Space ship returning to different earth

I read this short story a long time ago (+30 years).

A space ship is returning home to Earth from a battle. There are no people on board this ship, only an AI and a ship computer. When the ship try to contact Earth it gets no answer. Only after some time I get contact with Houston Control( I think).

The AI find out that he is on a different Earth and that he also travel back in time. ( The enemy the fleet fought still exists)

The space ship comes from an Earth were the Greek empire did not get destroyed.

In the end the AI crash the ship on the Capitol and get destroyed but the ship computer survives so that the human race has the knowledge how to build ships and fight the enemy.

Any idea what the name is of that short stories