[spaceships] Ohka Heavy Torpedo Bomber(TL 10/Realistic)

[adimar]

Hi all.
Here is another one of my spaceship designs this time: The Ohka Heavy Torpedo Bomber.
To understand the reasoning behind this design it needs to be understood that point defense batteries
(Fixed to the size of tertiary battery weapon on a SM+7 ship but increases the number of weapons.) can be very effective in destroying incoming missiles.
This together with the cost of missiles renders long range missile attacks practically obsolete vs. military targets.
This craft uses an Orion drive to be super armored, fast & difficult to hit.
So it can approach an enemy capital ship at close range and launch a barrage nuclear tipped missiles.
> This ship requires the armor & volume rule from Pyramid 3/34

Ohka Heavy torpedo bomber
TL 10, SM+5, Non aerodynamic
[F/1-4] Hardened Nano composite (44 dDr)
[F/5 ] 3 x Medium Battery (Fixed, High Thrust, Missile Launchers / Main Armament)
[F/6 ] Fuel tank
[F/C ] Control Room (No ejection)
[C/1-2 ] Hardened Nano composite (22 dDr)
[C/3 ] 2 x Medium Battery & SM+4 MHD turbine (Turret, Laser Very Rapid Fire/ Defensive Battery) .
[C/4-5] Defensive ECM (Total -4 to hit)
[C/6,C] Fuel tank
[R/1-5] Hardened Nano composite (55 dDr)
[R/6 ] External Pulsed Plasma (i.e. Orion Drive) (2g/24mps)

What do you think?
Adi

[weby]

Few thoughts:
-The acceleration seems low for a setting that uses orion drives. As example the TL 9 Trinity-class cruiser has 4G acceleration. So in a fight the lower TL target would be able to generate quite a lot of relative sideways vector.
-The utility of armor is a bit questionable in any encounter with any speed if the target has those huge numbers of the half ton weapons for missile defense. Conventional 8cm ballistic weapons will start to punch though the armor at the base relative velocity 50% of the time and "always" punch through at 2mps(and on average take the target to below -1*hitpoints).
-If people are throwing around nukes then even a proximity detonation from any size nuke will be devastating.

[Varyon]

Maybe I'm missing something, but lasers are much better for point defense than guns. While they do require energy, extrapolating from the Smaller Systems guidelines shows that, by reducing RoF to 2/3 normal, you could have a built-in MHD turbine that would power the system for 12 hours of continuous use. For the Ohka, Improved Very Rapid Fire Lasers instead of Very Rapid Fire Conventional would normally double your RoF, but with needing to add in the half-size MHD that means 4/3 normal, for RoF 400 for the whole system (instead of the 300 for the conventionals). This also gives at least +6 to hit (compared to proximity detonation; +10 otherwise, as small conventional weapons have sAcc of -10 while lasers have sAcc 0), and probably more (as lasers don't have to deal with relative velocity). The lasers do less damage - 6d(2) instead of ~30d (character scale, and assuming 1 mps relative velocity) - but unless you've got missiles that are extremely armored (which isn't going to leave much room for fuel, and certainly not much for a nuclear warhead), that 6d(2) should be enough to destroy them.

Also, as weby notes, all that armor isn't doing a lot for you. You could fit a lot more into the ship by going streamlined (making you harder to hit, which is more important) and replacing most of that rear armor with a magsail (which means you only need dDR 5, not dDR 50, on the rear). This can let you get away from using a complicated MHD/laser hybrid system, instead having a power plant take the place of one armor system and having that power a full-size laser battery - or maybe having multiple power plants and multiple batteries, as you'll be replacing quite a few armor systems.

[adimar]

Originally Posted by Varyon

Maybe I'm missing something, but lasers are much better for point defense than guns.

You are right, the original design had two SM+4 lasers and a SM+4 fusion reactor to power them.

Originally Posted by Varyon

Also, as weby notes, all that armor isn't doing a lot for you. You could fit a lot more into the ship by going streamlined (making you harder to hit, which is more important) and replacing most of that rear armor with a magsail (which means you only need dDR 5, not dDR 50, on the rear)

Problem with magsail is that any spacesail system it's an exposed system not protected by the spacecraft's armor. (Spaceships 1-pg.25) thus any hit would destroy this craft.
Now as for the armor not doing much, as you suggested earlier, The most common point defense weapon is a very rapid laser which does 1d-2(2) burn.
This will not even tickle the front armor of this craft (42 dDr/Hardened). To get a 50% penetration you need at least a 10mj laser which takes it out of the point defense weapon territory into the major battery firepower (To get a very rapid 10mj laser you need a 1gj battery which is a major battery on a SM+9 craft.)
Also the inclusion of 3 defensive ECM systems giving enemies -6 to hitting this craft means it would be very hard to achieve a hit with anything other than very rapid weapons.
The idea behind this craft is that it's a desperate last ditch effort by a collapsing regime to stop a vastly superior enemy by sending waves of relatively cheap kamikazes to take out it's capital ships.

Adi

b.t.w.: The name Ohka is taken from the ww2 Japanese kamikaze rocket propelled suicide gliders. Yokosuka_MXY7_Ohka

[weby]

Originally Posted by adimar

Now as for the armor not doing much, as you suggested earlier, The most common point defense weapon is a very rapid laser which does 1d-2(2) burn.
This will not even tickle the front armor of this craft (42 dDr/Hardened). To get a 50% penetration you need at least a 10mj laser which takes it out of the point defense weapon territory into the major battery firepower (To get a very rapid 10mj laser you need a 1gj battery which is a major battery on a SM+9 craft.)

If you are using non penetrating weapons like KJ scale lasers for point defense then massed armored missiles would make more sense.

The use of ballistic weapons as point defense on your craft suggested the use of such for point defense and then light vessels armor does not matter. But for 1d-2(2) energy weapons you should just armor the missiles.

A 1 ton/32 cm missile could trivially be armored to withstand such weapons from front making point defense useless.

[adimar]

Originally Posted by weby

A 1 ton/32 cm missile could trivially be armored to withstand such weapons from front making point defense useless.

I don't really think so.
If you look at a missile as a standard craft given the 10mps,5g (standard missile performance)
You need to devote:
3 slots of payload.
1 slot control center
2-3 slots for HEDM rocket engine (4g-6g)
13 slots for fuel tanks (including the x1.6 increase for 10.4 mps)
You are left with either one or no slots for armor.
Missile propulsion is calculated at the peak HEDM drive performance.

Maybe a design option could be added for heavy torpedo which has only Half the dV performance and is armored but that's not easy as well. An unstreamlined SM+2 (1 dTons) with all 6 frontal sections devoted to nanocomposite armor would have a 12 dDr frontal armor which when you take into account the (2) divisor of the laser weapon which might be barely enough to protect it from a 1d-2 frontal damage but is still totally vulnerable from the sides. (I can totally see missile defense boats parked a small distance from the capital ships who's all purpose is shooting the unarmored sides of these torpedoes.)
F[1-6] Nanocomposite 12 dDr
C[1-4] Fuel
C[5-6,c] Payload
R[1-4] Fuel
R[5-6] HEDM engines (4g, 4.8mps)
R[c] Control room

Adi

[Varyon]

A 16 cm missile as a spaceship would be roughly streamlined SM +0 (targeted at SM -1 due to streamlining). At TL 10, each system of Nanocomposite is roughly DR 7 (dDR 0.7), meaning you need three* of them to negate a 6d (1d-2 dDamage) laser, assuming you go with Hardened systems (otherwise, you'll need 6). If such missiles become common, however, you'll end up with point defense weapons instead being stronger lasers with lower RoF (or fewer strong lasers with the same RoF, which is nearly the same result) - at 1/10th RoF you get twice the damage, so you'd need 6 Hardened systems to protect the missile, meaning you've spent 30% of your mass budget simply on armor. And if the designers opt to take an accuracy hit to retain some of that RoF, they can use particle beams (which are sAcc -3, and half RoF due to no longer qualifying for Improved), and a TL 10 16 cm missile requires at least 50% of its mass in armor to protect against such weapons (with the front consisting entirely of Hardened Nanocomposite, and 4 more systems of armor elsewhere on the vessel, the Armor and Volume rules will boost the front armor to be just strong enough to deal with the beams).

Note also that Spaceships missiles aren't assumed to be what we typically think of as missiles - rather, they are multi-stage designs that throw out decoys and possibly multiple impactors, which would mean you couldn't design the initial missile as described above, as the actual impactor is much smaller yet still retains a maneuvering system (having 6 armor systems would mean a two-stage design - which is probably a low number of stages for such missiles - has the impactor consist of nothing but armor).

As for the Ohka's armor, yes, it would protect against the PD lasers, but then so would just having one system of streamlined Hardened Nanocomposite. If their targets mount ship-killing lasers, more armor may be useful (so long as the targets mount lasers for killing small ships), but from the Ohka's design I assumed ship-killing is typically done with projectiles. As far as the magnetic sails go, from the description I assume the Ohka is meant to be used for fast passes, where maneuvering isn't very important - they may well reel the sail in for an attack run, coasting through it. Alternatively, you can have a secondary magnetic sail (you're replacing up to 4 armor systems in the rear, after all), so if yours gets disabled in a run (and keep in mind the diffuse nature of exposed systems makes them tough to disable), you'll lose maneuverability for a short while until you deploy the second one**.

*GURPS rule of thumb is to armor against average damage. Higher rolls are somewhat unrealistic here, but sort of represent hitting weak points and the like. A more realistic approach to armor can be found in Armor Revisited (same Pyramid as Alternate Spaceships), which makes armoring in this manner more effective.

**I wonder if it would be possible for a low-armor vessel with a disabled/destroyed magsail to still use the Orion drive, but damage itself in the process.

[RogerBW]

I have a similar design, but I noticed a trick: you can throw warheads from EM guns. So your SM+5 Ohka fires 5×3×16cm missiles with range X; my SM+4 Hana with a spinal gauss cannon fires 50 10cm EM rounds at range S, each with a 25kt antimatter warhead. It's less effective because it has to get in close, but it's also much cheaper.

(Since I'm working at TL11 other tech assumptions probably aren't directly comparable, but it can force a fast pass in most situations.)

https://tekeli.li/wives-and-sweethearts/ship_hana.html

[Varyon]

Originally Posted by RogerBW

I have a similar design, but I noticed a trick: you can throw warheads from EM guns. So your SM+5 Ohka fires 5×3×16cm missiles with range X; my SM+4 Hana with a spinal gauss cannon fires 50 10cm EM rounds at range S, each with a 25kt antimatter warhead. It's less effective because it has to get in close, but it's also much cheaper

In addition to the reduced effective range (and the fact that nuclear warheads, which it appears OP wants to use rather than antimatter, require a minimum size of 16cm), there's also the problem that 10cm EM weapons have sAcc -7, while at TL10 16cm missiles have (presumably; my copy of SS only goes down to 20cm for missile sAcc for some reason) sAcc of +2. With guns and missiles not having their attacks penalized by Range*, that means an equivalent missile barrage will have an MoS 9 higher, for at least 4 more hits (more if the guns didn't hit on the number, as 10cm EM Guns have Rcl 4, while missiles have Rcl 2, when firing nuclear/AM warheads).

*SS "Guns" are more like "missiles that get a boost at the start." Also, something that's never made sense to me - if guns don't have to deal with Range, where the heck does their inherent sAcc penalty come from?

[weby]

Originally Posted by adimar

I don't really think so.
If you look at a missile as a standard craft given the 10mps,5g (standard missile performance)

I am not talking about standard missiles but instead something that can be shot in huge numbers at long range targets.

Maybe a design option could be added for heavy torpedo which has only Half the dV performance and is armored but that's not easy as well. An unstreamlined SM+2 (1 dTons) with all 6 frontal sections devoted to nanocomposite armor would have a 12 dDr frontal armor which when you take into account the (2) divisor of the laser weapon which might be barely enough to protect it from a 1d-2 frontal damage but is still totally vulnerable from the sides. (I can totally see missile defense boats parked a small distance from the capital ships who's all purpose is shooting the unarmored sides of these torpedoes.)
F[1-6] Nanocomposite 12 dDr
C[1-4] Fuel
C[5-6,c] Payload
R[1-4] Fuel
R[5-6] HEDM engines (4g, 4.8mps)
R[c] Control room

Adi

That is closer but a few notes:
-Really at those scales you should not use D scale and use I scale instead. At I scale the PD laser is 7d6 damage.
-The way GURPS armor is built armor as dice makes more sense. So proper armor to stop that AP 7d6 is hardened 7*3.5=25 or double that for non hardened.
-So a 1 ton vehicle adding 2 points to each location will have DR 40*1.2=48 all around so if hardened that is more than enough against even larger beam weapons.
-Payload is 0 units: Either you have no warhead and do collision damage or use a Mininuke from Ultratech that at TL 10 is 1 lb.

Thus if using HEDM: 1 control, 6 armor, 1 HEDM(as 2G was apparently enough to generate an intercept) and 12 fuel.

This weapon works as normal missile with slightly reduced performance.

But really more likely something like this: 1 control, 6 armor, 2 HEDM for final attack run and 9.9 fuel, 1 Plasma sail 0.1 power bank to start the plasma sail.

This weapon is fired from really far away based on data from huge sensor arrays then it flies towards the given point with mid-course corrections given as needed from home and then when it comes close it starts tracking the target and attacking independently. It has time to build a really high relative velocity and still have nice power for final attack maneuvers where the plasma sails are useless. When it hits the target using collision rules the half ton impact mass will punch through any realistic armor at those velocities.

Example:
Using Space ships formulas: attacking a 3 million ton 12 armor system dreadnaught with nanocomposite armor that ths has dDR 2160 will start to punch though at 5 mps relative speed: 6d*3*7(sm 2 vehicle)*Velocity means 2160/(6*3.5*3*7) is the required velocity =4.9 mps. anything over that does fast increasing damage. Note that this can be generated without the magsail against a stationary target, so with the magsail and an approaching target...

Using the full collision rules with the 1010 lb impact mass when the fuel is used up(worst case) the object has 41 HP. So damage on D scale is 41*"velocity yards/second"/1000 or solving for velocity with the 2160 as needed dDamage gives us velocity of. 52683 yards/second=29.9 mps, that is still fairly simple to get with some time and an approaching target with its own speed towards you. (a Further note just calculating the missile armor hitting the target would result in only 18.3mps relative speed needed)

And attacking smaller targets or less armored and you just devastate them...