Can anyone tell me where in the rules do I find tactical orbit strike?, or better still how does it work?.
Tactical Orbital Strike is the name of Kodiak's attack.
In the rulebook you can find the attack's details under the Kodiak section, on page 84.
It uses indirect fire rules, which are covered on Page 40.
They recently changed the weapon, giving it an AREA-S ability. This rule is also covered on page 40.