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Author Topic: How do warship Grav Decks handle thrust?  (Read 1892 times)

Alan Grant

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How do warship Grav Decks handle thrust?
« on: 11 November 2022, 14:25:39 »
The Grav Decks on jumpships are easy enough to understand. Since jumpships can't pull a lot of G-forces the grav decks represent the only significant source of gravity for the crew.

But warships are another story. They can pull some Gs. So I'm picturing a warship suddenly going max acceleration and that Grav deck is turning. If you are on the grav deck you would have G forces pulling you in two directions.

I'm wondering if we know anything about how they handle that. Do the grav decks stop and lock when the warship is accelerating?

Any insight is helpful.

monbvol

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Re: How do warship Grav Decks handle thrust?
« Reply #1 on: 11 November 2022, 15:25:27 »
I would think that when possible grav decks are stopped and locked when the Warship is under thrust.  Now being Warships it is not out of the question that they can get ambushed and not be able to safely stop and lock but they would do so as not stopping and locking does tend to do worse things then suddenly stopping and locking things to crew caught in those sections.

AlphaMirage

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Re: How do warship Grav Decks handle thrust?
« Reply #2 on: 11 November 2022, 15:36:25 »
Stop, lock, and retract probably. That takes time but honestly if you get jumped you were to close to the planet/jump point or not paying attention at all for several hours.

grimlock1

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Re: How do warship Grav Decks handle thrust?
« Reply #3 on: 11 November 2022, 15:56:30 »
It's conceivable that grav decks could be built such that the bearings can handle the thrust from normal or even combat acceleration.

Can warships translate without changing bearing? If so, a warship could conceivably start decelerating the grav deck, use that inertia to start a spin, and once the people in the grav decks have had time to laydown against the aft bulkhead, start a forward thrust. Then combine that with translational movement to reposition without changing bearing, and thus calling down the wrath of Moment of Inertia. It wouldn't do good things for the ship or crew but way better than just tanking hits from an enemy warship.
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AlphaMirage

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Re: How do warship Grav Decks handle thrust?
« Reply #4 on: 11 November 2022, 15:58:36 »
It's conceivable that grav decks could be built such that the bearings can handle the thrust from normal or even combat acceleration.

Can warships translate without changing bearing? If so, a warship could conceivably start decelerating the grav deck, use that inertia to start a spin, and once the people in the grav decks have had time to laydown against the aft bulkhead, start a forward thrust. Then combine that with translational movement to reposition without changing bearing, and thus calling down the wrath of Moment of Inertia. It wouldn't do good things for the ship or crew but way better than just tanking hits from an enemy warship.

As far as the rules are concerned I don't think so. Although using the grav deck as a flywheel would be an inspired use.

Frabby

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Re: How do warship Grav Decks handle thrust?
« Reply #5 on: 11 November 2022, 18:30:52 »
I never thought of what grimlock1 proposed, but I like it very much. (Of course, nothing in the rules.)

I always assumed grav decks would have a carousel mounting that would spread out under zero thrust and fold in under thrust while spinning, thus adding the forces. (You would obviously slow the rotation as thrust increases.) A bit like the folding grav deck elements shown for the Argo[i/] from the HBS game.
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idea weenie

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Re: How do warship Grav Decks handle thrust?
« Reply #6 on: 11 November 2022, 19:03:51 »
I never thought of what grimlock1 proposed, but I like it very much. (Of course, nothing in the rules.)

I always assumed grav decks would have a carousel mounting that would spread out under zero thrust and fold in under thrust while spinning, thus adding the forces. (You would obviously slow the rotation as thrust increases.) A bit like the folding grav deck elements shown for the Argo[i/] from the HBS game.

One fun part is if the Warship carries Dropships, you'd need to make sure the Grav deck is not long enough to reach a Dropship Collar.  It'd be annoying if the Grav Deck was still spinning when it was being retracted and sideswiped an occupied Dropship Collar.

monbvol

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Re: How do warship Grav Decks handle thrust?
« Reply #7 on: 11 November 2022, 19:10:51 »
One fun part is if the Warship carries Dropships, you'd need to make sure the Grav deck is not long enough to reach a Dropship Collar.  It'd be annoying if the Grav Deck was still spinning when it was being retracted and sideswiped an occupied Dropship Collar.

Considering what physics and the rules says happens if Dropships are still attached while under thrust that may only be the beginning of your problems.

DevianID

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Re: How do warship Grav Decks handle thrust?
« Reply #8 on: 12 November 2022, 00:55:59 »
I think youd only have the grav deck spinning when you had the sail unfurled too.  It feels like an extended stationary operation thing.  Getting ambushed while vulnerable is pretty hard in deep space, or should be.  For civilian peacetime vessels that don't move thats one thing, but I feel like a warship is pretty sensitive to anything vectoring towards it.

cray

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Re: How do warship Grav Decks handle thrust?
« Reply #9 on: 12 November 2022, 20:55:10 »
One fun part is if the Warship carries Dropships, you'd need to make sure the Grav deck is not long enough to reach a Dropship Collar.  It'd be annoying if the Grav Deck was still spinning when it was being retracted and sideswiped an occupied Dropship Collar.

Gravdecks are largely internal with the exception of a handful of WarShips and space stations. Per p. 139 StratOps (old):

Quote
Those geniuses who try to sneak onto a gravdeck by slipping
through the spaces between the bulkheads of a JumpShip
that enclose the deck are usually the messiest examples of
why non-standard gravdeck boarding procedures don’t work.
Clearance is minimal and the shearing eff ects of the stationary
and moving walls on a human body are spectacular. Imagine
being caught between a moving subway train and a tunnel
wall with insuffi cient clearance. The whole zero-G eff ect won’t
save you there.

WarShips generally don't need to run their gravdecks when under thrust because their thrust is usually 1G or more. While gravdecks that splay open to balance thrust and spin are possible (and are used on Luna), they aren't very necessary on WarShips.
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Re: How do warship Grav Decks handle thrust?
« Reply #10 on: 12 November 2022, 21:12:47 »
Cray beat me to it.
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VhenRa

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Re: How do warship Grav Decks handle thrust?
« Reply #11 on: 16 November 2022, 07:41:57 »
Anyone familiar with the recent HBS Battletech game would be familiar with how the Argo's grav-decks rotate for use under thrust.

Unless you can do something like that... you probably aren't using them under thrust.

cray

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Re: How do warship Grav Decks handle thrust?
« Reply #12 on: 17 November 2022, 22:13:42 »
Anyone familiar with the recent HBS Battletech game would be familiar with how the Argo's grav-decks rotate for use under thrust.

Unless you can do something like that... you probably aren't using them under thrust.

As brilliant as the Argo's flexing grav decks are, they're overkill. The allow the gravdecks to remain habitable without internal reconfiguration (e.g., shifting furniture from floor to wall) when the DropShip shifts to thrust and halts the gravdeck spin. Since the Argo is able to sustain 1.5Gs without straining you wouldn't need to mix thrust and spin.
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Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

kindalas

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Re: How do warship Grav Decks handle thrust?
« Reply #13 on: 18 November 2022, 23:44:27 »
Battlespace had a rule that if you ran a gravdeck and used thrust then the gravdeck would take damage until it was turned off.

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Re: How do warship Grav Decks handle thrust?
« Reply #14 on: 20 November 2022, 16:49:08 »
They would have safety systems in place, but also engineering to allow for that kind of  stress.

Think also of the stresses placed on a weapon mount or "Turret" under the same conditions. Without a means to permit it to function under stress; you couldn't aim weapons under thrust.
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cray

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Re: How do warship Grav Decks handle thrust?
« Reply #15 on: 20 November 2022, 17:35:07 »
They would have safety systems in place, but also engineering to allow for that kind of  stress.

Good observation. However, grav decks that need to balance thrust and spin in BT should only need to contend with a small amount of thrust - frex, a JumpShip station keeping at a jump point.

On vessels at high acceleration (1G+), grav decks have no reason to be operating. If a WarShip suddenly needs to light its engines while the grav deck is spinning then there is no reason for the grav deck to continue spinning. Designers of such vessels should've made provisions to slam on grav deck brakes and make it easy to clean up puke from occupied surfaces, but there'd be no reason to continue to endure both acceleration and spin beyond the first turn or two. Engineers working in a mass-restricted, budget-restricted environment would save mass and money by designing the grav deck not to work in all conditions.

This is different from weapon mounts, which would be designed to work in all conditions, orientations, and accelerations.
Mike Miller, Materials Engineer

**"A man walks down the street in that hat, people know he's not afraid of anything." --Wash, Firefly.
**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

Alan Grant

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Re: How do warship Grav Decks handle thrust?
« Reply #16 on: 04 December 2022, 16:44:55 »
Sorry to revive this thread, but I had a semi-related question.

Would a jumpship keep the gravdeck rotating during a jump?

I'm already imagining that a warship would not want to, just in case on the other side of that jump there was a danger or threat and the warship needed to fire up the maneuvering drives and react quickly. But most jumpships... does it matter?

AlphaMirage

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Re: How do warship Grav Decks handle thrust?
« Reply #17 on: 04 December 2022, 20:18:44 »
I think they retract them probably makes the calculations safer, anything near the KF field boundaries is disassembled at an atomic level so there shouldn't be any hazards on the other side but you don't want to chance a misjump because of something so simple.

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Re: How do warship Grav Decks handle thrust?
« Reply #18 on: 04 December 2022, 20:24:57 »
Grav decks aren't something you extend or retract, they're 100% internal.
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Re: How do warship Grav Decks handle thrust?
« Reply #20 on: 04 December 2022, 20:40:47 »
The Argo is another exception, but I think Weirdo has the rule right.

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Re: How do warship Grav Decks handle thrust?
« Reply #21 on: 04 December 2022, 21:08:33 »
Tell that to the Wagon Wheel Weirdo
That is still internal, those rings do not spin, the grav decks within them can spin.
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Re: How do warship Grav Decks handle thrust?
« Reply #22 on: 04 December 2022, 22:39:56 »
how do you get OFF the grav ring on a Warhip? Climb up a ladder until you hit zero-gee again?

uhhmmm, for NO REASON AT ALL!!! -opens Work In Progress, waits for answer-   :)) :D :))

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Re: How do warship Grav Decks handle thrust?
« Reply #23 on: 05 December 2022, 00:28:35 »
how do you get OFF the grav ring on a Warhip? Climb up a ladder until you hit zero-gee again?

uhhmmm, for NO REASON AT ALL!!! -opens Work In Progress, waits for answer-   :)) :D :))

this may be why it's 'internal'-because something has to connect the front to the back, and it's likely easier to have that spinning section floating inside a rim, than figure out a structural way to join the ends with a wheel in the middle.

except...then you still have the problem with something like the Wagon Wheel where you miss your timing and snip! there's now an upper you and a lower you and a hell of a lot of blood clogging air filters.
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Re: How do warship Grav Decks handle thrust?
« Reply #24 on: 05 December 2022, 01:22:58 »
There obviously has to be some sort of access hatch in the hub area; see Kubrick's 2001 grav deck scene.
If you feel the rotation is too fast (on smaller grav decks for example) then there could be some sort of spinning cabin there where you enter while it spins at the same ratio as the grav deck, i.e. stand still relative to you; then you spin it up (actually stop its rotation) to align it with the exit hatch in the hub.
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Alan Grant

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Re: How do warship Grav Decks handle thrust?
« Reply #25 on: 05 December 2022, 05:51:17 »
In Strategic Ops page 139 has a subsection called "how not to get on a gravdeck" it references "transfer cars" to get on and off gravdecks. But it's really just that reference without much explanation of how the car works. The rest of the section mostly focuses on the WHY, as in why you need/want something like that and not just jump onto a gravdeck moving at 3 miles per hour (give or take, depends on size of the grav deck) which it explains has a floor speed of 56 kph on a small grav deck, and a floor speed of 256 kph on the grav deck on an olympus.

Personally I struggle to visualize how that transfer car concept is engineered to work. I'm not questioning it, I just wish I had a model, or some art or a video, something that could help me conceptualize it.

EDIT: Found more, in the main body content of that page it says jumpships and warships must use a "subway system" of transfer cars paralleling the gravdeck's track.

It says space stations are more likely to use long elevator spokes to a slowly spinning hub. Because the station can be built without worrying about getting in the way of a KF drive, ammo feed, power lines, data lines etc.
« Last Edit: 05 December 2022, 06:13:51 by Alan Grant »

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Re: How do warship Grav Decks handle thrust?
« Reply #26 on: 05 December 2022, 15:58:31 »
Warship grav-decks don't have to be circumfural, do they?  Can't you place them with their spin axis perpendicular to the thrust axis?  How would those work?  a quarter of the deck, when stopped, would be upside down relative to the thrust, and half would be at 90 degrees from Down.
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grimlock1

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Re: How do warship Grav Decks handle thrust?
« Reply #27 on: 05 December 2022, 16:08:46 »
Warship grav-decks don't have to be circumfural, do they?  Can't you place them with their spin axis perpendicular to the thrust axis?  How would those work?  a quarter of the deck, when stopped, would be upside down relative to the thrust, and half would be at 90 degrees from Down.

So long as you don't burn the main engines while the deck is spinning, it doesn't matter how its oriented in the ship. But you will lose a lot of usable volume while under thrust.
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Re: How do warship Grav Decks handle thrust?
« Reply #28 on: 05 December 2022, 16:35:32 »
I just sort of use the Wagon Wheel Frigate as my guide on what they look like. But internal.

If you look at the Wagon Wheel, the central hub is still usable. There's still space in the central hull of the ship, you can fit the long K-F drive through there and other stuff. I imagine it's like that. But the "spokes" may be very small by comparison.

I wondered if there might be no spokes at all, if it might resemble something more like a train, wrapped around a cylinder. But I'm not sure that jives with physics.

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Re: How do warship Grav Decks handle thrust?
« Reply #29 on: 05 December 2022, 16:44:51 »
Warship grav-decks don't have to be circumfural, do they?  Can't you place them with their spin axis perpendicular to the thrust axis?
Quote
Yes.
  How would those work?  a quarter of the deck, when stopped, would be upside down relative to the thrust, and half would be at 90 degrees from Down.
That doesn't matter, because nobody's ever in a grav deck when the ship is under thrust, no matter which way it is oriented.
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