[FT] Space-to-surface combat

I seem to be in a rule-writing mood today. This is the FT end of orbital
bombardment, distilled from posts around the end of last year and with a lot
of my own invention...

Space-to-surface combat

It is assumed for the purpose of these rules that 1MU = 1000km. On this scale,
Terra is a 13MU diameter circle; a large asteroid (Ceres) is 1MU in diameter.
These rules deal only with solid planets with no atmosphere, or atmosphere
that is thin relative to the size of the planet.

It is further assumed that the _More Thrust_ rules for orbital and
atmospheric operatioNs are in use (pages 13-14).

Gravity

If the planet has significant gravity (more than 1 m/s/s - normally
anything over 2MU diameter), all weapons other than pure energy weapons
(beams, stingers and pulsers) which are fired or launched from it have
their ranges halved. Multi-turn weapons, such as capital ship missiles
and fighters, halve their movement on the turn of launch only. (Fighters
expend a CEF as well.) Fighters entering this gravity well (to land or to
attack ground targets) must have half their movement available at the point at
which the miniature reaches the edge of the planet.

Atmosphere

If the planet has a significant atmosphere, this will act as a level-2
screen against all attacks which pass through it. (This supersedes any screens
on the targets.) A fighter group flying through atmosphere expends a CEF each
turn on which it does so. (Thus a fighter group being launched from a world
with significant gravity and atmosphere expends 2 CEF just to get into the
fight.)

Landing thrust

A ship attempting to land on a planet must possess thrust equal to 2/3
(rounded down) of the surface gravity in m/s/s in order to do so safely.
If the planet has significant atmosphere, the ship must also be at least
partially streamlined; if it is fully streamlined, it can get by with
thrust of 1/2 (rounded down) of the surface gravity.

Planetary bases

Planetary weapon installations are constructed as space stations. They pay
normally for basic mass and hull boxes, since even on a world with breathable
atmosphere it's considered wise to have sealed systems. However, they do not
pay for armour; instead, they gain infinite free armour by being buried within
the planet. (That is, only damage that penetrates armour will affect them.)
They do not have core systems. Races with multiple armour layer technology may
buy additional armour layers to be placed behind the infinite layer.

A base must be placed at a specific point on the planet template, and may not
have more than three, adjacent, arcs of fire.

Ortillery

An ortillery attack does d6 damage to a planetary base, automatically
penetrating the armour layer (and screens). Its range is 12MU, and it
can only be used to attack a base on a planetary surface - even the
manoeuvre thrusters on a space station are sufficient to allow it to avoid
such an attack.

Splash damage

Splash damage is the reason for ortillery to exist. All that damage that's
soaked by armour doesn't just vanish; it's going to disrupt the surface of the
planet. If there are civilians about, they'll die in large numbers. Scenarios
may specify penalties for excessive splash damage.