Low Gravity

[rust]

The planet designed with GURPS Space for my new setting turned out to
have a surface gravity of 0.73 G, and now I wonder how to handle this
in our campaign.

It seems the Traveller core rulebook only mentions low gravity in a few
sentences about adaptation in the world building chapter, and I did not
find any more informations in others of the published Traveller books.

Right now I think that I will just divide all relevant values (e.g. weight
of material a character can carry, range of projectile weapons, etc.) by
the 0.73 as a rule of thumb.

However, if there is another easy and more realistic way to handle the
low gravity, please let me know - thank you.

 

[EDG]

That's probably the easiest best way to do it. I'm not sure about the physiological effects of long term habitation in that kind of gravity, it's probably close enough to earth's as to not cause too many problems.

 

[BP]

...
Right now I think that I will just divide all relevant values (e.g. weight
of material a character can carry, range of projectile weapons, etc.) by
the 0.73 as a rule of thumb...

I'm sure you meant multiply by 0.73 :wink:

You might want to use a modification of 'Zero-G' skill (which applies a -2 DM when lacking) - such as -1 DM for extreme activities (combat movement attempts/bodily combat/kinetic attacks).

In one of Brian Daley's (Han Solo) books, he has the Millennium Falcon adjust the gravity while in 'hyperspace' in order to be prepared to deal with a slightly different gravity.

Locals should have an edge in some things - however, players could have an edge in Strength and Endurance related activities (+ DM?) versus coordination related activities (Dex - DM).

And I would eliminate negative DMs for ZeroG-1 and above.

 

[EDG]

...
Right now I think that I will just divide all relevant values (e.g. weight
of material a character can carry, range of projectile weapons, etc.) by
the 0.73 as a rule of thumb...

I'm sure you meant multiply by 0.73 :wink:

No, he didn't. Dividing by 0.73 is the same as multiplying by 1/0.73, which is about x1.37.

So the a character can carry 1.37 times more weight in 0.73g than in 1g, the range of projectile weapons will be 1.37 times further in 0.73g than in 1g, etc.

Damage from falling however will still be 0.73 times that in 1g.

 

[rust]

I'm sure you meant multiply by 0.73 :wink:

As EDG wrote. :wink:

Just imagine the scout who usually carries 30 kg of equipment under 1 G.
Dividing his usual load of 30 kg by 0.73 gives the 41.09 kg he is able to
carry under the 0.73 G conditions with the same effort as he needs for
the 30 kg under 1 G.

 

[EDG]

It would make for some interesting flavour - for example, imagine that you're trying to jump from a high ledge onto somebody passing below you. If you're used to 1g and are on a 1g world, then it's a matter of timing, right? But if you're used to 1g and are on a 0.73 g world then you're going to have to account for the fact that you'll take longer to fall on your target - and if you forget that, even though 0.73g isn't too far off 1g, then you'll miss and land in a heap behind or in front of him. People who are used to that environment of course wouldn't have this problem since their reflexes have already adapted to the lower gravity.

We can use the usual equation of motion s=(ut+)0.5at² to calculate this - rearrange it to t=SQRT[(2s)/a] to calculate the time taken to fall. Assuming that you're not adding any more force to the jump and that you're just falling on your target, if you were falling 3m onto someone from zero velocity (u=0) on a 1g (10m/s) world then you'd and on him 0.77 seconds later. But on a 0.73g (7.3m/s) world you'd take 0.9 seconds to fall that distance - and extra 0.13 seconds.* Not much difference on the face of it, but possibly enough to screw up timing and make failure more likely.

*: Actually that's a ratio of x1.17, which is really the square root of 1.37. So whether you multiply by 1.37 or 1.17 really depends on whether the equation in question depends linearly on gravity, or is proportion to the square or square root of gravity.

 

[lastbesthope]

Remember, for some things it is mass that is important, and that doesn't vary with gravity.

LBH

 

[rust]

It would make for some interesting flavour - for example, imagine that you're trying to jump from a high ledge onto somebody passing below you.

Thank you for this information, there will be a number of ways to use it
during the early phase of the new campaign, when the colonists are still
adapting to the new environment - even unloading their crashed colony
ship by hand could become somewhat strange, with attempts to catch va-
rious pieces of equipment that move "too slow, but also too far".

Remember, for some things it is mass that is important, and that doesn't vary with gravity.

Yep, this is why I do not want to recalculate the weight of the equipment
used by the colonists, there may well be situations where I will need the
mass of the items, not their weight under local conditions.

 

[captainjack23]

Remember, for some things it is mass that is important, and that doesn't vary with gravity.

Yep, this is why I do not want to recalculate the weight of the equipment
used by the colonists, there may well be situations where I will need the
mass of the items, not their weight under local conditions.[/quote]

Rust,

Too, keep in mind that the colonists will be in the g field for quite a while...not only will they be used to the reduced weight and mismatching inertia pretty quickly, but also, muscle str really is "use it or lose it". Unless they are dedicated to working out, they'lll adapt pretty quickly to the generally easier demand, and probably lose muscle tone accordingly pretty quickly. If you've ever had extended bed rest (an extreme case, I admit), you'll know how fast this happens.

 

[rust]

If you've ever had extended bed rest (an extreme case, I admit), you'll know how fast this happens.

Indeed, unused muscles usually begin to shrink after about 24 hours
only, so I think some daily exercise would be necessary for those co-
lonists who do not have to do much physical hard work, like the admi-
nistrators and some of the scientists.

 

[captainjack23]

If you've ever had extended bed rest (an extreme case, I admit), you'll know how fast this happens.

Indeed, unused muscles usually begin to shrink after about 24 hours
only, so I think some daily exercise would be necessary for those co-
lonists who do not have to do much physical hard work, like the admi-
nistrators and some of the scientists.

Given that they live there , I wonder how dedicated they'll be.

 

[EDG]

Like I said, it depends on how bad 0.73g is compared to 1g. It's not THAT much lower than 1g so I wouldn't expect the physiological effects to be anywhere near as bad as microgravity or lunar gravity.

 

[rust]

Given that they live there , I wonder how dedicated they'll be.

Not very dedicated, I think.

The small minority who either will return to Terra after their mission
on the colony's planet has ended or who will have to travel on star-
ships with a 1 G board gravity now and then will perhaps do their dai-
ly exercises, and some "fitness freaks" will also do so, but most will
soon begin to ignore those exercises.

 

[captainjack23]

Given that they live there , I wonder how dedicated they'll be.

Not very dedicated, I think.

The small minority who either will return to Terra after their mission
on the colony's planet has ended or who will have to travel on star-
ships with a 1 G board gravity now and then will perhaps do their dai-
ly exercises, and some "fitness freaks" will also do so, but most will
soon begin to ignore those exercises.

And very unlike modern earthbound people, eh ?

 

[Woas]

What about other aspects of life? Like driving a ground (wheeled or tracked) based vehicle?
I ride motorcycles and let me tell ya, if a bike I was 'used to' weighing ~500lbs curb weight all of a sudden performed like a bike with a 365lb curb weight... that's a big difference.

 

[rust]

What about other aspects of life? Like driving a ground (wheeled or tracked) based vehicle?

I think with All Terrain Vehicles driven carefully across unexplored desert
terrain the problems would probably remain small, although I do intend
to give the characters negative modifiers for the first few days, until they
have adapted to the new environment.

As for the colony's shuttle, I think a well trained shuttle pilot will be used
to operations under different gravities, and the computer will probably al-
so help to handle the situation.

Other things could be more of a descriptive nature than of a rules nature.
For example, the plants in the colony's hydroponics dome will probably
look somewhat strange, growing taller and more spindly.

 

[iainjcoleman]

What about other aspects of life? Like driving a ground (wheeled or tracked) based vehicle?
I ride motorcycles and let me tell ya, if a bike I was 'used to' weighing ~500lbs curb weight all of a sudden performed like a bike with a 365lb curb weight... that's a big difference.

It's worse than that. It would be a bike with a 365lb curb weight that performs like a bike with 500lbs curb weight: the kinetic energy and momentum of the vehicle depend on mass (which doesn't depend on gravity) not on weight (which does). Probably quite disorientating until you get used to it.

In game terms, I think you want to do something simple. Give a -1 DM to all rolls where the lower gravity is relevant, until the PCs have been in the environment long enough to get used to it. How long is long enough? I have absolutely no idea, but for game purposes I'd probably call it a couple of weeks.

 

[BP]

I'm sure you meant multiply by 0.73 :wink:

No, he didn't. Dividing by 0.73 is the same as multiplying by 1/0.73, which is about x1.37. ...

- Carefully wiping egg off face...

I meant that as a joke - i.e. I meant to put 1.37. Human check = passed; Math check = failed. Thanks for fixing!

Damage from falling however will still be 0.73 times that in 1g.

Good point for those clumsy characters...

What about other aspects of life?...

Yeah - we've seen astronauts adjusting to spooning free-floating food - but, if the Gravity was just adjusted slightly I wonder what human reactions would be like with every day things...

On the humorous role-play side - a little color could be added for common coordination based activities that might suffer under lower G. Fork accidents might become an issue (food weighs less and so does one's arm). For the gentleman - opening a door with too much force, or an over enthusiastic courtesy bowing could lead to awkward or even insulting injuries. Trampoline jumping and tossing small children in the air could become [more] problematic.

 

[lastbesthope]

What about other aspects of life? Like driving a ground (wheeled or tracked) based vehicle?
I ride motorcycles and let me tell ya, if a bike I was 'used to' weighing ~500lbs curb weight all of a sudden performed like a bike with a 365lb curb weight... that's a big difference.

It's worse than that. It would be a bike with a 365lb curb weight that performs like a bike with 500lbs curb weight: the kinetic energy and momentum of the vehicle depend on mass (which doesn't depend on gravity) not on weight (which does). Probably quite disorientating until you get used to it.

You mean like a bike with a 500lbs equivalent curb mass.

In the UK 1 lb is 454g or 0.454 kg (I believe the US is different), so a 500lb weight bike has a mass of 227kg. on this 0.73g world it would weigh 365 pounds (which in 1g is equivalent to a mass of 165.71kg) but still has a mass of 227kg.

Less weight means grip from it's weight, less rolling resistance but most of the performance is mass limited. More likely to lock and spin your wheels. For normal bimbling about it'd be OK, but you'd lose the extremes of performance. Ignoring the effects of mechanical interlock between tyres and road, and assuming no aerodynamically generated downforce, a motorcycle's acceleration in a straight line is limited to 1 local g, so in a low g environment you'r acceleration would slow.

But in a high g environment you would get gains, more weight5, more grip, better acceleration, but then more rolling resistance to due to increased weight.

Think about it, F1 cars, etc, generate more downforce which allows them to accelerate faster, the same gain in performance would occur if the local g was higher than 1.

LBH(In discussion with his petrolhead father)

 

[EDG]

Ignoring the effects of mechanical interlock between tyres and road, and assuming no aerodynamically generated downforce, a motorcycle's acceleration in a straight line is limited to 1 local g, so in a low g environment you'r acceleration would slow.

Really? Huh. How does that work?