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#551 2020-03-23 18:34:48

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

The latest from Felix.  Very helpful update. Incorporates a "3D" representation of the Boca Chica site (from another site).

https://www.youtube.com/watch?v=rNangu73_tE

Starship development is going well - despite Covid19

Last edited by louis (2020-03-23 18:35:21)


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#552 2020-03-24 20:00:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

Good progress being made on SN4 as well as SN3.

https://www.youtube.com/watch?v=Ir5i0IzjuFU


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#553 2020-03-27 20:38:51

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

I love these videos! Is there any better sight than purposeful activity on a grand scale?

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

Here's hoping that Space X can weather the Coronavirus storm and continue with assembly. Things are looking good so far...


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#554 2020-03-29 19:52:07

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

Don't drop it!

https://www.youtube.com/watch?v=m80_jf5x3IE

SN3 being mounted on the launch pad...

Great work guys!


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#555 2020-03-31 04:36:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

Latest video from Boca Chica. It really gives you an excellent idea of the scale of the rocket. It's one thing to know its dimensions, another to see it up close with people working on its exterior for reference!

https://www.youtube.com/watch?v=jo9Ckxv6Wa8

Great to see work carrying on apace...

Here's Felix's latest as well:

https://www.youtube.com/watch?v=ty0Urm- … 1Q&index=1

Looks like they are going to use a hinged leg system on SN3 but Felix says it is unlikely to be the final iteration for the production model.

A lot will depend on those hinges when it comes to land on Mars!

Last edited by louis (2020-03-31 04:37:40)


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#556 2020-03-31 08:53:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,368

Re: Starship is Go...

The current leg is a hinge hydralic system and I would have thought that they would have gone with what works.
It works as its already been testeed for landing, heat of re-entry and such.
Adding a fairing shield over the current design is a minimal mass for higher entries of a use once format since starship would launch with legs being tucked in to start with..

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#557 2020-03-31 19:29:46

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

Well of course it has to work on potentially rougher ground than a dedicated landing site if it's going to Mars.

SpaceNut wrote:

The current leg is a hinge hydralic system and I would have thought that they would have gone with what works.
It works as its already been testeed for landing, heat of re-entry and such.
Adding a fairing shield over the current design is a minimal mass for higher entries of a use once format since starship would launch with legs being tucked in to start with..


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#558 2020-03-31 19:33:37

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

The word awesome is rather overused but in this case it's perfectly justified:

https://www.youtube.com/watch?v=WjUxjRTqK5I


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#559 2020-04-01 01:25:20

Mark Friedenbach
Member
From: Mountain View, CA
Registered: 2003-01-31
Posts: 322

Re: Starship is Go...

Louis, a rocket of that size is more likely to blast a crater in the ground and destroy its own landing gear if landing on random terrain. Among people who are seriously looking at this (like Dr Phil at UCF), it seems more likely that a precursor mission would be required to prepare a landing site for Starship arrival. This would involve sintering a rough but level landing pad.

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#560 2020-04-01 05:31:22

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

You think it would blast a hole in a granite mass? I doubt it. How is a granite mass different from a concrete landing pad? I don't think anyone is proposing landing on loose regolith.

Mark Friedenbach wrote:

Louis, a rocket of that size is more likely to blast a crater in the ground and destroy its own landing gear if landing on random terrain. Among people who are seriously looking at this (like Dr Phil at UCF), it seems more likely that a precursor mission would be required to prepare a landing site for Starship arrival. This would involve sintering a rough but level landing pad.


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#561 2020-04-01 17:34:08

Mark Friedenbach
Member
From: Mountain View, CA
Registered: 2003-01-31
Posts: 322

Re: Starship is Go...

Where would you possibly find an existing, level, flat slab of granite with no regolith covering and near where you wanted to land anyway?

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#562 2020-04-01 18:59:20

kbd512
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Registered: 2015-01-02
Posts: 3,348

Re: Starship is Go...

The surface of Mars is estimated to be covered, in most places, with at least 10 feet of fine dusty regolith.  Much of it undoubtedly contains loose rocks mixed in with it.  However, there are certain places that are relatively flat and free of loose debris.  However, I don't think I'd want to bet the lives of the crew and the mission on being able to land there.  None of this would be a significant problem with wide-track landing gear and large landing pads.  I think GW did a writeup on this some time ago.  If you can't guarantee where you'll land, then you design your landing gear to support the weight of the vehicle, without falling over, in the type of fine dusty sand they have in Iraq.  If you can land on an Iraqi sand dune, then you can land on Mars.

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#563 2020-04-01 19:49:15

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

https://www.youtube.com/watch?v=yxh5QfCtZwk

What do you think guys? Will it fly??

Are those perforations in the skin of the rocket at 5:10? Is this supposed to be something to do with cooling?

Last edited by louis (2020-04-01 19:59:32)


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#564 2020-04-01 19:52:52

louis
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From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

Have you not seen the NASA/JPL locations for possible landings in the Amazonis/Arcadia border region? They were supplied at Space X's request. There was also the NASA conference which solicited lots of suggestions for landing sites in line with defined criteria on gradient and landing surface etc.

Not everywhere on Mars is knee-deep in sand and loose regolith!

A couple of inches of sand cover can just be blown away.


Mark Friedenbach wrote:

Where would you possibly find an existing, level, flat slab of granite with no regolith covering and near where you wanted to land anyway?


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#565 2020-04-01 19:57:04

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

You don't have to bet the life of your crew. We have lots of satellite coverage. That can determine what sort of surface there is. Satellite photography can be resolved down to something like 10 cm objects (using computer analysis of repeated fly-overs).

The beauty and intelligence of Musk's approach is that you first send robot cargo craft to the general landing area, two years before humans land. No doubt that will allow you to do a detailed visual and laser/radar survey of the surrounding land to pinpoint a landing area for the human passenger Starship. People - like you - always seem to forget that! smile


kbd512 wrote:

The surface of Mars is estimated to be covered, in most places, with at least 10 feet of fine dusty regolith.  Much of it undoubtedly contains loose rocks mixed in with it.  However, there are certain places that are relatively flat and free of loose debris.  However, I don't think I'd want to bet the lives of the crew and the mission on being able to land there.  None of this would be a significant problem with wide-track landing gear and large landing pads.  I think GW did a writeup on this some time ago.  If you can't guarantee where you'll land, then you design your landing gear to support the weight of the vehicle, without falling over, in the type of fine dusty sand they have in Iraq.  If you can land on an Iraqi sand dune, then you can land on Mars.


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#566 2020-04-01 20:16:22

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,368

Re: Starship is Go...

Have we seen any voids and at what depths below the surface with radar?
Can we garantee that there are no cracks to make that surface over that void not weak to a large mass landing?

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#567 2020-04-01 20:19:54

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

If you  want to be an explorer don't expect someone to supply you with a 100% guarantee that you won't suffer any ill effects from your exploration of new territory.

However, I think a combination of satellite observation, scientific deduction (geological knowledge) and - most importantly - the robot landers that will arrive 2 years before humans land.

SpaceNut wrote:

Have we seen any voids and at what depths below the surface with radar?
Can we garantee that there are no cracks to make that surface over that void not weak to a large mass landing?


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#568 2020-04-01 20:38:13

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,368

Re: Starship is Go...

But do you want 100 deaths as that will end it all in just a single trip for man never to go again.... you can not just think you need to know....
Just how many ships are in that robotic landing?
Just how many are with that Manned landing assuming its a mixed cargo as well?

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#569 2020-04-01 20:45:49

kbd512
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Registered: 2015-01-02
Posts: 3,348

Re: Starship is Go...

Louis,

Satellites can't tell you how compacted the ground is.  If they could, then the US Air Force would use them before landing C-130's on soft terrain instead of sending a man ahead in a smaller aircraft or on foot to test the ground with a soil compaction probe.

In order for a spaceship to be reusable it has to come back.  Maybe you can land a nearly empty Starship with those tiny pads it has on it, but after you fill it with 1,200t of propellant you need a proper landing gear design for soft sand or it's going to topple over.  Furthermore, you don't always get to land exactly where you want to.  That's why you design the landing gear to land in the types of places where you intend to land.  At the very least, the cargo landers have to be able to land successfully, irrespective of how soft the terrain is, in order for this scheme to work.  The beauty and intelligence of designing landing gear for rough terrain is that you can reliably land on that terrain. smile

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#570 2020-04-01 23:28:42

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,831
Website

Re: Starship is Go...

I've been through this with Louis before,  and he chooses not to believe me either.  So don't feel alone,  Kbd512.

But I really do understand soil mechanics and bearing strength,  having designed foundations professionally.  I know how to build a slab foundation such that the walls and superstructure never crack,  even when you throw this slab on bentonite clay with a plasticity index exceeding 70.  I've designed such,  and they never cracked,  not in all these years.  Such slab foundations do NOT look much like the "usual" during construction,  but once the house is built and landscaped,  you won't see the difference. 

What Spacex currently has with those 6 legs (or the 3 fin-legs before it) is ONLY for landing on a thick,  steel-reinforced concrete pad that is surfaced smooth and very,  very level.  Mother nature does NOT make rock outcrop layers sufficiently smooth and sufficiently level to support landing a ship that tall on 6 legs spaced that close together. 

And until you stand on that rock layer with a drill or jackhammer,  you WILL NOT know how thick it really is.  Or whether there are cavities underneath,  leaving it locally unsupported.  Rock has poor bending strength,  because it has poor tensile strength.  It is great in compression,  and good in shear.  PERIOD.

In my opinion as a registered professional engineer for 41 years now,  I pretty much KNOW that Spacex has not thought through the rough field landing problem yet. 

They should have,  because they will sooner or later have to make a rough-field abort landing here on Earth,  most likely during flight testing,  so it's most likely sooner than later.  The soil penetration and topple-over risks are just as bad here on Earth,  or worse (higher gravity).

GW


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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#571 2020-04-01 23:57:36

Mark Friedenbach
Member
From: Mountain View, CA
Registered: 2003-01-31
Posts: 322

Re: Starship is Go...

I think my earlier point wasn't conveyed adequately. NASA is currently doing research on what large, hot, plasma plumes do to regolith surfaces in lower gravity, mainly for the purpose of landing on the moon but a lot of the research carries over to Mars. It's turning out that we got very, very lucky on Apollo without knowing it. One of the people doing this is Dr. Phil Metzger of UCF, and he's been great about answering questions on Twitter. Here's one specifically about landing Starship on a fine-grained regolith environment:

https://twitter.com/DrPhiltill/status/1 … 3942992898

In short summary, it seems that larger landers than Apollo risk creating a deep crater during landing, which in turn causes the rocks and dust to start getting blown out closer to vertical than we saw with Apollo, and risk damaging the other engines and landing gear. It also means that the hot plasma exhaust starts going deep into the ground, where it could get trapped in cavities, causing an explosive blowback event. Finally, regolith (on the moon or Mars) consists of extremely fine powders whose physics isn't really well characterized, and for which there isn't really any terrestrial analogue (even the course simulants we use), and we have a hard time predicting its behavior when subjected to the extremes of a rocket landing.

The current plan for the moon is to land a small, solar powered rover before any very large lander. The rover would be able to clear and level an area large enough to serve as a landing pad, and use microwaves (or perhaps lasers) to heat the regolith material. The resulting sintered material would work as a makeshift landing pad for the first couple of landings.

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#572 2020-04-02 07:14:01

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

But that is the point of the cargo craft landing first. That will give you a very good indication of ground conditions which you can then further investigate up close with lasers, radar and cameras, robotically, controlled from Earth.

GW Johnson wrote:

I've been through this with Louis before,  and he chooses not to believe me either.  So don't feel alone,  Kbd512.

But I really do understand soil mechanics and bearing strength,  having designed foundations professionally.  I know how to build a slab foundation such that the walls and superstructure never crack,  even when you throw this slab on bentonite clay with a plasticity index exceeding 70.  I've designed such,  and they never cracked,  not in all these years.  Such slab foundations do NOT look much like the "usual" during construction,  but once the house is built and landscaped,  you won't see the difference. 

What Spacex currently has with those 6 legs (or the 3 fin-legs before it) is ONLY for landing on a thick,  steel-reinforced concrete pad that is surfaced smooth and very,  very level.  Mother nature does NOT make rock outcrop layers sufficiently smooth and sufficiently level to support landing a ship that tall on 6 legs spaced that close together. 

And until you stand on that rock layer with a drill or jackhammer,  you WILL NOT know how thick it really is.  Or whether there are cavities underneath,  leaving it locally unsupported.  Rock has poor bending strength,  because it has poor tensile strength.  It is great in compression,  and good in shear.  PERIOD.

In my opinion as a registered professional engineer for 41 years now,  I pretty much KNOW that Spacex has not thought through the rough field landing problem yet. 

They should have,  because they will sooner or later have to make a rough-field abort landing here on Earth,  most likely during flight testing,  so it's most likely sooner than later.  The soil penetration and topple-over risks are just as bad here on Earth,  or worse (higher gravity).

GW


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#573 2020-04-02 08:02:50

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,831
Website

Re: Starship is Go...

Louis:

The point is that it is unlikely in the extreme that a Starship can make a successful landing,  whether as an unmanned cargo craft or not.  It is far more likely to penetrate in unevenly,  which forces it to lean,  and very little leaning makes a tall thing topple over.  It WILL explode when it does topple over.

If Spacex sends 2-3 unmanned cargo ships to Mars,  and they all get destroyed upon touchdown,  then what is the point of sending any more?  It's the wrong design to land safely.  That's a program killer,  and you bloody well ought to understand that.

I've still got to look at Mark's "DrPhil" stuff. 

GW

PS - initial look at "DrPhil" stuff is discouraging in that there may be another bad problem to solve,  but encouraging in that at least somebody is looking at it.  Meanwhile the surface bearing pressure/penetration issue and the static stability/topple-over issue that I keep raising still apply here. 

The landing mass for Starship on Mars is as yet an unpublished unknown,  but an educated guess says perhaps 120 m.ton inert structural mass,  plus 100 ton cargo plus around 10 tons unused propellant,  for about 230 metric tons.  For the 6-legged design they currently show,  that's about 38 tons per leg to support.  At 0.38 gee,  that's about 143 KN static force per leg. 

Double it for the touchdown impact-effect dynamics to about 289 KN force per leg,  which is typical design practice.  Now guess a landing pad surface area as a circle about 0.5 meter diameter.  That's something on the order of 0.196 sq.m bearing area per leg.  the peak dynamic touchdown bearing pressure is leg force/pad area which is just a hair under 1.5 MN/sq.m = 1.5 MPa.  The static pressure is near 0.75 MPa,  which would be OK.

Typical fine sand here on Earth has a max allowable bearing pressure limitation of 1-2 MPa.  You have to treat it as "the weakest link",
which is 1 MPa.  That kind of surface is identical to 98+% of the surface of Mars!  So landing the Starship is "iffy" at best.  Once the landing dynamics are over,  you are OK,  but the risk here is "stabbing" the legs into the regolith during the transient. 

If that happens,  they WILL penetrate unevenly,  and the ship will very likely topple over,  precisely because it is tall and narrow.  5-6 degrees out-of-plumb is fatal to a geometry like that.

As for refueling on Mars for the return,  the loaded weight is around 6+ times higher,  so the bearing pressure is also 6+ times higher.  Transient effects don't apply,  so that is 6+ x 0.75 MPa = 4.5+ MPa compared to max allowable 1-2 MPa.  It'll sink in unevenly and topple-over (and explode) as you try to refill it. Rather certainly.

I'm sorry to bust dreams here,  but the numbers DO NOT lie!

Those same numbers are about 3 times higher here for Earth gravity.  That increases the rough-field disaster risk.  Which is why I keep saying Spacex is going to run smack into this design shortcoming,  the first time they have to do a rough-field abort landing,  which will hopefully be while they are still in flight test.  And they will run into this.  Murphy's Law says so.

Last edited by GW Johnson (2020-04-02 08:32:06)


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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#574 2020-04-02 08:13:31

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,368

Re: Starship is Go...

When that first contingent of ships (unknown quantity presumed 6) arrive with cargo each ship (100mt or less onboard if fuel boiloff sensitive in addition to day/night side landing are not planned for) will be a minimal duplicates (no manifest of mass or quantity of any item created) of each other (not even the solar/battery can provide for the fuels for a single ships return collectively on 6 ships full of just that) and that the spacing of there landings are going to be with a elipse shaped circle 1 to 10 kilometer wide and long as there is no x to mark the spot, no gps or beacons already on the ground that we want to land within such as to get them closer together so as to have that equipment team its robots into a combined network or resources to prepare the way. Videos are not plans as you need words and numbers record in print to work calculations as they are referenced and revised with documents that all are making the use of just the latest and greatest not the out of date data which is still being comingled....

Thanks for the updated landing information GW.

We also need to add to the mass for any sort of disease or long lying health issue with PPE, equipment to save life in testing and vacine creation as a dead crew will end it all....

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#575 2020-04-02 09:37:57

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,657

Re: Starship is Go...

This is the best resource I know for landing sites:

https://www.nasa.gov/feature/mars-human … sentations

The possibility of sinking into a big hole doesn't seem to be a real threat. The lunar surface, knee-deep in powder seems just the wrong model for Mars.  Earth is a much better model.  With that in mind I am sure that there will be numerous test landing on the Earth's surface. With the higher gravity on Earth, that should provide a margin of safety in terms of comparison with Mars.


Mark Friedenbach wrote:

I think my earlier point wasn't conveyed adequately. NASA is currently doing research on what large, hot, plasma plumes do to regolith surfaces in lower gravity, mainly for the purpose of landing on the moon but a lot of the research carries over to Mars. It's turning out that we got very, very lucky on Apollo without knowing it. One of the people doing this is Dr. Phil Metzger of UCF, and he's been great about answering questions on Twitter. Here's one specifically about landing Starship on a fine-grained regolith environment:

https://twitter.com/DrPhiltill/status/1 … 3942992898

In short summary, it seems that larger landers than Apollo risk creating a deep crater during landing, which in turn causes the rocks and dust to start getting blown out closer to vertical than we saw with Apollo, and risk damaging the other engines and landing gear. It also means that the hot plasma exhaust starts going deep into the ground, where it could get trapped in cavities, causing an explosive blowback event. Finally, regolith (on the moon or Mars) consists of extremely fine powders whose physics isn't really well characterized, and for which there isn't really any terrestrial analogue (even the course simulants we use), and we have a hard time predicting its behavior when subjected to the extremes of a rocket landing.

The current plan for the moon is to land a small, solar powered rover before any very large lander. The rover would be able to clear and level an area large enough to serve as a landing pad, and use microwaves (or perhaps lasers) to heat the regolith material. The resulting sintered material would work as a makeshift landing pad for the first couple of landings.


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