Making EM Guns Viable in Space Combat (3e)

[Anthony]

Originally Posted by Rupert

The point is, it doesn't discuss how the armour is laid out at all, and just lists it by type.

In fact, given that there isn't an adjustment to size for heavy armor, it pretty much treats armor as being the same density as any other system. Which is only anywhere close to true for spaced armor.

[Polydamas]

Originally Posted by Rupert

The point is, it doesn't discuss how the armour is laid out at all, and just lists it by type. I would assume that the in0universe designers of armoured spaceships would lay it out and use spacing, etc., as appropriate against the threats they expect to see. We don't need to worry about these details, but only about the final effect (dDR), mass, and price because that's the level of detail Sapceships works at.

A good way to verify that would be to see if spaceship DR scales the same way that DR scales against bullets (and if DR seems to assume that 1" of RHA is DR 70). If it does, that's a sign that Pulver just projected the same model to a completely different environment. I don't think any of GURPS' engineering geeks have ever said that they were asked to create such a model, the pantropes tv guy created his model as a hobby.

Another way to verify is to see if the more protective types of armour have the properties which the engineers designing protection for spacecraft and space stations look for, or if they have the properties of tank armour from the 1940s and 1950s.

Edit: GURPS Spaceships pp. 10-13 seems to list the types of armour I would expect on a 20th-century light armoured vehicle, plus ice, rock, and organic (and imaginary extensions of 20th century technologies). Nothing about layers of bumpers or synthetic fibres.

[Varyon]

Originally Posted by Polydamas

You also talked about range, and in space the range of a projectile is "until it hits something" so maybe this term means something different to you.

Range in space combat is going to be more something like "Range beyond which getting out of the way is easy so long as the pilot isn't asleep." Against a "stationary" target, such as a planet or a space station, range may well be infinite, but against maneuvering spacecraft it's much, much smaller.

Originally Posted by Anthony

In fact, given that there isn't an adjustment to size for heavy armor, it pretty much treats armor as being the same density as any other system. Which is only anywhere close to true for spaced armor.

That's available as an optional rule in "Alternate Spaceships" (Pyramid #3/34), where the more armor you have the better each module of it protects (because the spaceship becomes smaller, and thus has less surface area for a given quantity of armor to cover), and there are certain breakpoints at which the spaceship becomes one or two SM's smaller than its weight would indicate.

Originally Posted by Polydamas

A good way to verify that would be to see if spaceship DR scales the same way that DR scales against bullets (and if DR seems to assume that 1" of RHA is DR 70). If it does, that's a sign that Pulver just projected the same model to a completely different environment.

At SM+9, an unstreamlined spaceship would have dDR 7 over 1/3rd of its surface per 5% of its mass that is Steel Armor. Let's have 15% (450 tons, or 900,000 lb) as Steel Armor, for dDR 7 - DR 70 - over the entire surface. Going off "Cutting Edge Armor Design" (Pyramid #3/85), DR 70 of High Strength Steel (which is RHA) would require (unsurprisingly) one inch of armor. Made of Solid Construction (which is appropriate for vehicular armor), DR 70 would weigh 40.6 lb per square foot, meaning 900,000 lb of it would cover a surface area of 22,167.5 square feet. A 15-yard-radius sphere (which would be an SM +9 spaceship) would have a surface area of 25,446.9 square feet. So, I'd say the values are close enough we can assume the Spaceships numbers simply extrapolate from how personal armor is scaled.
(As an aside, 900,000 lb of RHA armor of Solid construction would cost $2.7M in the armor design article, while 3 SM +9 Steel Armor modules only cost a total of $1.8M; I'd assume some sort of economy of scale is in play, or perhaps Spaceships simply makes different assumptions about the cost of the materials)

[Anthony]

Originally Posted by Varyon

Range in space combat is going to be more something like "Range beyond which getting out of the way is easy so long as the pilot isn't asleep."

Well, it's not quite that simple though it mostly is.

Let's say our setting has missiles that are capable of 1G of thrust for 200 seconds. This is quite conservative, we could build missiles like that today.

If it's able to thrust directly at its target, that missile can reach out to 200 kilometers. If it's required to use half a G for course correction, it can still reach out to 170. So, to dodge that missile at a range of 170 km, you either need a burst of acceleration of 1G or more, or you need to maintain half a G of thrust for 200 seconds.

The first is probably not possible in a setting that has missiles as low powered as those. The second may not be be possible either, and if it is, you just burnt 1 km/s of maneuver fuel and you're probably going to need to burn at least double that because you want to actually arrive at your destination.

Now, let's say we have dumb but super powerful mass drives that achieve 10 km/s, which is huge. The projectile takes 17s to arrive.

A target vehicle with 0.1G of thrust can use 1s of thrust (1% of the amount needed to dodge the missile) to dodge by 17 meters.

[Rupert]

Originally Posted by Varyon

That's available as an optional rule in "Alternate Spaceships" (Pyramid #3/34), where the more armor you have the better each module of it protects (because the spaceship becomes smaller, and thus has less surface area for a given quantity of armor to cover), and there are certain breakpoints at which the spaceship becomes one or two SM's smaller than its weight would indicate.

That does not account for the differences between armour types' density, only between the density of a ship without much armour and one with lots of armour.

[David L Pulver]

SPACESHIPS is a simple system, and so is GURPS when it comes to edge cases.

SPACESHIPS doesn't treat Whipple Shields very much because I didn't come up with a good model for them. (The logical approach is high volume ablative DR, but how effectively they are against non-hypervelocity attacks has to be considered as well). Also, because they effectively trade volume for protection, they don't work very well in SPACESHIPS. The system keeps some degree of simplicity by by abstracting out volume in favor of mass, as that worked best with my desire to present a simple but fairly realistic rocket equation integrated into the rules for fuels and drives. (If you want a system that does the other thing, and abstracts out mass, see most versions of TRAVELLER). However, the tradeoff is that SPACESHIPS has trouble with things that are volume-centric -- and Whipple Shielding armor is most fundamentally about trading volume for protection. Trying to solve this on top of adding a new model for hypervelocity impact damage was just a bridge too far. But yes, I do regret not covering this element in more depth, and if I find a simple way to do it and revisit the SPACESHIP rules, I would consider changing the rules to adapt something like this.

There are, however, dangers with messing too much with the basic damage mechanics of GURPS, since no one (for example) would want their high DR superheroes to have all the DR ignored when a meteoroid or equivalent weapon system hit them...



As a result, integrating and balancing the tradeoffs for it in a mass-centered system somewhat more complicated, and with space limited, I chose not to cover it. The other reason is that whipple armor is largely only tested and graded against micro-meteoroid type impacts, and there is limited available data on how well the armor will stand up to, say, energy beams, nuclear detonations, or larger caliber impacts, how compatible it would be with streamlining, etc. Finally, GURPS has rarely bothered to treat hypervelocity penetrations as anything other than high armor divisor impacts, so creating a whole new system in a book with limited space seemed ill-advised! I did consider a subsystem for this, but not in time to develop and playtest it.

[Refplace]

Originally Posted by David L Pulver

There are, however, dangers with messing too much with the basic damage mechanics of GURPS, since no one (for example) would want their high DR superheroes to have all the DR ignored when a meteoroid or equivalent weapon system hit them...

Which is why I like IT:DR for my heavy brick supers.

[Varyon]

Originally Posted by Rupert

That does not account for the differences between armour types' density, only between the density of a ship without much armour and one with lots of armour.

Fairly non-dense armors (various flavors of wood - including organic armor - as well as ice) are called out as not being eligible for the optional rule. The denser armors that it does apply to are generally sufficiently-dense compared to the rest of the vessel that treating them all as the same density probably works fine at Spaceships resolutions. I'm currently too tired to work out what relative density the Armor and Volume rules are assuming for the armor (but I'm eyeballing it at twice the density of other systems), but if you really want to differentiate the armors based on their density, it probably wouldn't be overly difficult to make a separate table for each armor option... but including tables for each probably would have eaten up all the space for that Pyramid article.

[Polydamas]

Originally Posted by David L Pulver

SPACESHIPS is a simple system, and so is GURPS when it comes to edge cases.

SPACESHIPS doesn't treat Whipple Shields very much because I didn't come up with a good model for them. (The logical approach is high volume ablative DR, but how effectively they are against non-hypervelocity attacks has to be considered as well). Also, because they effectively trade volume for protection, they don't work very well in SPACESHIPS. The system keeps some degree of simplicity by by abstracting out volume in favor of mass, as that worked best with my desire to present a simple but fairly realistic rocket equation integrated into the rules for fuels and drives. (If you want a system that does the other thing, and abstracts out mass, see most versions of TRAVELLER). However, the tradeoff is that SPACESHIPS has trouble with things that are volume-centric -- and Whipple Shielding armor is most fundamentally about trading volume for protection. Trying to solve this on top of adding a new model for hypervelocity impact damage was just a bridge too far. But yes, I do regret not covering this element in more depth, and if I find a simple way to do it and revisit the SPACESHIP rules, I would consider changing the rules to adapt something like this.

There are, however, dangers with messing too much with the basic damage mechanics of GURPS, since no one (for example) would want their high DR superheroes to have all the DR ignored when a meteoroid or equivalent weapon system hit them...



As a result, integrating and balancing the tradeoffs for it in a mass-centered system somewhat more complicated, and with space limited, I chose not to cover it. The other reason is that whipple armor is largely only tested and graded against micro-meteoroid type impacts, and there is limited available data on how well the armor will stand up to, say, energy beams, nuclear detonations, or larger caliber impacts, how compatible it would be with streamlining, etc. Finally, GURPS has rarely bothered to treat hypervelocity penetrations as anything other than high armor divisor impacts, so creating a whole new system in a book with limited space seemed ill-advised! I did consider a subsystem for this, but not in time to develop and playtest it.

Thanks for taking time to comment. Regarding the fact that post-1950 armour technologies such as Chobham or Whipple Bumpers take up more space than traditional hard dense homogeneous armour, it seems like that is a good in rules centered around mass instead of volume. It avoids the gotcha about "what if a spaceship has a high percentage of its mass as armour, shouldn't it be smaller, didjaeverthinkaboutthathuh?"

Regarding what has or has not been tested or modeled, I have a folder of studies which I will go through and summarize on my site sometime this year. While the US, Russian, and Chinese militaries probably keep their studies of modern armour technologies vs. weapons secret, I want to see what the actual studies say and what scenarios they have covered rather than trust some forumites.

I think Agemegos has a point that if GURPS were ever redesigned, it would be a good idea to eliminate Armour Divisor and Hardened, let damage be armour penetration, and just allow a wider range of damage multipliers eg. 1/10 for attacks which currently have AD (10) WM 1.0

[Anthony]

Originally Posted by Polydamas

I think Agemegos has a point that if GURPS were ever redesigned, it would be a good idea to eliminate Armour Divisor and Hardened, let damage be armour penetration, and just allow a wider range of damage multipliers eg. 1/10 for attacks which currently have AD (10) WM 1.

Eh, I'd probably invert that -- eliminate all wounding modifiers, have a wider range of armor divisors. When a game system calls something 'damage', people expect it to actually translate to wounding.