General 3D printing regolith concrete planetoid hulls?

[Spinward Flow]

LBB5.80, p22:

It is possible to select a planetoid as a hull, hollowing out spaces within it for drives and equipment. Such planetoids are generally available for the finding. However, a planetoid must allow 20%waste space (tonnage) for structural integrity; a buffered planetoid has greater ability to withstand combat damage, but must allow 35% interior waste space. Although a planetoid is essentially free, there is a cost of Cr1,000 per interior (non-waste) ton for fusion tunneling and hollowing of passages and compartments. In addition, there is a transportation charge (Cr100 per ton) to bring the planetoid into orbit above the shipyard.

When LBB5.80 was being authored and published, 3D printing of solid materials did not yet exist.
However, real world technologies have moved on in the past 40+ years and now it is possible to 3D print concrete into terrestrial housing by a variety of means.



Exploration of the solar system by NASA, ESA, JAXA, JPL and others has demonstrated that many of the planetoid bodies in the solar system are not "solid rocks" but rather loose piles of "puffy rubble" held together by their own gravity. However there are a few exceptions that have been discovered which are likely to be either solid stones or metallic types.

Terrestrial regolith inside an atmosphere, especially one with a significant hydrographic percentage, will tend to be weathered ... although exceptions can be found.

By contrast, vacuum world type lunar regolith will have no significant weathering process at all, even after billions of years of exposure to vacuum and solar radiation. Consequently, vacuum "baked" regolith can be expected to have very sharp edges and textures to fine particles ... which makes for an excellent ingredient for the manufacture of essentially concrete.

Combine "vacuum regolith concrete" using materials sourced from essentially mining waste of asteroids/planetoids and moons with a vacuum or trace atmosphere with 3D printing technology and suddenly you can create planetoid and buffered planetoid hulls for craft by additive manufacturing rather than by subtractive processing. Rather than needing to go out and find a 10,000+ ton planetoid to use for a hull (quantity: not wonderful) ... instead an orbital shipyard can use what amounts to planetoid mining and refined fuel processing waste streams to source the necessary chemistry and materials to 3D print planetoid and buffered planetoid hulls around habitable component compartments for designed craft.

In other words, you don't need to "find and tow" a planetoid of the desired size and composition to the shipyard ... instead, they can just "build" a planetoid/buffered planetoid "hull" around the interior spaces of your design. The regolith layer of planetoid/buffered planetoid hulls becomes "made to order" rather than something designers have to work around/with based on whatever pre-existing object can be found and brought in.



One man's trash is another man's treasure.

Opinions?

 

[whartung]

If concrete is "enough" to make a planetoid/buffered planetoid, then there's no intrinsic need for it to be 3D printed.

Arguably, if you've seen film of this things like the Hoover Dam being built, they ARE 3D printed, just very slowly using a crane and a bucket.

Obviously that's a wee bit of a stretch, as there's a zillion tons and yards of rebar going on as well. But from a mile away, the concrete and bucket are a very crude 3D print head.

So, the point being the were one to wish to make a planetoid, 3D printing isn't really necessary. It's better to use the "how to make a boat" principal with a planetoid, than build one up from scratch.

"Boat kit -- piece of wood and a knife. Instructions: Carve away everything that doesn't look like a boat."

 

[Condottiere]

I always thought I'd just get giant molds and pour in melted nickel iron.

 

[whartung]

Well that's what a buffered planetoid could be. You carve out reinforcing tubes in the planetoid, then fill them with melted material to strengthen in up.

The detail, though, is that it would probably still have to be reinforced like we reinforce the overpasses down here in Southern California.

We've learned a lot about the impact of earthquakes on things like freeway overpasses, and have a much better understanding of how they fail.

The problem with reinforced concrete (which is what our overpasses are made of), is that when the concrete falls away (due to the earthquake shock), there's nothing left to reinforce. The internal rebar structure can't support the roadway, and the whole thing collapses.

As a mitigation, they now wrap the pylons with a steel sleeve. This way, the concrete can crumble and break under the impact of the quakes all it wants. A metal cylinder filled with gravel (i.e. crumbled concrete) is "strong enough" to prevent collapse (the primary goal). The pylon could well later be condemned and need to be replaced, but that's a far different than having one that can potentially collapse.

So. Reinforced concrete is very strong, but doesn't take to vibration well, so a concrete hull, strong as it is, even reinforced, may not do well under barrage of heavy weapons.

Perhaps a fiber reinforced concrete would be a better material.

 

[Spinward Flow]

So. Reinforced concrete is very strong, but doesn't take to vibration well, so a concrete hull, strong as it is, even reinforced, may not do well under barrage of heavy weapons.

Perhaps a fiber reinforced concrete would be a better material.

Basic idea is that you have a blanket of ablative regolith on the surface which would be replaced/repaired relatively cheap (with mining and fuel refining waste byproducts) with the up armored ship underneath relatively unscathed. That way you only need to "repair the sod" on top of the roof after a battle, and the task is "dirt simple" to do.

 

[willtron3030]

LBB5.80, p22:

In addition, there is a transportation charge (Cr100 per ton) to bring the planetoid into orbit above the shipyard.

I'm fascinated with the idea that someone has a profitable business model for that kind of intrasystem hauling.

 

[willtron3030]

...

Obviously that's a wee bit of a stretch, as there's a zillion tons and yards of rebar going on as well. But from a mile away, the concrete and bucket are a very crude 3D print head.

So, the point being the were one to wish to make a planetoid, 3D printing isn't really necessary. It's better to use the "how to make a boat" principal with a planetoid, than build one up from scratch.

"Boat kit -- piece of wood and a knife. Instructions: Carve away everything that doesn't look like a boat."

A pirogue rather than a coracle. Sounds right.

 

[Spinward Flow]

I'm fascinated with the idea that someone has a profitable business model for that kind of intrasystem hauling.

The most important factor would be to a have a powerful maneuver drive so as to be able to tow "big rocks" (that are bigger than your ship) at 1G back to the shipyard.

So a ship like say ... my TL=11 400 ton 5G Pursuit Corvette design can tow external loads of up to 1600 tons at 1G (because 400+1600=2000).

If we assume an Earth (1 AU) to Asteroid Belt (2.8 AU) retrieval, that means a travel distance of 1.8-3.8 AU, depending on relative orbital distances to travel.

At 5G, a 1.8 AU transit takes between 36 and 48 hours (call it 48 hours for maneuver margin) up to 60 hours for 3.8 AU.
So call it 48-60 hours of outbound transit time.

Then let's say the planetoid to be hauled back is ... 1500 tons, so the "bounty" on that plantoid is going to be Cr150,000 (at Cr100 per ton).

At 1G for the return journey you're looking at 96 hours for 1.8 AU up to around 132 hours for 3.8 AU.

So basically a minimum of 6 days to a maximum of 8 days to complete the round trip. That is broadly comparable to the time it takes to make an interstellar jump. So essentially around Cr150,000 for a week's worth of work. Do that four times a month and you're up to Cr600,000 per month just in planetoid towing revenue. Do that for 10 months out of the 13 month year and you're looking at earning MCr6 per year ... or MCr7.2 per year if you're working 12 out of 13 months per year. That's MCr240 to MCr288 in revenue earnings over 40 years ... the latter of which is really close to the purchase price of MCr286.0752 for a Pursuit Corvette in volume production (which obviously a less than idea ship design for this kind of work, but I'm just setting this up as an example of how to think about it). A subsidy arrangement could easily make such work profitable for a ship (or boat) operator.

Also note that Cr100 per ton for planetoid towing is exactly the same as the sell price for unrefined fuel, so there's that extra comparison as a bonus. So instead of hauling rocks, a ship could instead be outfitted as a tanker with a load of Modular Cutter Modules configured for fuel tanking so as to haul fuel from a gas giant to a mainworld that does not have any appreciable water resources (D'Ganzio comes to mind for this, but the same would be true for many Asteroid Belt mainworlds as well, such as Macene).

And all of that is assuming that the ship is actively maneuvering the planetoid (or fuel) the whole way, rather than just heading out, finding likely planetoids and "maneuver chucking them" on a course bound for a "reception zone" for maneuver orbit retrieval near the shipyard (so just throw the rocks and let them coast on orbital inertia most of the way). That way a single ship can "throw" a greater tonnage over time from the planetoid belt and thus earn more revenue for their "prospecting" work.

Also note that such a "just throw rocks at them" approach could also be used by mining interests, such that instead of sending the ore refinery out to the planetoids, instead you just throw the planetoids on a course near to the ore refinery where they can be scooped up and brought in for processing.

 

[Condottiere]

Probably by product, or secondary revenue stream.

 

[kilemall]

IMTU the lunar regolith after helium-3 processing is sent up to solar foundries in LaGrange points that melt them down into forms primarily for the O’Neill colonies.

 

[coliver988]

saw this and thought it could apply to this thread: https://www.msn.com/en-us/news/technology/asteroid-bennu-s-mysterious-missing-craters-suggest-impact-armoring-protecting-the-surface