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

louis · 2019-11-01 17:45:43

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

SpaceNut · 2019-11-01 19:36:28

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.

GW Johnson · 2019-11-02 10:41:57

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)

louis · 2019-11-02 11:13:07

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

Oldfart1939 · 2019-11-07 13:26:54

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.

louis · 2019-11-07 15:42:55

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.

SpaceNut · 2019-11-07 17:59:49

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.

louis · 2019-11-07 19:00:42

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.

elderflower · 2019-11-12 10:22:52

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).

louis · 2019-11-12 15:32:51

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).

SpaceNut · 2019-11-12 20:24:42

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....

louis · 2019-11-13 09:54:18

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)

SpaceNut · 2019-11-13 16:54:36

+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.

SpaceNut · 2020-12-30 19:23:09

Most of this discusion was Centered on a Mars landing where a wide base of leg structure would be needed to spread the mass of the landing Starship accross the landing pads for an unprepared area that is not like what starship tried and failed recently on earths concrete area.
The sn 9 and 10 hopefully can get better at as thats critical to do.

Oldfart1939 · 2021-01-02 10:13:27

Nothing can substitute for the real world experience of landing in a field or on a beach. Mar has boulders strewn around and no matter how clever the design--LANDING ON ONE OF THEM WILL NOT BE A PLEASANT EXPERIENCE! GW used the phrase "Technical arrogance." There is a steep learning curve ahead for engineers at SpaceX.

The engineers at SpaceX seem to have forgotten their Sophomore courses in Statics and Dynamics regarding stability. I got credit in both those courses, by the way.

Last edited by Oldfart1939 (2021-01-02 10:17:46)

SpaceNut · 2021-01-02 10:26:34

I would say those small legs did not do very well with the landing forces seen so far but there will be more attempts. Hopefully with less landing acceleration.

tahanson43206 · 2021-01-02 11:44:52

For all contributing to this topic ...

Is there any interest in the idea of contracting to build a landing tower to catch arriving Mars-bound Starships the way Elon is talking about catching boosters using a (very smart) and (very strong) hook?

Elon might be receptive to buying a service from an innovative company able and willing to set up shop for him ahead of his arrival.

The customer need is clear. Is there a provider able to fill that need?

(th)

SpaceNut · 2021-01-02 13:59:28

Unless we go with a small preload style mission with manned crew in the under a dozen size then its starship as that's what other want and only want.

tahanson43206 · 2021-01-02 14:58:43

For SpaceNut .... this would be a contractor from which Elon would purchase services.

Elon is most decidedly NOT the only game in town, although he ** seems ** to be far in the lead.

This could be a Tortoise vs Hare situation ....

I'm expecting to see slumbering groups of people awaken to new life, under the stimulus of Elon's leadership.

(th)

SpaceNut · 2021-01-02 16:26:18

Other than NASA With its cost plus contractors there are no private industries putting any R&D money into missions.

Elon and space x will not be buy services that cost more than his own.

SpaceNut · 2021-03-04 18:18:59

SpaceNut wrote:

I missed it.... you seen one exploding at the pad you have seen them all.
One issue for the current profile is for use in a coast to coast as the return to earth from orbit, moon or mars are quite a bit different.
Starship SN10 successfully lands before RUD’ing on the pad
https://youtu.be/XOQkk3ojNfM?t=36975
apparently those spindally legs did not hold up....
Engines did perform better as the deep throttle of each seemed smooth without the hatsh bell ring seen before. The aft fire seems to indicate a need as fire erupted even after landing contact engine shut off.

Seems we have the answer for landing and it failed to hold up....as well as the concrete pad it would seem that it will not be enough since the legs will need to be better for an unfinished surface...

edit to add content

As for the cause of the fire which is from leaks, that would seem to be a workmanship issue rather than design I would hope as its getting better with each build....

SpaceNut · 2021-03-07 10:52:44

louis wrote:

SpaceXcentric's latest video - includes a segment from Lab Padre showing the failed deployment of all legs - a few didn't lock. Might also explain why they couldn't quench the fire as the Starship body was in contact with the ground - no space to get at the engines.
https://www.youtube.com/watch?v=GxFrS5nL_80

SpaceNut · 2021-03-07 10:53:52

The illustrates the need for a concrete pad as well since rocks that are in the field of landing can not be predicted to not damage the engines and with the surface not level it makes the problem even greater. This problem is not just for mars but for a version that is for the moon as well since there is the regolith sink depth that will need to be accounted for....

louis wrote:

I think you are underestimating the extent to which NASA can (a) identify hard level rock surfaces (to a depth of many metres) and (b) identify rocks on the surface using computerised analysis of repeat photos (different orbits) of the same area. IIRC correctly they can resolve down to about 60cms.
Remember as well that Space X are sending cargo ships first so when they land they can make v. detailed images of the landing area, selecting the best for the human landers. With automated rovers on board, they can even clear away rocks.
Anyway, all this can be tested on Earth first, and the Moon later. I think a lunar landing will be more difficult than a Mars landing.

SpaceNut · 2021-03-07 10:56:12

Edit just important paragraph remains

GW Johnson wrote:

As best I understand it, when Spacex shuts down a Raptor, they stop one propellant flow first, and thus quench the chamber fire by its lack, with the other propellant still running. I don't know which one is first, but I'd guess methane first, then oxygen. Then they shut it off, too. The engine expels the cooler gas to fully depressurize, just at lowered velocity. These expelled gases mix with the air in the engine bay for a short time. Not zero, but short.
If my guess about how Raptors shut down is correct, the engine bay is enriched in oxygen for that time. Any fuel leakage would be very flammable and extremely easy to ignite. Or any solid material in the bay that was smoldering for any other reason, would brighten up and burn faster for a time.
I would not think they would shut off the oxygen first, because that would fill the bay immediately with methane fuel. That guarantees a huge fire as air percolates back in. Any source of ignition, even just hot parts, can set off the conflagration. Methane is almost as notorious as hydrogen about easy ignition. (It's also almost as notorious as hydrogen about being easy-to-leak.)
What I saw with SN-10 was "good" until they completed the flip back to vertical. When they shut down two of the engines, there was a very large fire visible, streaming out of the bay, continuously all the way to the ground, as it descended on the one engine. That means there was a rather significant leakage flow of methane into the bay, feeding the large fire. I think this fire was big enough to do significant damage to plumbing and wiring. It would also heat up the thin sheet metal that is the "thrust puck", but which is also the main oxygen tank.
When it got near the pad, there was too much dust and smoke for me to see anything until the cloud cleared after the landing. Then it was quite clear the ship was standing roughly 5 degrees out of plumb. Which in turn means there was something wrong with some, but not all, the landing legs. All those on one side were "short" in some way.
I find that landing leg trouble unsurprising, to say the least. I don't know how they are operated, but either plumbing or electricity (or both) are used. Doesn't matter which, it was exposed to a big fire in the bay for a significant time, and fire is hell on wiring or plumbing. Odds are the bay fire caused the leg malfunction.
I did see it standing there with a small fire showing on the higher side of the base of the tilted ship. It burned like that for a while, until sometime after they shot a water stream into the vicinity of the ship. If there was still a fire burning in the bay, that was not visible from outside. I think there was still an ongoing fire in the bay, that it was leaking methane burning with air in the bay, and that it finished burning a hole in the thrust puck/oxygen tank.
When the oxygen hit the methane-air fire in the bay, ka-boom! Which is why the bay walls and aft fins were ripped from the ship, with the explosion pressure wave lifting the entire ship around a hundred meters skyward. That was a fast deflagration by the way, not-at-all a detonation! Those are even more powerful. By far. There would be no recognizable ship left, just small pieces, if that had been a detonation.
They really, really need to get control of leaking methane and the raging engine bay fires it can so easily cause. That's three prototypes fundamentally destroyed by this issue. Could be faulty valves, leaking pipe joints, or even welds cracking. It has long been known (over a century now) that many of those things which perform perfectly well in ground tests, often come apart under real-world stresses in flight. Usually stresses not accounted-for in the design analysis. Usually also causing loss of the craft.

As for the landing leg design, well, I have offered my assessment about that before (and it was not, and still is not, at all good). The first time one of these vehicles makes a forced landing off-site, without that flat reinforced concrete pad, well, the resulting loss of vehicle (and maybe crew) will induce them to do that job better. The longer they put that off, the more expensive it will become.
You won't get to choose what you land upon, in an emergency. It might be a soft sand dune or a bog of soft mud. Or a plowed field. Or a golf course with water hazards. You had best design for this ahead of time. Why? Because nothing is as expensive as a dead crew, especially one dead from a stupid management decision.
GW

SpaceNut · 2021-03-07 10:57:05

GW Johnson wrote:

Louis:
Paragraph 6 from post 967:
"I find that landing leg trouble unsurprising, to say the least. I don't know how they are operated, but either plumbing or electricity (or both) are used. Doesn't matter which, it was exposed to a big fire in the bay for a significant time, and fire is hell on wiring or plumbing. Odds are the bay fire caused the leg malfunction."
Yes, fire can distort mechanisms. It usually does. It also destroys controls, which causes failures even when mechanisms remain undistorted. If the fire destroys hydraulic plumbing, or the controls for hydraulics, the mechanisms operated by hydraulics cannot function. Same for electrically-operated stuff: wiring is extremely vulnerable to fire, whether control wiring or the electric motors themselves.
GW

Back to the drawing board space x....

New Mars Forums

Announcement

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

#14 2020-12-30 19:23:09

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

#15 2021-01-02 10:13:27

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

#16 2021-01-02 10:26:34

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

#17 2021-01-02 11:44:52

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

#18 2021-01-02 13:59:28

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

#19 2021-01-02 14:58:43

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

#20 2021-01-02 16:26:18

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

#21 2021-03-04 18:18:59

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

#22 2021-03-07 10:52:44

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

#23 2021-03-07 10:53:52

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

#24 2021-03-07 10:56:12

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

#25 2021-03-07 10:57:05

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

Board footer