Hi,
At some point the pc's will decide to blast the crap out of a planet, now are the Lances and Macrobatteries not strong enough to actually destroy a planet but they should be strong enough to level a city.
If the planet has a atmosfeer the Thunderstrike and Mars Pattern Macrocannons are likely to be useless since their projectiles would possibly burn up in orbit (though because of their size they just might not).
But all Laser and Plasma weapons are likely cause massive destruction.
How difficult would it be to:
Target a settlement or small ruin?
Target a Hive?
A Battlefield?
And what type of defense weapons do some planets have, are they roughly the equivelent of ship weapons or perhaps even heavier?