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Old 04-24-2017, 07:53 AM   #1
Huscurian
 
Join Date: Jan 2012
Default [Science] The Hard Science of Low Gravity versus High Gravity

I have a question, a scientific one, that may play into GURPS.

I have a setting that I've formulated in my mind. I also have gotten started on characters for my two players, who will be playing together. However, the setting is high-tech with some ultra-techy stuff thrown in.

The real question becomes, how do you account for the mass, the propulsion/acceleration/thrust, and/or the trajectory or speed of a projectile on low or high gravity worlds?

The setting does include strong, muscular men, but most of them are genetically engineered. Humans, the minority of the world, are strong like them but not as strong as they are.

This is one of those things that I'm trying to decide. On low gravity worlds, people are much more likely to be leaner, elongated, and have lighter mass, having far difficulty in working out and gaining muscles. On high gravity worlds, it's possible with the density of the gravity, the person could have larger muscles, and endure the tougher conditions of the world.

Let me give an example.

Let's say that a BDRM equipped with a railgun, a recoil-less burst-mass driver, is driving along the desert plains. Alongside the BDRM is a IS-3, a heavily modified tank carrying a laser cannon, self-propelled torpedo tubes, and anti-personnel guided flechette missiles. They're driving at the maximum speed of 40 MPH. They approach infantry within their range. The IS-3 fires off its anti-personnel flechette missiles (small, compact ones) with the BDRM firing its burst-mass driver (small round bolts like Battlestar Galactica) at the same time to eliminate this new obstacle.

How do you account for the factors in low or high gravity, given on account that the BDRM is less heavier than the IS-3?

I hope this thread provides some interesting answers.

Last edited by Huscurian; 04-24-2017 at 07:56 AM.
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Old 04-24-2017, 08:37 AM   #2
ericthered
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

I'm not sure what you're asking.

I see two possible questions here. The first is if gravity should effect damage and to hit rolls for balistic weapons on planets with non-earth gravity. I wouldn't change damage and to attack roll should at most get a -2 for familiarity at longer ranges. If you have to roll artillery, there is no effect, as long as you have the gear and information you need to properly aim on this planet.

The second is if ST requirements for weapons change with gravity. I don't know about that one.
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Old 04-24-2017, 09:03 AM   #3
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

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Originally Posted by ericthered View Post
I'm not sure what you're asking.

I
Me neither. I don't even know what a "BDRM" is though "IS-1" appears to be a designation for an individual vehicle type rather than broad class of vehicles.

I'm not sure why differences in weight of the firing vehicles would be important compared to the differences in firing two different classes of weapons.

Generally though more gravity means everything hits the ground sooner. divide Max Range by the gravity increase but leave 1/2D alone. 1.2D could change with atmospheric density.
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Old 04-24-2017, 10:46 AM   #4
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

Gravity makes no difference to damage, and no difference to accuracy assuming the shooter and/or weapon is correctly adjusted to local conditions. (Although different gravity would change the range at which small-arms shooters can safely ignore bullet drop.) Obviously it does make some difference to range. It could have an impact on the acceleration of missiles, but it would need to be awfully heavy gravity to be noticeable - even a relatively sluggish missile like a TOW has thrust in great excess of gravity.

Firearm ST usually seems to have to do with weight and I think it's been suggested that it be matched against Lifting rather than Striking ST, so I'd see a decent case for scaling ST with the square root of local gravity. There may be some weapons (perhaps pistols?) where ST has more to do with handling recoil, which would not be affected by local gravity.

Firing platform weight is largely irrelevant to GURPS rules. There's a possible range of low gravities where you might carry or mount weapons with enough recoil to significantly displace the firer, for which I don't think there's any strong GURPS coverage. But it's rather an outside case. (In genuine microgravity, there's a Pyramid article addressing things somewhat. Maybe you could hack something for not-quite-micro gravity out of that.) In heavy gravity there's really nothing really exciting going on.
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Me neither. I don't even know what a "BDRM" is though "IS-1" appears to be a designation for an individual vehicle type rather than broad class of vehicles.
Both are soviet AFVs, BDRM being a misspelling of BRDM...
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Old 04-24-2017, 10:57 AM   #5
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

The BRDM is a reconnaissance vehicle. IS-3 is a heavy tank.

Essentially, you want to know what effect high or low gravity has on ballistic projectiles and missiles, right? Basic set talks about thrown weapons on page 350, but I don't see anywhere it talks about ballistic weapons. I don't see anything in HT or UT either.
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Old 04-24-2017, 11:01 AM   #6
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

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The BRDM is a reconnaissance vehicle. IS-3 is a heavy tank.

Essentially, you want to know what effect high or low gravity has on ballistic projectiles and missiles, right? Basic set talks about thrown weapons on page 350, but I don't see anywhere it talks about ballistic weapons. I don't see anything in HT or UT either.
You got that right. BRDM (my bad, misspelled it correctly.) and IS-3 are both Soviet vehicles. Also thanks to Ulzgoroth for mentioning it first.

Yes. That's correct. I also want to know if high or low gravity would affect the speed and mobility of the vehicle.

Here's also another question. If there are genetically modified superhumans, is it possible for superhumans on high gravity worlds to perform higher jumps? Would the result of a landed jump be a hard one, for instance, possibly creating a small crater inside a soft surface instead of a hard one? Would their attacks be hard-hitting and quick even on high gravity worlds? What would it be like if the person being attacked got struck? Would they fall to the ground faster and harder or possibly be flung farther?

Last edited by Huscurian; 04-24-2017 at 11:04 AM.
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Old 04-24-2017, 11:48 AM   #7
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

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Yes. That's correct. I also want to know if high or low gravity would affect the speed and mobility of the vehicle.
That probably has no simple or generic answer. Obviously, lower gravity reduces ground pressure, which makes it easier to drive over soft surfaces, reduces losses to friction, and makes driving up slopes involve less work. OTOH lower ground pressure can also mean less grip on the surface, which could hurt acceleration and handling in some cases. How this stacks up is almost certainly going to be very much a vehicle-by-vehicle issue beyond the scope of current GURPS 4e support.

Maybe in Vehicle Design System when that comes around? But not necessarily.
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Here's also another question. If there are genetically modified superhumans, is it possible for superhumans on high gravity worlds to perform higher jumps? Would the result of a landed jump be a hard one, for instance, possibly creating a small crater inside a soft surface instead of a hard one? Would their attacks be hard-hitting and quick even on high gravity worlds? What would it be like if the person being attacked got struck? Would they fall to the ground faster and harder or possibly be flung farther?
The Basic Set already covers jumping, read it. What you're asking about landing I can't decypher.

Gravity will have basically no effect on melee strikes.

Realistically, people aren't normally flung by being hit. GURPS has unrealistic knockback rules under which it's more likely. I'm not sure if those scale with gravity, but it would be relatively easy to do so if you wanted to. (For a horizontal launch range scales with the inverse square root of gravity). Falling already scales with gravity.
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Old 04-24-2017, 12:13 PM   #8
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

Vehicles are tuned to work ideally in the gravity they are currently in. I suspect changing the gravity away from optimal will change the performance of the machine for the worse, be the change greater or less than optimal gravity. These changes are probably minimal until you get to the x1.5 or x.5 range.

I could certainly see a vehicle intentionally designed to switch between different gravities though, and you can certainly engineer for a different gravity than earth.
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Old 04-24-2017, 12:18 PM   #9
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

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Vehicles are tuned to work ideally in the gravity they are currently in. I suspect changing the gravity away from optimal will change the performance of the machine for the worse, be the change greater or less than optimal gravity. These changes are probably minimal until you get to the x1.5 or x.5 range.
I doubt this very much. Many vehicles want to be lighter but can't be without compromising non-performance-related mission requirements.
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Old 04-24-2017, 12:55 PM   #10
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Default Re: [Science] The Hard Science of Low Gravity versus High Gravity

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Originally Posted by Ulzgoroth View Post
The Basic Set already covers jumping, read it. What you're asking about landing I can't decypher.

Gravity will have basically no effect on melee strikes.

Realistically, people aren't normally flung by being hit. GURPS has unrealistic knockback rules under which it's more likely. I'm not sure if those scale with gravity, but it would be relatively easy to do so if you wanted to. (For a horizontal launch range scales with the inverse square root of gravity). Falling already scales with gravity.
I'll check the section for jumping.

So no effect on melee strike OK, perhaps that would have to be a cinematic effect of being knocked back as if they're paper.

Then I am going to lean toward heavier gravity.

Quote:
Originally Posted by ericthered
Vehicles are tuned to work ideally in the gravity they are currently in. I suspect changing the gravity away from optimal will change the performance of the machine for the worse, be the change greater or less than optimal gravity. These changes are probably minimal until you get to the x1.5 or x.5 range.
I don't know about vehicles being ideally tuned to work with low or high gravity worlds but I'm pretty sure that I could work around it by justifying that those tanks, vehicles, and others are simply a part of the world, former remnant of the "Earth That Was".

So I would daresay that no effect would be put on those vehicles except being hit by weapons, etc.

Another question though. On low or high gravity, would the reaction time and the length of halting a vehicle determined by speed be longer or shorter? I would suspect that on high gravity worlds, the stopping power of the vehicles would be longer dependent on the speed and mass of the vehicle while on low gravity, it can depend on the loss of handling, mobility that could lengthen the reaction time and stopping a vehicle to a complete halt. Correct me if I'm wrong.
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