From the manual:
BattleSpace, The Battletech Game of Space Combat simulates battles in space between the Houses of the Inner Sphere and the invading Clans. Battlespace was designed to allow players to run a campaign in space.
Both a stand-alone game and an expansion.
As a stand alone game, you can play out battles between large ships and squads of fighters, as well as dogfights between individual aerospace fighters.
As an expansion, you can incorporate both of those levels of play into your Battletech games.