Register Register

Author Topic: Spacebus Smallcraft  (Read 617 times)

Lagrange

  • Lieutenant
  • *
  • Posts: 1155
Spacebus Smallcraft
« on: 18 October 2022, 21:36:49 »
In my continuing quest for logistics mastery, I've been looking at a space-only smallcraft for short-haul cargo transport and maximum load/offload speed.

The Spacebus devotes over 80% of tonnage to cargo with 4 doors providing independent entry into the cargo hold enabling up to 4 different squads of 5 people to shift cargo in and out. 

If each crew member uses a Strongarm Exoskeleton and the cargo is containerized, then the Spacebus can be emptied of 16 10 ton cargo containers in <2 minutes, refilled with 16 new 10 ton cargo containers in <2 minutes, launched in 1 minute, and recovered aboard a new largecraft in 5 minutes for a complete load cycling time as short as 10 minutes.

With bulk cargo (i.e. noncontainerized), the cycle time of course takes longer.  If the cargo is evenly divided amongst the 4 squads each of which is shifting 40 tons, then the offload time is 40 tons / 5.25 tons/minute <8 minutes, so an offload/load/launch/recover cycle takes 22 minutes.   In the worst case, there is a single 160 ton object which takes 30.5 minutes to offload by a single team, implying a cycle time of 67 minutes.  A common difficult case is a 100 ton Mech/ASF/Vehicle which has a 45 minute cycle time (for a Mech) or 26 minutes for ASF/vehicles.

The Spacebus itself is a relatively fragile design, unable to survive a gravity well or withstand any substantial source of damage.  The steerage quarters are austere and the fuel budget is a minimal 1.5 tons which lasts for most of a day using the highly efficient smallcraft engines.  Altogether, the Spacebus is highly utilitarian and thoroughly civilian design which effectively accomplishes logistical transport amongst nearby largecraft in space.

Code: [Select]
Spacebus smallcraft
Type: Civilian Spheriod
Mass: 200 tons
Technology Base: Inner Sphere (Standard)
Introduced: 3025
Mass: 200
Battle Value: 304
Tech Rating/Availability: D/X-E-D-D
Cost: 4,661,530 C-bills

Fuel: 1.5 tons (120)
Safe Thrust: 1
Maximum Thrust: 2
Heat Sinks: 4
Structural Integrity: 2

Armor
    Nose: 30
    Sides: 30/30
    Aft: 30

Cargo
    Bay 1:  Cargo (160.5 tons)      1 Door   

Ammunition:
None

Escape Pods: 0
Life Boats: 0
Crew:  1 officer, 2 enlisted/non-rated

Notes: Mounts 7 tons of standard aerospace armor.

Weapons
and Ammo              Location   Tonnage  Heat   SRV  MRV  LRV  ERV
None

Note here that the cost of the Spacebus (4,661,530 C-bills) is similar to the cost of 20 Strongarm Exoskeletons (3,040,000 C-bills, not including training) which can be deployed to load or unload it.

Variants:
A couple variants are handy.

The Quarterbus trades 150 tons of cargo for 30 workers quarters creating a highly transportable set of quarters with 2 months of life support.
Code: [Select]
Quarterbus smallcraft
Cost: 6,176,530 C-bills

    Bay 1:  Cargo (10.5 tons)       4 Doors   
Crew:  1 officer, 2 enlisted/non-rated, 30 passengers
Some Quarterbuses have first class quarters instead for more luxurious accommodations.

The Volksbus is a short duration bulk transport for 480 people.  It's most obviously useful taking a berth on the Cavern allowing people to be carried hundreds or thousands of light years over the 3 days of life support provided by the cargo.
Code: [Select]
Volksbus smallcraft
Cost: 21,876,530 C-bills
Cargo
    Bay 1:  Infantry (Foot) (80)    2 Doors   
    Bay 2:  Cargo (80.5 tons)       2 Doors   
Crew:  1 officer, 2 enlisted/non-rated, 448 bay personnel

idea weenie

  • Major
  • *
  • Posts: 4217
Re: Spacebus Smallcraft
« Reply #1 on: 19 October 2022, 10:19:35 »
Drop some of the 7 tons of armor and use the freed up mass to give it more fuel capacity?


Of course as a SpaceBus I am sure some people have added passenger capacity.  If it is only expected to go for 1 day, then putting 5 days worth of Life Support on board would be a good idea.  If they only accept 20 people per 5-ton Foot Infantry Bay, that keeps the math easy.  So At 20 Man-Days per ton of Life Support, then if carrying 20 people, it would need 5 tons of Life support cargo capacity, for a total of 10 tons.  Since it has 160.5 tons of cargo capacity, that is a max of 16 sets of passengers, or 320 people.  The remaining half ton is for the Crew's Life Support, providing 100 man-days, or a month of Endurance since it has to be split among 3 people.

Lagrange

  • Lieutenant
  • *
  • Posts: 1155
Re: Spacebus Smallcraft
« Reply #2 on: 19 October 2022, 12:36:28 »
Drop some of the 7 tons of armor and use the freed up mass to give it more fuel capacity?
The 1.5 tons of fuel provides almost 40 hours of thrust at 0.5 g.  That's plenty for the application I have in mind, which involves short hops between different large craft.  If something more like interplanetary transport is desired, more fuel is certainly a good idea.  In fact, you'd probably want something like 10 more tons.  Since I'm trying to minimize the number of designs, I'd be tempted to just carry some extra fuel as cargo if long haul flights are needed.

W.r.t. armor, my primary question is: what is the right level of robustness for a civilian design?   This has one more ton of armor than the KR-61 (which seems to be the least armored design in TR3057).  Since the SI is only 2 though, it ends up being similar in terms of the scale of a survivable accident.   
Of course as a SpaceBus I am sure some people have added passenger capacity.  If it is only expected to go for 1 day, then putting 5 days worth of Life Support on board would be a good idea.  If they only accept 20 people per 5-ton Foot Infantry Bay, that keeps the math easy.  So At 20 Man-Days per ton of Life Support, then if carrying 20 people, it would need 5 tons of Life support cargo capacity, for a total of 10 tons.  Since it has 160.5 tons of cargo capacity, that is a max of 16 sets of passengers, or 320 people.  The remaining half ton is for the Crew's Life Support, providing 100 man-days, or a month of Endurance since it has to be split among 3 people.
Yeah, it makes sense. 

More generally, a modified Spacebus could _be_ the cargo.  For example, you could easily fit 30 steerage quarters + 10 tons of supplies for transportable living quarters with a 2 month supply anywhere needed in space.  It's a bit expensive compared to some other options, but the transportability is quite nice.

Daryk

  • Lieutenant General
  • *
  • Posts: 30480
  • The Double Deuce II/II-σ
Re: Spacebus Smallcraft
« Reply #3 on: 19 October 2022, 20:05:09 »
LaGrange is designing a pallet jack, not a jump point to planet shuttle...  ^-^

AlphaMirage

  • Captain
  • *
  • Posts: 2572
Re: Spacebus Smallcraft
« Reply #4 on: 19 October 2022, 20:10:04 »
I expect one day he will give us a ready made package of Triad Combat Platforms and the associated Logistics equipment designed for everything from a raid to full on Great House takeover.

Full 'LockMart mode' Lagrange

Taron Storm

  • Warrant Officer
  • *
  • Posts: 579
  • Founding Member of Chaos Inc Merc Brigade
Re: Spacebus Smallcraft
« Reply #5 on: 19 October 2022, 20:25:37 »
 ;D

Dragon Cat

  • Lieutenant Colonel
  • *
  • Posts: 7459
  • Not Dead Until I Say So
Re: Spacebus Smallcraft
« Reply #6 on: 19 October 2022, 21:02:26 »
I like it, I like the passenger idea too makes perfect sense to me

On the cargo version I'd turn the crew quarters into an office, breakroom and one quarters that way your crew would have the comfort to work assign a second crew to it and rotate through the shift
Below are links to my fan fiction pages.

https://bg.battletech.com/forums/fan-fiction/alternate-timeline-with-thanks-(full)/

https://bg.battletech.com/forums/fan-fiction/alternate-timeline-with-thanks-full-part-2/

As always please enjoy and if you have any questions about my AU (or want to chat about ideas I could incorporate into it) feel free to PM me.

idea weenie

  • Major
  • *
  • Posts: 4217
Re: Spacebus Smallcraft
« Reply #7 on: 19 October 2022, 21:18:50 »
W.r.t. armor, my primary question is: what is the right level of robustness for a civilian design?   This has one more ton of armor than the KR-61 (which seems to be the least armored design in TR3057).  Since the SI is only 2 though, it ends up being similar in terms of the scale of a survivable accident.   Yeah, it makes sense. 

If this is a civilian design, the low armor makes plenty of sense.

More generally, a modified Spacebus could _be_ the cargo.  For example, you could easily fit 30 steerage quarters + 10 tons of supplies for transportable living quarters with a 2 month supply anywhere needed in space.  It's a bit expensive compared to some other options, but the transportability is quite nice.

Now I'm imagining a Mule, Mammoth, or Behemoth Dropship with a mess of Small Craft Bays, whose only job is carry a massive number of Small Craft like this on a single Docking Collar.  You can drop them all off without worrying about passenger movement (since the passengers would be kept in their Small Craft), and the Dropship can perform basic maintenance in orbit.  The key is that it would need either a space station to transfer the people to, or some other way for the passengers to get to the planet's surface.  (two more Small Craft designs, with 3/5 thrust, one with a cargo capacity of ~120 tons and the other with a passenger compartment?  The cargo one will need 2 trips to transfer cargo from the SpaceBus to the surface, while the passenger version will have less Life Support since it will only travel from orbit to surface when it is safe)

Rough guide (all data from MML 0.48.0):
* Mule (gains 39 SC capacity): 2 bays @ 2715 capacity + 1 bay @ 2714.5 tons capacity -> 2 bays @ 13 Small Craft & 115 tons cargo + 1 bay @ 13 Small Craft Bays & 114.5 tons cargo
* Mammoth (gains 185 Small Craft): 5 bays @ 7563 tons cargo capacity -> 5 bays @ 37 Small Craft & 163 tons cargo capacity (existing 4 Small Craft were not touched)
* Behemoth: (gains 372 Small Craft): 2 bays @ 18780 tons cargo capacity + 2 bays @ 18779.5 tons cargo capacity -> 2 bays @ 93 Small Craft & 180 tons cargo capacity + 2 bays @ 93 Small Craft & 179.5 tons cargo capacity (existing 20 Small Craft were not touched)

So you lose the ability to carry any single item over 123 tons, but you can deliver it to any point on a planet without needing to stop at a Spaceport first.  You also save the time of transshipping the cargo onto a Dropship, as cargo can be moved onto all of the Small Craft simultaneously.  Good for colonies with low levels of ground transportation ability, and fast turn-around of materials.

The problem becomes that a regular cargo Mule can carry 8.2 kilotons of cargo and costs ~163.3 million C-Bills.  A Beehive Mule by itself would cost 212.4 million C-Bills, 39 Cargo Small craft is an additional 181.8 million C-Bills, for a total of 394.2 million C-Bills.  The Beehive would only be able to carry ~6.5 kilotons of cargo (38*160+1*123+2*115+1*114.5).

So the Mule has a ratio of ~20k:1 in terms of C-Bill cost vs tons carried, while a Beehive is ~60k:1 in terms of C-Bills cost per ton carried.  So for triple the shipping price in order to get cargo faster and delivered on-site, this would be useful.


LaGrange is designing a pallet jack, not a jump point to planet shuttle...  ^-^

Jump point to planet is about 10 days (using Sol - Terra as the base).  I was thinking 5 days of Life Support in case something terrible happens while transferring from planetary orbit to lunar orbit or even LaGrange point distance.  You are right, reducing it to 2 days Life Support would make the 20-person setup take up 7 tons instead of 10, meaning that you go from fitting in 16 groups of 20 people to fitting 22 sets of 20 people at a time, with 6 tons of cargo still available.

Daryk

  • Lieutenant General
  • *
  • Posts: 30480
  • The Double Deuce II/II-σ
Re: Spacebus Smallcraft
« Reply #8 on: 20 October 2022, 03:20:03 »
Fuel is the reason that idea doesn't quite work...  8)

idea weenie

  • Major
  • *
  • Posts: 4217
Re: Spacebus Smallcraft
« Reply #9 on: 20 October 2022, 13:37:45 »
Fuel is the reason that idea doesn't quite work...  8)

The 5 days of Life Support allows it to be a decent life boat for someone nearby to pick up.

My main concern was seeing the 1.5 tons of fuel and not thinking it was enough.  I forgot how wonderfully efficient BT engines are.  It is capable of almost 40 hours at half a G (thanks Lagrange), so figuring 30 hours standard.  Half the time for accel, half the time for decel, so I need to figure out how far it can get in 15 hours, then double that distance to get total range (without going into emergency)
Code: [Select]
D = 1/2 a*t^2
D = 1/2 (4.9 m/s^2)*(15 hours)^2
D = 2.45 m/s^2 * (15 hours * 3600 seconds/hr)^2
D = 2.45 m/s^2 * (15 * 3600 seconds)^2
D = 2.45 m/s^2 * (54000 seconds)^2
D = 2.45 m/s^2 * (54 * 1000 seconds)^2
D = 2.45 m/s^2 * 54^2 * 1000^2 * seconds^2
D = 2.45 * m * 2916 * 1000 * 1000 * 1 km/1000 m
D = 2.45 * 2916 * 1000 * 1000 * m * 1 km/1000 m
D = 7144.2 * 1000 * km
D = 7,144,200 * km

It then decelerates for the other ~7.1 million km, for a total range of ~14.2 million km.
Earth to Moon is ~385,000 km (easily achievable)
Earth to L1 is ~1.5 million km (achievable)
1 AU = ~150 million km (not achievable)

Lagrange

  • Lieutenant
  • *
  • Posts: 1155
Re: Spacebus Smallcraft
« Reply #10 on: 20 October 2022, 16:15:16 »
Thanks all for the encouragement  :)

Full 'LockMart mode' Lagrange
Maybe... would be fun to work it out.

...
Yeah, I think of this as the "intra-planetary-orbit" scale.   A few notes:

(1) Another good number to compute is the turn-around distance: how far can you go such that you have fuel to accel, decel, return accel, and return decel?  That's 1/4 of the maximum accel/decel distance.
(2) It is possible, although not ideal, to do interplanetary scale trips via an accel/coast/decel since life support from .5 tons for 3 people works for 30 days.  In general though, you'll typically want to bring some extra fuel as cargo.
(3) Looking at the physics of fusion, you actually only get ~6 hours of thrust at 0.5g from 1.5 tons of fuel.  That's still decent for intra-planetary orbit transfers, but you need to be more careful.

Daryk

  • Lieutenant General
  • *
  • Posts: 30480
  • The Double Deuce II/II-σ
Re: Spacebus Smallcraft
« Reply #11 on: 20 October 2022, 17:26:21 »
Don't forget landing and lift off...  8)

Taron Storm

  • Warrant Officer
  • *
  • Posts: 579
  • Founding Member of Chaos Inc Merc Brigade
Re: Spacebus Smallcraft
« Reply #12 on: 20 October 2022, 18:25:43 »
I can see the Belters and Rockjacks using these

idea weenie

  • Major
  • *
  • Posts: 4217
Re: Spacebus Smallcraft
« Reply #13 on: 20 October 2022, 20:04:54 »
Yeah, I think of this as the "intra-planetary-orbit" scale.   A few notes:
(1) Another good number to compute is the turn-around distance: how far can you go such that you have fuel to accel, decel, return accel, and return decel?  That's 1/4 of the maximum accel/decel distance.
(2) It is possible, although not ideal, to do interplanetary scale trips via an accel/coast/decel since life support from .5 tons for 3 people works for 30 days.  In general though, you'll typically want to bring some extra fuel as cargo.
(3) Looking at the physics of fusion, you actually only get ~6 hours of thrust at 0.5g from 1.5 tons of fuel.  That's still decent for intra-planetary orbit transfers, but you need to be more careful.

Turn-around distance:
Standard fuel endurance is <40 hours, I'll again use 30 hours.  Half the fuel spent on the way out half the remaining spent on the way back.  This translates to 15 hours out, 15 hours back, meaning each accel/decel leg is 7.5 hours.  Distance is based on t^2, so half the time, 1/4 the distance, or about 3.55 million km.
Code: [Select]
Proof:
D = 1/2 a * t^2
D = 1/2 (4.9 m/s^2) * (7.5 hrs * 3600 seconds/hr)^2
D = 2.45 m/s^2 * (7.5 * 3600 * seconds)^2
D = 2.45 m/s^2 * (15 * 1800 * seconds)^2
D = 2.45 m/s^2 * (30 * 900 * seconds)^2
D = 2.45 m/s^2 * (27 * 1000 * seconds)^2
D = 2.45 m/s^2 * 27 * 27 * 1000 * 1000 * seconds^2
D = 2.45 m * 27 * 27 * 1000 * 1000
D = 2.45 * 729 * 1000 * 1000 * meters
D = 1786.05 * 1000 * kilometers
D = 1,786,050 * kilometers
Accel leg is 1,786,050 kilometers, this means decel leg is another 1,786,050 kilometers, for a total distance of 3,572,100 km out and using half the fuel.



2) For the fun part of accel/coast/decel, the fun part is trying to graph out what is the minimum cargo used between Life support and extra fuel.  I could do it with calculus, but instead I'll do it with a spreadsheet.  I got 49687 seconds of accel, and another 49687 seconds of decel, leaving 6194274 seconds of coasting over a trip if 10 AU resulted in 1.075 tons of Life Support and 1.058 tons of Fuel being consumed, over a time of 71.7 days (of which 70.5 is spent coasting).  (Spreadsheet is attached)



3) Physics of fusion is using real-life numbers?  At that point you are getting 2.5 hours effective (the last half hour is for emergencies), so 1.25 hours out and back.  1.25 hours/15 hours = .08333 as much, so the actual distance is .00694 as much distance, or only 98,000 km (about 5400 space hexes, or about a quarter of the way to the Moon).


Don't forget landing and lift off...  8)
Thrust of 1/2 means it only performs 1 landing maneuver in its lifetime.   ;)

Daryk

  • Lieutenant General
  • *
  • Posts: 30480
  • The Double Deuce II/II-σ
Re: Spacebus Smallcraft
« Reply #14 on: 20 October 2022, 20:06:33 »
Also true, unless you count vacuum worlds...  ^-^

idea weenie

  • Major
  • *
  • Posts: 4217
Re: Spacebus Smallcraft
« Reply #15 on: 20 October 2022, 20:33:22 »
Also true, unless you count vacuum worlds...  ^-^

True, worlds with G levels low enough mean it can land safely

 

Register