Archive for January, 2021

Avoiding heat worked example

Posted in Intercept with tags , , , on January 31, 2021 by Mr Backman

The players consist of a recently recruited crew aboard the SDB Bigfoot in the Mertactor system of the Spinward marches. Mertactor lies at the edge of the Imperium and the Sword worlds federation just a dozen parsecs coreward, with the Fifth frontier war ended 5 years ago the tensions run high. The players are ordered to travel from the main world of the Mertactor system (unimaginatively named Mertactor) to the planet Ember orbiting closer to the star. This will be a worked example using the system travel maps and the heat damage system, the maps and rulebook can be found here.

Mertactor Traveller map

Mertactor system

The star of Mertactor runs slightly  hotter and brighter than our sun so the hospitable zone is further out. For the purposes of this example we assume the system consist of these planets:

  • Orbit 1 (0.4 AU) Heat +3 (Mertactor 1), a semi molten asteroid
  • Orbit 2 (0.7 AU) Heat +2 Ember, like Mercury, destination
  • Orbit 3 (1.0 AU) Heat +1 Penelope, like Mars but much hotter
  • Orbit 4 (1.6 AU) No heat Mertactor, the main world, starting point
  • Orbit 5 (2.8 AU) No heat (Mertactor 5), uninhabited asteroid belt

Mertactor inner system

Flying route

The referee show the players were the planets are on the system travel map (we use the inner system travel map with each square being 0.1 AU and each turn is 12 hours, 2 turns per day). It is time to start planning the trip. The crew debate whether flying straight towards Ember as fast as possible or avoiding the heat from the sun is their best option.

The pilot and tacticians argue for flying in a straight line, accelerating half the time turning around and decelerating the other half, the way system travel is depicted in Traveller. The repair crew veto against this however saying she don’t think the command will be very happy if they damage the ship getting there . The pilot counters by saying that these repairs can be done en route. She counters with “I’m not going out on the hull while we are pulling 3G and give my ass cancer from the solar wind!”

After some debate the pilot start plotting a route that will minimize the time the ship is inside orbit 3 to reduce the risk of heat damage.

Mertactor plotted route

The plotted route

The plotted route will bring them to Ember in 5 days and 12 hours and only 1 day (two 12 hour turns ) will be inside orbit 3, the last turn will be either landed on the planet or staying in its shadow. The pilot is pretty pleased with himself but the last segment parts of the trip could probably be improved (can you do better?).

Turn 9 will take them inside orbit 3, 4 days and 12 hours into the trip. Turn 10, 5 days into the trip will bring them on orbit 2 at high speed so they’ll need another turn to slow down to zero. This is the way you land on planets; move your ship onto the planet (you have not yet landed) and on the next turn thrust have your ship on the planet two turns in a row (you have now landed). If you move onto a planet and won’t slow down to zero the next you won’t crash on the planet as the system travel map squares are much much larger than the planet, there is plenty of room by the sides (the inner system map we use have 15 million km squares but a large planet like Earth is ~10 000 km in diameter and even a large gas giant is ‘merely’ ~100 000 km in diameter).

So, shall we roll for heat damage then, for turn 9 and 10 but not 11 as that turn have them landing on Ember itself and the recruits had enough sense to land on its dark side where the entire planet protect them from the sun.

Mertactor plot rolling heat damage

Heat damage

On turn 9, 4 days and 12 hours into the flight, we go inside orbit 3 and might take heat damage. Actually staying on the orbit line itself is also considered to be inside the orbit, this makes perfect sense as the planet themselves are ‘on’ the orbit track’ and should be included for heat and sun factor considerations.

Can we do anything to reduce heat damage? There are two ways to reduce heat, Sunstance or power radiators and we’ll look at both them in turn.


The ship must be streamlined or airframed to adopt the Sunstance, ‘normal’ or open frame hulls may not. Sunstance consist of the ship facing the sun and be popped in (which means you cannot scan using Visual, IR or Radar and you cannot attack with your weapons, you will keep your tracked targets if any and you can still control already launched missiles except attacking with them). The argument why this works is that a streamlined or airframed ship is built with a small frontal cross section reducing the amount of heat transferred from the sun.

  • Sunstance modify Heat by -1

The Dragon class SDB is streamlined and their thrust makes them face towards the sun so if they pop in their sensors and weapons they can do this. The crew decide they are far enough from Ember to risk popping in their sensors and going blind (2 squares or 30 million km, nearly 80 times the distance from Earth to the moon). They wouldn’t see much even if they tried (and were much closer) as they would stare straight into the sun with their sensors if they did.

The SDB will use Sunstance on turn 9 but not turn 10 and they won’t face the sun that turn.

Powered off radiators out

Powerplants generate huge amounts of power which must be bled off into space or the ship would melt and the crew would fry. The more power per volume of ship the less protected the radiators can be, this is classified into three categories of radiators; protected, vulnerable or fragile. When a ship power down the powerplant they pop in the radiators to make it less vulnerable but if a ship power off their plant but keep its radiators extended they can use the radiators to cool the ship from Heat.

  • Protected radiators modify Heat by -1
  • Vulnerable radiators modify Heat by -1
  • Fragile radiators modify Heat by -2

The Broadsword class SDB has a huge powerplant and its radiators are fragile. The problem is that the ship uses powered thrust so they cannot thrust and use their radiators to bleed off heat at the same time, when the powerplant is on the radiators are fully occupied with shedding the heat generated by the powerplant itself.

The SDB won’t cool using Powered off radiators out as they need power to thrust.

Rolling heat damage

Rolling heat damage

One should only roll heat damage if the ship is in sunshine (not landed on the Darkside of a planet or asteroid and not in the shadow column of a planet or asteroid) and the orbit modifier is +1 or more (and thus the Sunfactor is 7 or higher). The damage is rolled at the end of the turn and is only affected by the ships state at the end of the turn. This means that even if the ship did some fancy turning after thrusting trickery, as long as it end up popped-in and facing the sun the Sunstance modifier apply.

Where the heat damage occur, if any, depends on in what direction the ship is facing: If it faces towards the sun roll 2D6 and use the lowest, if the ship is facing away from the sun roll 2D6 and use the highest, in all other cases simply roll 1D6 for location.

  • 1 Hull Mechanical repair from outside the ship
  • 2 Crew Mechanical repair from inside the ship
  • 3 Core Electronic repair from inside the ship
  • 4 Surface Electronic repair from outside the ship
  • 5 Power Engineer repair from inside the ship
  • 6 Power Engineer repair from outside the ship

As heat damage is rolled every turn we roll the damage roll differently depending on the turn length we use. Look up the turn length on the left table and then roll with modifiers applied on the right table. 

Turn 9 heat damage

The SDB is thrusting towards the sun using Sunstance. As the ship is facing the sun hit location is rolled using 2D6 and using the lowest.

SDB roll a 1 and 6 and use the 1, a Hull hit.

We have a Heat modifier of +1 from orbit 3 and -1 from Sunstance. The turn length is 12 hours so we roll 2D6 and use the highest , a result of 6 uses exploding dice but no matter how many 6s that came up in the original roll, you still roll exploding dice by rolling 1D6 and add the result divided by 2 rounded down, keep rolling if you got a 6.

SDB roll a 3 and a 5 so they use 5. The modifier was +1 -1 so the result is 5. Scratch damage to the Hull.

Turn 10 heat damage

The SDB is thrusting onto the planet but it won’t be considered landed or in shadow until after the next turn. The ship does not face the sun so the Sunstance does not apply, the good thing is that this means they can pop-out their sensors and weapons again.

The SDB isn’t thrusting towards the sun and neither is it thrusting away from the sun, hitlocation is simply rolled by a 1D6.

SDB roll a 3, a Surface location hit.

We have a Heat modifier of +2 from orbit 2 now and no modifier for Sunstance. We roll 3D6 again and use the highest.

SDB roll a 6 and 5 so they use 6. A 6 means exploding dice, they roll a 4 which adds 2 to the die roll. A die roll of 8 with a modifier of +2 is 10, Severe damage to the Surface location!

After this the SDB is safe in the shadow of Ember and the repair crew is setting out to Jury-rig or repair the Surface location, the scratch damage on the Hull has no effect yet so it’s ignored.


If you look carefully at the plotted course you’ll notice a mistake I deliberately put there, the fact that turn 9 didn’t thrust at all! This means they could have powered down their powerplant too and probably avoided the Hull Scratch damage it got despite the Sunstance. I put it there as a hint for the apt reader to come up with a better route.

It is actually possible to do an approach using both Sunstance and powered own radiators out for the two damage rolls. See if you can solve it! You could also try the hell bent for leather Traveller appoach of heading straight for the planet and taking the heat, see where that would land you.

If you can’t stand the heat, stay out of the kitchen!