Archive for the Design system Category

Changes to Intercept

Posted in Design system, Intercept, Rules, Traveller on April 8, 2013 by Mr Backman

Some of you may not know it but I keep doing updates to the rules, maps, datacards and design system on a regular bases, just download the Intercept bundle here. Quite a lot of updates have accumulated without andy update posts but I will try to summarise the most recent changes below. To see what version you have simply look at the headings row of the design system for version date. I always update Ship.xls and Data.xls in tandem.  You can see the version of the Data.xls where you see the Ship.xls version number.  To update your designs you need to copy each column labeled Edit from your old design and paste* it into the new Ship.xls, then close the old design and save Ship.xls as the old designs name overwriting it. When you paste it is much safer to do the Paste->Paste values to ensure that you won’t overwrite and formatting.

Updating the Ship.xls sheet

All kinds of thrusters now correctly reports their actual thrust, the two values are Loaded / Unloaded performance. The Mtrl type field now goes from 0-3 with ever decreasing masses for most of a ships components. If you find your designs too low in acceleration and delta-V you should increase your material types to lighter but more expensive versions.

Editable Sun factor

Sun factor
There is now a light yellow field for the Sun factor. It should be easy to recalculate Vis(Hull) and IR(Hull) for other values of the Sun factor but now you can simply enter the value you want in the yellow box. Sun factor is +6 in the life zone of a solar system and goes up by 1 for each orbit inside and down by 1 for each orbit outside down to Sun factor 0. Mercury is +8, Venus is +7, Earth and Luna is of course +6, Mars is +5, Asteroid belt is +4, Jupiter and its moons are +3, Saturn and its moons are +2, Uranus and its moons are +1 and Neptune and its moons are 0. Pluto isn’t even a planet but as its orbit is never much closer than Neptune it is always 0 in Sun factor. Ships in Planet shadow subtract the Sun factor from Vis(Hull).

Living space
Living space and Life support determine the quality of life for the crew past the endurance of its crew stations. More living space per crew member means longer trips without physical or psychological effects. This is mostly here for roleplaying uses but if you design your own ships for competitive play make sure yiu stipulate the expected trip time requirements, ships using Jump drives should have at least one week endurance as this is the time the ship spends in hyperspace. Note that the Closed Lifesupport option requires lots of room for the green house but that entire volume is also treated as Living space and this is reflected on your ship designs.

Living space and crew comfort table

  • 1 m3 per crewmember Cramped 1 day cruise
  • 2 m3 per crewmember Normal 1 day cruise
  • 5 m3 per crewmember Roomy 1 day cruise
  • 10 m3 per crewmember Cramped 1 week cruise
  • 20 m3 per crewmember Normal 1 week cruise
  • 50 m3 per crewmember Normal 1 month cruise
  • 100 m3 per crewmember Cramped 1 year cruise
  • 200 m3 per crewmember Normal 1 year cruise
  • 500 m3 per crewmember Roomy 1 year cruise

Well, that is all for this update, more to come regarding the rules changes later (when I will also document the polar plane gravity sling stealth manuver sometimes called the Marre Red).

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!













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


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.


  • 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
  • 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


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


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?

Gravity in boardgames

Posted in Boardgames, Design system, Intercept, Other vector movemet systems, Scenarios on May 13, 2010 by Mr Backman



Space combat games are typically played on black hexgrids with no terrain features at all. Some games add asteroid fields, planets, nebulas, electric storms etc and some even try to incorporate the gravity field around planets. This is at least something we know, real planets do have gravity fields around them and climbing up the gravity well takes serious effort; just look at how big the Saturn V needed to be in order to send three guys to the moon and back.

What can we say about gravity then? Well, it pulls you back toward planets, a ship can remain indefinitely in orbit without thrusting, the higher above the planet a ship orbits the longer it takes; 1.5 hours in low orbit, 24 hours in Clarke orbit and a whole month per lap when you are as far away as the moon. We also know that if a ship has enough speed it can escape the gravity of a planet, this speed is called escape velocity for obvious reasons. Orbits don’t have to be circular either, they can be elliptical with one part getting real close to the planet and the other part taking it back further out, these orbits are also stable and require no thrust to maintain.

Prior examples

The first boardgame I came across that used vector movement was also the first that tried to depict gravity in a sensible manner, that game was Mayday. Mayday borrowed its gravity rules from Triplanetary and the mechanics where simple: If your vector, including its endpoint but excluding its startpoint, intersected one or more hex adjacent to a planet its future position would be affected. Another game with gravity rules was a game called Orbit war that was published in the Space gamer and then became a full blown boardgame.

Intercept version

In Intercept we want to do more than just being in orbit or not. Having several stable orbits with different periods allow us to model low tech orbital warfare with limited endurance fission/fusion rockets and spotting limited by the horizon. We can do elliptical orbits but that is something that just happen to work, free chrome one could say.

How do you do gravity in Intercept then? If your ship is inside a planet’s gravity well (6 squares for Earth) check what arc of the
planet you are in and adjust your drift in the direction of your current position towards the planet. Yes, gravity pull is based on the
position of your ship versus the planet but applied on the drift of your ship. If your ship is on the planet itself you do not adjust for
gravity (what direction would that be?).

That is all folks; if the ship is inside the gravity well but not on the planet you note the direction towards the planet and move your drift in that direction.

Scenario: Fission duel

This is a simple scenario with two equal ships battling it out in orbit above a planet. the ships start in the same orbit on opposite sides of the planet knowing where the opponent is but they cannot track him because the planet blocks LOS. The ships are 1G fission thrusters with 8 turns of thrust endurance and they are armed with a single small missile turret. You must carefully maneuver your ship close enough for your missiles 2G range single turn range. The ship has a crew of two; 1 pilot and 1 gunner/sensor op, there is no repair crew so there can be no repairs. Use the orbit from the image, ship A starts at x=0, y=-1, ship B starts at x=0, y=1 with the drift positions as shown. As I said earlier, this scenario is especially suited for deterministic play.

Gentlemen, start your fission drives, let the duel commence!

Major victory: Your opponent is a mission kill (incapable of firing and incapable of maneuvering) and you manage to land on the planet.

Minor victory: Your opponent is a mission kill and you are not.

Draw: Both ships incapable of maneuvering  and in such orbits that they will never get within 2G of a missile shot.

Make your own TL 8 Fission thruster equipped ships, equal or custom designed by each player. 100 MCr each is my suggestion for price.

Intercept bundle update

Posted in Design system, Intercept, Rules on April 29, 2010 by Mr Backman

I have made some changes to the rules, mostly regarding Sensors. There were also some changes to the missiles, especially the larger ones. These changes are in the new rulebook as well as the new Data.xls file. Just replace your old Data.xls with the new one and all your designs will be updated. You can download the Intercept bundle here. Sensors had some changes in terminology and how radar works, the integration bonus rule also changed. Missiles now have a -2G penalty for being cold launch instead of the -1 before, and the larger missiles endurance was reduced, the missiles also got longer control range to fit the range bands. The initiative rules was cleared up a bit and a tie breaker for better control stations was added (Bridge stations > Full stations > Limited stations, mostly to rationalise why warships have such large bridges).

I have not made any changes to Ship.xls as such updates are more troublesome for my users. When I get around to it I will add a Very large turret option (taking x10 the Large turret of weapons) and adding a Very small laser of 5 MW mainly for use as point defense against missiles. I should also do something about fuel purifier, skimmer, cracker, and methane converters. These babies would allow a ship to store liquid Ammonia or Methane instead of the usual liquid Hydrogen to pack more fuel per m3. The drawback would be that you must convert it into hydrogen before you can use it for the jump drive. My take on the mysterious Fuel purifier is that Jump drives use hydrogen not as fuel but as matter to build up the jump field, and that Hydrogen that has been purified from Deuterium and traces Helium etc work better. Finally, I should also add some kind of energy storage banks so you can build ships that must power up their banks before they can fire, Attack vector style.

If someone wants anything added, changed or explained please use the Comment feature, I will gladly answer any questions regarding Intercept, I am a bit surprised about the lack of comments given the number of downloads and views. Come on guys and girls, don’t be shy.

Move along, there is nothing interesting here. I am a perfectly normal human worm-baby.