Missile speeds in space

[narcissus]

This has probably already been covered before, so please link me if it has.

I was running a space fight today between the PCs' ship and 2 Naruni Rapiers with long range missiles. Initially I was like "a volley of missiles is fired at you from 1000 miles (while the Rapier is still undetectable)", and then i did the calculations, and it would have taken 30 mins for the missiles to reach their target (2k mph). And the Rapiers can fly at Mach 16 in space (12k mph), so the Rapiers will reach their target in 5 mins, 6x faster than the missiles they shot. And the PCs' ship can fly at Mach 15 (~11k mph) so could easily outrun the missiles.

How do people reconcile this and make missiles actually useful in space?

[drewkitty ~..~]

Space range: rated range x2.
Add the missile speed on top of the speed the firing platform. The missiles are going their rated speed relative to the firing platform

[Wise_Owl]

Okay, two answers here...

Simple Answer; Don't worry about it. It's space fantasy. Fire missiles, Missiles go Boom, people dodge or don't.

Complex Answer: Maximum Speed makes no sense in Space unless you are talking about the speed of light.

In an atmosphere on a planet, like earth, something with Thrust has a maximum speed as the thrust is the force foreward, causing acceleration and increasing in Velocity. The air causes a force of Friction in the opposite direction, this force varies with speed. So as velocity increases, friction increases until the FOrce of Friction equals the Force of Acceleration from Thrust and you have a maximum speed. This is simplified a little(there are a host of other factors.)

In Space there is no such force of friction. A Force working on a body causes acceleration as long as it occurs. So in space the important factor is neither acceleration(though that does matter) or a non-existant maximum speed, but Delta-V. That is the ammount of change in velocity the object can exert. In classic chemical rockets this is basically acceleration x (Fuel Capacity/Fuel Consumption Rate). If you have a sci-fi drive of some sort that has no fuel, and can just go kind of 'forever' Acceleration than does become the dominant factor.

TDLR?: Palladium books as far as space are concerned are not scientific or even really sensical in lots of cases. Max speed as a 'stat' barely makes any sense, and a 'range' makes even less sense. Just go with whatever, it's space Fantasy, Pew-Pew!!

[green.nova343]

Short answer: as mentioned before, missile speeds & ranges are doubled in space, but to keep it simple just focus on the missile range & speed.

Long answer: unless your tech is using some sort of reactionless drive that acts like Star Trek impulse/warp drives or Star Wars drive systems, there isn't a "maximum speed" in space. However, then you have to start worrying about acceleration rates, fuel consumption, etc., which is extremely cumbersome & complex. Otherwise, you run into the problem of your launch platform running into its own missile volley.

Mid-sized answer:

• the listed ranges & speeds for missiles, whether in atmosphere or in space, assume that the missile is being launched from a (mostly) stationary platform.
• To find the modified speed/range for the missile, multiply the normal range by the sum of the normal missile speed & the launch platform's speed, & divide by the normal missile speed. The equation is R₂ = R₁ x V₂ / V₁, V₂ is the speed of the missile plus the launch platform, V₁ is the speed of the missile by itself
• Unless we are talking about missiles that have ranges measured in the tens to hundreds of thousands of miles, the space speed & range for a missile should reallybe x10....as should the sublight speeds of all fighters & starships. But if you're not comfortable with that, stick with the x2 multiplier.
• To make it simpler, if the launch platform's speed is less than 10% that of the missile's base speed, don't even bother adjusting the missile range, at least not for Medium-range missiles & smaller. Since you're adding at most 10% more range to the missiles, it won't really make that much of a difference (maybe 1/2 a mile for MMs & SRMs, 4-8 miles for MRMs).

So, from your example, a Rapier fires off some LRMs. Let's assume Nuclear/Multi-Warhead (Mach 3, 1800 miles range base). We double for space (Mach 6, 3600 miles range). We plug them into the formula: V₂ = V₁ (Mach 6) + launcher speed (Mach 16) = Mach 22, so R₂ = 3600 miles (R₁) x Mach 22 / Mach 6, or 13,200 miles. It'll take your missiles 54 minutes to get to the target, but your Rapiers will still be about 20 minutes out...or, to put it another way, your Rapiers will still be about 3,600 miles from their targets, well outside of sensor or visual range (although the missiles probably gave the target a warning that something is out there).

Just to blow your mind...consider instead a volley of HE/Medium SRMs (5 miles, 500MPH in atmostphere; 10 miles, 1,000MPH in space). The calculation gives them a speed of 11,720MPH (Mach 17.49) & a range of 117.2 miles in space. They'll reach their target in 36 seconds...in which time the range to the target from the Rapier will shrink from 117.2 miles to 10 miles...still far enough out that the enemy has a -4 penalty to shoot back at you if using visual sensors (or half normal bonuses & -30% to Read Sensory Instruments if using radar & other non-visual sensors)

Also consider the Armor Piercing MRMs (base of 60 miles/1600MPH, increased to 120 miles/3200MPH in space). Factoring in the Rapier's speed, the MRMs have a range of 522 miles & a speed of 13,920MPH (flight time is 135 seconds). By the time they hit the target, the Rapier is still 120 miles out from the target -- -30% to be detected on non-visual sensors (half normal bonuses) & completely invisible to visual sensors (so unable to fire if only visual sensors are available or if they fail their Read Sensory Instruments skill role).

[ShadowLogan]

As mentioned previously missiles (and other potential elements here) have their speed/range modified while in space, sometimes generically so and sometimes with a case-modifier that applies only in that case (I'm speaking megaversally here).

I would also recommend that you add the launching platforms relative speed to the missiles speed (it's not stated anywhere that I know of, but it likely falls under the "common sense" clause of the rules). What do I mean by relative speed, well if you are both (shooter and target) moving toward each other ADD their respective speeds (you're at Mach 6 and they are at Mach 5, the missiles get a Mach 11=6+5 boost), if they are moving away from each other, you would SUBTACT (previous Mach 6 and 5 result in a Mach 1=6-5). For simplicity I'd treat anything in between as whichever you think is closer in that situation (and a perfect side on shot I'd say you could ignore the target's speed and add the shooters speed).

As for a "maximum speed in space". That will vary by propulsion type for reaction based systems (like chemical rockets) due to physics involved in terms of practicality (Delta-V becomes increasing less efficient to increase over a specific multiplier of the propulsion system's exhaust velocity) and to go faster either require you to use staging (as each stage is spent it is released with the resulting speed being retained) or "free boost" physics (like a gravitational slingshot, which isn't "free") or something like a Bussard ramjet (sucking in stray gas in the vacuum of space to use as fuel). Now Reaction-Less based propulsion systems aren't going to have a "maximum speed" per say (aside from Speed of Light in Realworld) for the Rifts Phaseworld setting sense the Contra-Gravity Drives are of this type and used for FTL (the fact they have "max speed" could be explained I'm sure).

I did the math on a spreadsheet a long time ago to get the Time to Target, and the time to cover 1000ft distance (for defensive actions with guns to determine if you get 1 or 2 attacks to defend) so I know what you are saying about travel time. They all (aside from mini) have that travel time problem when fired from max. range that amounts to taking more than 15seconds (a few SRMs don't, but those are the gas/smoke/retardant type).

[green.nova343]

As mentioned previously missiles (and other potential elements here) have their speed/range modified while in space, sometimes generically so and sometimes with a case-modifier that applies only in that case (I'm speaking megaversally here).

I would also recommend that you add the launching platforms relative speed to the missiles speed (it's not stated anywhere that I know of, but it likely falls under the "common sense" clause of the rules). What do I mean by relative speed, well if you are both (shooter and target) moving toward each other ADD their respective speeds (you're at Mach 6 and they are at Mach 5, the missiles get a Mach 11=6+5 boost), if they are moving away from each other, you would SUBTACT (previous Mach 6 and 5 result in a Mach 1=6-5). For simplicity I'd treat anything in between as whichever you think is closer in that situation (and a perfect side on shot I'd say you could ignore the target's speed and add the shooters speed).

As for a "maximum speed in space". That will vary by propulsion type for reaction based systems (like chemical rockets) due to physics involved in terms of practicality (Delta-V becomes increasing less efficient to increase over a specific multiplier of the propulsion system's exhaust velocity) and to go faster either require you to use staging (as each stage is spent it is released with the resulting speed being retained) or "free boost" physics (like a gravitational slingshot, which isn't "free") or something like a Bussard ramjet (sucking in stray gas in the vacuum of space to use as fuel). Now Reaction-Less based propulsion systems aren't going to have a "maximum speed" per say (aside from Speed of Light in Realworld) for the Rifts Phaseworld setting sense the Contra-Gravity Drives are of this type and used for FTL (the fact they have "max speed" could be explained I'm sure).

I did the math on a spreadsheet a long time ago to get the Time to Target, and the time to cover 1000ft distance (for defensive actions with guns to determine if you get 1 or 2 attacks to defend) so I know what you are saying about travel time. They all (aside from mini) have that travel time problem when fired from max. range that amounts to taking more than 15seconds (a few SRMs don't, but those are the gas/smoke/retardant type).

Damn, I knew I forgot something. Yes, the relative speed of the target factors in as well, & understanding when to add or subtract that velocity.