 on: 12/04/2020 09:13 pm »
I'd like to throw out an idea I don't believe I've seen dissected yet.  I'm not a good artist but I've attached a sketch trying to show what it would look like. 

Using the hard points and staying within the base of the starship cylinder, what if instead of extending cylinders as legs they extended arches as legs.    They could have 2 half circle arches that together form a circle of 30ft diameter which would follow the base of the skirt. These two arches would be hinged to the starship at their apex using the hardpoints existing for super heavy attachment.  When released they would fold straight down with the end points of the arches ending up outside the skirt circumference.  The end points of the arches act as four feet outside the skirt diameter giving a base with a diameter of 42.4ft.  The Starship sits on the apex of the two arches and their four feet. 

Upsides are that it gives a wider base than the diameter of the ship while keeping all the leg structure out of the way of engines and control surfaces.  The arches provide some energy absorption and take the forces of landing back to the mount points used for super heavy.  Gravity does a lot of the work of deploying them.  The apex would be 15ft high placing the skirt and engines 15ft above ground which is healthy clearance.

Lastly, while you get 4 "feet" with two arches.  You could also do two sets of arches for four arches total; offsetting the two pairs of arches by 90 degrees.  The feet would all fold out to the same places giving the same 4 "feet" areas but each "feet" area would now have the ends of two arches.  So four arches would mean you could lose any 1 arch without loss of any feet; or any 2 opposite arches without loss of any feet.  Losing two adjacent arches would cost a foot.

Weight?  No idea, probably a lot?


A little rapid prototyping with the kids.

1. Legs & Starship
2. Legs folded inside the skirt
3. Legs extended Starship standing
4. Redundant arrangement; ends of two arches form 1 foot.



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Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #45 on: 12/04/2020 09:14 pm »

I like this, but having the flap legs pivot down from the inside of the flap rather than the outside would give a much larger footprint overall. And if it were up to me I would just put two oversized Falcon 9 booster legs on the leeward side.

You wouldn't need any windward legs if you just fold the flap legs forward, giving you a respectable four-point footprint.

I tried folding the wings and using them as windward feet, but the footprint is just WAY too small in the Y-axis; the wings are too short to extend beyond the skirt...they're closer to the axis of the vacuum bell. The ship would fall over backwards :/

Otherwise, is this what you're talking about:

Maybe for replacing all windward legs with just flap legs, they could fold directly outward from the outside edge of each flap (rather than from the bottom). If ypu design it right you might not have to deal with movable heat shield sections, too.

I like DusanC's analogy to the Dreamchaser front landing skid. It demonstrates well that a retractable landing arm should not have issues with heat shielding.
I think that a good solution is to just shield a leg that statically extends below the skirt by however long it needs to be for a mission, and fold it out at landing.
« Last Edit: 12/04/2020 09:17 pm by Corvus Corax »

Offline Phil Stooke

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Re: The fascinating problem of the starship landing legs
« Reply #46 on: 12/04/2020 09:21 pm »
"The fascinating problem of the starship landing legs"

"But Holmes, the landing legs did nothing in the night-time"

"That is the fascinating problem"

Offline wannamoonbase

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Re: The fascinating problem of the starship landing legs
« Reply #47 on: 12/04/2020 09:21 pm »
I'm enjoying seeing the creative ideas.

Ya'll got ideas.  Mine mostly end with high speed jacking screws that adjust themselves just before landing based on radar feedback.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline 50_Caliber

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Re: The fascinating problem of the starship landing legs
« Reply #48 on: 12/04/2020 09:23 pm »
I'd like to throw out an idea I don't believe I've seen dissected yet.  I'm not a good artist but I've attached a sketch trying to show what it would look like. 

Using the hard points and staying within the base of the starship cylinder, what if instead of extending cylinders as legs they extended arches as legs.    They could have 2 half circle arches that together form a circle of 30ft diameter which would follow the base of the skirt. These two arches would be hinged to the starship at their apex using the hardpoints existing for super heavy attachment.  When released they would fold straight down with the end points of the arches ending up outside the skirt circumference.  The end points of the arches act as four feet outside the skirt diameter giving a base with a diameter of 42.4ft.  The Starship sits on the apex of the two arches and their four feet. 

Upsides are that it gives a wider base than the diameter of the ship while keeping all the leg structure out of the way of engines and control surfaces.  The arches provide some energy absorption and take the forces of landing back to the mount points used for super heavy.  Gravity does a lot of the work of deploying them.  The apex would be 15ft high placing the skirt and engines 15ft above ground which is healthy clearance.

Lastly, while you get 4 "feet" with two arches.  You could also do two sets of arches for four arches total; offsetting the two pairs of arches by 90 degrees.  The feet would all fold out to the same places giving the same 4 "feet" areas but each "feet" area would now have the ends of two arches.  So four arches would mean you could lose any 1 arch without loss of any feet; or any 2 opposite arches without loss of any feet.  Losing two adjacent arches would cost a foot.

Weight?  No idea, probably a lot?


A little rapid prototyping with the kids.

1. Legs & Starship
2. Legs folded inside the skirt
3. Legs extended Starship standing
4. Redundant arrangement; ends of two arches form 1 foot.

I like that design, it tucks away really nicely and then gives a pretty wide stance when it rotates out. They could even tuck the foot pads into the inner part of the engine chamber.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #49 on: 12/04/2020 09:24 pm »
I'd like to throw out an idea I don't believe I've seen dissected yet.  I'm not a good artist but I've attached a sketch trying to show what it would look like. 

Using the hard points and staying within the base of the starship cylinder, what if instead of extending cylinders as legs they extended arches as legs.    They could have 2 half circle arches that together form a circle of 30ft diameter which would follow the base of the skirt. These two arches would be hinged to the starship at their apex using the hardpoints existing for super heavy attachment.  When released they would fold straight down with the end points of the arches ending up outside the skirt circumference.  The end points of the arches act as four feet outside the skirt diameter giving a base with a diameter of 42.4ft.  The Starship sits on the apex of the two arches and their four feet. 

Upsides are that it gives a wider base than the diameter of the ship while keeping all the leg structure out of the way of engines and control surfaces.  The arches provide some energy absorption and take the forces of landing back to the mount points used for super heavy.  Gravity does a lot of the work of deploying them.  The apex would be 15ft high placing the skirt and engines 15ft above ground which is healthy clearance.

Lastly, while you get 4 "feet" with two arches.  You could also do two sets of arches for four arches total; offsetting the two pairs of arches by 90 degrees.  The feet would all fold out to the same places giving the same 4 "feet" areas but each "feet" area would now have the ends of two arches.  So four arches would mean you could lose any 1 arch without loss of any feet; or any 2 opposite arches without loss of any feet.  Losing two adjacent arches would cost a foot.

Weight?  No idea, probably a lot?


A little rapid prototyping with the kids.

1. Legs & Starship
2. Legs folded inside the skirt
3. Legs extended Starship standing
4. Redundant arrangement; ends of two arches form 1 foot.




Great idea, this is essentially what I was proposing above but will more elements. The point of contention seems to be all the various load paths and the best way to accomplish the simplest design.

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #50 on: 12/04/2020 09:27 pm »
I'm enjoying seeing the creative ideas.

Ya'll got ideas.  Mine mostly end with high speed jacking screws that adjust themselves just before landing based on radar feedback.

In my initial unfolding design (The more complicated one ala Falcon 9), in the animation you can see I tried to indicate some kind of LIDAR that would preposition the legs based on the terrain below each foot before landing. Not sure how technically or, Elon simple, this setup would be?

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #51 on: 12/04/2020 09:29 pm »
I'd like to throw out an idea I don't believe I've seen dissected yet.  I'm not a good artist but I've attached a sketch trying to show what it would look like. 

Using the hard points and staying within the base of the starship cylinder, what if instead of extending cylinders as legs they extended arches as legs.    They could have 2 half circle arches that together form a circle of 30ft diameter which would follow the base of the skirt. These two arches would be hinged to the starship at their apex using the hardpoints existing for super heavy attachment.  When released they would fold straight down with the end points of the arches ending up outside the skirt circumference.  The end points of the arches act as four feet outside the skirt diameter giving a base with a diameter of 42.4ft.  The Starship sits on the apex of the two arches and their four feet. 

Upsides are that it gives a wider base than the diameter of the ship while keeping all the leg structure out of the way of engines and control surfaces.  The arches provide some energy absorption and take the forces of landing back to the mount points used for super heavy.  Gravity does a lot of the work of deploying them.  The apex would be 15ft high placing the skirt and engines 15ft above ground which is healthy clearance.

Lastly, while you get 4 "feet" with two arches.  You could also do two sets of arches for four arches total; offsetting the two pairs of arches by 90 degrees.  The feet would all fold out to the same places giving the same 4 "feet" areas but each "feet" area would now have the ends of two arches.  So four arches would mean you could lose any 1 arch without loss of any feet; or any 2 opposite arches without loss of any feet.  Losing two adjacent arches would cost a foot.

Weight?  No idea, probably a lot?


A little rapid prototyping with the kids.

1. Legs & Starship
2. Legs folded inside the skirt
3. Legs extended Starship standing
4. Redundant arrangement; ends of two arches form 1 foot.




Great idea, this is essentially what I was proposing above but will more elements. The point of contention seems to be all the various load paths and the best way to accomplish the simplest design.

Yeah the curved arms might not take loads very well.
It would be neat to deploy the legs sequentially and then have them lock together at the feet to prevent them from spreading outward/breaking due to deflection from bending loads.

Offline Corvus Corax

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Re: The fascinating problem of the starship landing legs
« Reply #52 on: 12/04/2020 09:32 pm »
I'm enjoying seeing the creative ideas.

Ya'll got ideas.  Mine mostly end with high speed jacking screws that adjust themselves just before landing based on radar feedback.

In my initial unfolding design (The more complicated one ala Falcon 9), in the animation you can see I tried to indicate some kind of LIDAR that would preposition the legs based on the terrain below each foot before landing. Not sure how technically or, Elon simple, this setup would be?

Oh I definitely suspect that it is a very simple problem compared to everything else going on. Assuming you can telescope and/or rotate the feet to change their height (the absurdly hard part) then I'm pretty sure it would only take a single survey instrument, like a radar, to map the terrain in realtime and pass those data into the geometry algorithm for the legs.

Offline nameUnavailabl

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.

This misses out on the ground clearance. The reason why they were planning to increase the current legs by 60% in V1.1


Offline wes_wilson

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Re: The fascinating problem of the starship landing legs
« Reply #55 on: 12/04/2020 09:48 pm »
I missed that they were officially outside the skirt...  >:(
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Offline wannamoonbase

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Re: The fascinating problem of the starship landing legs
« Reply #56 on: 12/04/2020 09:51 pm »
A delight from August

https://twitter.com/kimitalvitie/status/1291457743082201093?s=20

I think these are pretty.  Love the sound.

They are close to being inline to transferring the load into the vertical for the existing vehicle load path.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline adrianwyard

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Re: The fascinating problem of the starship landing legs
« Reply #57 on: 12/04/2020 10:15 pm »
Well if you guys think my simplified design was Rube-Goldbergy check out my initial design pass  ::) Hahahahha.

As you say there are a lot of mechanisms working in your animation, but are they necessary? It looks to me as though you could just swing the legs out in one motion from the main hinge. In the following sketch I just extend the (red) telescoping/shock absorbing section by 25% as it swings out.

Edit: It occurs to me that this arrangement would be strong in the up/down direction and left/right direction but not in the the forward/back (as you look at the sketch). To address that the hinge and lower spar would need to be beefy - perhaps the lower spar could be made wider or doubled up into a V.

Given how strong (heavy) really robust self-leveling legs will need to be I wonder if you'd be better off with just three that can handle all cases rather than many that only handle near perfect landings.

...and I fully agree with recent reminders that ground clearance is essential, and the more the better.
« Last Edit: 12/04/2020 10:49 pm by adrianwyard »

Offline Pheogh

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Re: The fascinating problem of the starship landing legs
« Reply #58 on: 12/04/2020 10:34 pm »
Well if you guys think my simplified design was Rube-Goldbergy check out my initial design pass  ::) Hahahahha.

As you say there are a lot of mechanisms working in your animation, but are they necessary? It looks to me as though you could just swing the legs out in one motion from the main hinge. In the following sketch I just extend the (red) telescoping/shock absorbing section by 25% as it swings out.

...and I fully agree with recent reminders that ground clearance is essential, and the more the better.

That is great! and did consider that approach. The one (animation) that is currently up is an experiment I was running to see if I could come up with a way to get maximum horizontal reach and by trade you could also convert that to vertical if you needed it.

Anyway, with this in mind the reason I couldn't use a fixed structure like you are proposing is that the clearance with the 3 raptors is pretty tight, especially when you get the Vacuum Raptors in there. So in my animation you can see they tuck to avoid the Raptors and then extended once clear of the skirt. The other interesting problem I ran into (and thus the need for the "tuck") is that the telescoping bar would impact the skirt on the inside as the flip out occurs. Lots of fun spatial problems to solve.

I did a beauty render over break that i'll try and post tonight.
« Last Edit: 12/04/2020 10:35 pm by Pheogh »

Offline adrianwyard

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Re: The fascinating problem of the starship landing legs
« Reply #59 on: 12/04/2020 10:55 pm »
Got it. What if you only had to find room for three (beefy) simple swing-out legs? (I edited my post below suggesting the lower spar be a V, i.e. looking more and more F9-like).
« Last Edit: 12/04/2020 10:57 pm by adrianwyard »

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