Space structure material

[jryodabobs]

High tech propulsion, including tethers, is fascinating stuff. However, if people are to operate and conduct business in space for extended times, more mundane matters must also be addressed. Don't let the current government-led space malaise stop progress. Real progress has always come from bright young minds unemcumbered by the view that "it can't be done". We who read and think about this stuff want to see people populating space on a permanent basis. Goddard has actually begun looking into what it would take. Let's help them and all the others who see our future as space-based or at least space-focused.

Let's try to harness the worldwide brainpower interested in space development to solve one real challenge. Then another. Then . . .

Try this: If one were to build a solid structure in an area of space requiring protection from space radiation, micrometeoroid strikes, and orbital debris, upmass efficiency demands a rigid (or semi-rigid) external structure capable of absorbing many such hits without penetration or replacement. This should be a valid need whether the structure will be actually located in space or if it is to be on a planet or other orbiting object such as a moon.

The structure should be capable of yielding a complex shape made up of rectangles of different sizes and shapes. Think of bricks, but much larger.

The structure's panels should facilitate assembly by EVA-suited people as well as replacement if that became necessary. So, it must be de-assemblable (if I may use that word).

If the panels could double as a many-faceted solar panel, that would be efficient. Loss of elements from a strike would be acceptable, because there would be many elements. Only one face of each panel should be part of the solar array.

If you were to be charged with developing such a panel, what materials would you use, how would you attach the panels to others in order to avoid gaps that would allow penetration, and what panel sizes would you develop? How would thermal expansion and contraction be handled?

Since I'm no expert in this area, it would be helpful if those with materials expertise could participate in this discussion.

[alexterrell]

It would be good to be able to process Kerogen (http://en.wikipedia.org/wiki/Kerogen) as this is present in most C Type NEOs (as well as, probably, Phobos and Deimos).

If this can be converted into Polyethylene  / RXF1 (http://science.nasa.gov/science-news/science-at-nasa/2005/25aug_plasticspaceships/) then you have a good source of material. (Stronger and lighter than aluminium, and better in a radiation environment).

Could this be injection moulded into faces and bolted together to make solids?

[TyMoore]

It certainly could be. Although, I would wonder about the need for reinforcements because of the overall flexibility of the structure. Also, out-gassing, and UV and radiation embrittlement problems are an issue. Also, polyethylene's behavior in wide temperature extremes could be an issue.

I don't see these as insurmountable problems at all--just challenges to be tackled.

[jryodabobs]

It would be good to be able to process Kerogen (http://en.wikipedia.org/wiki/Kerogen) as this is present in most C Type NEOs (as well as, probably, Phobos and Deimos).

If this can be converted into Polyethylene  / RXF1 (http://science.nasa.gov/science-news/science-at-nasa/2005/25aug_plasticspaceships/) then you have a good source of material. (Stronger and lighter than aluminium, and better in a radiation environment).

Could this be injection moulded into faces and bolted together to make solids?

Thank you! Your response contains the kind of thinking I had hoped to stimulate.

[butters]

I would use a composite of ultra high molecular weight polyethylene fiber (Dyneema or Spectra) bound in nylon or polyester, fabricated in a thermoplastic forging process similar to that developed by FiberForge. 

UHMWPE fiber has the highest strength-to-mass ratio of any practical material, stronger than commercially-available carbon or kevlar fibers, and its very high hydrogen content makes it an excellent radiation shield. 

It has been used by NASA for a 12-mile tether experiment and by DoD as a ballistic reinforcement in composite body armor.  So it should stand up well to MMOD.

[jryodabobs]

I would use a composite of ultra high molecular weight polyethylene fiber (Dyneema or Spectra) bound in nylon or polyester, fabricated in a thermoplastic forging process similar to that developed by FiberForge. 

UHMWPE fiber has the highest strength-to-mass ratio of any practical material, stronger than commercially-available carbon or kevlar fibers, and its very high hydrogen content makes it an excellent radiation shield. 

It has been used by NASA for a 12-mile tether experiment and by DoD as a ballistic reinforcement in composite body armor.  So it should stand up well to MMOD.

Do you mean the fibers could be "spun" into cloth that could be wrapped around something solid, or that the fibers could be turned into blocks?

[alexterrell]

I would use a composite of ultra high molecular weight polyethylene fiber (Dyneema or Spectra) bound in nylon or polyester, fabricated in a thermoplastic forging process similar to that developed by FiberForge. 

UHMWPE fiber has the highest strength-to-mass ratio of any practical material, stronger than commercially-available carbon or kevlar fibers, and its very high hydrogen content makes it an excellent radiation shield. 

It has been used by NASA for a 12-mile tether experiment and by DoD as a ballistic reinforcement in composite body armor.  So it should stand up well to MMOD.

Do you think Spectra, or something close to it, can be manufactured in space on NEOs?

[alexw]

    One of the Mars-mission forums (not NSF) pointed to in a recent post somewhere here had a thread recently mentioning the virtues of basalt fibre.  Supposedly, you might just be able to melt it down on a NEO and extrude it, and the tensile strength may even be sufficient for tethers.
    -Alex

[JohnFornaro]

Don't let the current government-led space malaise stop progress.

Workin' hard on that aspect, believe you me.

But anyhow, for space stations and such, the materials will have to be stong in tension.  For planetary habitats, especially those that are buried under ground, compression will be the main property desired.

If you were building a toroidal ring station, the pieces might very well be rectangular cyliner shapes.  If you were building a spherical station, the pieces might want to be geodesic, that is, more a combinatin of pentagons and hexagons.

I would think more along the line of polyethyelene sandwich, with an outer skin of steel or aluminum, in certain parts of the structure, say, the ribs.  If your structure were large enough and the skin thick enough, you could tap holes in the outer layer and attach stuff after the fact, as needed.

[jryodabobs]

I would think more along the line of polyethyelene sandwich, with an outer skin of steel or aluminum, in certain parts of the structure, say, the ribs.  If your structure were large enough and the skin thick enough, you could tap holes in the outer layer and attach stuff after the fact, as needed.

Thanks, John. Sounds like the consensus is to generate an extruded poly-something, with the goal being to create it locally from in situ materials. Stiffen that with heavier metal material only where necessary.

All of that seems to imply a space-based manufacturing facility that can transform the extrusions and metals into actual structures. The facility I guess would have to be on a body, and not in orbit or at a Lagrange point, since it would be extensive in volume and have to contain support for the people and probably robots doing the work.

Seems like a major construction project, regardless of where it is located. Decades in development. Is it realistic to anticipate that funding from an international partnership along with a multitude of partner companies could be cobbled together and then retained for the better part of a century that it would take to plan and accomplish this?

[Hop_David]

The structure should be capable of yielding a complex shape made up of rectangles of different sizes and shapes. Think of bricks, but much larger.

Legos in space? There could be economies realized with mass produced modular units.

However, rectangular bricks aren't the only option.

For example, equilateral triangle panels can be used to make octahedra and tetrahedral bricks. Which stack to fill space as do conventional rectangular bricks. Structures made from octahedra and tetrahedra are known as octet for short.



Truncated octahedra are also a space filling brick. These can splice onto cubic as well as octet structures, acting as a bridge between these two types of structures:



There are more possibilities for modular bricks than rectangular solids.

[jryodabobs]

Legos in space? There could be economies realized with mass produced modular units.

However, rectangular bricks aren't the only option.

For example, equilateral triangle panels can be used to make octahedra and tetrahedral bricks. Which stack to fill space as do conventional rectangular bricks. Structures made from octahedra and tetrahedra are known as octet for short.

Truncated octahedra are also a space filling brick. These can splice onto cubic as well as octet structures, acting as a bridge between these two types of structures:

There are more possibilities for modular bricks than rectangular solids.

Beautiful! All of us are smarter than any of us.

[orbitjunkie]

I haven't seen it mentioned on the forum before, but I'm really intrigued by the possibilities of Electron Beam Free Form Fabrication (EBF3). Basically an electron beam on the end of a robotic arm has some kind of continuous feed (e.g. a metal wire) that it continually zaps and melts into place. It's one kind of rapid prototyping or direct manufacture capability.

http://www.nasa.gov/topics/aeronautics/features/electron_beam.html

They mention that it requires vacuum and a small scale version has already flown on the Vomit Comet, with plans for an ISS test, too.

There are other possibilities for rapid manufacture. Notably lots of plastics are used right now. But this is cool since it seems to work with metals like Al, Ti and some allows. Although the materials themselves may not be revolutionary, this could provide a revolutionary way to work with materials we already know and use. The article also mentions how it might be used along with other kinds of materials for novel types of structures.

A few questions come to my mind with this technology:

1. How hard would it be to do this kind of direct manufacture (DM) for human rated aerospace systems? You'd want to avoid additional machining if you could, so bulk structural elements are probably preferred. And how fine a scale can you get it? (I doubt you'd be able to DM, say, an engine turbo-pump, but what about pipes or manifolds? Nozzles? Tanks?) How would you test and certify things built this way in space?

2. Could it be feasible to consume expendable hardware you brought along and convert it to something else? That kind of capability could mean really cool things. What would you do with all the metal in an upper stage or ET already in orbit?

3. How far can you take this concept? How about autonomous little EBF3 robots to crawl/fly around to repair things. Could seriuosly cut down on EVAs required. Perhpas this could be used to repair certain kinds of damage without the full part. Obviously only to some limit...

[jryodabobs]

3. How far can you take this concept? How about autonomous little EBF3 robots to crawl/fly around to repair things. Could seriuosly cut down on EVAs required. Perhpas this could be used to repair certain kinds of damage without the full part. Obviously only to some limit...

Thanks. I'm also aware of a fairly recent patent by a JSC engineer for creating complex shape small diameter tubes in space. Obviously there are a lot of smart people who have been preparing for this challenge for decades. Now if somehow the hoard can just be turned loose to execute . . .

[mlorrey]

Mars has literally trillions of tons of hematite crystals lying around on the martian surface (the blueberries in the rover pics). Once we get some industry going there, martian steel will be the most useful and affordable structural product.

[Robotbeat]

Mars has literally trillions of tons of hematite crystals lying around on the martian surface (the blueberries in the rover pics). Once we get some industry going there, martian steel will be the most useful and affordable structural product.

Forget that, iron meteorites are littering the surface of Mars! Based on the rovers' findings, I'd guesstimate roughly 1 ton of free metal every 1 or 2 square kilometers. Within 100km radius of a base, there could be roughly 50,000 tons of free metal!

[mlorrey]

Mars has literally trillions of tons of hematite crystals lying around on the martian surface (the blueberries in the rover pics). Once we get some industry going there, martian steel will be the most useful and affordable structural product.

Forget that, iron meteorites are littering the surface of Mars! Based on the rovers' findings, I'd guesstimate roughly 1 ton of free metal every 1 or 2 square kilometers. Within 100km radius of a base, there could be roughly 50,000 tons of free metal!

True that. No need for any convoluted exercises with basalt or spinning nanotubes out of CO2. Just install some nuke plants and start melting stuff down.

[Hop_David]

Forget that, iron meteorites are littering the surface of Mars! Based on the rovers' findings, I'd guesstimate roughly 1 ton of free metal every 1 or 2 square kilometers. Within 100km radius of a base, there could be roughly 50,000 tons of free metal!

True that. No need for any convoluted exercises with basalt or spinning nanotubes out of CO2. Just install some nuke plants and start melting stuff down.

Basalt? Nanotubes? If you're talking about material for an elevator or tether, iron is ridiculous.

http://en.wikipedia.org/wiki/Ultimate_tensile_strength#Typical_tensile_strengths

Martian iron might be good for local use. But Mars' gravity well and atmosphere precludes Martian iron as an export to anywhere but Mars' neighborhood, in my opinion.

[aero]

Mars has literally trillions of tons of hematite crystals lying around on the martian surface (the blueberries in the rover pics). Once we get some industry going there, martian steel will be the most useful and affordable structural product.

Forget that, iron meteorites are littering the surface of Mars! Based on the rovers' findings, I'd guesstimate roughly 1 ton of free metal every 1 or 2 square kilometers. Within 100km radius of a base, there could be roughly 50,000 tons of free metal!

True that. No need for any convoluted exercises with basalt or spinning nanotubes out of CO2. Just install some nuke plants and start melting stuff down.

OK - Let's see a design for a system to harvest, say 3,000 tons of free metal, bringing it back to the smelter. And sending the kids out to pile the iron rocks into fence rows is disallowed. Just to make this more of a challenge, we are addressing the first 3,000 tons, starting with ton number one.

[jryodabobs]

Thanks, Aero, for bringing this discussion back to its original intent. Let's really solve one real problem at a time.