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

Quaoar · 2021-03-18 09:55:36

louis wrote:

I expect the TAF factor cuts both ways - it allows them to adopt fresh approaches to long standing issues that sometimes work better (and a lot cheaper). That's the sort of approach that allowed Tesla to get a lead in EVs - they didn't just bolt on batteries to an existing vehicle model.
On the subject of legs, I was wondering about a supplementary stability set up. So you keep the stubby legs but at the bottom of the rocket you have three or maybe five extendors that follow the rounded contours of the rocket (so not like the Falcon 9 with its fold down legs going up the rocket body). As the rocket lands, these extendors, connected to the rocket body by hinges move out from the rocket body and stabilise the rocket on landing. With a circumference of over 28 metres to play with 5 of these curved legs could each be 5 metres in length. But that might be too much. I'm thinking (intuitively and probably wrongly!) perhaps 3 metres would place less strain on the hinge. Just another thought as well - if they were on springs and held back mechanically, leg deployment might used far less energy - just a case of moving 5 bolts out of place. There might need to be mechanism to lower the legs slightly so they make good contact with the ground.
You might be able to fire all the bolts with pyrotechnics which I understand have proven to be a very reliable technology in rocketry over the years, to effect mechanical movements.

Probably, now it's too late to change the design, but wouldn't it better to build a belly-lander with main rockets on the tail, landing/take
-off rockets on the belly, plus four landing legs?
A belly-lander is much more stable and would be a more practical surface habitat for the astronauts, who don't need to take a complex elevator every time they return from an exploration, but a simple ramp with steps.

RobertDyck · 2021-03-18 10:58:01

Quaoar wrote:

Probably, now it's too late to change the design, but wouldn't it better to build a belly-lander with main rockets on the tail, landing/take
-off rockets on the belly, plus four landing legs?
A belly-lander is much more stable and would be a more practical surface habitat for the astronauts, who don't need to take a complex elevator every time they return from an exploration, but a simple ramp with steps.

That would require separate engines. And stress on the tank is in the wrong direction. A cylindrical tank is strongest on its end. During high speed atmospheric flight, you need a narrow rocket with pointy end first for minimum drag. And if the goal is to relaunch, you want the rocket oriented after landing the same way it will have to be for launch.

louis · 2021-03-18 15:43:20

Yes, I guess a belly lander would make a lot of sense for a rough field landing. But not so much for take-off. Must surely increase the risk of damage to the rocket?

Quaoar wrote:

louis wrote:
I expect the TAF factor cuts both ways - it allows them to adopt fresh approaches to long standing issues that sometimes work better (and a lot cheaper). That's the sort of approach that allowed Tesla to get a lead in EVs - they didn't just bolt on batteries to an existing vehicle model.
On the subject of legs, I was wondering about a supplementary stability set up. So you keep the stubby legs but at the bottom of the rocket you have three or maybe five extendors that follow the rounded contours of the rocket (so not like the Falcon 9 with its fold down legs going up the rocket body). As the rocket lands, these extendors, connected to the rocket body by hinges move out from the rocket body and stabilise the rocket on landing. With a circumference of over 28 metres to play with 5 of these curved legs could each be 5 metres in length. But that might be too much. I'm thinking (intuitively and probably wrongly!) perhaps 3 metres would place less strain on the hinge. Just another thought as well - if they were on springs and held back mechanically, leg deployment might used far less energy - just a case of moving 5 bolts out of place. There might need to be mechanism to lower the legs slightly so they make good contact with the ground.
You might be able to fire all the bolts with pyrotechnics which I understand have proven to be a very reliable technology in rocketry over the years, to effect mechanical movements.
Probably, now it's too late to change the design, but wouldn't it better to build a belly-lander with main rockets on the tail, landing/take
-off rockets on the belly, plus four landing legs?
A belly-lander is much more stable and would be a more practical surface habitat for the astronauts, who don't need to take a complex elevator every time they return from an exploration, but a simple ramp with steps.

SpaceNut · 2021-06-03 20:35:44

These are the landing legs of the Falcon 9 at launch

How they appear once opened

Here is the math for a stable landing for these legs

tahanson43206 · 2021-06-04 04:25:46

For SpaceNut re #64

Thanks for those images and the drawing .... by any chance, does your source include an explanation of how the brace arms are stowed and deployed? The illustration shows the brace arms locked into position at the ends of the aeroshell, but not how they get to that state.

The tops of the brace arms are shown pivoting around a fixed mount on the side of the rocket.

The brace arms may be hydraulic or perhaps spring loaded ... there is a hint of a line in the drawing, suggesting the brace arms may be segmented and (perhaps) stowed in a collapsed state.

(th)

louis · 2021-06-04 05:24:57

Thanks - that's helpful!

I think there is a danger of thinking this is a more difficult problem than it will be in reality.

1. The landing site will be chosen for being under 5% gradient over a large area.

2. The landing area will be surveyed closely by satellite.

3. Robot Starships will land before human passenger Starships.

4. There is no wind force on Mars that could blow over a Starship standing on a less than 5% gradient.

5. There will be lots of test landings on Mars analogue surfaces on Earth. Much will be learned from that.

6. The human landers can be given some ballast, or the cargo packed in such a way, so as to improve stability.

How the legs issue will be resolved will be fascinating!

I am more concerned about the launch to Earth. So much could go wrong in filling propellant tanks...maintenance won't be easy...and how many testing procedures can you run on Mars compared with Earth (I doubt we can replicate them all).

SpaceNut wrote:

These are the landing legs of the Falcon 9 at launch
https://i.imgur.com/UwzAzpY.png
How they appear once opened
https://www.cgstudio.com/imgd/l/39/5a50 … egs_08.jpg
https://www.cgstudio.com/imgd/l/34/5a50 … egs_07.jpg
Here is the math for a stable landing for these legs
https://i.stack.imgur.com/w03Q1.png

SpaceNut · 2021-06-04 19:10:25

The falcon 9's legs use hydraulic fluids and it ran out when trying to extend it on several of them early on.

The Falcon 9 core itself is about 47.7 meters tall, 3.1 meters in diameter.
Leaving a gap between each attachment of the 4 legs would need to change as GW has indicated as well as placement.

Oil rig or not landing the first stage booster may also require legs simular to the falcon 9's as well.

https://www.spacex.com/media/starship_u … ide_v1.pdf

I believe its an 8 meter core diameter.

The full-size prototypes of the 165-foot-tall (50 meters) Starship spacecraft would be top heavy with its payload location.
With the Super Heavy, the 230-foot-tall (70 m) booster would require even heavier duty legs for a good landing to happen.

I think both have changed a bit from this drawing
starship-and-super-heavy-booster-spacex-3d-model-obj-fbx-stl-blend-dae-gltf.jpg

tahanson43206 · 2021-06-06 10:39:45

YouTube video showing closeup of landing legs Falcon 9 First stage.

https://www.youtube.com/watch?v=Tox9uu4QtMg

Here's a model of the legs showing possible action: https://www.instructables.com/Building- … ding-Legs/

(th)

SpaceNut · 2021-06-20 08:24:33

GW has been working on another landing leg version for the starship
http://exrocketman.blogspot.com/2021/06 … ept-2.html

concept%2B2.png

these look more like the suborbital ship of Bezo

dp-jeff-bezos-blue-origin-conducts-20180718

Oldfart1939 · 2021-06-20 10:19:44

Just an eyeball estimate from GW's drawings: it would appear that the stability would be decent but less than optimal. I am making a WAG that it could be as much as 20 degrees from vertical and still survive without tipping over. It depends on the true COG location.

NewMarsMember · 2021-06-23 08:10:40

While we wait for GW Johnson to secure a replacement for his laptop, we have updates by email ...

Gary Johnson
Tue, Jun 22, 9:51 AM (1 day ago)
to me
Lessee, I have two concept design studies on "exrocketman" for landing legs. There's illustrations in both. The first has lots of bending, the second loads the legs all-compression. I think these two extremes probably bound the spectrum of practical designs which Spacex might use, so I don't plan to do any more.
I've noticed a lot of readership on "exrocketman" on articles related to ramjets and the aerothermodynamics of high speed flight. One of those was an article about the SA-6. I thought I might add one about ASALM-PTV, another ramjet.
GW
(th)

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#51 2021-03-18 09:55:36

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

#52 2021-03-18 10:58:01

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

#53 2021-03-18 15:43:20

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

#54 2021-06-03 20:35:44

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

#55 2021-06-04 04:25:46

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

#56 2021-06-04 05:24:57

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

#57 2021-06-04 19:10:25

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

#58 2021-06-06 10:39:45

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

#59 2021-06-20 08:24:33

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

#60 2021-06-20 10:19:44

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

#61 2021-06-23 08:10:40

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

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