In what will be the last post of this series on spacecraft combat, we’ll be looking at two SDVs duelling. Both are essentially identical except for their main armament: One mounts a particle beam, the other one a railgun.

I’m using SDV90s for that, which are about 21,000 tons loaded, have 1961cHP and are SM +6 or +11 (front/side). They have an acceleration of 0.22g (52km/s), 0.86g (10km/s), or 2.15g (3.5km/s). Their armour is 55/5/16, wih a cPF of 10/1/2 (except for the bridge module, which has cPF of 1,000).

One (Röntgen) is armed with a 350’ particle accelerator (which does 6dx200 rads from the front and 12d rad for the bridge). The other one (Newton) mounts ten railguns instead, each of which does 1.12d(3)xV damage - it therefore just manages to do some damage at default closing speeds, but needs a closing speed of 2km/s do at least do some damage.

Both are also armed with four heavy lasers, eight heavy laser towers, and ten light lasers, plus three coilguns.

The Scenario

As before, we’ll start at extreme range, which is 12,000 kilometres, and at a closing speed of 5km/s - this means an encounter in 40 minutes or 25 space combat turns.

Except that the SDV can manoeuvre. Newton will probably aim to close the distance. As before, Röntgen cannot avoid this - she would need to point her back towards Newton, and the heavy lasers can penetrate the back armour. Also, this would mask the particle beam.

Newton therefore starts accelerating in her medium gear; this is 0.89g. She will do so for six turns, which costs her half the available dV, then continue accelerating at 0.22g. In total, she’ll spend 28km/s during the engagement.

Röntgen will start.

Turn 1

At 12,000 kilometres and extreme range, the only relevant weapons are heavy lasers to scour the surface clean. Therefore, gunnery rolls are irrelevant (except for critical successes; none of them rolled any). Each of the SDVs has a total of 12 heavy lasers. Röntgen rolls five 1s and one six, removing one ksf of hull radiator from Newton and destroying five heavy lasers. Röntgen takes 137.5 heat points, and has 612.5 remaining.

Newton rolls one six and one one, destroying one heavy laser and one ksf of hull radiator. She fires ten railgun bursts; these will arrive on turn 16. They cannot be evaded through acceleration. Newton takes 152.5 heat points and has 657.5 remaining.

Turn 2

11,500km, still extreme range. Repeating last turn’s exercise, Röntgen now fires her remaining 11 lasers, destroying five more lasers and 4 ksf of radiator. Heat points now at 474 remaining.

Newton only has two heavy lasers remaining; these roll a single 6 and remove another ksf of radiator. 456 heat points remain. This turn’s railgun salvoes will impact on turn 14.

Turn 3

At 10,900km, we’re still at extreme range (and will remain so until turn 6). All of Newton’s lasers are now destroyed, together with another 6 ksf of radiators. This pushes heat points to 316.5 remaining; however, Röntgen can now extend her normal radiators again. This will take effect next turn.

Newton fires her railgun; those 20 bursts will also impact on turn 14. 293.5 heat points are remaining.

Turn 4

Distance is 10,200km. Since Newton does not have any lasers left over to attack Röntgen with, Röntgen has extended radiators and is starting to cool down again. Röntgen now begins firing at the incoming salvoes.

For this, I’m instituting a rule simplification: A railgun burst is either full-strength, half-strength, or destroyed. A successful point defence roll destroys a full-strength or half-strength burst; if you fail your point defence roll by five or less, you reduce a full-strength to a half-strength burst, and if you fail it by more than five, you don’t damage it at all.

Anyway, this makes twenty bursts to arrive on turn 16 and 40 to arrive on turn 14. Röntgen has three failed rolls on her 11 lasers, eliminating 9.5 bursts. 30.5 remaining in the turn-14 slot.

Newton also has to extend radiators and hopes that Röntgen will be too busy to target them. It also adds yet another 20 bursts, this time to the Turn 13 slot.

Turn 5

Distance at 9,500km. Last turn at extreme range. Röntgen’s heavy lasers all hit, eliminating all but 9 of the Turn 13 bursts.

Newton yet again adds 20 more bursts to Turn 13.

Turn 6

Distance at 8,600km. This turn, it’s on! First, Röntgen can now defend with an additional ten light lasers. At two failures, it eliminates 20 bursts - it barely manages to hold on!

And now, for the particle cannon. At 350’ and against a cPF of 10, it does 6dx100 radiation damage, and 6d against the protected systems. That’s 2200 rads against everything, and 12 against the bridge.

Newton adds 20 more bursts for Turn 13.

Turn 7

Distance at 7,600km. Röntgen’s defence yet again eliminates 20 bursts. Its particle cannon fires again, doing another 900 rads and bringing the total to 3,100.

Newton yet again adds 20 bursts for Turn 13. This is the last turn she’s accelerating using medium gear, and internal gravity drops from 0.89g to 0.22g.

Turn 8

Distance is 6,600km. Röntgen slowly makes headway, killing 20.5 bursts. 8.5 remaining in the Turn 13 bucket. Its particle cannon increases Newton’s rads to an even 6,000. We now roll to check for disabled systems. That’s 3, 2, 2 for coilguns (none eliminated), 1 for the drive, 2 for the reactor, and two disabled sensors. Two railguns are disabled, too.

Accordingly, Newton only adds 16 bursts for Turn 13.

Turn 9

Distance is 5,500km. Röntgen fails four times, one of them critical, and only eliminates 18.5 bursts. This leaves 6 in the Turn 13 bucket. Its particle cannon adds another 2,200 rads, for yet another turn of electronic damage. Another two sensors are eliminated, but no railguns are.

Newton restocks Turn 13 bucket to 22 bursts.

Turn 10

Distance is 4,500km, and Röntgen reduces turn 13 bucket to 3.5 bursts. The particle cannon adds yet another 2,600 rads, but this is not yet enough to cause a damage roll.

Newton adds another 16 bursts.

Turn 11

Distance at 3,500km for the first turn at effective range: Normal particle cannon damage! Röntgen fails eight times and turn 13 has 2.5 bursts remaining. Particle cannon adds 2,400 rads for a total of 13,400. Damage roll! This disables the reactor. But that’s okay - we have left-over power because all of our lasers are gone. It also eliminates another railgun.

Newton adds another 14 bursts. This is going to be close!

Turn 12

Distance is 2,300km. Failing twice, Röntgen eliminates all of the turn-13 bursts and one of the turn 14 ones. Its particle cannon adds 4000 rads; another damage roll. This kills nothing, though.

Newton fires 14 bursts, which will arrive next turn.

Turn 13

Distance now at 1,100km. Röntgen fails twice, which eliminates all of the incoming bursts and another two for next turn’s (bringing this down to 28.5). 5200 rads bring the total to 22 600 and doesn’t do any damage either.

Newton adds fires her last salvo of 14 bursts.

Turn 14

Encounter. First, 19 burst are eliminated, for 23.5 remaining. Emergency manoeuvre! Röntgen is in high gear, accelerating madly at 2.15g. That costs 60% of her dV! Final modifier is +12 (acceleration) - 11 (SM) for +1; four salvoes hit. Two of these are from Turn 2 and move at 9km/s, the other two are from the last turn and move at 15km/s. They do 10d(3) and 16d(3) damage respectively. Effective armour is 18, and 14 and 24 damage penetrates from the first two. This is multiplied by ten for after-armour effects and causes a total of 380 injury. The other two bursts do 29 and 34 penetrating damage and increase this to 1 010 damage. This is slightly over fifty percent damage and means five major damage rolls. These disable the particle beam, kill two crew members, and disable two heavy laser towers.

The following turns

Röntgen should still be easily able to eliminate the last incoming salvo and then disable Newton at her leisure.

Note that, contrary to the relatively “clean” description above, conditions on board both spacecraft are probably quite horrible: Röntgen suffers from several gaping holes which have halved sAcc. On the other hand, all people outside a storm shelter on Newton have taken 22 600 rads. To quote THS,

A dose of over 4,000 rads induces cerebrovascular death: Within an hour, the victim loses 2 hit points and 2 IQ, and rolls vs. HT to stay conscious. Repeat every hour. Other symptoms include diarrhea, vomiting, dizziness, low blood pressure, stupor, incoherence, hyperexcitability, loss of coordination, and uncontrollable trembling. Unconsciousness is followed by convulsions and then death (when IQ or HT reaches zero). Any single dose of 200+ rads also causes sterility and blindness for a few months; a dose of 500+ rads makes it permanent.

That is very gruesome, and requires everybody to remain in the storm shelter. In there, they have taken a total of 220 rads. That’s “only” enough to cause temporary sterility and blindness, and they have to roll against HT at -5. On a success, they suffer from radiation burns and lose 1d of ST, DX, and IQ for several days, on a failure they also lose 4 HT permanently, suffer from several disgusting gastrointestinal things, and need hospital care for probably a month or so.


In summary, this seems interesting. It’s actually quite close - the Newton going first would probably have caused it to win, although with roughly the same damage - each additionally disabled laser would have caused several more kinetic hits.

Bonus Round: Original Railgun

The above is with the railgun generated from 3e Vehicles. But what happens if we use the (slightly modified) railgun from Deep Beyond? I’m assuming similar guided weapons available with 1km/s dV and half damage (4dxV). Newton then mounts four of these.

The first change is that the first bursts impact on turn 7 instead of turn 13. Also, since there are only eight bursts per turn instead of 20, point defence is sufficient to deal with all of them.

If it weren’t, one hit would do 4dx20, for example 280 damage, of which 225 penetrates and which kills the target (2250 injury). So, these are extremely dangerous, but can be defeated by sufficient point defence.

This suggests the main tactic is using your own lasers to eliminate the enemy’s, then finish the target with the railgun. Although, given the numbers (two lasers needed per enemy railgun), you trade-off pretty exactly in spaces if not mass or energy. Quite interesting, and it sounds fairly engaging.