Specialized fabbers: How small can they get?

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DataPacRat DataPacRat's picture
Specialized fabbers: How small can they get?

Spare morphs are pretty small; adding a 4-liter fabber, the "most common" size, like some robots have, would more than double its volume. How small is it reasonable for a specialized fabber to get?

Say that I've got a Spare modified with an internal metallic-hydrogen rocket. How compact could a fabber that makes MH fuel out of available hydrogen be? What sort of tradeoffs would be involved, such as in production rate? (The specific scenario I'm imagining is a Spare being used as a courier, tootling around the solar system, containing an ego who wants to be able to travel to asteroids where there may not be a cornucopia machine available to refuel from.)

Relatedly - anyone have a good idea on how expensive MH is, when bought or fabbed? (In order to work out fabrication time.) The closest I've got to clues are the mapping missile from Gatecrashing and the internal rocket from Transhuman, both with a Moderate cost, though that includes both the hardware and a load of fuel.

Thank you for your time,


DocRodgers DocRodgers's picture
While this is, of course,

While this is, of course, debatable, my head-canon is that the 4-liter value is at least partly because fabbers have a small box built in to hold whatever the fabber is making. This would be part safety (Keeping the nanobots from spreading out too far) and partly convenience. (just leave the fabber in the corner until it's done and you won't have anything appearing out of nowhere on you)

Now, given what you seem to be going for here, I would suggest just using a specialized Nanobot hive with a Proteans swarm loaded into it. This will give you the same basic function, being able to collect resources and turn it into finished goods, without having to worry about that much bulk. Given their size, being more comparable to shotgun shells, it would be a lot easier to build one into a Spare morph.

Although, even with all that in mind, I'm not sure how to get Metallic-Hydeogen with any of this tech...

DivineWrath DivineWrath's picture
Metallic Hydrogen requires

Metallic Hydrogen requires extraordinary amounts of pressure to make. Its beyond our current ability to produce at this time.

In Eclipse Phase, Metallic Hydrogen likely requires a specialized building to produce. I don't think its possible to make that stuff using a fabber small enough that a spare can carry.

Trappedinwikipedia Trappedinwikipedia's picture
I'm pretty sure fabbers can't

I'm pretty sure fabbers can't make MH, the pressures involved are just not the the sort of thing which can be done without specialized equipment.

Making industrial amounts of ammonia takes about 15-25 MPa of pressure, and the plants are huge. EP is *way* more advanced than the present, but also working with about 20,000 times as much pressure, so I'd expect the machinery to still be pretty noticeable. The pressure vessel alone is probably larger than most fabbers.

That said, MH is probably pretty cheap, once the required, and fairly significant factory investment is made hydrogen is easy to get, and the plant can probably produce huge amounts of the stuff pretty easily, and EP mostly has the storage problems solved.

That said, a Diamond Anvil Cell is lot very large, and should probably be able to make extremely small amounts of MH, so if time isn't a problem that's a route to it. I'm not sure how large the sample volume of those are, but it could be months or years to refuel with that method.

DataPacRat DataPacRat's picture
One thought in contrast to

One thought in contrast to the "it's probably not possible" approach is that, at least according to 1e rules, it's entirely possible for a cornucopia machine to print out a fully-fueled mapping missile in three hours. (Heck, the 'personal rocket pack' on page 345 is MH fueled, and only takes 2 hours.) If it's possible for desktop fabrication to do that, then the most likely conclusion is that the clever people living in Eclipse Phase have come up with enough clever workarounds to solve problems that seem insurmountable to us, way back over a century pre-Fall.

Fortunately, we already have a hint of what sort of handwavery might be involved: "Although naturally unstable, it can be stabilized with carefully controlled electrical and magnetic fields, and these field generators are an integral part of every metallic hydrogen fuel tank." Suggesting that there may be some subtle details of MH's EM properties which can be taken advantage of to ease manufacturing.

As a possible compromise of the thoughts so far - maybe that shotgun-shell-sized protean nano-hive doesn't turn H2O into MH directly, but puts together a hundred-years-better-than-today electromagnetic-enhanced desktop-sized diamond-anvil-cell to do the actual MH refining?

(We already know we're nowhere near the limits of DACs, even ones that can be made with today's crude machine tools - for example, http://aip.scitation.org/doi/abs/10.1063/1.2387890?journalCode=rsi .)

Thank you for your time,


Trappedinwikipedia Trappedinwikipedia's picture
Fab times assume you have the

Fab times assume you have the appropriate feedstocks on hand though, which likely includes metallic hydrogen feedstock for those things. Similar to how nuclear bombs, many sensors, and antimatter grenades require their own complex feedstocks.

I don't think the stabilization methods would help make it, as you still need ~495 GPa to have metallic phase hydrogen to keep stable. It's sort of like if you had a way to stop ice from melting, you'd still need to cool water enough to get ice before you could keep it that way.

I think a DAC would work for a portable system, but in space I expect refueling to take a while, hours to weeks depending on the amount needed (and IIRC it's best not to think too hard about the fuel fractions of EP morph-spaceships, so really a vaguely plausible number just needs to be made up).

Doing a little bit more research I would err on the side of shorter numbers. MH rockets need to use some other propellant (often water) to prevent the reaction chamber from evaporating (as there are no known materials which remain solid at ~7000 k), so you'd need a fairly small amount, mixed with fairly easily acquired water, depending on the performance needed, and the heat the ship or morph can survive (which is going to drop a fairly large amount with something small, potentially too much to be very useful). That's getting a little too physics-y for EP though.

DataPacRat DataPacRat's picture
Trappedinwikipedia wrote:MH

Trappedinwikipedia wrote:
MH rockets need to use some other propellant (often water) to prevent the reaction chamber from evaporating (as there are no known materials which remain solid at ~7000 k), so you'd need a fairly small amount, mixed with fairly easily acquired water, depending on the performance needed, and the heat the ship or morph can survive (which is going to drop a fairly large amount with something small, potentially too much to be very useful).

The trouble is that, as far as I've been able to dig up, if you use enough non-MH mass to reduce the MH plasma's temperature to something solid matter can handle, you drop its performance to well below the numbers we've been given in EP. Fortunately, there's another way to solve this problem: use a 'magnetic nozzle' to confine the superheated plasma away from the solid parts of the rocket entirely. Since we already need to use EM fields just to keep MH in fuel tanks stable, it seems plausible enough to extend the EM manipulations through the whole rocket apparatus.

( http://www.projectrho.com/public_html/rocket/torchships.php#id--Torch_Drive_Heat--Magnetic_Nozzles )

Quote:
That's getting a little too physics-y for EP though.

Eh, I don't mind physics-y. :)

Thank you for your time,


ThatWhichNeverWas ThatWhichNeverWas's picture
Before the Dark times. Before College.

DataPacRat wrote:
Relatedly - anyone have a good idea on how expensive MH is, when bought or fabbed? (In order to work out fabrication time.) The closest I've got to clues are the mapping missile from Gatecrashing and the internal rocket from Transhuman, both with a Moderate cost, though that includes both the hardware and a load of fuel.

I did the math based on these a while back. I don't have it to hand atm, but iirc it came out at a maximum cost of about 1cr per gram, probably less.

As a fun aside, MH is my headcannon fuel for plasma weapons.

In the past we've had to compensate for weaknesses, finding quick solutions that only benefit a few.
But what if we never need to feel weak or morally conflicted again?