BattleTech Spacecraft Dimensions

[Bren]

Alright, I realize many of you had a pavlovian shudder just clicking this thread ... but I'm interested in puttering away on a project involving DropShip and JumpShip sizes.

-- Initial disclaimer: I am a neophyte when it comes to almost all things space and spaceship related (including science fiction and BattleTech). --

Goal: bring the sizes of the various craft down as much as possible.

As I see it, the main factor determining the 'shrinkage' of DropShips should be the 'Mechbay volume. Shrink the DropShip so it can fit the required number of 'Mechs properly and I think we have a reasonable starting point.

My main problem is lack of knowledge in this area. If anyone with brains on naval, space, or hard science fiction matters would like to help me out - I'm all ears.

Once numbers start flying around my plan is to 'sketch' things out in 3D, vaguely like my rough go below. How much volume does 20 crew require on a modern submarine? How much volume is required per aircraft in a modern aircraft carrier hangar? ect.

(12 Atlas 'Mechs arranged on two 'decks' in a Union shape - a lot of room ...)


Let me know if anyone's interested.

[marauder648]

Very intriguing :)  With a Union you'd have to assume that the bottom three rows are all engines/storage space/fuel, the middle three are for the Mech bays and their associated equipment/crew quarters whilst the two three rows are all command, crews and electronics 

Looking at a Sphere that big with the Mechs inside from side on there's little space but it does kinda make sense.

[cavingjan]

Do you intend for the mech bays to allow complete repair work or just minor field repairs? The space around the mechs seem too small to allow an appendage to be taken off and maneuvered around.

Do you intend for the mechs to be carried as cargo or to be able to do combat drops? The mechs seem very far on the interior. You would lose most of that outer hull space to hallways for the mechs to get to the doors. It looks like you would have enough space if you were intending one door per level but that would make it take forever to unload.

Is this for an extended trip or just short duration trips?

[The_Caveman]

There's an older cutaway drawing (I think from DropShips & JumpShips) of a Union. As you can see the scale of the 'Mech bays is absolutely titanic, taking up almost 50% of the ship's internal volume. Much of the rest goes to the enormous transit drive, space for the landing gear to fold away, and the boarding ramps needed by the 'Mechs (which can't be too steep as you don't want your cargo falling down on its way out the door). That big round thing underneath the 'Mech bay is the fuel tank, holding over 3,000 cubic meters of liquid hydrogen.

There's a more modern cutaway, in which you can see two Sparrowhawk fighters and a Wraith BattleMech onboard for scale. It seems huge until you realize how much of that deck space is needed just for the 'Mechs to walk around inside without bumping into things. About the only way you could really reduce the scale of the 'Mech bay would be to have each 'Mech in its own self-contained pod on the outside of the hull....but then it would be really hard to conduct major repairs.

The over-scaling isn't as bad as people claim. Although the mass is too low. If a Union had the same density as a small bulk cargo ship (wet), it'd mass about 55,000 tons. We just have to assume that whatever construction materials DropShip hulls are made of, it's much stiffer and less dense than structural steel. Which, given that the fiction frequently mentions foamed metals in the context of aerospace craft, does make a fair bit of sense.

[marauder648]

From the books and even the old publications like the original Star League book i've got at home you get a real sense that the metals are not only very light but obscenely tough.
Even the primative Mackie's armour which was described as being as thick as a finger denied a round from a MBT's gun (presumably a 105mm or 120mm gun of design similar to what we use as they said it was a Merkava).  The story describes that the round would have gone through half a meter of solid steel.

So yeah the stuff they make Mech's with is insanely tough by our standards and I do have to agree that the foamed metals they make would also be very light and this would reduce the mass when combined with the really sturdy stuff they are made of as you'd not need a huge thick mass of it to have protection.

Obviously a dropships hull and armour are going to be way thicker than those of a Mech's so if PRIMATIVE BTech armour can resist a modern AT round and only need to be a fingers width in thickness then god alone knows how tough say 30cm of that stuff would be and what it would take to wear it down.  The book does mention that they use a latice weave of man made diamonds in the construction of the armour and thats where the strength mostly comes from layer after layer of these diamonds on a carbon-nano fiber lattice and thats sheathed in a metal of some nature.  That sounds pretty darn tough to me.

[Kidd]

Magic metals or composites similar to the real world Aluminum Oxynitride, which cameod recently as the human hamsterball in Jurassic World. Its a good candidate for magic cockpit armour, I believe something like a mere half inch can stop a .50 cal round. The advanced BT tech is not just about the technical difficulty of creating the substances, its also achieving the cost efficiency.

Doing calculations for roleplaying in a Union DS, I gave Mechs a floorspace of about 10 sq meters and 16 meters overhead (for the Mech alone). Good news is that a Union has 2 decks of 4 and 8 mechs so that cuts down the size. Because of the curvature of the ship you end up with a lot of space at the back of a Mech cubicle even allowing plenty of volume for Dropship cargo, bulkhead, armor, machinery etc. Its an interesting exercise in pi.

[Bren]

Do you intend for the mech bays to allow complete repair work or just minor field repairs? The space around the mechs seem too small to allow an appendage to be taken off and maneuvered around.

Do you intend for the mechs to be carried as cargo or to be able to do combat drops? The mechs seem very far on the interior. You would lose most of that outer hull space to hallways for the mechs to get to the doors. It looks like you would have enough space if you were intending one door per level but that would make it take forever to unload.

Is this for an extended trip or just short duration trips?

A note on the quick 3D mock-up I posted - it was just meant to show the obvious issue of the ship being too large; 12 of the more bulky 'Mechs in the game compared with the dimensions of a Union DropShip. Almost no attention was paid to layout.

Space around 'Mechs: this was one of my main queries ... how much space is required for these things now? Things seem pretty tight on carriers presently. Though my ignorance comes into play here. Are the aircraft below shown in a 'storage' capacity and not fully open to being serviced? Or are there designated service locations on the carrier to which an aircraft can be moved for more intensive work (eg: engine change)?



On that note, does every 'Mech on a DropShip have to be fully serviceable by techs at all times? Or can the majority be in tight storage and individual units moved to a more open repair bay for more intensive work.

I guess the short way to address your questions would be; how have these issues been dealt with in the fiction, and if so, is there any reason not to continue the trend?

If it hasn't been dealt with in fiction - as a starting point, how is it done on carriers today?

[Vition2]

'Mechs can be transported 2 ways: as bulk cargo or in readiness within a 'mech cubicle.  Each 'mech bay is stated as having all the equipment required to conduct up to maintenance level refits (includes up/down-grading the engine rating or replacing a location with custom parts), it would be nice if there was a different type of cubicle/bay that allows for quick deployment but not the heavy equipment required for the repair of heavy damage (say at 110-25 tons instead of 150).  Bulk cargo on the other hand, takes a few extra minutes to get ready and able to roll out of the dropship and doesn't allow for combat dropping, iirc.

Now, since these are fairly large ships, I could see the weight of the 'mech cubicles being spread out, in a similar way that the weight of quarters include recreational areas - though they aren't specifically defined. 

[cray]

Even the primative Mackie's armour which was described as being as thick as a finger denied a round from a MBT's gun (presumably a 105mm or 120mm gun of design similar to what we use as they said it was a Merkava).

The stats for the Merkava have been published, and they're not the 20th Century Israeli Merkava series. They're a later Terra Alliance/Hegemony design with an AC/5, which has a muzzle velocity above early 21st century railguns.

But, yes, very tough. WarShips generally have armor in terms of foil thickness that is able to stop nuclear-level energies.

[Daryk]

I've served aboard more than one aircraft carrier and more than one submarine, and have two sets of deck plans (one for a Manatee and one for a Mark VII landing craft) down on the fan design board.  I'm very interested in this discussion, and agree with The_Caveman that the over scaling isn't that bad, at least not on the smaller ships I've drawn up so far.  Auxiliary equipment takes up a lot of space (life support, back up generators, pumps, fans, water recycling, etc. etc.).

As for your specific question about aircraft in the hangar bay, what you don't see are the many shops for doing maintenance on components, and yes, there's even a test bench for a dismounted engine if that's necessary.  If you have to remove an engine, it requires some creative parking, probably with some of the aircraft on the roof (flight deck) to make room.  You also don't see the huge amount of space for spare parts, fuel, and ordnance.  Aircraft carriers are huge, but just about every space has something crammed into it.  You'll also note that every one of those aircraft folds up in some way.  Even in the hangar bay, space is at a premium.

As for submarines, they are not huge.  More space is given to equipment than personnel, and the trend for the more modern boats I've seen is to make that situation worse.  The trick isn't necessarily finding room for their racks, but also for the galley, mess deck, and heads.  If you check my Mark VII plans, I crammed 36 personnel into just under half of a 14x8x5 meter space (the top half).  Triple stacked racks on a submarine aren't easy to climb into (nor are they on aircraft carriers, but the carrier racks have more head room).

[kato]

Are the aircraft below shown in a 'storage' capacity and not fully open to being serviced?

Given that Battletech uses individual cubicles for storing and servicing in almost a general fashion, the helicopter hangars on frigates (for minimized space) may be a better size comparison, in particular individual helicopter hangars - since these serve for both transport and servicing, often also stocking the relevant parts and such for the unit to be serviced there.

[The_Caveman]

You can't move 'Mechs around with a tug either, they have to be able to walk, which imposes some constraints on the minimum deck space required. And unlike an aircraft carrier, a DropShip in space doesn't have the luxury of moving things "up on deck".

[HobbesHurlbut]

The stats for the Merkava have been published, and they're not the 20th Century Israeli Merkava series. They're a later Terra Alliance/Hegemony design with an AC/5, which has a muzzle velocity above early 21st century railguns.

But, yes, very tough. WarShips generally have armor in terms of foil thickness that is able to stop nuclear-level energies.

Wait you mean it's not a rifle cannon? I thought Merkava was armed with one explaining how Mackie's armor stopped her shots easily.

[Bren]

You can't move 'Mechs around with a tug either, they have to be able to walk, which imposes some constraints on the minimum deck space required.

Additionally, 'Mechs can pack into a DropShip to the tune of one every ten seconds (EDIT: per door) - an indication of the space available. That said, space is cramped enough that critical damage is done to bay doors in 2.78% of boardings.

[Vition2]

That said, space is cramped enough that critical damage is done to bay doors in 2.78% of boardings.

I wouldn't worry about this at all, Fluff doesn't equate to rules, and vice versa.  There's only so much granularity you can get from 2d6 - and while I'd love to see an update to many rules/RATs to 3d6, it seems unlikely to happen.

[Bren]

Is there a general consensus on how large aerospace fighters are? I've always had in my head the largest 100-ton types are about F-111ish in size, but maybe that's too big?

[HobbesHurlbut]

Is there a general consensus on how large aerospace fighters are? I've always had in my head the largest 100-ton types are about F-111ish in size, but maybe that's too big?

They have fusion rockets for engines and plow through atmospheres on pure thrust. Look at what plane that weight around 100 tons and find out what their dimensions are. ;)

[The_Caveman]

They have fusion rockets for engines and plow through atmospheres on pure thrust. Look at what plane that weight around 100 tons and find out what their dimensions are. ;)

ASFs are about the size of 'Mechs, just a bit longer and flatter. They're vastly heavier for their size than conventional aircraft because they rely mostly on thrust to stay airborne. If they were the size of conventional aircraft of the same weight, they would be too fragile for atmospheric reentry.
ASFs are built to withstand hypersonic maneuvering and take the punishment of space battles, not to fly efficiently or gracefully in lower atmosphere. They're pretty much flying bricks.

[marauder648]

The 100 tonne ASFs are basically bricks, hell most of the ASF designs simply would not fly and are as aerodynamic as a house thats decided to take up hand gliding.  They fly for the most part through pure balls the the walls thrust and nothing more although I'm not sure how fast they are, I've heard that something like Mach 7 is perfectly normal for them.

Factor into that that each and every ASF is a SSTO space craft as well.

[I am Belch II]

Sizes in Battletech have always been a little off.

A Nimitz carrier had hanger space for about 50 planes the air wing could of been as high as 90.

[The_Caveman]

The 100 tonne ASFs are basically bricks, hell most of the ASF designs simply would not fly and are as aerodynamic as a house thats decided to take up hand gliding.  They fly for the most part through pure balls the the walls thrust and nothing more although I'm not sure how fast they are, I've heard that something like Mach 7 is perfectly normal for them.

Factor into that that each and every ASF is a SSTO space craft as well.

Strictly speaking anything can fly as long as you put enough thrust behind it. Most ASFs are designed around the lifting body principle, so they'll produce enough lift to get airborne as long as there's enough thrust to offset their abysmal lift-to-drag ratios. Look up the Northrop HL-10 and Martin X-24B for comparable real-world ideas (albeit on a much smaller scale).
In high atmosphere (black sky), ASFs can operate comfortably at speeds of Mach 7-10. Once you get down into low atmosphere (blue sky), most ASFs max out around Mach 2, with the very fastest able to break Mach 3. These speeds are basically only made possible by the outlandish thrust and massive heat dissipation available to ASFs. The really crazy thing is ASFs can execute sharp maneuvers at these speeds, which would be impossible if they were built like conventional aircraft--they'd snap their own wings off. Even the designs with relatively high wing aspect ratios like the Riever and Corsair have extremely thick, overbuilt wings compared to a conventional aircraft of the same general layout.

[Frabby]

Discussing ASF reminded me of something that may be pertinent to this thread: There are CV refits of the Union mentioned in canon that implicitly replace all the 'Mech capacity for ASF capacity. Seems to suggest the sizes for vehicles and their bays are roughly equal.

[marauder648]

Makes sense :)

[Bren]

Ok, trying to consolidate ideas here ...

Engine	I see no reason to not keep the engine in similar proportions to existing cutaway art.
.........................
Fuel	3038 cubic metres of liquid hydrogen fuel cubes out to 14.483 metres as a good start point.
.........................
Cargo Bay	Any thoughts as to how large a 74 ton cargo bay should be? I assume this doesn't include the normal stores for operating the DropShip? Food, toilet paper, light bulbs, ect. I assume the 17 tons of cannon and missile ammunition is not included. Is toilet paper still used? Or did the Star League figure out the three sea shells. Lostech?
.........................
'Mech Bay	For Mech cubicles I like the on-ship helicopter hangars as a start point. For larger repair areas, I'm thinking the size of two cubicles, so that both 'Mech bays are similar in size (ie: 8 'Mechs in bay one, 4 'Mechs and 2 repair areas in bay two).
.........................
Fighter Bay	Again, I like the on-ship helicopter hangar relative proportions as a good start point.
.........................
Doors/Ramps	Dimensions intuitive based on large 'Mech and fighter sizes.
.........................
Landing Gear	Proportions set by existing art.
.........................
Bridge	My initial thought; one deck 'high' at the nose of the ship, large enough for ten people to work.
.........................
Crew Area	In addition to the standard 42 crew, how many extra people should be able to stay aboard? At least 14 I would guess (MechWarriors and fighter pilots). 'Mech and Aero techs in addition to this? Or are these included in the base 28 'bay personnel'?
.........................
Escape Pods	Dimensions as listed in Tech Readout.

Any thoughts?

[Vition2]

Only a couple suggestions:

Crew area - this should be the outer/uppermost deck or decks.  The 28 bay personnel include both the mechwarriors/ASF pilots and their associated techs.

Bridge - size is probably good, but you want it below the crew area, technically the crew area is non-critical components while the bridge is critical so any extra layers between it and space is better.  Include at least a couple living quarters at this level, your captain and probably XO should be able to get here in less than 30 seconds in an emergency.

[kato]

Any thoughts as to how large a 74 ton cargo bay should be?

Just use the standard dimensions for ISO containers if you want to keep it small. 74 tons is around 3.4 TEU for the highest payload-to-volume ratio, hence about 113 m³. Basically that's a 20" container expanded by half in all three directions - i.e. 8.5x3.5x3.5 meters (27.8x11.5x11.5 ft). Could always make it roomier than that of course, but as a minimal-size indication it should work.

For Mech cubicles I like the on-ship helicopter hangars as a start point. For larger repair areas, I'm thinking the size of two cubicles, so that both 'Mech bays are similar in size (ie: 8 'Mechs in bay one, 4 'Mechs and 2 repair areas in bay two).

You could also make it one-and-a-half cubicles by size - given mech sizes that should be a few meters "breathing room" on either side of the mech, should be enough. Then stick the cargo in there "stacked on the side" in the remaining half cubicle. That would also allow using the same ingress/egress routes for your cargo as for the mechs, allow you to dual-use the "repair area systems" (cranes and such) in cargo stowing, and from a fluff point keep spare parts and such near where they're needed.

[Daryk]

For 'mech cubicles, I used 6 meters square.

[Arkansas Warrior]

For 'mech cubicles, I used 6 meters square.

Even though mechs are up to 12 meters tall?  Also, quads should be significantly longer than bipedal designs of the same weight.

[The_Caveman]

Even though mechs are up to 12 meters tall?  Also, quads should be significantly longer than bipedal designs of the same weight.

Y'know, quads are so rare in-universe that I wonder if most DropShips would even be equipped to handle them.

Kinda makes me imagine one really strange Union out there in the 'verse that's set up to carry a full company of Scorpions.

[Frabby]

I always figured Quads would fold in their legs like spiders do (for the Scorpion and most others), and/or like camels do (for the Goliath), and would fit into a standard 'Mech cubicle upright. I'm not aware of any special rules for Quads regarding 'Mech bays or combat dropping. Come to think of it, since their PSRs are 1 easier they're actually better for dropping.