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#1226 2021-06-01 18:35:02

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 22,148

Re: Starship is Go...

The legs have a two fold problem in that thermal protection to some of them must be afforded that is not reusable and the other is the mass penalty for legs to support the mass change of the starship as compared to a Falcon 9. Final fork is the need still for a harder surface than sand mixed rock that is uneven though it looks flat.....

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#1227 2021-06-03 08:21:24

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,384
Website

Re: Starship is Go...

I'm considering a concept based on an upgrade to the Falcon-9 legs,  scaled up to Starship size.  There would be a pad surface that folds out from the tip.  The two on the windward side would have heat shield tiles on the outer surface.  It would be hydraulically actuated,  so as (1) to refold upon takeoff,  and (2) to provide both hydraulic shock absorption and accommodate uneven ground. 

I'm not going to actually design these;  that's for Spacex to do,  and they bloody well already know that.  But I can give them some numerical criteria to start their design.  I'm working on it,  pencil-and-paper style.  Nothing to show yet.

As for leaving legs behind,  I think that's a bad idea.  There are 3 scenarios where you want to take the legs with you when you launch,  because you need to land again.  (1) an off-site abort landing on Earth:  you offload any payload, make the necessary repairs,  reload a partial propellant load,  and fly it out to a proper site,  and land again.  (2) the Mars mission with return to Earth:  it has to land direct on Earth,  there is no stopping in orbit.  (3) Any moon mission that delivers cargo to the moon from Earth,  and returns to Earth for use,  must land direct on Earth;  there is no stopping in orbit.

Those 3 scenarios are pretty common items.  That being the case,  what is the point of one-shot legs left behind?  You cannot do the baseline Mars and Moon missions,  nor handle an off-site abort Earth landing,  if you go that route. 

GW

Last edited by GW Johnson (2021-06-03 08:23:08)


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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#1228 2021-06-03 09:34:14

tahanson43206
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Registered: 2018-04-27
Posts: 6,070

Re: Starship is Go...

For GW Johnson re #1227

Thanks for letting us know you are working on the legs design!

Regarding the idea of vessels from outside LEO being forced to land on Earth .... I suspect you'll find that the fast majority of future space vessels designed for inter-body travel will NOT land on a surface ... of any kind.

There may be a primitive, early stage of development when that is all humans are capable of.  I'm assuming it is that stage you are thinking about.

The Large Ship (as I understand it) is NOT intended to land on the surface of ANY solar system body, so clearly the mechanics of slowing into LEO and into LMO will have been solved by the time that vessel is flying.

(th)

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#1229 2021-06-03 10:05:32

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,108

Re: Starship is Go...

My thoughts on the Mars vessels for landing & return to Earth. The Lunar Lander concept with the engines high on the vehicle is the most workable concept that I've seen for landing in rough areas. This comes at a weight penalty of additional engines, but protects the vehicle from exhaust debris damage on landing. I suspect the first ones will need to land this way without prepared landing pads, and could be considered one-way transporters. Have large and adequate legs to avoid tip-over. Maybe the freighter vessels could be so designed and executed?
Musk has already commented that the first freighters would be one way trips.

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#1230 2021-06-03 10:37:37

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

How about combining the current collapsible legs with three stabilisers - a hinged steel  construction (a bit like a sideways ladder) that would come down immediately on landing, forming an outward V (locked into place) with the lower side of the V resting on the surface - not weight bearing but stabilising, preventing any toppling. I'm thinking maybe 4 metres long on the surface and 8 metres high when folded against the side of the rocket. So three (or 4 or 5 ) of those.


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

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#1231 2021-06-03 16:20:06

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,108

Re: Starship is Go...

Louis-
4 Meter long landing legs only make the circle of support  for landing 9m +4m +4m. 17 meters diameter is too small and it needs to be a higher fraction of the vehicle height for stability. GW has given numbers that are reasonable to prevent tip-over.

Last edited by Oldfart1939 (2021-06-03 16:21:24)

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#1232 2021-06-05 19:54:43

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...


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

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#1233 2021-06-05 20:00:56

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Ballast has got to come into this equation. If you can pack heavy cargo in the lower 10% section then that is going to have an effect on stability.

What are the factors on Mars that will cause a Starship to topple over compared with Earth? The only ones I can think of (given the JPL landing sites) are:

1. Too hard landing (a matter of good rocket control technology, not leg design).

2. Ground subsidence (I don't believe that is likely given the data that can be derived from Mars satellites).

3. Sliding on landing (a matter mainly of good technology but leg design can help).

4. Gradient greater than 5% (that ain't gonna happen).

Oldfart1939 wrote:

Louis-
4 Meter long landing legs only make the circle of support  for landing 9m +4m +4m. 17 meters diameter is too small and it needs to be a higher fraction of the vehicle height for stability. GW has given numbers that are reasonable to prevent tip-over.


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

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#1234 2021-06-05 23:43:06

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,108

Re: Starship is Go...

Louis-
I suggest you go and buy  basic textbook on Statics. You are making statements about a subject that is simply straight physics as understood by every engineer that graduated from a university. Statics is the study of forces on objects at rest. We're talking about a very simple concept of center of gravity or center of mass. It must be over a polygon shape as defined by the points of contact of the legs with the supporting surface. If the system is leaning and the CG is over the edge of the polygon--it topples over.

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#1235 2021-06-06 05:17:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

But the CG is lower with low level ballast isn't it? I'm just saying that's one of the factors to take into consideration.

Oldfart1939 wrote:

Louis-
I suggest you go and buy  basic textbook on Statics. You are making statements about a subject that is simply straight physics as understood by every engineer that graduated from a university. Statics is the study of forces on objects at rest. We're talking about a very simple concept of center of gravity or center of mass. It must be over a polygon shape as defined by the points of contact of the legs with the supporting surface. If the system is leaning and the CG is over the edge of the polygon--it topples over.


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

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#1236 2021-06-06 05:57:45

tahanson43206
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Registered: 2018-04-27
Posts: 6,070

Re: Starship is Go...

For Oldfart1939 ...

Thanks for your patience in trying to explain the concepts you've presented in this topic.

A (possibly subtle) point in this discussion is that Louis is both right and wrong at the same time.  He has a mental picture (based upon his words) that is correct, but a rocket cannot be constructed as he is imagining, so he is wrong about the real world situation.

Somewhere recently, a member posted diagrams/graphics showing precisely what you are talking about.

If someone can find that post I'd appreciate having the link here is this topic.

(th)

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#1237 2021-06-06 08:23:29

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

I'm pretty sure I've seen diagrams suggesting there would be storage space below the tanks, parallel to the rocket nozzle area I guess, which I think you might be able to pack with small robots and EV batteries.

tahanson43206 wrote:

For Oldfart1939 ...

Thanks for your patience in trying to explain the concepts you've presented in this topic.

A (possibly subtle) point in this discussion is that Louis is both right and wrong at the same time.  He has a mental picture (based upon his words) that is correct, but a rocket cannot be constructed as he is imagining, so he is wrong about the real world situation.

Somewhere recently, a member posted diagrams/graphics showing precisely what you are talking about.

If someone can find that post I'd appreciate having the link here is this topic.

(th)

Last edited by louis (2021-06-06 09:19:47)


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#1238 2021-06-06 09:41:48

tahanson43206
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Registered: 2018-04-27
Posts: 6,070

Re: Starship is Go...

For Louis re #1237

It would be helpful if you could show the diagrams you're reporting having seen.

(th)

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#1239 2021-06-06 09:45:59

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,108

Re: Starship is Go...

I think Louis is possibly referring back to an early Elon Musk comment about having cargo area at the extreme aft of the Starship and possibly surrounding the engine bay; this was in one of his televised broadcasts that announced the "Dear Moon" mission. I suspect that with the Raptor engine problems, that concept has probably gone by the boards

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#1240 2021-06-06 10:35:24

tahanson43206
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Registered: 2018-04-27
Posts: 6,070

Re: Starship is Go...

For all who might wonder how Falcon 9 legs work ...

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

This YouTube presenter visited a Falcon 9 that is on display at a SpaceX facility after it successfully landed.

The video does show the actual parts on display, and the discussion offered by the presenter, show that the legs are simply released from the top, and they spring out under the influence of gravity and (quite possibly) pressure inside the extension tubes.

There is a  brief segment showing the legs extending during flight, just before landing, but there is not a lot of detail.

I would appreciate anyone who might be able to come up with actual engineering drawings to add them to this, but this video is definitely a useful start.

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

(th)

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#1241 2021-06-06 16:28:31

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Yes I'll hunt across millions of posts on multiple sites just to...er no I won't. It's a recollection I have. That's all I can say.

But if you look at this diagram:

https://www.humanmars.net/2021/01/cutaw … rship.html

You can see there is definitely space between the hull and the raptor engines (ie below the tanks). It looks like it could be as much as 1.5 metres in width, so 2 x 1.5 metres - 3 metres as a cross section. It is here I would ensivage the stowage being. You could probably pack in small robot vehicles. I don't know how safe it would be to house batteries as well but they would obviously be great as ballast. A robot scout vehicle would be useful - one that could go into action very soon after landing.


tahanson43206 wrote:

For Louis re #1237

It would be helpful if you could show the diagrams you're reporting having seen.

(th)


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

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#1242 2021-06-06 16:29:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Thanks OF...seems I didn't imagine it after all. See my other post above - there is definitely space there for some storage.

Oldfart1939 wrote:

I think Louis is possibly referring back to an early Elon Musk comment about having cargo area at the extreme aft of the Starship and possibly surrounding the engine bay; this was in one of his televised broadcasts that announced the "Dear Moon" mission. I suspect that with the Raptor engine problems, that concept has probably gone by the boards


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

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#1243 2021-06-06 17:19:48

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 22,148

Re: Starship is Go...

The full starship will have 3 more engines optimized for space use that will fill out the compartment.

edit
yes louis but they are not flying with them currently is what I was pointing out....

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#1244 2021-06-06 18:37:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

You didn't look closely enough. The diagram shows six engines. 3 space vaccuum and 3 sea level. In any case, that's irrelevant as they won't crowd out the potential storage space. Engines have to be below the tanks and that's what creates the storage space. 

SpaceNut wrote:

The full starship will have 3 more engines optimized for space use that will fill out the compartment.


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

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#1245 2021-06-06 18:47:20

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Nice evocation of life around Boca Chica. Hope they don't kill off all the birdlife with Starbase City.

https://www.youtube.com/watch?v=HyjM3HxjSUU

Loving that 48 wheel carrier thing!

Don't think I've ever seen an actual downcomer in the wild!

OK make that 72 wheel!

Last edited by louis (2021-06-06 18:49:40)


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

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#1246 2021-06-10 16:59:52

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

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

Excellent detailed presentation on the launch tower and mount being built at Boca Chica.


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

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#1247 2021-06-11 14:23:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Felix's latest video:

https://www.youtube.com/watch?v=-r6JsCBThPo

It includes a section on the rocket company, Relativity Space.  A dark horse sprinting to the finish line!

It's interesting that their rocket technology depends on 3D printing. This could be very relevant to Mars colonisation.


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

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#1248 2021-06-11 17:44:20

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,483

Re: Starship is Go...

Bumping in view of multiple posting of links without commentary.


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

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