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#1 2019-11-01 17:45:43

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,329

Six-legged freaks - can the Starship land on those legs?

I posted this on another thread but thought people might not have spotted it...and I think it is something that interests a lot of people here...those Starship landing legs...could they really provide a stable solution to landing?

In this video from Felix he addresses issues relating to the landing legs on the Mk 1 in detail:

https://www.youtube.com/watch?v=3Ybf1c4VgsA


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2019-11-01 19:36:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,360

Re: Six-legged freaks - can the Starship land on those legs?

It ends up being 3 legs in the center with the longer reach 3 legs doing the brunt of the work at the larger diameter hopefully to keep it from toppling.

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#3 2019-11-02 10:41:57

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,755
Website

Re: Six-legged freaks - can the Starship land on those legs?

The 6-leg design offers a means to adjust leg length for slightly-uneven ground,  as well as a slight shock absorption mechanism for the landing.  It does improve the footprint geometry over a 4-leg design,  and especially that of a 3-leg design. 

It does NOT address the ~3.9 m distance to the nearest-edge-of-footprint relative to a roughly 31 m center-of-gravity height.  That's max 7 degrees of tilt for ANY reason!  It also does NOT address landing weight / total pad area,  which must be less than 0.1 MPa for the vast bulk of Mars's surface,  even at any of the landing sites being considered. 

What they have in those first flight test articles cannot even abort to a landing on a beach or a farm field during flight tests here on Earth.

First time that happens,  and it crashes,  you'll see them finally address that issue in their design.  What I see is an outfit stumbling over its own technical arrogance,  coupled with the technical ignorance of never having landed on anything but a reinforced concrete slab or a hard steel deck. 

GW

Last edited by GW Johnson (2019-11-02 10:43:05)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#4 2019-11-02 11:13:07

louis
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From: UK
Registered: 2008-03-24
Posts: 5,329

Re: Six-legged freaks - can the Starship land on those legs?

Well it's certainly intriguing. I don't think any of us would have proposed such a design, whatever the level of our technical know-how. Definitely seems counter-intuitive. But I do wonder sometimes if we are being too "Earth-bound". The weather on Mars is benign. We don't have to worry about hurricanes, strong tornadoes, floods (well, pretty much) or lightning strikes...even the seismic activity is close to zero. So as long as you know you are landing on, say, a 3% incline, you could argue that the more traditional big tripod is overdesign for Mars.


GW Johnson wrote:

The 6-leg design offers a means to adjust leg length for slightly-uneven ground,  as well as a slight shock absorption mechanism for the landing.  It does improve the footprint geometry over a 4-leg design,  and especially that of a 3-leg design. 

It does NOT address the ~3.9 m distance to the nearest-edge-of-footprint relative to a roughly 31 m center-of-gravity height.  That's max 7 degrees of tilt for ANY reason!  It also does NOT address landing weight / total pad area,  which must be less than 0.1 MPa for the vast bulk of Mars's surface,  even at any of the landing sites being considered. 

What they have in those first flight test articles cannot even abort to a landing on a beach or a farm field during flight tests here on Earth.

First time that happens,  and it crashes,  you'll see them finally address that issue in their design.  What I see is an outfit stumbling over its own technical arrogance,  coupled with the technical ignorance of never having landed on anything but a reinforced concrete slab or a hard steel deck. 

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#5 2019-11-07 13:26:54

Oldfart1939
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Registered: 2016-11-26
Posts: 1,794

Re: Six-legged freaks - can the Starship land on those legs?

Louis, there is no such thing as overdesign when landing on an unknown surface. The 6 landing legs, no matter how cleverly they are designed, do not have enough weight bearing surface area to accommodate the mass of a refueled Starship, even with reduced gravity on Mars. I sure as Hell wouldn't want to land in such a vehicle without some sort of outrigger type stabilization against tip over and additional weight bearing capacity. As GW has pointed out, the engineers at SpaceX really don't know yet that they don't know. This learning curve has the potential to be both catastrophic and expensive.

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#6 2019-11-07 15:42:55

louis
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From: UK
Registered: 2008-03-24
Posts: 5,329

Re: Six-legged freaks - can the Starship land on those legs?

Well this is what puzzles me: it seems such an obvious design fault, they must realise that it is not exactly a conventional solution. They must have their reasons...Space X are normally pretty open about their logic for certain design features - will be interesting to see what explanation they give in due course.

Oldfart1939 wrote:

Louis, there is no such thing as overdesign when landing on an unknown surface. The 6 landing legs, no matter how cleverly they are designed, do not have enough weight bearing surface area to accommodate the mass of a refueled Starship, even with reduced gravity on Mars. I sure as Hell wouldn't want to land in such a vehicle without some sort of outrigger type stabilization against tip over and additional weight bearing capacity. As GW has pointed out, the engineers at SpaceX really don't know yet that they don't know. This learning curve has the potential to be both catastrophic and expensive.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#7 2019-11-07 17:59:49

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,360

Re: Six-legged freaks - can the Starship land on those legs?

Since we are trying to land near volcanic slopes there is also likely to be underground tunnels from the activity that with the weight of landing could break through as a man in Hawaii did just walking over one falling to his death.
Hawaii man dies after falling into lava tube on his property

th?id=ON.995BBCDEA27469A3683548F9B2F1FF01&pid=News&w=256&h=158&c=14&rs=2&qlt=90

The Lava tubes are something that is going to be irregular in diameter, twisting direction and thickness from the surface.

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#8 2019-11-07 19:00:42

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,329

Re: Six-legged freaks - can the Starship land on those legs?

But they can be detected my radar reflection I am pretty sure. Any significant gap in the rock is going to show up on the radar sensors on the Mars satellites.  My physics is pretty ropey/non-existent but I am pretty sure that unless the tube is close to the surface it's going to have v. little effect on the weight-bearing nature of the rock mass at the surface.  And, as I said, the satellite radar will pick up tubes close to the surface.


SpaceNut wrote:

Since we are trying to land near volcanic slopes there is also likely to be underground tunnels from the activity that with the weight of landing could break through as a man in Hawaii did just walking over one falling to his death.
Hawaii man dies after falling into lava tube on his property

https://www.bing.com/th?id=ON.995BBCDEA … s=2&qlt=90

The Lava tubes are something that is going to be irregular in diameter, twisting direction and thickness from the surface.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#9 2019-11-12 10:22:52

elderflower
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Registered: 2016-06-19
Posts: 1,149

Re: Six-legged freaks - can the Starship land on those legs?

I think we only have to accept the empty starship landing load with the basic leg configuration. Reinforcement can be applied later before refuelling begins. Maybe by bored piles or load spreading mats or additional support structures. These can be left behind when the ship lifts off again.
The aspect of this that does concern me is stability due to sloping ground. To stabilise a leaning ship is not a simple task (see the efforts to stabilise a certain tower in Italy for example).

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#10 2019-11-12 15:32:51

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,329

Re: Six-legged freaks - can the Starship land on those legs?

I do know that NASA landing site requirements are for less than a 5% slope. Presumably Space X will run with that requirement. Of course, in reality it will probably be less than 3%. It will be possible to accurately measure the landing site elevation and I am sure they will err on the side of caution. So the issues are really boulders and/or ground instability. Computer enhancement of images can identify rocks down
to 5 cms it is claimed:

https://www.popularmechanics.com/space/ … e-on-mars/

Even if you can't get down to that I think the danger from boulders can be removed.  Certainly the cargo ships should be able to take much more detailed pics of the landing area when they travel to Mars in advance of humans. 

elderflower wrote:

I think we only have to accept the empty starship landing load with the basic leg configuration. Reinforcement can be applied later before refuelling begins. Maybe by bored piles or load spreading mats or additional support structures. These can be left behind when the ship lifts off again.
The aspect of this that does concern me is stability due to sloping ground. To stabilise a leaning ship is not a simple task (see the efforts to stabilise a certain tower in Italy for example).


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#11 2019-11-12 20:24:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,360

Re: Six-legged freaks - can the Starship land on those legs?

If 5 % was all there was to it we would only be thinking of an upward slope but it can also be a downward slope since the number of legs is odd and that would or could have both in the landing zone that was not prepared.
for a 10 m diameter thats going to be 0.5 m and since the outer legs are of a greater diameter that error can get larger and not in the same direction....

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#12 2019-11-13 09:54:18

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,329

Re: Six-legged freaks - can the Starship land on those legs?

Every upward slope is also a downward slope! Surely!!

SpaceNut wrote:

If 5 % was all there was to it we would only be thinking of an upward slope but it can also be a downward slope since the number of legs is odd and that would or could have both in the landing zone that was not prepared.
for a 10 m diameter thats going to be 0.5 m and since the outer legs are of a greater diameter that error can get larger and not in the same direction....

Last edited by louis (2019-11-13 10:19:14)


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#13 2019-11-13 16:54:36

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,360

Re: Six-legged freaks - can the Starship land on those legs?

+5' is not a -5' slope as there is a 0' slope. Such that it can happen that 1 leg is at 0' , with 1 leg at +5' , with the final leg at -5' slope which means a total slope for adjacent could be 10' from level or 0'. The assumption is that you limit the overall slope to no more than 2.5' so that you can satisfy the 5' tangent leg slope. It also assumes that the inner legs are not oposing in direction of the others and not higher.

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