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Author Topic: Battletech Logistics  (Read 751 times)


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Battletech Logistics
« on: 10 November 2022, 10:46:03 »
This is a master thread tying together a toolkit of logistics units and discussing their use.  Comments are welcome, particularly if I'm missing something.  All of these units use 3025 tech making them a least-common-denominator approach which is plausibly useful over many centuries both before and after. 

The units are:
Together these form a set of composable elements which can effectively and efficiently address most transport tasks across most timelines within the rules.

The Skybus can transport 120- tons which 2 squads of 5 Strongarms can unload and reload on a planetary surface in 4 minutes for containerized cargo or 5 minutes in zero g.  Flight times vary but max out for at 90 minutes for an earth-like planet.  Note that the Strongarms can be carried as cargo by reducing the capacity slightly if they are otherwise unavailable at the landing field.  The Skybus requires frequent replacement of damaged nose armor from reentry or landing with typical pilots but has a large buffer.  Total cost: 8.2M for Skybus and 10 Strongarms

Orbital transport
The Spacebus can transport 160- tons which 4 squads of 5 Strongarms can unload and reload in 4 minutes in zero g with 30 hours worth of fuel at a half g, handling typical orbital traffic scales.  Longer duration travel can be supported by carrying additional fuel as cargo at the expense of cargo.  Also note that 4 squads of 5 Strongarms take <10 tons so they can be carried if necessary with some reduction in cargo capacity.  Total cost: 7.7M for Spacebus and 20 Strongarms.

The Sloth transports 76+ kilotons of cargo very cheaply from planetary orbit to planetary orbit or jump point.  On either end Skybus (with 2 squads of 5 Strongarms) or Spacebus (with 4 squads of 5 Strongarms) can rapidly load or unload.  For example, 72 Spacebus could shuttle between two Sloths for a complete transference of 2 cargos in about 135 minutes.  Although the use of a station instead of a dropship for interplanetary transport is unconventional, it appears to check out economically---transport takes a factor of x3.17 longer than a full g transit while being x10 cheaper.  Also note that L1 Jump point to planetary orbit takes <12 hours at 1/10th g which is negligible next to the baseline 7.5 day duration of a jump cycle.  Total cost is 38M (amortized) + 7.7M+ per destination. 

For high value time critical long hauls, the Cavern dropship provides almost the same transport profile at a full g although with a factor of 10 greater cost.  Total cost is 433M (amortized)+ 7.7M+ per destination.

The Voyager Jumpship provides jump capability for 2 Cavern Dropships at a cost only 20% greater than a Cavern.  It's onboard fuel easily supports 2 fuel-based recharge and jump cycles with the fuel in a Cavern supporting an additional 2+ for a combined range of 6+ jumps using fuel alone.  There are two interstellar usage patterns:
  • Zenith/Nader -> Zenith/Nader jump travel.  This approach allows visiting a new system 30 light years from the last every 22.5 days to support transport in-system and an outsystem return by the Cavern.  It can be done safely with a control roll 5 navigator.
  • Zenith/Nader->L1 Jump point->Zenith/Nader jump travel.  This approach enables visiting a new system 60 light years from the last every 15 days.  As discussed here, jumping in and out of L1 jump points requires only the equivalent skill level of 'regular' gunnery which translates into control roll 3.  The investment in more and better trained KF navigators seems entirely worthwhile.
This usage mode makes sense for hinterland colonies that economically justify a visit only rarely---once every few months.  The Voyager jumpship has a similar cost to the Cavern so the benefit of considering smaller dropships in this usage mode is marginal.   Total cost is 941M (amortized)+8.2M+ per colony.

Jump Circuit
If a colony is visited more often than ~1/month, a jump circuit makes more sense.  To see this, note that the cost of participating in a Jump Circuit is essentially a Voyager and a Sloth Transport which is a bit more than half the cost of a Cavern + Voyager while providing more regular visits.  It can also make sense for any colony that is 'on the way' between two particularly important systems. 

The basic Jump Circuit uses Voyager jumpships with one or two Caverns undocking on arrival and spending 2 hours docking with the next jumpship in the circuit while Spacebus transports large amounts of cargo to/from a Cavern and a Sloth transport station at an L1 jump point.  The Sloth can then shift into close planetary orbit in about a half day where Skybus can transport cargo to/from the ground.

There is a trick here---you use an 'undulating jump circuit'.  In any given system, a Voyager either jumps into a Zenith/Nader point or the L1 point for service.  This is necessary because L1<->L1 jumps are  extra difficult.  Particularly important systems use the L1 link for faster service.  This may in some cases require inserting an extra Voyager so that the number of stops between important systems is even.

One difficulty here is the Strongarm squads which need rotation every 4 stops (=8 hours).  Since this is an 'even' stop the Strongarm squads can be transported to/from a planet via a Sloth using openloop life support in cargo (i.e. .2 tons/person/day) which requires about 144 tons for a half day.  Alternatively, Skybus from the planet can transport folks back and forth in a similar fashion.

For minor colonies where the jump circuit uses Zenith/Nader jump points, at least 2 Sloths may be desirable since they naturally run on a 60 day cycle for Sol.   More can be added, but once you reach 8 Sloths for weekly service it becomes preferable to just insert an extra Voyager for L1 jump point service.

Since a Jump Circuit naturally evolves over time, the ability to shift it is desirable.

A jump circuit's natural length is 90 stops of 2 hours each.  Longer jump circuits complete a loop every 15 days instead of 7.5.  Shorter jump circuits are of course possible.   A 90 jump circuit costs ~50B c-bills which is both quite high and yet not that large compared to the cost of warships.  Think of it as 3 Foxes.

When a Jump Circuit is in use, the Arc Recharge station provides a cheap way to accelerate the use.  Instead of jumping once every 7.5 days, you can jump once every 6.5 days providing a 15% decrease in latency and increase in throughput.  The natural length of a jump circuit shortens to 78 stops, which is still plenty long for most uses.  Total cost/stop is at least 582M including Voyarger, Arc, Sloth, Skybus, and 10 Strongarms.  The circuit rider has a minimum cost of 915M including Cavern, 72 Skybus + 1440 Strongarms.  A circuit can support twice that if desired.

Military Circuit
For a military applications, the security of the jump circuit becomes paramount.  Since there are a far to many points to defend on a jump circuit, security via secrecy is the obvious choice.  This can be achieved by using minor interstellar objects capable of generating a Zenith/Nadir point with variation over such destinations over time to decay away any loss of secrets.   The exact currently valid locations would be a closely guarded secret.

The need to rotate Strongarm squads remains.  To service them, a Way Station variant of the Sloth provides a means to support the full crew in quarters for an extended period of time.  One Way Station is needed every 4 stops on a military jump circuit.  The cost per stop is thus 533M(Voyager)+28M(Arc station)+154M/4(Way Station) ~= 600M c-bills.  The circuit rider is the same.

Since a military circuit services no systems by default, it's inherently less economical.  The military circuit could defray costs by providing additional service to/from the military circuit via an L1 jump point.  This is expensive as each such jump effectively requires an additional Cavern and Voyager (~941M C-bills), almost twice the capital cost of participating in a commercial circuit.

Maintenance, Transport, and Modification
The delicate and difficult to repair/replace component here are the KF-drives.  These are relatively easily damaged via a misjump, face a +5 penalty on repairs, and cost hundreds of millions of c-bills to replace.   Given this, a good repair system can pay for itself relatively rapidly.  The Ratchet jumpyard provides a pressurized repair bay (-5 bonus) capable of repairing the Voyager jumpship.  It can carry a Way station through a jump, then unload and dock with it to support repairs while they are in progress. 

The Ratchet can also be used for transport, assembly, or repair of all largecraft except for itself and the Arc Recharge station.  The Arc and the Ratchet can be serviced by a Ratchet variant which uses an unpressurized repair bay (-3 bonus).  This easily deals with repairs on the Arc.  For KF-drive damage to the Ratchet, it is return for tech teams to take x4 time (-3 bonus) to help compensate for the lack of a pressurized repair bay.

Temporal variations
The most recently developed piece of gear is the Space Ops Adaptation system for the Strongarms (3011).  Without that, their ability to shuffle cargo in space is reduced by a factor of 1.75.  This primarily impacts the amount of cargo which can be loaded and off loaded from a Cavern during a Jump Circuit stop but leaves the overall structure viable.

Before the space ops adaptation, you need to go back to pre-KF boom times (~2500) before these elements do not exist. 

With more advanced technology, not much changes.  For the Voyager, it may make sense to upgrade the armor and add laser AMS.  Clan technology frees .004% of mass on the Cavern and Spacebus as well as .012% on the Skybus.  LF-batteries don't make much sense for jump circuits economically so they could only make sense in a military jump circuit.  The introduction of battle armor adds the ability to armor the exoskeletons (sounds useful), but does not otherwise impact their ability to transport cargo.


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Re: Battletech Logistics
« Reply #1 on: 23 November 2022, 17:35:26 »
Given the Whittle Network discussion, I added a recharge station to accelerate the jump circuit and a discussion about the minimal costs for each option.


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Re: Battletech Logistics
« Reply #2 on: 10 December 2022, 10:44:59 »
Added discussion of the Ratchet repair yard.