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GURPS Spaceships for Intercept

Posted in Design system, Intercept, Rules on January 13, 2011 by Mr Backman

The GURPS Spaceships design system is a really neat and elegant system and those using it may want to play out battles using my Intercept rules. I am no expert in using GURPS Spaceships so there will be errors in my treatment, please comment or e-mail me so they can be corrected.

Sensors and signatures

GURPS Spaceships (from here on called GS) doesn’t have all the sensor types of Intercept so we must make some assumptions about that. Intercept Visual/IR sensitivity is GS sensor level -6, scientific arrays also have a Neutrino detector at GS sensor level -9 and Tactical arrays have Mass detectors at GS sensor level -10, and yes, the multipurpose arrays includes both of them. Intercept Radar sensitivity is 2 x (GS sensor level -6).

  • Visual / IR scan = GS sensor level -6.
  • Radar scan = 2 x (GS sensor level -6).
  • Neutrino scan = GS sensor level -9 if the ship has a scientific or multipurpose array.
  • Mass scan = GS sensor level -10 if the ship has a tactical or multipurpose array.

Signature modifiers

Use these modifiers when directed to in the text for each signature

  • Stealth sig = 2 x (TL – 6), ignore Chameleon systems.
  • Neutrino stealth = 2 x (TL – 9) if Stealth, ignore Chameleon.
  • Mass stealth = 2 x (TL – 10) if Stealth, ignore Chameleon.
  • Acceleration sig (<1.0G) = -1
  • Acceleration sig (1.0G+) = +0
  • Acceleration sig (3.0G+) = +1
  • Acceleration sig (10.0G+) = +2
  • Powerplant sig (1-2 powerpoints) = -2
  • Powerplant sig (3-9 powerpoints) = -1
  • Powerplant sig (10-29 powerpoints) = +0
  • Powerplant sig (30+ powerpoints) = +1
  • Thrust type sig = Use the GS IR signature modifiers, basically +6 for fission thrust and +8 for fusion thrust (GS page 44-45)

Visual signature

This is the signature from reflected light, either from the central star or from starlight. The central star has a Sun factor of +6 when the ship is in the hospitable zone, +1 for each orbit inwards and -1 for each orbit outwards of the hospitable zone down to a Sun factor of +0. Use the Visual(HullShadow) when the ship is in shadow of a planet.

  • Visual(Hull) = Ship SM – 6 + Sun factor (typically + 6) – Stealth sig
  • Visual(HullShadow) = Ship SM – 6  – Stealth sig
  • Visual(Thrust) = Ship SM + Thrust type sig + Acceleration sig (unaffected by Stealth)

IR signature

The IR signature comes from basic thermal radiation from the hull, the heat from any active powerplants and from reaction engines. The IR(Hull) signature is affected by proximity to the central star as +1 per orbit inside the habitable zone if the ship is not in planetary shadow.

  • IR(Hull) = Ship SM – 6  – Stealth sig +1 per orbit inside habitable zone if not in planetary shadow.
  • IR(Power) = Ship SM + Powerplant sig – Stealth sig
  • IR(Thrust) = Ship SM + Thrust type sig + Acceleration sig (unaffected by Stealth)

Radar signature

The radar signature comes from microwaves or ladar pulses bounced off the hull and back to the sensor. This two-way trip is why the scan size modifiers are doubled for radar.

  • Radar(Hull) = Ship SM – Stealth sig +2 if not streamlined

Neutrino signature

The neutrino signature comes from fission or fusion reactors in the ship or from fission or fusion rockets. GS doesn’t have neutrino stealth so we assume they come with TL 10+ Stealth tech.

  • Neutrino(Power) = Ship SM + Powerplant sig (ignore cosmic powerplants) – Neutrino stealth
  • Neutrino(Thrust) = Ship SM + Thrust type sig + Acceleration sig (unaffected by Stealth) (ignore if chemical, HEDM or electric) (unaffected by Stealth)

Mass signature

The mass signature comes from the ships mass, any operating contragrav lifters, artificial gravity and gravitic compensators. GS doesn’t have mass stealth so we assume they come with TL 11+ Stealth tech.

  • Mass(HullNoFloorfield) = Ship SM – 6 (if no artificial gravity nor gravitic compensators) – Mass stealth
  • Mass(HullFloorfield) = Ship SM (if artificial gravity or gravitic compensators) – Mass stealth
  • Mass(ThrustContragrav) = Ship SM + 6 (unaffected by Stealth)
  • Mass(ThrustReactionless) = Ship SM + 6 + Acceleration sig (unaffected by Stealth)

Movement and performance

Intercept is designed for the ships with 1-6 Gs of acceleration and enough remass to keep accelerating for a couple of hours, solar sail and Ion thruster ship will be sitting ducks in this system.

Combat and damage

One can use the hitlocation and damage rules for GURPS Spaceships as they are and only use the Intercept sensor rules. Fine, go ahead, but those who like the easier to use Intercept version should read on.

GURPS uses dDam based on square root of energy, dHP based on the square root of mass and dDP based on linear thickness. Intercept uses logarithmic DAM, DAB and ARM so this part needs some heavy converting. I will use the Intercept damage system as it is so much simpler to use so the GS values has to be converted into Intercept values. We know that when at least 10% but less than 50% hull HP is suffered in an attack the hull section is Disabled, if 50% or more is suffered the hull section is destroyed. When the ship as a whole has suffered 200% of original damage it must roll HT to avoid breaking up and if reduced to 600% HP it automatically is destroyed. How do we convert that into Intercept terms?

Let’s say that Critical damage (ie disabled) is at 30% of dHP then all the other damage levels follows as Light damage = 3%, Severe damage = 10% damage, 30% damage = Critical damage and 100% damage = Destroyed. Destroying the entire hull requires 300% damage and we ignore HT altogether. So where will our baseline be, what level of dHP equals DAB 0? To make a long story short I have already had the table in the oven for the customary 90 minutes, I’ll just put on my oven mittens so we can take a look at that freshly baked table.

Use the table below for converting just about everything into Intercept ARM, DAM and DAB. Look up your values in the dHP/dDAM column using the table value that is equal or lower than your GURPS value. Each D6 averages 3.5 which means that 14, 28, 140 etc will be short shifted in rounding so you might consider rounding 14 -> 15, 28 -> 30 etc. Oh, wait. I have a better idea: I fix the table for you!

 

 

 

 

 

 

 

 

 

 

 

Weapons

GURPS Spaceships weapons are a bit tricky as they cover such a huge span, even down to the slightly ridiculous shell firing guns. Intercept assumes lasers that  fire tens of thousands of kilometers even for small weaponry while GURPS Spaceships have much smaller ranges (GURPS Spaceships is probably more realistic that way but I needed weapons to fire effectively out to ranges where dodging from  lightlag would come into play).

We assume all 1/2D ranges from GURPS in miles to be ten times that in Intercept, in kilometers, 1000 miles becomes 10 000 km, the 1/2D range is the effective range in Intercept. Calculate the average points of dDam from the weapon (each D6 gives 3.5 points) and look up the corresponding DAM on the table above. GURPS use armor divisors instead of a separate PEN value so we start with a PEN value equal to DAM and then modify according by the armor divisor:

  • Armor divisor 1.5: PEN+1
  • Armor divisor 2: PEN+2
  • Armor divisor 3: PEN+3
  • Armor divisor 5: PEN+4
  • Armor divisor 7: PEN+5
  • Armor divisor 10: PEN+6

Hitlocation

Intercept uses a simple hitlocation system with six locations while GS has three sections with six locations each, plus two core systems added as an obvious fudge to keep each system 5% of hull mass. We will keep the GS hitlocations and add our own rules on how to hit them. In reality we will need two hitlocation systems for GS, one for regular combat and one for the optional deterministic system.

The regular system simply have you roll 1D6 and adjusting what six hull sections can be hit based on the direction of the attack. This is basically the same as in GS with the addition of Front left/right direction with hits half in the Front section and half in the Central section, and the Rear left/right direction where half the hits goes into the Central section and the other half into the rear section. This system makes the top three Front hull systems and the bottom three Rear hull systems less likely to hit.

The Deterministic (diceless) system uses the same tables below but with the following changes:

  • Fair hit The target picks the section among the six eligible from that attack direction.
  • Good hit The attacker picks the section among the six eligible from that attack direction.
  • VGood hit The attacker picks the section among all 20 hitlocations. Yes, he can even choose one of the two [core] sections.

Front

  • 1 Front hull 1
  • 2 Front hull 2
  • 3 Front hull 3
  • 4 Front hull 4
  • 5 Front hull 5
  • 6 Front hull 6

Front Left/Right

  • 1 Front hull 4
  • 2 Front hull 5
  • 3 Front hull 6
  • 4 Central hull 1
  • 5 Central hull 2
  • 6 Central hull 3

Side left/right

  • 1 Central hull 1
  • 2 Central hull 2
  • 3 Central hull 3
  • 4 Central hull 4
  • 5 Central hull 5
  • 6 Central hull 6

Rear left/right

  • 1 Central hull 4
  • 2 Central hull 5
  • 3 Central hull 6
  • 4 Rear hull 1
  • 5 Rear hull 2
  • 6 Rear hull 3

Rear

  • 1 Rear hull 1
  • 2 Rear hull 2
  • 3 Rear hull 3
  • 4 Rear hull 4
  • 5 Rear hull 5
  • 6 Rear hull 6

Miscellanea

Example Star-Flower class Tramp Freighter from GS [TL 11^] The Star flower is a SM +8 design so the ships signatures will be the following:
Visual(Hull) = +8 (SM – 6 + Sun)
Visual(HullShadow) = +2 (SM – 6)
Visual(Thrust) = – (the standard reactionless engines give off no visual signature, except maybe the cheesy blue glow CGI artist add to every ships they lay their hands on)
IR(Hull) = +2 (SM -6)
IR(Power) = +6 (SM -2 for the two power points from the fusion reactor)
IR(Thrust) = – (the standard reactionless engines give off no IR)
Radar(Hull) = +8 (the ship is streamlined so it gets no extra +2)
Neutrino(Power) = +6 (SM -2 for the two power points from the fusion reactor)
Neutrino(Thrust) = – (the standard reactionless engines give off no neutrino signature)
Mass(HullNoFloorfield) = +2 (this is if the ship has its artificial gravity off )
Mass(HullFloorfield) = +8 (this is when the ship has its artificial gravity on)
Mass(Thrust) = +14 (the 2G reactionless drives gives off a strong mass signature)

The ship sensors are as follows:
Visual sensitivity = +4 (GS sensor level 10 – 6)
IR sensitivity = +4 (GS sensor level 10 – 6)
Neutrino sensitivity = – (the ship lacks scientific array)
Mass sensitivity = – (the ship lacks a tactical array)

Next comes the ships sections ARM and DAB and its weapons DAM and Effective range:
Ship ARM  = 9 (dDR of 7 gives us ARM of 9)
Ship DAB = 8 (dHP of 70 gives us a DAB of 8 for the entire ship)
DAM = 11 (we convert the 10 MJ laser turret’s 4D6 to 14 dDam)
PEN = 13 (PEN is the same as DAM modified by the armor divisor of 2 which gives us PEN+2)
Effective range = 1 square (we use the tables in GURPS Spaceships 3 using the 1000 mile column as our 10 000 km).
There is no maximum range in Intercept, the PEN and DAM just go down by -3 for every rangeband beyond effective.

Using Imperial units for Science Fiction is like using Roman numerals for physics. The metric system has been with us since the French revolution, when will you colonials catch on?

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Playthrough session

Posted in Intercept on December 12, 2010 by Mr Backman

Me and Cicci played out a battle between a TL 14 Scout on one side (with a single large laser in its turret) versus a TL 12 Subsidized merchant and it’s Launch. In our Traveller game she usually flies a Scout while my kids have a Subsidized merchant and a Launch, this was a test to see if the low tech Sub and launch could actually beat the Scout.

Both sides started secretly at the top or bottom box rows of the map (yes, they could have started on the same row, even the same square). The Sub was to touch any square adjacent to the planet and then exit out the same map edge it came from, the Scout was to stop it from doing that. We used the new 3.1 sensor rules which was much easier than the old  ones to use. The Scout spotted the Launch early on but didn’t see the Sub until it was close to the planet (I was drifting the Sub most of the time to save on Visual/IR signatures and also to save on fuel). The Scout shot out the Subs’ powerplant and the Launch killed the Scout’s thruster. The Sub could limp back out as its fusion drive requires no power, leaving the crippled Scout in orbit around the planet. Marginal victory for the Sub and Launch.

The game (as always) made for some changes in the rules and components. The main change was that the hybrid hitlocation system could somewhat unfair, a higher degrees of success should always result in equal or better options but that was not the case for the poor Scout player. She attacked the Sub from its RearLeft arc and as she got a Good hit the rules forced her to hit the Powerplant. Had the hit been fair she would have rolled randomly and had the hit been VGood she would have picked the location but a Good hit forces a certain hitlocation, in this case pretty much the worst location as neither weapons nor thrust relies on power in a Sub. I rewrote the hitlocation rules as follows:

Regular hitlocation

  • Fair hit Roll hitlocation
  • Good hit Attacker choose to roll or use facing
  • VGood hit Attacker picks hitlocation

Deterministic hitlocation

  • Fair hit Hitlocation based on attack facing
  • Good hit Hitlocation based on attack facing
  • VGood Attacker picks hitlocation

The big mapboard should have sensor boxes on the to make it easier to go between the boards. Not an important change for sure but still needed I think. I also added the option to make missiles with longer endurance at the expanse of thrust, this option can be used together with the coldstart option. Missile versions:

  • Regular Performance and as stated, price as stated.
  • Cold start Subtract 2G from thrust and double price.
  • High endurance Subtract 1G from thrust, double the endurance but keep price. Reduce PEN and DAM by -2.
  • Cold start high endurance Subtract 3G from thrust, double the endurance and double the price. Reduce PEN and DAM by -2.

Aerobraking never entered into the fight but I kind of liked the older version better, the one before the 3.1 update. I think I’ll go back to the more accurate and more complicated version, mainly because the chance of crashing into the planet goes up. If one cannot see through the planet one shouldn’t easily fly ‘through’ it either.

The final change was to add back in the very first integration rules where you get a cumulative +1 in Scan for each subsequent scan with the same ship, sensor and scan area. This integration bonus can never go higher than +3 and must be from the same ship and sensor type and it must be continuous from turn to turn. Actually, this rule highly overstate how well integration time behave in reality, realistic rules would give you +1 after 10 turns of integrating, +2 after 100 (yes, that’s more than a full day), one could rationalise this by assuming that the scan is actually concentrated on the parts of the scan area with better signal to noise than the average. The real reason for doing it this way is to give the playef a way to boost signal a bit, if you have the time and the target is stupid enough to linger.

After playing we looked at each other’s plotting traces and Cicci showed how sneaky/munchkin she can be. She deployed at the narrow, rightmost square-column knowing I would never waste scan area there and also helping her avoiding the sun direction. Sneaky! maybe I should shave off any partial boxes from the small plotting map? All the changes except adding boxes to the large map have been added to the Intercept bundle (including a fix for the sneaky trick Cicci discovered).

Favourite unit for space combat calculations: Rick, one Rick equals about 3 km/s and it’s the speed where matter has the same kinetic energy as TNT.

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Sensor rules 3.1

Posted in Intercept on December 2, 2010 by Mr Backman

Ah, finally something new at this website! My excuse; well, mostly work actually but I have also been fiddling with some En garde inspired rules for Traveller which I will post here whenever I have enough stuff written.

I have playetested Intercept with my girlfriend mostly but also with some of my colleagues at work and certain errors cropped up regularly enough to warrant investigation. Intercept is a double-blind system without a referee so it requires a great deal of trust between the players. If a player does his scanning wrong it is hard to detect the error until after the session when the players typically look at each other’s plotted maps. The errors were of three kinds:

  • Coordinate errors People weren’t as used to cartesian coordinate systems as I thought they’d be. If one could merely point at the box or boxes scanned on the common map a lot of errors would go away.
  • Planet LOS errors The planet Line-Of-Sight rules were hard to do right as one had to match the square scan against the jagged blocked arc.
  • Aerobrake errors We had only a few of those because aerobraking is so rare but whenever a player tried such a stunt the chances were high that he would do it wrong.

Coordinate improvements

The plotting map is now divided into 5 square x 5 square areas called boxes. These boxes are easy to see on the map and if player A says he scans in the x = +5, y = +15 box (or simply points at the box on the common plotting map) the other player can easily check if his ship is inside or outside of the box. No more counting on scan radii to see if one is inside or not (or using the my custom-made plexiglass scan guides). Scanning individual squares (either 1 x 1 or 3 x 3 squares) require a bit more scrutiny but the 3 x 3 square scans can only be done in the same or adjacent boxes of the scanning ship and the 1 x 1 square scans can only be performed inside the scanning ship’s box itself. These small scans are rarely used and are dead giveaways to the scanner’s own position and as they are so rare the players can agree beforehand to not allow them if you both feel they add too much complexity.

Planet LOS changes

Planet LOS is much simplified thanks to the addition of map boxes. Check what arc of the planet the scanning ship is in and the boxes along the opposite centerline are illegal for scans. If a scan includes the central box containing the planet the scanner must tell his opponent what arc is blocked, the arc opposite of the scanner’s arc that is. Yes, scanning the central box gives the opponent more information that before but that is a small price to pay for a much simpler LOS system with far less errors. If you are scanning the tiny 1 x 1 squares or 3 x 3 squares you still have to abide the old rules which simply states that the scans cannot include squares in the opposite arc from the scanner. As 1 x 1 and 3 x 3 square scans are so rare one could agree on not allowing such scans if you both feel they add too much complexity.

Aerobrake changes

Aerobrake manuevers are typically done before being spotted as it allows you to slow down the ship while still being stealthy (no large Visual, IR, Neutrino or Mass signatures from the drive) and must therefore be easy to do without asking your opponent how it works. The new aerobrake rules uses requires the ship’s Present to be on the planet for aearobrake to take place, if the ship merely crosses the planet square it has flown above or below it. A ship can actually maintain a steady polar orbit by jo-jo-ing back and forth across the planet as long as its Present never end up on the planet.

The singularity; Rapture for nerds – Ken MacLeod

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Guy Fawkes update

Posted in Intercept on November 7, 2010 by Mr Backman

Well, I missed posting the 5:th of November but I decided to keep the heading regardless.

I have added a page where all download links for Intercept are kept together so you don’t have to click around for them (all downloads are also available in the links section to the right). Aside from this blog maintenance I have made some changes to Intercept itself, large enough to warrant a new version number (3.1.0). The rules book and design system files including all the ready-made designs have been updated with the new rules.

Sensor scanning have been simplified with the introduction of boxes, read the Sensors rules section to learn how to do sensor scanning the new way. I have also changed how Mass(Hull) signature work; ships lacking floorfield or having their floorfield turned off now have a much reduced signature. I also removed the Idle power rules; powerplants are now at full power or completely off.

As a side note: My family have a tradition of blowing up the parliament every 5:th of November in honor of Guy Fawkes and the V for Vendetta movie. We do this by making a model of the british parliament building and then blowing it up with fireworks. Great family tradition for us, a bit creepy for onlookers. My daughter Josefin came up with the idea when she was ten (spoken in a suitably proud fathers voice).

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