The following rules are designed to model the use of planets within a Full Thrust game, both as an obstacle to navigation, and also for scenarios where the planet itself is of importance. There are rules in More Thrust (p. 13) for handling planets, but they are very simplistic and don't fit in well with the vector movement system introduced in the Fleet Book.

All these rules assume vectored movement is being used. If you're using cinematic movement, then these rules won't make much sense.

Normally, Full Thrust doesn't care about real world measurements, and simply uses the 'turn' and the 'movement unit' (depicted as “ in the rules, and often taken as an inch on the table top). If we start using real world objects though (such as planets), it becomes necessary to translate these abstract terms into real world units.

A turn is taken to be fifteen minutes, and 1” is assumed to represent one thousand kilometres. From this, we can work out that a ship thrust factor of 1 is equivalent to an acceleration of approximately 1.125 ms-2. To keep things simple, I'll assume that 1g is equal to a thrust factor of 8.

Unless you have a very big table, you might want to consider using 1“ = 1cm on the table top. This provides a lot more room for manouevre around the planets, and also makes modelling planets easier.

The easiest way to model a planet is to cut a circle out of a piece of cloth or paper, and simply place it on the table top. This also makes it very easy to place planetary installations on the planet, since they can be drawn/placed on top of the planet.

Another easy way is to buy a polystyrene sphere from a craft shop, cut it in half to form a hemisphere and paint it to look planet-like. The largest spheres I've found though are only 10cm in diameter, so this works best for either dwarf planets or if you're using centimetres. See the picture above for an example.

Every large body, from planets to stars and black holes, will exert gravitational attraction on nearby ships. This attraction will act as an acceleration directly towards the body, just as if the ship were thrusting towards it. Since a thrust of 8 is considered to be equivalent to 1g, so the force of gravity at the surface of an Earth-like world will cause an acceleration of 8”.

Each planet is considered to have gravity bands which reach from its surface out into space. The first band is out to 4“, the second to 8”, the third to 16“ - and so on, doubling in distance each time. For an Earth-like world, the gravity in the first 3 bands is 6”/turn, 2“/turn and 1”/turn. This means that any ship that begins a turn within 4“ of Earth will get dragged towards the surface by 6”.

The steps to work out the effects of gravity are as follows. We assume that vectored movement is being used, and that a vector marker is used to show each ship's position at the end of the next movement.

At the beginning of movement, work out the distance between the ship and the surface of the planet. If the ship is outside any effective gravity bands for that planet, then the planet has no effect (e.g., outside 16“ for an Earth-like world).

Lookup the gravitational acceleration for that planet for that range. There is a table below which lists acceleration values for some common worlds.

Work out the gravity vector from the ship towards the centre of the planet for this acceleration. This vector has a magnitude equal to the acceleration, and a direction pointing to the centre of the planet.

Apply the gravity vector to the ship's vector marker.

Apply any acceleration due to the ship's thrust.

Move the ship and its marker.

It is the distance of the centre of the ship to the surface of the planet that is important - the position of the vector marker has no effect.

The acceleration due to gravity on a ship depends on the size of the planet and the distance the ship is from it. For a planet of Earth size and mass, the following zones of influence are suggested.

Remember that the distances given above are the distance from the surface of the body. The Sun will not fit into any sensible gaming area, and is given merely to show how insignificant everything else is. Even Jupiter would require at least 2.5m (at centimetre scales) to allow for manoeuvring at the edge of its gravity well.

Where acceleration less than 1” is given, it can be ignored. However, this does mean that small worlds such as Mercury would have no effect, so it's listed anyway in case you want to use it.

The following example shows the Light Cruiser Colbert approaching a planet. At no point does the Colbert apply any thrust of its own. The world is slightly smaller than the Earth, with statistics as follows:

We begin the example with the Colbert 10,000 km (10“) from the planet's surface. The Colbert has a current velocity of 12”/turn (as denoted by the red vector marker in the diagram).

The gravitational acceleration at this point is 1“/turn, in a direction about 45 degrees to the Colbert's current heading. This acceleration is applied to the vector marker (vector shown in green above).

This moves the Colbert to its new location, somewhat closer to the planet but halfway around it.

At the new distance of 6” (shown in red), the gravitational acceleration is 2“/turn. Again this is applied to the vector marker. Note that the marker is moved in the direction that the Colbert would be moved by gravity.

Though most combat in Full Thrust occur entirely in space, it is sometimes necessary to assault military targets on a planet's surface. Doing so is similar to attacking another ship or space station, but planetary bases are often hidden beneath an atmosphere, and may be further protected by rock.

A thick atmosphere can be quite effective at preventing a large number of attacks, especially energy weapons. The most effective weapons against targets within an atmosphere are Ortillery weapons, which ignore any atmospheric effects.

Atmospheres come in different types: Very thin, Thin, Standard, Dense, Very dense.

+ Also counts as one level of shield.
++ Also counts as two levels of shields.

Beam weapons have their range modified by the atmosphere, which may mean smaller beam weapons cannot penetrate at all. For example, the range against targets within a Standard atmosphere is increased by 18“. This would mean that a class 1 weapon cannot reach, and a class 2 weapon would do only 1d damage if less than 6” above the target.

Torpedo attacks have their 'to hit' chance reduced, and have each damage die reduced as well (to a minimum of zero per die).

Grasers are affected in a similar way to beam weapons, but the range penalty is doubled. The damage die of each graser hit is also reduced as per a torpedo. Grasers aren't very good at penetrating atmospheres.

Heavy missiles aren't designed to enter an atmosphere, and have a chance of simply burning up on re-entry. For each missile, roll a die, modified by the 'torpedo' column above. On a 1+, the missile makes it through to the target.

However, any missile that does hit the target is more effective, due to the extra shock wave produced by the atmosphere. Against unarmoured targets, multiply the damage by the missile column for that type of atmosphere. A typical heavy missile will do around 210 points of damage against a settlement (see below).

Similar to heavy missiles, they are not good at entering an atmosphere, but more effective if they do hit. Reduce the number of missiles that hit by the penalty, and multiply damage as for heavy missiles.

An ortillery system is a non-nuclear strike designed to penetrate bunkers and other heavily defended targets. As such, they are not as effective against civilian targets as missiles, but no civilised invasion should be attacking civilian targets anyway.

Ortillery rolls to hit like a pulse torpedo, but with a range band of 3“.

On a hit, it does 2d6 damage to the target, with half (round down) penetrating any armour.

A civilian population centre shouldn't normally be the focus of an orbital attack, but sometimes these things happen. A settlement has a number of 'hull boxes' equal to the square root of its population.

Wiping out a city can be a major undertaking, and most starships aren't equipped to do this in any reasonable period of time. Since settlements are generally unarmoured, using missiles or ortillery systems is the normal way to go.

Settlements have four rows as per starships. The first row represents about 10% of the population killed or displaced. The second row represents another 20% (30% total), the third another 30% (60% total), and the fourth is the last 40% of the population.

Military targets are costed similar to ships - each point of hull or armour costs 2 points. Armour can be layered, at extra cost, by any nation. They do not have to pay cost for the total size of the installation.

Military installations may have point defence systems (against fighters or missiles) or Surface-to-Space weapons. An installation on an airless planetoid can use any weapon system used by ships, for the same cost.

See Ground Based Installations for some sample designs.