Space Lobsters and Gravity....

[Peter Cairns]

A while back when there was a thread about when people would want CM:SoD, set there seemed to be a fair bit of support for relatively near future.

I quite liked the idea of it being set in the real solar system, similiar in period ( if not style) to "Total Recall", or "Outland".

However looking at the various moons and things all but Venus really only has a fraction of earths gravity, so the question is this, looking at say, the Moon, Mars and Titan, what would the performance of something like an M-16 be compared to earth, in terms of range, recoil and hitting power.

I am sort of guessing that there are a lot of people who know a lot more about ballistics than me on this forum.

I was looking at some of the Cassini stuff from Nasa a while back and it looks like Saturn has two small shepard moons in it's rings one of which overtakes the other. I wonder if you could shoot at people on the other moon as it passed?

Now that would be a crazy scenario.

Peter.

[Cpl Steiner]

Originally posted by Peter Cairns:

However looking at the various moons and things all but Venus really only has a fraction of earths gravity, so the question is this, looking at say, the Moon, Mars and Titan, what would the performance of something like an M-16 be compared to earth, in terms of range, recoil and hitting power.

Mars has a surface gravity of 0.38g (where Earth = 1g). With a third the gravitational pull of the Earth, a bullet should therefore have a greater range on Mars than on Earth. Similarly, the Moon, with a surface gravity of 0.17g, and Titan, with a surface gravity of 0.14g, should extend the range even further than Mars. However, there is no atmosphere on the Moon, a very thin atmosphere on Mars, and a thicker atmosphere than Earth's on Titan. Drag would therefore come into play on Titan to reduce the range, whilst on the Moon and Mars, a bullet would probably have a much further range because there is little or no drag. This would suggest a bullet fired on Titan might have similar range to that on Earth (lower gravity but thicker atmosphere) whilst on Mars and the Moon, it would be significantly greater due to the lower gravity and the lack of appreciable atmosphere.

For spotting distances, the distance to the horizon for a 2m high viewpoint on Earth is about 5 km. On the much smaller bodies mentioned, it is reduced. On Mars, it is about 3.7 km, on the Moon, it is about 2.6 km, and on Titan, it is about 3.2 km. Interestingly, although the Moon and Titan have about the same surface gravity, Titan is bigger, hence the greater horizon distance. This is due to Titan's lower density.

Hope this helps!

[Peter Cairns]

Thanks, Steiner,

I pretty much suspected that ranges would go up, but I am still in the dark about recoil, I never quite go the hang of the difference between mass and weight.

As to guns in general, there is the issue of whether a round will fire in a vacumn, and indeed what happens when you fire a gun in a methane rich atmosphere like Titan. I

suppose you could have a fuel air cartridge, like a car cylinder which when ignited exploded, that way it would carry it's own air. Then again compressed air guns might work too.

In part what I am thinking about is this, is there enough variety in enviroments to make the game worth while.

You could have Venus scenarios, where you could only stay out of vehicles for a short while, though why you would go in the first place might rule it out.

Certainly Mercury and the Moon would let you have darkside battles, but it would be abit like playing on a black and white screen.

Light is a problem with most of the moons as well, because if you take away the artifical colours often used, in reality most of them are a dull grey, like constantly fighting at dawn or dusk, which might look pretty boring even if it was realistic...

Having said that with recent photographs show that there are some really wierd terrain types which could be fun....

Peter.

[Thomm]

The recoil forces would be the same.

Their effects on a standing person would be different. It would be easier to top the shooter over in lower gravity.

The rounds would fire no matter what, because all the explosive needs is confined in the cartridge.

Best regards,

Thomm

[Peter Cairns]

Does that mean that without the need for rounds to be shaped you could use flat noesed cylinder rounds, that woulf blow people clean off their feet?

Peter.

[Cpl Steiner]

Originally posted by Peter Cairns:

Certainly Mercury and the Moon would let you have darkside battles, but it would be abit like playing on a black and white screen.

The "Dark Side of the Moon" is a common misconception, in that it isn't truly dark all the time. It is just the side permanently facing away from Earth, so we can never see it from here. It still has days and nights just like the Earth.

Have you ever read "The Forever War" by Joe Haldeman? It has some of the best descriptions of fighting on small airless bodies like the Moon that I have ever read, and besides that, it's also a damn fine book.

One point Mr. Haldeman made was the danger of fighting on very cold worlds like Titan. If your space suit wasn't properly insulated, your own body heat could cause some of the icy rocks to vapourise explosively, with potentially fatal results. I imagine hot projectiles flying around might have a similar effect.

[Michael Dorosh]

Originally posted by Rollstoy:

The recoil forces would be the same.

Their effects on a standing person would be different. It would be easier to top the shooter over in lower gravity.

If the bullet doesn't knock the target over, how can the recoil knock down the firer?

[Thomm]

Their = The recoil forces'

--->

The effect of the recoil forces on a standing person (that is, the shooter) would be different. It would be easier to knock the shooter over in lower gravity.

...

Would be the same for the target, though!

Best regards,

Thomm

[Thomm]

DP

[acrashb]

Originally posted by Peter Cairns:

Does that mean that without the need for rounds to be shaped you could use flat nosed cylinder rounds, that would blow people clean off their feet?

Peter.

Momentum is conserved in collisions. Any cartridge that would blow a person "clean off their feet" would do the same to the person firing. Movies are tripe in this regard - the impact of the bullet is similar to the impact of the gun on one's shoulder or hand.

'flat-nosed rounds', which today we call 'wadcutters', would be easier to manufacture and have some positive effects when penetrating sloped armour. That's all.

[Splinty]

Since the surface temprature on Venus is hot to melt lead and the air pressure dense enough to crush steel, I think firing a rifle would be rather difficult.

[Other Means]

I think all this will be done in "Dropteam", brought to you by your friendly neighbourhood BFC.

They have variable gravity, air density etc addressed there.

A Fuel-Air explosive in a methane atmosphere would just be an Oxygen explosive, which would be cool.

The downside of low gravity would be that your shells would easily achive escape velocity and just go into space.

And yes, The Forever War was a cool book.

[Peter Cairns]

So lets get this right,

If you wanted the same power, recoil would knock you off your feet, so less power would be needed.

What about some kind of recoil device as in artillery, or won't that work either.

I don't see escape velocity being an issue, but the hugely increased range and effectiveness of AA fire wmight well be, It's dangerous enough flying in a combat zone as it is.

Another issue would be deliberately putting things in to orbit in the hope that they hit things. I'd hate to be brought down only to discover it was by small arms ammo fired by my own me on the other side of a moonlet...

Peter.

[Mace]

Oh course you could just....

*shameless plug*

....buy Dropteam when the game's released, because that takes gravity and atmospheric density into account in it's physics engine.

[Peter Cairns]

Mace,

True, but then we could all buy T-72 instead of CM:SF and save all this time and waiting.

Come to think of it we could all just keep playing CMBO, or close combat or two paddle ping pong, hell lets throw out our computers and play domino's

Peter.

[Bruce70]

Correct, oxygen is not required for firing a rifle. Despite the fact that in Firefly Jayne has to put Vera in a spacesuit in order to fire in a vacuum. (Not that I wish to take anything away from such a great series)

Low gravity plus high atmos. press. might give you reasonable range but the velocity of the round would drop more quickly - so the effective range would be significantly less. On top of that wind and turbulence would have a greater effect on accuracy than on earth. Atmos. press. is a far bigger factor for effective range than gravity is.

Recoil would not be a problem in any but the most extreme cases (eg. in space!), provided you fire prone. Does anyone have any experience firing on ice?

If you get the size and density of the moon, and muzzle velocity just right you may have to worry not only about friendly fire, but also self fire!

[Peter Cairns]

I wonder how far you could throw grenades om Mars, the Moon and some of the smaller moons....

Petr.

[flamingknives]

Pretty damn far.

On top of the low gravity, there is the relationship between gravity and atmospheric pressure. A low gravity object will, by definition, have low pressure atmosphere. I think it might be a directly proportional relationship, but I could well be wrong.

[Peter Cairns]

flamingknives,

If I have got it right (and it might be very wrong) then Boyles law ( another great SCOTTISH scientist) states that P=VT,(Pressure = Volume times Temperature).

Now on a moon like Titan, where we have very low temperatures and a dense gas, such as Methane, then the ground pressure could be quite high for even small gravity. I think gravity will sort of determine the "volume" although it depends on the gas.

If we were talking air ( mostly Nitrogen, and some Oxygen), then even those at that gravity would be low pressure, but I am not sure about the weight of the gas involved.

I am pretty sure that with similiar gravity to earth it is the temperature that is pushing up the pressure on Venus. odd thing iif it was just about gravity and heat, how is it that time and again the surface pressure we find have turned out to be very different from the predictions.

I remember that when the Viking lander sent back it's results the pressure was something like 20% of what NASA expected.

Peter.

[Rother]

Originally posted by acrashb:

Momentum is conserved in collisions. Any cartridge that would blow a person "clean off their feet" would do the same to the person firing. Movies are tripe in this regard - the impact of the bullet is similar to the impact of the gun on one's shoulder or hand.

Really? I'll use my rifle as an example just because I know the numbers. Bullet energy=300gr./2,700fps/4,850ft.lbs. of energy. Rifle recoil energy=63,000gr./16fps/36ft.lbs of energy. Those are pretty rough numbers but close enough for this. You're failing to take into consideration is the rifle weighing more than 200 times what the bullet weighs. Believe me when I say I can knock a 1200lb moose literally right off it's hooves and yet remain standing. I will agree that the movies way over do it though.

[Peter Cairns]

Rother,

I'd go with F=MA, Force=Mass x Acceleration.

Now from this point of view a 5.56 bullet weighs about 5 grams, so at a muzzle velocity of 1000m/s then we get

1000 x 0.005 =5kn ( I think). Now if a M-16 with sight and ammo weighs 5kg, then you get

5kn = 1m's x 5Kg, so the recoil shouldn't be that bad. The fact that you don't go back a meter is to do with the fact that the gun has a recoil mechanism ( the big spring that works the ammo feed) and that you have 100kg or so of body mass braced behind the but plate.

The diffficult bit is how that energy produced a more pronounced effect on an unbraced 600kg Mouse at the other end, and that must be to do with hoe the energy gets dispersed over a smaller area, which is a bit beyond me...

Peter.

[Thomm]

Originally posted by Rother:

Believe me when I say I can knock a 1200lb moose literally right off it's hooves and yet remain standing. I will agree that the movies way over do it though.

I guess that a big part in explaining this plays the fact that you are prepared for the recoil force of the rifle whereas the moose is not prepared for receiving the blow of the impact of the bullet.

Best regards,

Thomm

[Rother]

Peter, velocity squared. Otherwise you get the idea.

Rollstoy, state of mind has nothing to do with it. It's the difference between 36ft lbs and 4,800ft lbs that has everything to do with it.

Here's a page that can explain recoil energy much better than I can. clicky the linky has a neat little chart too so you don't have to do a bunch of math.

For bullet energy you have to do your own homework. That's as easy as finding porn.

[Cogust]

It's no the bullet's energy that's throwing people of their feet, it's the momentum of the bullet that does the trick and that momentum is the same to both the shooter and the target. Momentum is always conserved and the formula is Momentum=mass*Velocity and the same applies to both the shooter and the target.

The bullet's energy (E=m*v2/2)is only important when considering things like penetration and damage, not when calculating the impact of the round.

My guess is that the moose goes down due to the damage inflicted by the round (shock will most likely make it loose control of it's muscles) and not by the impact of the round as the moose receives exactly the same momentum that you as the shooter gets fromt he recoil.

[Rother]

Momentum...fascinating. I wish I never got kicked out of physics classs. I plugged in the numbers from my example above and for all practical purposes the momentum is equal yet the energy is vastly different. My brain is having a hard time dealing with this. A perfect example of why you kiddies should stay in school.