Author Topic: BattleTech Spacecraft Dimensions (Read 18512 times)

Bren · « **on:** 05 January 2016, 00:54:03 »

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 · « **Reply #1 on:** 05 January 2016, 05:16:28 »

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 · « **Reply #2 on:** 05 January 2016, 08:27:41 »

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 · « **Reply #3 on:** 05 January 2016, 09:12:29 »

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 · « **Reply #4 on:** 05 January 2016, 10:55:21 »

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 · « **Reply #5 on:** 05 January 2016, 11:16:35 »

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 · « **Reply #6 on:** 05 January 2016, 13:28:33 »

Quote from: cavingjan on 05 January 2016, 08:27:41

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 · « **Reply #7 on:** 05 January 2016, 14:15:24 »

'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 · « **Reply #8 on:** 05 January 2016, 18:44:31 »

Quote from: marauder648 on 05 January 2016, 10:55:21

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 · « **Reply #9 on:** 05 January 2016, 20:06:05 »

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 · « **Reply #10 on:** 05 January 2016, 20:29:30 »

Quote from: Bren on 05 January 2016, 13:28:33

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 · « **Reply #11 on:** 05 January 2016, 20:39:07 »

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 · « **Reply #12 on:** 05 January 2016, 20:45:51 »

Quote from: cray on 05 January 2016, 18:44:31

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 · « **Reply #13 on:** 05 January 2016, 20:54:28 »

Quote from: The_Caveman on 05 January 2016, 20:39:07

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 · « **Reply #14 on:** 05 January 2016, 22:39:41 »

Quote from: Bren on 05 January 2016, 20:54:28

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 · « **Reply #15 on:** 06 January 2016, 01:39:49 »

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 · « **Reply #16 on:** 06 January 2016, 01:57:58 »

Quote from: Bren on 06 January 2016, 01:39:49

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 · « **Reply #17 on:** 06 January 2016, 02:11:10 »

Quote from: HobbesHurlbut on 06 January 2016, 01:57:58

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 · « **Reply #18 on:** 06 January 2016, 05:08:22 »

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 · « **Reply #19 on:** 06 January 2016, 08:11:11 »

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 · « **Reply #20 on:** 06 January 2016, 09:25:22 »

Quote from: marauder648 on 06 January 2016, 05:08:22

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 · « **Reply #21 on:** 06 January 2016, 11:39:50 »

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 · « **Reply #22 on:** 06 January 2016, 12:59:29 »

Makes sense :)

Bren · « **Reply #23 on:** 06 January 2016, 13:04:44 »

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 · « **Reply #24 on:** 06 January 2016, 13:27:12 »

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 · « **Reply #25 on:** 06 January 2016, 13:42:40 »

Quote from: Bren on 06 January 2016, 13:04:44

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.

Quote from: Bren on 06 January 2016, 13:04:44

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 · « **Reply #26 on:** 06 January 2016, 18:42:55 »

For 'mech cubicles, I used 6 meters square.

Arkansas Warrior · « **Reply #27 on:** 07 January 2016, 14:19:08 »

Quote from: Daryk on 06 January 2016, 18:42:55

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 · « **Reply #28 on:** 07 January 2016, 14:24:20 »

Quote from: Arkansas Warrior on 07 January 2016, 14:19:08

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 · « **Reply #29 on:** 07 January 2016, 16:53:45 »

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.

Daryk · « **Reply #30 on:** 07 January 2016, 19:53:00 »

Quote from: Arkansas Warrior on 07 January 2016, 14:19:08

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

Sorry, I should have said 6 meters square and 14.5 meters tall.

marauder648 · « **Reply #31 on:** 09 January 2016, 06:32:22 »

That makes sense, we can also imagine that Mech's when travelling between worlds have a kind of lock down position for travelling.

You can imagine that when the Gunsmith for example powers down and is basically preparing for a move its legs lock up and the exposed area slots into the lower leg, so the upper leg and lower leg can meet and it basically squats down somewhat. tanks have to be prepared for say a road move and i'd assume Mech's have something similar.

Daryk · « **Reply #32 on:** 09 January 2016, 07:56:19 »

When laying out the Manatee's packed cargo bay, I used MegaMek models expanded to about four meters wide. Of course, I was only using medium and light mechs, so 6 meters wide might be cramped for an assault. For the Manatee, that's probably not a problem, as they were the first attempts at dedicated mech carriers, explicitly converted from cargo ships.

How wide are those Atlas models you're using? I'd suggest having at least a meter of clearance on both sides so the mech can turn around in the cubicle.

Bren · « **Reply #33 on:** 09 January 2016, 09:06:03 »

I was using the MechWarrior Online art for the rough Atlas. If the 'Mech is 12 metres tall it's about 8.5 metres wide. I'll probably tweak my 'example Atlas' somewhat - but I'm guessing I wont be too far off of the Piranha Games stuff.

Daryk · « **Reply #34 on:** 09 January 2016, 09:47:18 »

I've noticed the MWO art seems to be wider in general, though I'm not sure why. If they really are 8.5 meters wide, I'd probably go with 12 meters square for a cubicle. 14-15 meters should still leave enough vertical clearance for an overhead crane.

Bren · « **Reply #35 on:** 19 December 2016, 13:34:51 »

Got into gear a bit lately on this.

Here is a WIP.

[Fuel] - [Landing Gear] - [Engine] - [Mechs] - [Fighters]

Union Class DropShip
Canon Dimensions

Warhammer BattleMechs
12 metres tall

Chippewa Fighters
'Gut Feelin' dimensions

Bren · « **Reply #36 on:** 19 December 2016, 13:38:44 »

Here's the first 'Go' at it.

I didn't think this through much at all - I just wanted to get a mark on the board as a point of comparison.

Mechs and Fighter dimensions unchanged. All DropShip dimensions reduced to 60% original size.

NOTE: Once you've expanded the image/attachment, right click and 'view image in another tab' for easier viewing.

Daryk · « **Reply #37 on:** 19 December 2016, 19:39:31 »

I don't think the smaller version has enough space for all the people. Access/loading ramps might be a problem too...

Bren · « **Reply #38 on:** 19 December 2016, 20:57:17 »

Some uneducated numbers I'm throwin' around:

Los Angeles class Sub
Crew: 129
Volume: 7572 m³
59 m³ per person

.55 Volume Union DropShip
Crew: 56
Volume: 5924 m³
106 m³ per person

I think we're in good shape there ... especially considering the submarine volume there is the entire sub, not just the control/crew area.

I'll start eyeballing the ramp/door business ...

Daryk · « **Reply #39 on:** 19 December 2016, 21:16:49 »

I've served aboard a Los Angeles class submarine, and I assure you over half of the pressure hull volume goes to just the engine room, and your overall figure appears to include the ballast tanks outside the pressure hull. I also drew up deck plans for a Manatee down in the Aerospace Design sub-forum, and my guess about the Union is informed by that.

Bren · « **Reply #40 on:** 19 December 2016, 21:26:36 »

My submarine volume figure includes everything seen in the image - so there should be plenty of room in the '55%' Union for crew and control.

Bren · « **Reply #41 on:** 20 December 2016, 01:28:19 »

Googling around some cutaways ... am I correct in assuming the red portion in the attached diagram is the 'control and crew quarters' portion of the sub?

If so, I have tons of room to still play with in the '55%' Union.

EDIT: oops, forgot attachment ...

Daryk · « **Reply #42 on:** 20 December 2016, 04:01:35 »

I recommend you check out my Manatee plans before assuming there's "tons" of room. And don't forget fuel tanks. Liquid hydrogen is 14 cubic meters per ton.

Bren · « **Reply #43 on:** 20 December 2016, 10:45:49 »

In terms of 'tons' I'm just making assumptions based on volume per crew member - in which the 55% union has many times the space as a Los Angeles class.

Fuel should be an easy one to tackle. Going off of the StratOps figure of 71kg per m³:

The canon Union has the volume for 351.58 tons.
Stats figure is 215.00 tons
'55%' Union at the moment has volume for 117.00 tons.

So I have some rejigging to do ... (this might come down to the nitty-gritty ... is the true scientific figure closer to 71kg or the 71.43 figure you gave. I might need all the cm³ I can possibly shave off ...)

kato · « **Reply #44 on:** 20 December 2016, 11:12:42 »

Quote from: Bren on 20 December 2016, 10:45:49

is the true scientific figure closer to 71kg or the 71.43 figure you gave. I might need all the cm³ I can possibly shave off ...

The density of hydrogen of course depends on the temperature and pressure. You can find a broad chart and table here. If necessary just use the highest figure : 75.287 kg/m³ at 30 MPa and 48.16 K (2855.74 m³ for 215 tons).

On a side note, technically in construction rules it's not the fuel that weighs that much; it's the - full - fuel tank. If you want to get creative use NASA's figure of 50% add-on weight for liquid containers on spacecraft (regardless of volume!), which pulls you down to 1903.82 m³ for above 215 tons which would include 71,666 kg for the tank itself - at the density of steel that's only a maximum of 12 mm wall thickness (as a sphere, otherwise less).

bluedragon7 · « **Reply #45 on:** 21 December 2016, 12:57:12 »

Quote from: Daryk on 19 December 2016, 19:39:31

I don't think the smaller version has enough space for all the people. Access/loading ramps might be a problem too...

To me it looks too cramped as well, if the density is a big problem for someone ( it isn't for me) I would rather make it heavier than smaller.

Bren · « **Reply #46 on:** 21 December 2016, 14:42:40 »

Quote from: bluedragon7 on 21 December 2016, 12:57:12

To me it looks too cramped as well ...

With 2.2m (7.2ft) high levels, I can easily fit three 'decks' at the top of the 55% union. With my very rough geometry the two 'crew and control' sections have about the same volume - and the Union has about half the people.

Bren · « **Reply #47 on:** 21 December 2016, 14:54:46 »

Quote from: kato on 20 December 2016, 11:12:42

The density of hydrogen of course depends on the temperature and pressure. You can find a broad chart and table here. If necessary just use the highest figure : 75.287 kg/m³ at 30 MPa and 48.16 K (2855.74 m³ for 215 tons).

On a side note, technically in construction rules it's not the fuel that weighs that much; it's the - full - fuel tank. If you want to get creative use NASA's figure of 50% add-on weight for liquid containers on spacecraft (regardless of volume!), which pulls you down to 1903.82 m³ for above 215 tons which would include 71,666 kg for the tank itself - at the density of steel that's only a maximum of 12 mm wall thickness (as a sphere, otherwise less).

Good thinking. If 1900 is all I have to shoot for - I'm in good shape.

bluedragon7 · « **Reply #48 on:** 21 December 2016, 15:45:53 »

Quote from: Bren on 21 December 2016, 14:42:40

With 2.2m (7.2ft) high levels, I can easily fit three 'decks' at the top of the 55% union. With my very rough geometry the two 'crew and control' sections have about the same volume - and the Union has about half the people.

I was talking about the mech bay, hangars, ramps, chutes etc.
In my opinion you need more space around each unit if you do more than store it as cargo.

Wrangler · « **Reply #49 on:** 21 December 2016, 15:58:33 »

Are you going to include the machine spaces, where the equipment that runs the dropship are housed?

Their squashed on a Union, where engines are but they are there..

Bren · « **Reply #50 on:** 21 December 2016, 16:08:38 »

Sorry Wanger, I'm not sure what you mean. Can you clarify referencing Caveman's image in post #3?

Wrangler · « **Reply #51 on:** 21 December 2016, 21:35:06 »

Quote from: Bren on 21 December 2016, 16:08:38

Sorry Wrangler, I'm not sure what you mean. Can you clarify referencing Caveman's image in post #3?

I was saying in your schematics of the Union. Your ship should include spaces for the engineering compartment, which engines are linked to. The ship's life support system and more importantly the powerplant for the entire ship should be taken into account on your schematics. I refer to spaces like that a machine spaces. Since not everything is in the "Engine" Room of the ship.

Amaris Fan Club · « **Reply #52 on:** 22 December 2016, 16:40:20 »

If you're thinking about spacecraft dimensions then you're probably thinking of drawing deckplans someday, which means that what you're really thinking about is how many little squares on a piece of graph paper equipment of a certain tonnage should take up.

Personally I prefer using the K.I.S.S. method to figure this out (Keep It Simple, Steal from traveller.)

In Traveller a single square is 1.5 by 1.5 meters, with the decks being 3 meters tall. Each square is 1 ton. This was based on liquid hydrogen having a volume of about 14 cubic meters, so the 1.5 x 1.5 x 3m decks (living space) plus about 3 meters of deck material worked out well.

It works out well for Battletech too for a couple of reasons; A standard Map Hex is 30 meters wide, and a standard Level is 6 meters tall. Both numbers divide into 1.5 m cubes nicely. The tallest battlemechs are also 12 meters tall too, another nice coincidence. Make each standard deck on a ship 1 level tall and you get 3 meter thick decks with 3 meters of living space above them, with equipment taking up one ton per square. Even better, you don't have to draw things like plumbing and air ducts, as these are all located within the deck itself. Larger decks, like those containing battlemech bays should be two or three levels tall, 9 meters is plenty of headspace for small mechs, and any 'mech can fit in a 15 meter tall bay (remember only one of the decks is there, so it's 3 meters of deck material plus 9 or 15 meters of open space above it.)

Under this system things on a standard deck are 1 ton per hex, while a taller deck can hold 2 or 3 tons. This makes drawing things easy; a first class cabin is ten tons so it takes up 10 squares, say 5 x 2. A 'mech bay is 150 tons so it takes up about 75 squares on a 2 level high deck, so call it 10 x 7 squares with 5 squares left over for the bunk space provided for the pilot and tech.

But what about all that extra space for corridors and ramps and galleys that the fluff says takes up most of the volume of these items? I say just draw it as big as you want. It's empty space so it doesn't mass much, and BT spacecraft are famously less dense than empty soda cans so go to town with it (Looking at the art dropships seem to have a density of about 80 m3 per ton.) You can base the additional volume for this space on the ships' description - a small ship with cramped crew cabins probably has a tiny galley with fold-out tables whereas a large liner with 1,000 first class passengers probably has everything from ballrooms to bowling alleys (is zero-g bowling fun? I wonder...) This also works out for the empty space in dropships like the Union. Those ships are used as mobile repair shops as often as transports so it makes sense for the ship to have a huge internal space for the techs to work on the 'mechs. Finally, those immense warships probably have equally immense areas of empty space within them; the fluff states that the armor consists of multiple layers separated by empty space and it makes sense to put a fair amount of space between the internal equipment too (you don't want an exploding laundry machine taking out the fire control computer do you?)

One last note regarding cargo bays: These should have a lot of volume, much bigger then their tonnage indicates. This is because spaceships unlike (water)ships don't sink if you overload them, they just accelerate slower. It should be perfectly acceptable to load two or three times as much stuff in a cargo bay as it is rated to carry, as long as you recalculate the thrust rating of the engines. I've never seen that mentioned in the fluff or rules but it probably happens in the "real" BT universe all the time. After all, a mercenary unit that captures 5 clan omnimechs isn't going to leave them behind because their Leopard is full, they'll stack them in every available open space and then just pray that the ancient ships engines can still manage to reach orbit.