Poseidon class water tanker (primitive early dropshuttle)

[truetanker]

MagLevs use their Engine as a power source, so need for a separate plant. And rails are just one Ferrosteel rail surrounded by ferrocrete sides. BOTH are easy to transport, technically nothing states how may " rails " per ton, but a good amount would be like 50 hexes worth per ton?

TT

[kato]

BOTH are easy to transport, technically nothing states how may " rails " per ton, but a good amount would be like 50 hexes worth per ton?

For maglev, if we use the Transrapid test facility in Germany as a sample, as weight per meter we'd have 6.4 tons concrete, 1.1 tons steel and 0.1 tons other materials (They're currently planning its demolishing, hence why the figures for the 31.8 km track are available. Those figures don't include the 60,000t foundations.). In other words, maglev comes in at 227 tons weight per hex for the track. For supporting a vehicle weight of 75t per hex, not a 475t Nolan.

Including concrete sleepers i calculate the mass for standard rail as axle weight per hex as a nice round figure - i.e. 25 tons/hex. The steel alone is about 4 tons/hex including attachments.

You can arguably in either case cut the concrete down to just cement and use local water and aggregates. That brings standard rail to 6.1 tons/hex and maglev to 55.2 tons/hex.

[truetanker]

I typo'ed

It should have been 50 tons per hex...

But that is sound math.

TT

[kato]

That's the simple math, the hard math is when you try to model trade flows using Poseidon-based infrastructure.

My current sample model uses Epsilon Indi as a hub in which only one million tons per year are transported between Terra and 9 colonies. Already needs 12 Deimos-cored jumpships of pre-2150s times and occupies 80% of the described Poseidon capacity at Epsilon Indi.

[Daryk]

That sounds like interesting math, at least to me...  ^-^

[kato]

My current sample model uses Epsilon Indi as a hub in which only one million tons per year are transported between Terra and 9 colonies. Already needs 12 Deimos-cored jumpships of pre-2150s times and occupies 80% of the described Poseidon capacity at Epsilon Indi.

Had to lower my ambition in that btw.

Preliminary model uses 16 Deimos-cored jumpships in weekly departures from Terra and a Poseidon infrastructure with 12 Poseidon + 2 Pontos at Epsilon Indi (i.e. full capacity as described), four other Poseidon/Pontos bases plus small-station based infrastructure at New Home and Epsilon Eridani - and i've finally found a purpose for dropshuttles at the low end of the size spectrum there this way.
Basically it plots out a set of jumproutes that manage to shuffle some 30,000 tons cargo and 1,350 passengers per month from Terra to ten other worlds - combined, not each.

Rather interestingly, the confining factor - yield per jumproute - is not so much defined by what kind of jumpships or dropshuttles you use - potential gains are marginal, really -, but instead entirely by infrastructure and fuel supply on-site.
In order to raise our yield significantly we either need to get dropshuttles prepositioned on site that empty out our cargo holds - thus also needing proper spaceports - or we position Poseidons literally everywhere in scores to offset the cost of using large jumpships (a 100+kt jumper has a single-jump fuel requirement equivalent to a full Poseidon load, a 200+kt jumper twice that!). The advent of jumpsails then rather quickly makes our Poseidon fleet obsolete as it removes exactly that prohibitive fuel cost.

[Daryk]

At what point does it make more sense to go after ice in orbit vice on the ground?

[Alsadius]

At what point does it make more sense to go after ice in orbit vice on the ground?

That depends heavily on how much fuel you need to take off. Using typical current rockets, >95% of launch weight is lost getting to LEO(e.g., the Space Shuttle could put about 95 tons in LEO, out of a combined mass of close to 3500 tons), but Battletech rockets are far more efficient than that. The implied Isp is so high that sticking a hose into an ocean and then taking off seems more efficient, for most purposes, than trying to find icy asteroids. Abundance and ease of processing winds up being more important than the rather low takeoff costs.

[Daryk]

It's not take off consumption I'm thinking about... it's the fuel burned getting back and forth to the jump point.

[truetanker]

I thought that Iceroids were used in processing and basic drinking, as most planets had little or contaminated sources.

TT

[Cryhavok101]

I watched Ice Pirates recently, and this discussion reminded me of it. People could be harvesting ice from space to replenish water being removed from a planet's ecosphere as fuel... but battletech is probably not far-sighted enough to be bothering with that lol.

[truetanker]

I watched Ice Pirates recently, and this discussion reminded me of it. People could be harvesting ice from space to replenish water being removed from a planet's ecosphere as fuel... but battletech is probably not far-sighted enough to be bothering with that lol.

Did you survive the procedure too?  [blank] lol... Poor 'droids...

TT

[Daryk]

I'm just looking at the economics of the situation.  Kato has done some very detailed work.

[kato]

At what point does it make more sense to go after ice in orbit vice on the ground?

Realistically, from a support/supply viewpoint? Never, as the frost line is always outside the habitable zone by definition.

What would make sense though is dragging an icy asteroid to the jump point.

The kicker in this is mostly the availability of water-ice-rich asteroids. On a cost basis versus a Poseidon installation, we basically for all jump-capable tug installations require water-rich asteroids; in-system tugs in 2150 suddenly double efficiency (to where we can select 6-7% asteroids), and later developments beyond that only mean that by the mid 23rd century we can just as well mine hydrated clathrates for fuel. Like the Poseidon system-wise it would become obsolescent with the advent of jump sails though.

So we basically need to
a) be after 2150 for the technology and before 2200 for obsolescence
b) have the infrastructure to build and support in-system tugs in a system
c) need a certain minimum capacity requirement to make it worthwhile (broadly speaking more than 3 Poseidons in a system)

On point c), given the earlier introduction of Poseidon and thus economic write-off, even medium-sized Poseidon installations would remain worthwhile while the ships remain operational even with the potential of dragging around asteroids unless capacity requirements change.

Arguably, ice asteroid refuelling can become rather worthwhile if one considers Lagrange jump points at gas giants on the edge just behind the H2O frost line but within e.g. the CO2 frost line.

[Cryhavok101]

If you were going to have a version of battletech where belters expanded past the solar system and into other system's oort clouds, would it make sense for them to use this stuff?

[Daryk]

Thanks Kato, that's exactly what I was asking! O0

[kato]

If you were going to have a version of battletech where belters expanded past the solar system and into other system's oort clouds, would it make sense for them to use this stuff?

The ice asteroid tugs? Sure. In combination with a factory that rebuilds the asteroid into a habitat while extracting the water - even ditching the 130,000 tons of olivine and crystals we're still talking 20,000 tons of prime metal for a single asteroid for one of those tugs after all.

[kato]

P.S. Just took the fuel for the tugs themselves into account. Result: Not worth it. Or rather, you need higher water proportions. And you need to go for Lagrange points. And space stations.

Workable scenario A:

- A 7,000 ton in-systems tug works getting asteroids to the L1 point of the local gas giant.
- They basically grab the asteroid and give it a nudge, not thrusting until needing to brake into position.
- These maneuvers burn only 6 burn-days of fuel (36.5t) to move the asteroid over a distance of 7.25 AU over more than 3.5 months.
- A space station at the Lagrange point folds the asteroid into a gantry assembly for disassembly.
- The asteroid - using C1 carbonaceous asteroids - is then disassembled over the next 4 months.
- About 425,000 tons of waste material - olivine - have to be moved away from the Lagrange point every year.
- Result yield for refueling operations is about 12,000t fuel and 1,500t of usable metal for export.

Workable scenario B:

- Two 7,000 ton in-systems tugs tag-team each other getting asteroids to the zenith or nadir jump point of the star.
- They basically grab the asteroid and give it a nudge, not thrusting until needing to brake into position.
- These maneuvers burn 650t fuel per year to move the asteroid over a distance of 10.4 AU within two months.
- The tugs burn another 6,550t fuel per year holding the asteroids in position at the jump point
- The asteroid - using only C1 carbonaceous asteroids - is then disassembled over the next 2 months.
- About one million tons of waste material - olivine - have to be moved away from the Lagrange point every year.
- Result yield for refueling operations is approximately 17,000t fuel per year, additional exports are minimal at 1,000t metal.

Assuming a cost in the region of 140 million for such a in-system tug - primarily in its engine - and an at least comparable price for the space station for scenario A, the above has a benefit-cost-factor of 0.75 for scenario A and 1.04 for scenario B versus Poseidon. Or in other words - a Poseidon can be cheaper, assuming the cost for the ground installations of a Poseidon also needs to be invested in some way for the two scenarios at equal proportion.

Scenario A can be expanded with more tugs feeding the station assuming the inherent capability exists in it; at two tugs we get a benefit-cost-factor of almost 1.0 versus Poseidon, at three tugs we're at 1.1. We'll quickly run into overcapacity issues here though, since with three tugs we already maintain as much capacity as a 8-unit major Poseidon installation. Scenario B has the overcapacity issue from the start, at near-equal costs to Poseidon; it is a viable alternative proposal for 4+ Poseidon sites.

Edited: Revised/recalculated numbers.

[Daryk]

Couldn't the waste material be used as reaction mass to keep the rest at the point of disassembly?

[kato]

Not in a rules-conformant way ;)

I think. We could probably derive something from mass drivers. Those are kinda prohibitive in size and cost though.

[Daryk]

Sad, but true... I saw the idea on a space exploration site that was discussing Von Neumann machines for exploiting the asteroid belt.  Basically, they'd use the waste material from whatever mining they'd do as reaction mass to get to the next asteroids...

[kato]

Above calculation adapted. Scenario B comes out more favourable than before, but runs a basic overcapacity issue for the kind of scale we're talking about. As said i could see such a system in use at Terra on a larger scale for example, though - the 16-jumpship model i'm working with needs around 60,000 tons of fuel at Terra per year.

As regards the olivine waste material, one should note that it does have its use technically, most as foundry sand nowadays. Current production on Earth is about 8 million tons per year.

[kato]

Basically, they'd use the waste material from whatever mining they'd do as reaction mass to get to the next asteroids...

Been tinkering with it a bit, and it can work by attaching a module with a couple Gauss rifles to the asteroid - broadly: 3 firing once every turn (!) for a small asteroid of the same kind of size we can tow.

However, the reaction mass required to be fired off to keep the asteroid in position under the BT-default 0.1g requirement is quite high; effectively, if we assume 80% of that asteroid as potential reaction mass, we exhaust our supply within only 3.5 weeks. To maintain this position for the same time firing the engines of the tug instead we only need about 334 tons of fuel, the equivalent of 8.4% of our asteroid.

Since the waste material is present when we mine the asteroid for its H2O is present anyway, a mixed-mode of firing both these small mass drivers and the tug's engines optimized towards fuel production cycles should be more efficient.

A possible early 2130s model for this could be (for use at Terra):

• eight 3,900-ton tugs employed in a 20-week cycle moving asteroids to a jump point, during which 5 asteroid/tug combinations are present at the jump point at any time
• we move about about 13 asteroids per year to the jump point with that combination.
• each tug additionally deploys a pair of 100-ton support vehicles ("mining rigs") on the surface of the asteroid which each carry mining gear employed in a stationary, anchored position and a single primitive "mass driver" emulating a later prototype gauss rifle that fires off waste material to provide partial thrust
• the tugs in "stationary operations" at the jump point only firing their engines to that point (90% actually) to which their own fusion reactor can be used to produce hydrogen from water supplied from the mining rigs.
• the combination, given the use of 15%+ H2O content asteroids, provides a tap-off of about 772 tons of fuel every week (~40,000 tons per year) to a tanker spacecraft resupplying jumpships at the jump point.

Advantages of the combined propulsion:

• The small mass drivers on the mining rigs are actually worthwhile, as the effective fuel production for tap-off is increased by 25% that way.
• It simplifies loading procedures on the mass drivers - since you're thrusting "down" already anyway you only have to chuck the material in the waste tube where a series of coils then accelerates it out down towards the sun.
• The connection/supply lines between mining rigs and tug can be simplified to mainly a water hose providing water for fuel production on the ship itself. Tap-off by tanker spacecraft could occur directly from the mining rigs e.g. on a daily basis.
• Provided we're "bumping" in two-shot-per-turn cycles, the fusion propulsion from the main spacecraft can adjust to even out thrust to a constant impulse.

The mass drivers used in the above would be primitive gauss rifles that are "dumbed down" to conform more to current coilgun technology in a stationary application. The math used in calculating their requirements is also probably not quite sound.

[Daryk]

Another idea to reduce fuel consumption: solar sails (not the drive charging kind)!  These could actually be the forerunners of the charging kind...

[kato]

Light Sails, available for satellites from 2165, SO p.323.

[idea weenie]

Could you reduce the acceleration?  I.e. traveling at 1G might take 10 days, and use (for example) 1000 tons amount of fuel, but traveling at 1/4 G means you would take 20 days, and wind up only using 500 tons of fuel.  Slower accelerations would reduce the fuel use at the square root of the G rating, while multiplying the transit time by the square root of the G rating.

Then you might also have Hohmann transits for straight cargo, where you perform a low thrust at the beginning, let the cargo coast for most of the trip, and only decelerate it at the destination.  Advantage is vastly reduced fuel usage, the disadvantage is time used.


One idea to even out the thrust rating from the mass driver shots might be springs connecting the firing plate to the mounting craft.  The mass drivers fire, the springs compress, and the craft slowly moves in the opposite direction.  The springs eventually reach their maximum compressing, and the platform starts heading back into position.  At the neutral position the mass drivers fire again, compressing the springs again.  It is a scaled down version of what would be used for an Orion drive.

[kato]

Already doing that, both low-g and Hohmann transit. In the above model when the tug retrieves an asteroid it docks to it and gives it a push at 0.125g (the max it can run) for only 100 hours. It then floats without further acceleration for the next 36 days, before braking again for another 100 hours at 0.125g.

Strategic fuel use in BT is calculated geometric, not squared btw.

It's mostly the fuel to keep the asteroid stable at the jump point that's high; 0.1g required for the combination of asteroid and tug weighing 97,500t means that it's burning the equivalent of 2.4g for the tug only, at a constant rate - and that means you're burning 13.5t per day nominal on fusion only.

Each gauss-rifle-equivalent mass driver reduces that requirement by about one-twelfth, although to "feed" each one employed you need to "convert" about one-72nd of the asteroid per day. If using mass drivers that way you'll also want to pick out C2 asteroids with less H2O content to optimize production-to-waste-material cycles (5.47% would be optimal, at a conversion rate of about 47.6t/hour, thus - with four mass drivers and a tug providing the rest - eating up the asteroid in 3 weeks).

One can optimize tug usage further by using one to push it before disengaging and another grabbing it inflight to brake it and then maintain it. That could be done to yield the "jump point side" tug spending three weeks out of four producing fuel. Using four 3,900t tugs on that side and a single tug for pushing in the asteroid belt would optimize fuel production to about 123t per day continuously (with each of the four using four mining rigs), of which on the jump point side we'll have to reserve about 4t/day for the grab-and-brake maneuvers.

(let's set aside the geometric reduction of the asteroid's size during production btw, that just complicates it further...)

For the economic side, the investment per ton capacity at the jump point is close enough to a Poseidon model that i'd actually have to fully stat out the tugs and gauge their cost; it's in the region of 17,000-18,000 C-Bills per ton capacity for the 2130s either way.

[Daryk]

13.5 tons per day?  I'm looking at StratOps page 147, and it looks like you should only need 0.977 tons per day of fuel for station keeping at 97,500 tons...

[kato]

13.5 tons per day?  I'm looking at StratOps page 147, and it looks like you should only need 0.977 tons per day of fuel for station keeping at 97,500 tons...

Naval Tug Adaptor. TO P.335, while the 6th to 8th paragraph have been erratad the ninth regarding fuel consumption remains valid.

The 3,900 ton tug needs to fire at the equivalent of 2.4g to maintain the whole 97,500 tons at 0.1g. Hence it needs to spend 2.4 burn-days per day, or with a 2130s civilian dropshuttle 2.82*2.0*2.4 = 13.536 tons per day.

Technically for proper rules-compliant fractional accounting in quarter thrust points we actually need to go to the full 3.0g (towing at 0.125g) and for fun calculate through fuel points expenditure; since SFU is a relatively roundabout way of abbreviating that i'd argue we can just go with the above 13.5t per day.

[Daryk]

I think the TO fuel consumption only refers to tactical scale, not station keeping.  Of course, it's your project, so you can interpret it any way you like.