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Author Topic: Cavern Dropship  (Read 656 times)

Lagrange

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Cavern Dropship
« on: 21 October 2022, 19:54:19 »
The Cavern Dropship is the ideal logistic device for a jump circuit.  It's available cargo tonnage of 74621+72(Spacebus)*160=86141 tons exceeding a Behemoth while still requiring only a single docking collar on a jumpship. 

The time to undock from one jumpship (1 minute) and then safely redock on another jumpship is a key limiting factor.  The base time to redock is 30 minutes, but it requires a control roll with a -1 bonus per extra 15 minutes.  In addition, there is a +2 penalty associated with any dropship larger than 20K tons.  Thus the time to safely redock with a baseline control roll of 5 is 30+15*5 = 105 minutes. Adding in a small cushion for transfers and convenience, this implies 2 hours per jump in the circuit.   In other words, we can move 85K tons 30 light years every 2 hours or 1.3M ton-light years/hour.  Although faster jump circuits certainly exist, it's difficult to improve ton-light years/hour. 

Given this number, we can also compute the maximum length of the circuit.  Safely recharging a jumpship requires 175 hours with a control roll of 5 which is 7.3 days.  Rounding up slightly for convenience, this is 7.5 days or 4 jumps / month for a jumpship.  For a dropship riding the circuit though, it can travel 90 jumps covering 2700 light years in 7.5 days, which is sufficient distance for most purposes.

Another key question is: how much tonnage can be interchanged during a 2 hour stopover in a system?  Recovery of smallcraft is typically the limiting factor since that takes 5 times longer than launching.  As an example, a Spacebus can be recovered in 5 minutes, unload containerized cargo in <2 minutes using 4 teams of 5 Strongarm exoskeletons, load in <2 minutes, and then launch by the 10th minute.  A single door can recover 2 craft at a time or 4 over that duration and there are 9 doors, implying 36 smallcraft bays could be kept in constant use with a full duplex cargo delivery of 2880 tons every 5 minutes after the first 5 minutes. Overall this works out to 66240 tons in 115 minutes which empties and refills 78% of the Cavern in a single 2 hour stop.   The excess tonnage available provides spare capacity for cargo traveling more than one hop.

There are 72 smallcraft bays to support noncontainerized cargo as well.  The Spacebus can do a full cycle with general cargo in 22 minutes.  For this, all 72 smallcraft bays must work, with the capacity to do 20 full duplex cargo exchange cycles per door recovery slot for 18*20*160 = 57.6K tons offloaded and loaded on.  Bulkier items like assault mechs take yet more time with a maximum of a 67 minute cycle time for a 160 ton mech.  In that situation, the bottleneck becomes the number of bays, each of which can complete 2 cycles for a total of 144 superheavies offloaded and a new set of 144 loaded on.

One key factor for any jump circuit rider is cost.  The cost here is substantial, although pains have been taken to minimize it.  The Cavern itself is 433M, significantly cheaper than the Behemoth.   The 72 Spacebus attached to the Cavern cost 336M and the 1440 Strongarm cost 219M for a total systems cost of 988M.   That's pricy, but amortized over all the nodes of a jump circuit it is relatively small.  On a maximum length jump circuit, the cost is just 11M/stop.  Even on a 9 stop circuit, the 110M/stop amortized cost is small compared to the cost of a jumpship.

The 'who owns what' question is important to address.  The Cavern keeps the crew of all Spacebus and has extra quarters for all associated bay personnel.  By rotating the pilot every 8 hours and taking a Spacebus offline for a 90 minute maintenance cycle at slow stops the Spacebus can be constantly used.   The exoskeletons also mostly stay on the Cavern with occasional 10 minute maintenance cycles using tech teams that visit briefly at stops.  The exoskeleton crew members however rotate 1/4 every stop so each crew member serves through 4 stops doing an 8 hour shift, then spend the rest of the week getting ready for the next shift.

Successfully executing the 2 hour stopover really requires a computer-mediated schedule to efficiently handle the mixture of containerized, noncontainerized and bulk cargo which needs to offloaded and loaded in each direction quickly.  Luckily, computers are pretty good at that sort of thing.

Code: [Select]
Cavern Dropship
Type: Military Spheriod
Mass: 100,000 tons
Technology Base: Inner Sphere (Standard)
Introduced: 3025
Mass: 100,000
Battle Value: 660
Tech Rating/Availability: D/X-E-D-D
Cost: 439,185,600 C-bills

Fuel: 300 tons (3,000)
Safe Thrust: 1
Maximum Thrust: 2
Heat Sinks: 210
Structural Integrity: 10

Armor
    Nose: 64
    Sides: 64/64
    Aft: 64

Cargo
    Bay 1:  Small Craft (72)        9 Doors   
    Bay 2:  Cargo (74621.0 tons)    0 Doors   

Ammunition:
None

Escape Pods: 14
Life Boats: 14
Crew:  5 officers, 19 enlisted/non-rated, 360 bay personnel, 144 passengers

Notes: Mounts 36 tons of standard aerospace armor.

Weapons:     Capital Attack Values (Standard)
Arc (Heat) Heat  SRV     MRV     LRV     ERV   Class       
None

Tradeoffs:
Civilian or Military?  Military has much better strategic thrust but is a little bit more expensive.  Strategic thrust is irrelevant in the primary role, but neither is cost since it's amortized over many jumps.   Overall, I went with military on the theory that it substantially improves independent use.   

Where are the crews?  Keeping enough exoskeleton crews on staff for shifts eats up quite a bit of tonnage and greatly increases the cost. It plausibly makes more sense for them to rotate off to stations or planets where over the intervening week they can assist with other cargo movement. 

Fuel capacity?  The 300 tons of fuel is more than adequate for a trip in-system from a zenith/nadir jump point.

Smallcraft bay count?  It's not particularly clear whether a smallcraft being recovered needs a smallcraft by to recover into.  I assumed 'yes' conservatively, and then doubled the number of smallcraft to improve the flexibility to deal with noncontainerized cargo.  You could go for more smallcraft bays if the goal was constantly transporting super heavies.   The wasted tonnage isn't a serious concern since the Spacebus is 80% cargo, but the cost does go up due to the extra support requirements.

Alternate Use
Repurposing into a Behemoth style usage pattern when/where is feasible.  The fuel reserves are small enough relative to potential smallcraft that operation in this capacity should be done in systems which can resupply fuel.  Since smallcraft and exoskeletons are a significant expense, having just a few associated with the Cavern in a Behemoth usage mode with the majority in use around a planet makes sense.  As an Alt-Behemoth, the Cavern is somewhat cheaper, with somewhat greater overall storage capacity, and a significantly greater smallcraft capacity for faster cargo turnover.

Comments?

Edits: swapped from civilian to military design for fuel consumption reasons.

Daryk

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Re: Cavern Dropship
« Reply #1 on: 21 October 2022, 19:58:46 »
A mere 9 doors will increase the time needed to employ those embarked Small Craft.

Lagrange

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Re: Cavern Dropship
« Reply #2 on: 21 October 2022, 20:06:49 »
A mere 9 doors will increase the time needed to employ those embarked Small Craft.
Yeah, 9 is the most doors we can have unfortunately.  It seems not terrible though?  We can fill all 72 Smallcraft bays in 20 minutes and cycle through most of the cargo at every 2 hour stop.

Daryk

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Re: Cavern Dropship
« Reply #3 on: 21 October 2022, 20:36:17 »
Don't forget to transfer additional cargo if docked...  ^-^

Lagrange

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Re: Cavern Dropship
« Reply #4 on: 22 October 2022, 09:08:21 »
Don't forget to transfer additional cargo if docked...  ^-^
On the 2 hours/jump schedule, you only have 15 minutes connected to the Jumpship.  That would enable an extra 390 tons of containerized cargo or 78 tons of bulk cargo.  It does help---that more than covers support needs.

There are a few other cargo tricks as well.  For example, if you all you want to do is _load_ (rather than offload & load) then:
  • ASF can be flown directly into a smallcraft bay and stashed in cargo.  This takes 15 minutes or less per ASF enabling the loading of 396 ASF each up to 100 tons in size.
  • 160 ton items or super-heavy mechs can actually be loaded faster (every 25 minutes) by storing a Spacebus as cargo since smallcraft gain an x2 bonus for cargo transport while mechs do not.  Using that, you could load ~360 super heavies.

There's also an offloading trick.  If the destination to offload can't support the full Spacebus flow, you can just offload into space for some items.  Then, once the Cavern has moved on down the jump circuit, a few residual smallcraft can slowly pick up the space dump.

Daryk

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Re: Cavern Dropship
« Reply #5 on: 22 October 2022, 09:22:14 »
I'm sure that latter trick doesn't make ATC happy...  8)

DOC_Agren

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Re: Cavern Dropship
« Reply #6 on: 22 October 2022, 18:13:15 »
I'm sure that latter trick doesn't make ATC happy...  8)
Normally I would say in cbt that not an issue but these will operate on "fixed" high value routes with good ATC systems
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Daryk

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Re: Cavern Dropship
« Reply #7 on: 22 October 2022, 18:23:20 »
Exactly my point...  :)

CVB

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Re: Cavern Dropship
« Reply #8 on: 23 October 2022, 06:40:41 »
Haven't run the numbers,  but would it improve the cycle to use a Jumpship capable cargo Space Station instead of a cargo Drophip? Since the transfer from JS to JS is only a couple thousand meters, a full DS engine might be overkill... And would such an SS be allowed to mount a Dropshuttle bay to exchange mid-sized loads via 5000t Dropshuttles? Basically a (partial) LASH instead of a pure  intermodal container ship.
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Daryk

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Re: Cavern Dropship
« Reply #9 on: 23 October 2022, 06:49:07 »
An interestring concept: https://maritime-executive.com/editorials/remembering-lash

But I think your idea more like a transloading pier than a LASH vessel.

Lagrange

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Re: Cavern Dropship
« Reply #10 on: 23 October 2022, 08:53:53 »
Haven't run the numbers,  but would it improve the cycle to use a Jumpship capable cargo Space Station instead of a cargo Drophip?
There are a few issues here.
  • Docking times are doubled, which means that ton-light-years/hour and maximum cycle length are both approximately halved compared to the dropship solution.
  • I'm basing plans around 3025 tech as a least-common-denominator while Jump-capable stations are extinct 2850 and reintroduced 3048.
  • The station must be "fully shutdown" while docked.  It's unclear what the durations of shutdown & powerup are---they might be only a minute which could be easily absorbed in a 4 hour layover. Or, it might be more time, adding more latency.
Since the transfer from JS to JS is only a couple thousand meters, a full DS engine might be overkill...
Definitely overkill thrustwise.  The doubling of docking time is a bummer.
And would such an SS be allowed to mount a Dropshuttle bay to exchange mid-sized loads via 5000t Dropshuttles?
It looks like 'yes', but only 1 dropshuttle bay would be allowed because it's at most 1 for a 100k ton space station. 

There are a couple alternatives for really large objects.
(a) You can dock the Cavern with a space station and take cargo on board.  This is very slow---it would take 12 hours for a 4k ton object while a dropshuttle bay would only take 55 minutes.  Given the slowness, you would need to step out of the jump cycle.  If you take a jump cycle off, you could load or unload 55K tons of oversize objects.
(b) You can use the jumpship's collar itself as the multiplexing point.   This is equivalent to dropping the Cavern from a cycle as far as other loads go, but it can make sense in some circumstances.

Hellraiser

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Re: Cavern Dropship
« Reply #11 on: 24 October 2022, 22:06:22 »
exceeding a Behemoth while still requiring only a single docking collar on a jumpship. 
...
Mass: 100,000 tons
...
Comments? 

So if your playing w/ the quirk that the Behemoth at 100KT requires 2 Docking Collars, why would this ship at the same 100KT then NOT require 2 Docking Collars?

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Lagrange

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Re: Cavern Dropship
« Reply #12 on: 25 October 2022, 05:50:01 »
So if your playing w/ the quirk that the Behemoth at 100KT requires 2 Docking Collars, why would this ship at the same 100KT then NOT require 2 Docking Collars?
At a basic level, the rules allow it.

But as  far as explanation, the Cavern has a more spherical shape better suited to envelopment in a KF field.