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#26 2018-05-12 15:51:20

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

SpaceNut,

As a function of mass and volume, it's possible to ship electronics components as complete spare parts to have complete replacements available.  However, anything with a lot of metal in it needs to be created on-demand on Mars.

It will be necessary to fabricate replacement engine parts, so major components must be designed in a manner that makes it possible to print new parts using 3D printers and recycled materials from damaged or defective parts.  3D printing is already done in some of SpaceX's more simplistic engines, but I believe that major components of the main engines like the injector plate assemblies, turbine blades, turbine housings, and nozzles need to be designed and built in a manner that permits use of this technology when, not if, required.  It's ignorant to think that engine parts won't fail and it's also impossible to carry enough raw materials to fabricate new components from scratch.  Rocket engines necessarily tear themselves apart in normal operation as a function of the performance demanded of them.  Obviously the propulsion engineering team should design components to live as long as they possibly can, but contingency plans for inevitable failures should be in place as well.

The machine shop module must include the ability to smelt metals, remove impurities, and grind the recycled product into powders to provide feed stock for remanufacturing and refurbishment to limit the quantities of metals powders that must be imported.  If you have your own machine shop, then you don't need a continuous supply of spare parts from Earth, just finished machines and a little raw material to repair those machines when necessary.

Aluminum wiring should be specified to reduce mass and higher voltages should be specified to reduce current flow and thus the required gauge or volume of the wiring.  The use of a 24V bus and copper wiring may be fine for a capsule like Orion because the wiring runs are short, but everything being built by SpaceX is being built at significant scale and the mass economics of that scale must be carefully considered.

To reduce the need for specialized connectors and associated materials, wiring connections should be made using poly magnet sleeves that "lock" with a quarter or half rotation.  There's a company named "Polymagnets Correlated Magnetics" that "prints" North/South patterns on permanent magnets that cause repulsion at one distance or orientation and attraction at another distance or orientation using a pair of special magnets with varying imprinted patterns.

Anyway, this is just a couple of the examples of the very thoughtful "maintainable in an austere environment" engineering work that needs to go into this project.

In my opinion, NASA and JPL should proceed with the MARCO POLO project to test the ability to extract water from regolith for LOX/LCH4.  If this is the lynch pin technology that makes surface exploration affordable, then this is what the next lander should test.  It's an engineering technology demonstrator mission, rather than a science experiment, but also includes one science experiment to try to find life in the ground.

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#27 2018-05-12 17:31:14

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,701

Re: Landing legs for the BFR

Each paragraph I will answer to as best that I can rather than quote and comment...

1. I agree that continuing to stay and the ability to create will need to have the key electronics for sure until we are able to transition away from deliveries of these devices from Earth. One we have the component manufacturing capability in place to do so and having 3D priniting as one of the first is a must. With the next that ability to make what we feed them with.

2. The chances for a failure of the key components is just the reason I indicated that we need some more robust technology developed, tried, proven and tested before counting on them for mars.

3. That sure is a transition step from supplying from earth and is a must to be able to expand operations on mars and of course that will allow for man to increase the return cargo back to earth as a result of being able to build there own rockets in time but for now recycle them if they can be and repair the parts that you can with the shop that is created for mars.

4. Will pass on aluminum wire for now as what I know is that it burns and then become less effective due to heat build up from being the lower sized conductors in homes resulting in fires. I also do not know enough about using multi strands versus a solid conductor that makes up the same conducting ability for aluminum that is possible from copper wire under the same application which takes away from the skinning effect of current that is to high as it does not pass through the core of the solid wire buit on the surface. This may be fine but will do the research to gain the knowledge.

5. nice information of the magnets to research as trhat makes single large conductors mate together quickly and would stay together via the discribed locking method.

6. agreed more engineer needs to be done to keep from contaminating mars or its crew once we do go.

7. "Marco Polo" hum...do you mean key items not fully developed for a mars use... if so agreed.. we will know once moxie is sent for oxygen creation soon, the next as you indicate is getting water and or hydrogen to make fuel would be the next from insitu sources of materials and we do need a final answer on going solar only, going with nuclear only or going with a mix of solar and nuclear to allow for a backup for the energy needs....

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#28 2018-05-13 03:01:36

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

SpaceNut,

The Airbus A380 uses Aluminum wiring to save weight.  The issues pertaining to using Aluminum wiring in houses was mostly a function of improper installation and connection methods.  All high voltage electrical transmission lines are made from Aluminum as a function of weight.

The polymagnets have been designed as both "twist to lock" connectors and Hall effect sensors for brushless DC motors.  Coatings can make the magnets electrically conductive, too.

MARCO POLO is a NASA ISPP experiment to produce LOX/LCH4 using Martian regolith and atmosphere.

Mars ISRU: State-of-the-Art and System Level Considerations

MOXIE is just a SOXE and O2 liquefaction experiment.  MARCO POLO is a complete ISPP plant.

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#29 2018-05-13 03:10:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

I would definitely like to see full testing in a rocky desert on Earth. Multiple hops would be a good way of testing, starting with areas of small rocks and building up to boulder-strewn areas.

Then I'd like to see long orbital/circumlunar and finally lunar landing testing, followed by a final Mars Mission simulation (several months in zero G followed by living on the Moon for several months and return after several months in zero G).

Oldfart1939 wrote:

All launches made so far have been from prepared launch pads with a strongback utilized for the rocket. Maybe they should attempt a launch from Cape Canaveral using just the landing legs as a starter? Use one of the recycled Block 4 rockets and see how THAT goes. Sooner or later, SpaceX needs to demonstrate that technology. Maybe some landings in Texas out in the desert? That would be a great stability demonstrator. No amount of enthusiasm and "trusting Elon to have something up his sleeve" can ever substitute as actual bad case scenarios experiments.


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

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#30 2018-05-13 03:16:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

One issue mentioned previously but I haven't seen discussed recently is whether rolled metal has particularly qualities (e.g. strength) you don't get from 3D printing.  Obviously if it does, that presents a problem. However, I remember doing some research, and it certainly was the case that medieval metal workers used to be able to produce very hard steel without rolling mills - simply by manual firing processes...so it may be an area where research is required as to how to achieve the results we get from mills on Earth in a 3D printing environment.


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

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#31 2018-05-14 16:48:02

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

3D printed parts are subsequently baked in an oven to obtain mechanical properties similar to MIM (Metal Injection Molding).  Rolling metal is a form of work-hardening of the material.  I guess it all depends on what you want to use it for.  If you meant to suggest that 3D printed designs may require different geometry and materials to obtain equivalent strength to other processes, then you're correct.  After sufficient infrastructure exists, the Martians can make their own metal smelters, forging presses and dies, CNC machines, etc.

Since we can already 3D print a rocket engine or a jet engine, I would like to know what you want to do with metal sheet, tube, or bar stock?  Make metal pipes or pressure vessels or forgings?  You'd want purpose built machinery for that.

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#32 2018-05-15 09:25:59

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,500

Re: Landing legs for the BFR

It's been a long time since I took metallurgy in school, but the strongest parts are generally forged. Louis mentions that medieval blacksmiths made very strong stuff, and that was due to the metal grain structure resulting from forging and heat treatment. It is still done today in making tools; forged wrenches and such, are considerably stronger than those made by investment casting. Cheap tools are not really cheap, because they routinely break (the kind of crap sold at various cheap stores), since they aren't forged.

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#33 2018-05-15 09:38:24

elderflower
Member
Registered: 2016-06-19
Posts: 879

Re: Landing legs for the BFR

Don't by cheap tools. They break at the most inconvenient moment at considerable risk to your knuckles.
And there's forging done properly from a billet and then there's forging that consists of a single blow on a cast form so the seller can say he forged it!

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#34 2018-05-15 10:14:41

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,185
Website

Re: Landing legs for the BFR

Some materials work-harden by cold-working,  and don't respond to heat treatment except annealing back soft.  Aluminum and austenitic stainless steels come to mind. 

Some others don't cold-work-harden effectively,  but do respond very well to hot work-hardening (forging),  and also to heat treatments,  which can get very complicated.  Most of the steels,  alloy steels,  and martensitic stainlesses fall in this category.

There is much more to toughness than just hardness (tensile strength).  You also need elongation,  which is mostly the plastic strain past the effective yield point,  however that gets defined.  It gets down to the integral of the stress-strain curve,  which is a measure of the energy a material can absorb before breaking. 

And strain rate gets into that in a really big way:  high strain rates (sudden loading) sharply lowering the strain at failure,  which lowers the integral of the stress-strain curve,  and thus lowering the energy to break the part.  That's brittleness. 

This is where wrought metal materials still have a big edge over 3-D-printed metal materials.  You have to make your 3-D part bigger and heavier to compensate for the brittle behavior,  although doing that is fairly straightforward.

I think I said elsewhere in another thread I've seen machines that make small metal 3-D printed parts of full density and tensile strength.  They are anything but desktop machines.  They are quite large,  heavy,  and power-consumptive.  That is what it still takes today to make a full-density printed part.  They're still short on elongation, so the parts are still more brittle than a wrought part,  but no longer too brittle to serve in most cases. 

The folks that make the good machines and the good parts are quite proud of them,  so the price tag is still quite high.  Eventually (several years),  the remaining brittleness problem will be solved,  and so will the price problem.  But it may be decades to centuries before the big,  heavy,  power-consumptive problem gets solved.  (Blast furnaces never did really shrink.)

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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#35 2018-05-15 17:42:07

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,701

Re: Landing legs for the BFR

Marco polo is just what it will be to get steady amounts from the unknown level of power to heat for the unknown water content from each shovel full loaded into the apparatus. The design is geared for the shaleton crater on the moon and may need modifications for mars as the moon was looking to use the ferensal lense solar for the heating of the soil in a chamber.

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#36 2018-05-15 17:54:12

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

We'll need quicker throughput and bigger machines for Mars if the model is the Space X mission.  That might require more power input, but power is the least of our problems on Mars I would say.

SpaceNut wrote:

Marco polo is just what it will be to get steady amounts from the unknown level of power to heat for the unknown water content from each shovel full loaded into the apparatus. The design is geared for the shaleton crater on the moon and may need modifications for mars as the moon was looking to use the ferensal lense solar for the heating of the soil in a chamber.


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

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#37 2018-06-22 12:04:29

Quaoar
Member
Registered: 2013-12-13
Posts: 401

Re: Landing legs for the BFR

Just out of curiosity, but how to protect the landing legs from being damaged by the rocket blast during take off from mars?

Last edited by Quaoar (2018-06-22 12:05:02)

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#38 2018-06-22 13:02:04

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

Maybe the landing legs need to be made of sterner stuff than the rest of the ship.  If that's not an option, then there's a solution that won't weigh too much and should solve the problem.  Clear the landing area of larger debris and then stake a high grade stainless steel mesh or chicken wire to the ground that won't melt for the few seconds it's exposed to the blast from the engines.

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#39 2018-06-22 14:45:43

Quaoar
Member
Registered: 2013-12-13
Posts: 401

Re: Landing legs for the BFR

kbd512 wrote:

Maybe the landing legs need to be made of sterner stuff than the rest of the ship.  If that's not an option, then there's a solution that won't weigh too much and should solve the problem.  Clear the landing area of larger debris and then stake a high grade stainless steel mesh or chicken wire to the ground that won't melt for the few seconds it's exposed to the blast from the engines.

Thanks

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#40 2018-06-25 03:05:17

elderflower
Member
Registered: 2016-06-19
Posts: 879

Re: Landing legs for the BFR

The Mars or Moon legs could be left behind. fit a second set, which could be smaller and less rugged, maybe less numerous, for Earth return if we use propulsive landing on Earth. Or land in a big lake, avoiding salt water corrosion.

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#41 2018-06-25 04:17:42

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

Presumably the landing legs currently avoid major damage on landing...or is the rocket blast on launch more than on landing? Seems unlikely to me...

Quaoar wrote:

Just out of curiosity, but how to protect the landing legs from being damaged by the rocket blast during take off from mars?


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

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#42 2018-06-25 04:29:47

elderflower
Member
Registered: 2016-06-19
Posts: 879

Re: Landing legs for the BFR

You aren't landing a full rocket, Louis. Just self weight and payload. So landing thrust is much less than takeoff.

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#43 2018-06-25 07:33:49

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

I don't care if the entire rocket is trashed and never flies again, so long as the people inside it are alive and well when they arrive on Mars.  I'm not all that concerned about the landing gear, except for the base width.  It's just too narrow to land a 150t mass (57t on Mars) sitting 30 meters above the gear.  I've never seen a M1 tank landed that way.  Until I see that happen, I'm skeptical.  I'm sure it can be made to work.  The only question is how many test articles make the blooper reel before the bugs are worked out and whether or not SpaceX and their investors can afford that.  The heat shield is as light as balsa wood, so it can't be that resistant to damage from debris, and that mandates some kind of inspection prior to reentry.

Anything that can handle that kind of weight will be durable.  I'm a lot more concerned with the effects of partially loading composite pressure tanks over many months, since I've no idea what effect that sort of temperature delta has on the material over the long run, and the condition of the turbopumps, given the insane pressure levels involved.  I would say that the RGO bi-layer is mandatory to prevent embrittlement or oxidation of the tanks.  Super-high pressures tends to trash turbine blades rather quickly, even with the best steels money can buy.  A stock of small parts and/or a 3D printer is mandatory.  The things that tend to fail generally don't weigh very much, which is a good thing.  It's always a $2 plastic widget that's holding the entire engine together.  Don't forget to tighten the Jesus Nut while you're at it.  I can tell you that in general aviation, anytime you unbolt something, the bolt is trash, so a stock of fasteners is a must.  It's pretty simple and was explained to me by Tom Wottreng, a fairly well known engine builder and aircraft mechanic.  The act of tightening the bolt or nut and the vibration from operation of the engine, work hardens the materials.  You permit that to happen just once and then you trash the fasteners.  Believe it or not, we don't get rocket scientists to actually work on these things.  Except for the design and the software, they're not that complicated.  However, all of the field repair procedures must be thoroughly tested.

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#44 2018-06-25 09:35:11

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

Noted, thanks.

elderflower wrote:

You aren't landing a full rocket, Louis. Just self weight and payload. So landing thrust is much less than takeoff.


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

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#45 2018-06-25 09:37:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Landing legs for the BFR

I've been wondering whether you have to keep your return vehicle warmed up throughout your stay. I suspect the answer might be yes.

kbd512 wrote:

I don't care if the entire rocket is trashed and never flies again, so long as the people inside it are alive and well when they arrive on Mars.  I'm not all that concerned about the landing gear, except for the base width.  It's just too narrow to land a 150t mass (57t on Mars) sitting 30 meters above the gear.  I've never seen a M1 tank landed that way.  Until I see that happen, I'm skeptical.  I'm sure it can be made to work.  The only question is how many test articles make the blooper reel before the bugs are worked out and whether or not SpaceX and their investors can afford that.  The heat shield is as light as balsa wood, so it can't be that resistant to damage from debris, and that mandates some kind of inspection prior to reentry.

Anything that can handle that kind of weight will be durable.  I'm a lot more concerned with the effects of partially loading composite pressure tanks over many months, since I've no idea what effect that sort of temperature delta has on the material over the long run, and the condition of the turbopumps, given the insane pressure levels involved.  I would say that the RGO bi-layer is mandatory to prevent embrittlement or oxidation of the tanks.  Super-high pressures tends to trash turbine blades rather quickly, even with the best steels money can buy.  A stock of small parts and/or a 3D printer is mandatory.  The things that tend to fail generally don't weigh very much, which is a good thing.  It's always a $2 plastic widget that's holding the entire engine together.  Don't forget to tighten the Jesus Nut while you're at it.  I can tell you that in general aviation, anytime you unbolt something, the bolt is trash, so a stock of fasteners is a must.  It's pretty simple and was explained to me by Tom Wottreng, a fairly well known engine builder and aircraft mechanic.  The act of tightening the bolt or nut and the vibration from operation of the engine, work hardens the materials.  You permit that to happen just once and then you trash the fasteners.  Believe it or not, we don't get rocket scientists to actually work on these things.  Except for the design and the software, they're not that complicated.  However, all of the field repair procedures must be thoroughly tested.


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

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#46 2018-06-25 10:21:40

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Landing legs for the BFR

Louis,

I don't want to find out what happens to a vehicle constructed of composites when it's exposed to a temperature delta of 100C+ hundreds of times, never mind exposure of the propellant tanks to even more severe temperature deltas.  I think I can speak for the Martian colonists when I say that they want their pressurized cabin kept warm and their propellant tanks kept cold.

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