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Author Topic: A couple of questions regarding Grav Decks.  (Read 2233 times)

Frabby

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Re: A couple of questions regarding Grav Decks.
« Reply #30 on: 19 June 2018, 01:13:30 »
No idea if sleeping in gravity feels better than sleeping in zero-g, so I don't know if we can assume there's any mental health benefit.
There's the danger of suffocating in your own CO2 bubble when sleeping in vacuum. But you don't quite need to throw a grav deck at this particular problem.
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Weirdo

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Re: A couple of questions regarding Grav Decks.
« Reply #31 on: 19 June 2018, 09:55:13 »
I keep hoping to find an environment where my wife won't insist on running some kind of fan at all times, but nooooo...you have to dash my dreams. :'(

I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?
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Frabby

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Re: A couple of questions regarding Grav Decks.
« Reply #32 on: 19 June 2018, 13:29:35 »
I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?
I don't recall where I heard about CO2 bubbles, sorry. But they were mentioned as a non-obvious space travel hazard, so I suppose this means breathing alone (at least slow breathing while asleep) may not be enough.
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cray

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Re: A couple of questions regarding Grav Decks.
« Reply #33 on: 25 June 2018, 17:14:19 »
No idea if sleeping in gravity feels better than sleeping in zero-g, so I don't know if we can assume there's any mental health benefit.

Sleep is annoying on primitive, zero-G space stations. Even eliminating the noisiness of the ISS, zero-G conditions tend to come with nausea, a falling sensation, and assorted aches and pains that disrupt sleep. Astronauts are estimated to get an hour less sleep than people on similar gravity-based schedules.

I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?

The "cabins" in the US section of the ISS are "well ventilated". "The catch is that they need to tether themselves to something to avoid floating away in the air currents."

I don't recall where I heard about CO2 bubbles, sorry. But they were mentioned as a non-obvious space travel hazard, so I suppose this means breathing alone (at least slow breathing while asleep) may not be enough.

Generally, air is pretty well stirred in real spacecraft for multiple reasons. Besides CO2 control, moving air is the only way to control cabin temperature - otherwise, stationary cold plates or heaters will have the same sort of "bubble" problem as CO2 build-up. Moving air also tends to be key to dust, dirt, and lost item control - Skylab astronauts learned to check air intakes anytime small items disappeared, and there are now filtered air intakes in common eating areas and the toilets. (Crappers are one big wet-dry shop vac. After the Assteroid problem on Apollo 10 and loud astronaut objection to using plastic baggies throughout Gemini and Apollo, Skylab and subsequent US spacecraft have included proper toilets. Defecation is handled by what is basically a large-bore vacuum cleaner. Zero-G toilets in BT also suck, so to speak, hence the popularity of grav deck-based toilets.)
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R.Tempest

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Re: A couple of questions regarding Grav Decks.
« Reply #34 on: 26 June 2018, 00:20:10 »
 What about showers/baths/sinks to brush your teeth at? Would you need to offset the drain slightly in a sink in the direction opposite the spin of the deck?

cray

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Re: A couple of questions regarding Grav Decks.
« Reply #35 on: 26 June 2018, 18:06:52 »
What about showers/baths/sinks to brush your teeth at? Would you need to offset the drain slightly in a sink in the direction opposite the spin of the deck?

Nope. The little bit of curve to dropped items is negligible at a scale of 1-2 meters.

Also, does moving the drain around every help your average slob get everything in the sink or toilet? :)
Mike Miller, Materials Engineer

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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.

R.Tempest

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Re: A couple of questions regarding Grav Decks.
« Reply #36 on: 27 June 2018, 02:25:33 »
 Point. Definitely a point.

Von Jankmon

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Re: A couple of questions regarding Grav Decks.
« Reply #37 on: 29 June 2018, 22:59:32 »
Thankfully this is a part of Battletech canon taken neatly from real physics and space architecture concepts.

http://www.artificial-gravity.com/JBIS-52-7-Hall.pdf

The above is an excellent introduction to the design involvement and doesnt get in the way of jumpship design.

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R.Tempest

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Re: A couple of questions regarding Grav Decks.
« Reply #38 on: 30 June 2018, 01:11:17 »
 Very interesting. I will have to read it a few more times.

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Re: A couple of questions regarding Grav Decks.
« Reply #39 on: 30 June 2018, 06:33:38 »
Interesting indeed!  Just reading the list of physiological issues makes me want to add a grav deck to the Scout.  It's not like there isn't room (or even tonnage).

R.Tempest

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Re: A couple of questions regarding Grav Decks.
« Reply #40 on: 30 June 2018, 14:57:47 »
 My impression is that thrust induced G-force has little or no ill effects. Spin induced G however has some problems. I expect the disorientation from moving left or right would be directly related to the diameter of the deck (bigger is better). Having a running track might also problematic.
 These are all issue's that probably won't be resolved until something is built either in orbit or as part of long voyage spacecraft.

cray

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Re: A couple of questions regarding Grav Decks.
« Reply #41 on: 02 July 2018, 17:27:34 »
I expect the disorientation from moving left or right would be directly related to the diameter of the deck (bigger is better).

Yep. Strategic Operations captures some of the diameter-spin speed-puke factor details. The rules of thumb I pulled from NASA studies for StratOps were:

3-4rpm+: No one ever quite adapts fully, and the inner ear will always note weirdness when the head is turned
1-3rpm: People can adapt and not be overly bothered by spin effects
<1rpm: The inner ear might not really notice the spin

At 1rpm, 1G requires an 1800m diameter (approximately). All canon, rules-legal, 1G gravdecks will be noticeable to human inner ears.

Quote
Having a running track might also problematic.

Actually, less than you'd expect. If you're keeping your inner ears oriented fairly constantly in one direction (e.g., running around the circumference of a gravdeck), then they're fine. Skylab astronauts managed to run around the tiny interior of that station without horking. Meanwhile, sitting still in one spot of a narrow-diameter, high speed gravdeck (e.g., Disney's Mission: Space) and turning your head can be disorienting (personal experience - had to hold my head still).
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**"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
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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.

Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #42 on: 02 July 2018, 18:35:11 »
*snip*
At 1rpm, 1G requires an 1800m diameter (approximately). All canon, rules-legal, 1G gravdecks will be noticeable to human inner ears.
*snip*
Oh?  ???

Were the construction rules errata'd, or does it still say "250+ meter" grav decks are 100 tons?

cray

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Re: A couple of questions regarding Grav Decks.
« Reply #43 on: 03 July 2018, 16:36:04 »
Were the construction rules errata'd, or does it still say "250+ meter" grav decks are 100 tons?

My 3rd printing of TacOps, p. 407 (c2013), lists:

*Under 100m diameter: 50 tons
*100-250m diameter: 100 tons
*Over 250m diameter: 500 tons
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
**"Peace is that brief glorious moment in history when everybody stands around reloading." --Thomas Jefferson, or not

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.

Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #44 on: 03 July 2018, 16:50:50 »
Ah, so there has been an errata.  There's still that pesky "Over 250m" bit though, implying that even an 1,800m diameter grav deck would only be 500 tons.

While I have you here Cray, since the rules no longer support the Scout JumpShip having a double sized station keeping drive (for gravity maneuvering), will a grav deck be added to its official stats?  I'm pretty sure the 50 tons are there to support that...

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Re: A couple of questions regarding Grav Decks.
« Reply #45 on: 04 July 2018, 10:44:54 »
Nope, just checked my books, and I was mis-remembering the break points.  It's been 50/100/250+ for quite some time now.  Thanks for straightening me out Cray!

As far as a grav deck on the Scout, the largest diameter the deck plans I was working on has 82 meters internal, with a one meter thick hull that could mean 84 meters is what to use for the construction rules (both are under 100m, so no worries, really).

Using that extremely useful "Comfort Zone" chart in the paper Von Jankmon linked, it looks like a ~40m radius can't quite get to 1G at 4 rpm.  The good news is that it looks like 0.5G is possible in the 2-3 rpm range, and the AToW rules don't inflict major penalties until you're below 0.2G.  Of course, the rules are silent on what percentage of your day you have to spend in less than 0.2G to receive those penalties (they were written assuming low planetary gravity).

Construction-wise, this actually could cause a problem with the KF core.  I took the "door" looking part of the nose (that's off centerline) as the core replacement/maintenance hatch.  If the core doesn't have to be the entire length of the ship, this could be essentially ignored by just leaving a "tube" that could be aligned with the core when the grav deck isn't spinning.  If it DOES have to be the length of the ship, then I need to start over (which I basically have to do anyway since I lost the thumb drive that had the most recent Visio file) to put the core on the exact centerline.  That would still leave a bit of a trick for getting to and from the grav deck, but it's not insurmountable.

At the very least, a grav deck will help soak up some of the HUGE volume available inside even a "small" JumpShip like a Scout.

Robroy

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Re: A couple of questions regarding Grav Decks.
« Reply #46 on: 04 July 2018, 11:34:18 »
I use this.

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm

It uses grav deck radius vs. BTs diameter. Basically from what I have seen using it is it does not like going over 2 rpm before becoming uncomfortable.

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Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #47 on: 04 July 2018, 12:37:15 »
That's a handy calculator, thanks!  :thumbsup:

Using it, it looks like 0.4G will get under Cray's 3 rpm figure a the rim, but of course requires a period of adaptation.  0.4G is also twice the AToW 0.2G limit, so I think it works for a JumpShip crew.

Walking the radius in at 3 rpm makes it look like you can get about 5 4 useful decks of space before the Tangential Velocity gets uncomfortable.  On the deck plans I'm working on, the "strip" of hull at maximum radius is 11 meters wide (or tall, if you look at the ship lengthwise), so that would be ~260 2,800 square meters at the rim.  Going with 2.5 meter "tall" decks (to include headroom, thickness of the decking, and necessary cabling and piping), the total usable comfortable deck space would be ~1160 10,300 square meters.  Another ~770 square meters are on the five decks above that before the Tangential Velocity gets really uncomfortable.  The last five decks (leaving a 9 meter diameter "tube" in the center to move cargo) yield about 375 square meters of quite disorienting space (probably for storage).

EDIT: Various corrections to calculations I did while distracted by my wife and children.
« Last Edit: 04 July 2018, 22:45:58 by Daryk »

Robroy

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Re: A couple of questions regarding Grav Decks.
« Reply #48 on: 04 July 2018, 15:17:56 »
One thing is, according to the spin calculator, the Merchants 40 meter grav deck is all kinds of uncomfortable. In order to get any benefits the rpm gets to high.

It seems that to be comfortable and get any benefit you need a 100m diameter deck, min.

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Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #49 on: 04 July 2018, 16:17:59 »
At a full 1G, certainly... that's why I mentioned 0.4G above (to keep it in the comfort zone).

Robroy

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Re: A couple of questions regarding Grav Decks.
« Reply #50 on: 04 July 2018, 18:04:34 »
Sorry. Was not commenting on your plans. Just what I was seeing from spin calculator.

Your 82m deck will at worse need a little time to get use to, but that can probably be said for most grav decks.

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Robroy

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Re: A couple of questions regarding Grav Decks.
« Reply #51 on: 04 July 2018, 18:08:20 »
While we are talking grav decks, is it said anywhere how wide they are?

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Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #52 on: 04 July 2018, 18:20:50 »
Nope... I think Cray deliberately left that vague in the rules.  I'm only using 11 meters because I'm trying to stick to the art from the original DropShips and JumpShips book.

R.Tempest

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Re: A couple of questions regarding Grav Decks.
« Reply #53 on: 04 July 2018, 18:25:31 »
 The description for the Star Lord says its deck is 20 meters wide.

Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #54 on: 04 July 2018, 18:31:48 »
Since the rules are vague, you could technically rotate the whole ship...

Von Jankmon

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Re: A couple of questions regarding Grav Decks.
« Reply #55 on: 05 July 2018, 07:10:29 »
Small grav decks make more sense than it first appears, you can have a small deck with fairly minimal gravity, it just has some gravity.  It would include sleep couches, wash units and toilets.  All of which benefit from not being in microgravity.

Even better are spindles, basically line the edge of a 'giant spin dryer' with contoured sleep couches.  Split your watches into sleep as well as work shifts.  Send in a sleep shift strap them in and then turn it on for a couple of hours.

With high rotation spin one of the problems will be gravitational differences between head and foot level, spinning sleep couches eliminate most of those problems.

Spindles could also be built very small fitted with contoured seated couches and spun for higher G, say 2-3G for 20 minutes at a time as a health/exercise/spa treatment for space crews.  Independent motion is what causes nausea, people can take a high spin in a single seated position easily.

Spindles would take up negligible mass and volume and could be calculated according to mass allocation for crew.  A spindle with intermittent high spin/strong G will be of more use to a crew health than a weakly but constantly spinning low G grav deck.  Though you need both.  A grav deck with a lounge and toilet facilities makes sense.

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Daryk

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Re: A couple of questions regarding Grav Decks.
« Reply #56 on: 05 July 2018, 07:50:59 »
I'm finding an 82 meter diameter isn't all that small.  Even with a strip only 11 meters wide, there appears to be enough room for medical, exercise, messing and berthing with plenty to spare.  2,800 square meters is actually quite roomy, and that's just the highest G deck out at the rim (granted, it's only 0.4G at 3 rpm).  Three more decks remain squarely in the comfort zone, and they're all over 2,000 square meters each, though with slightly less "gravity".

cray

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Re: A couple of questions regarding Grav Decks.
« Reply #57 on: 05 July 2018, 16:08:18 »
Nope... I think Cray deliberately left that vague in the rules.

Yep.

Since the rules are vague, you could technically rotate the whole ship...

Yep. I was sketching out a non-canon WarShip/troop transport that does just that, giving vast 'Mech bays and troop quarters at ~0.5G.
Mike Miller, Materials Engineer

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**"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
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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.

BirdofPrey

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Re: A couple of questions regarding Grav Decks.
« Reply #58 on: 05 July 2018, 17:11:28 »
Considering ships have to be laid out with decks perpendicular to the path of travel for anything that moves at a significant fraction of Gs, wouldn't it be more efficient to hang a counterwieght off the front of the ship and spin around that center of mass rather than trying to spin the ship about its own axis?

cray

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Re: A couple of questions regarding Grav Decks.
« Reply #59 on: 05 July 2018, 19:34:51 »
Considering ships have to be laid out with decks perpendicular to the path of travel for anything that moves at a significant fraction of Gs, wouldn't it be more efficient to hang a counterwieght off the front of the ship and spin around that center of mass rather than trying to spin the ship about its own axis?

Doing that would inhibit the use of the ship's drive. Spinning along the thrust axis presents a gyroscopic complication while under thrust, but isn't impossible. On the other hand, spinning end over end means the drive is pointing the wrong way for half of the ship's rotation.
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
**"Peace is that brief glorious moment in history when everybody stands around reloading." --Thomas Jefferson, or not

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.

 

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