Mjolnir is a system on the border of Polaris space. Deep in the polaris storyline, Mu'Randa will give you missions to defend Mjolnir from Federation task forces and when landing on the space-station in Mjolnir, you will be paid 100,000 credits (after the task-force has been driven away).
Mjolnir was the name of a cyborg who helped save the Polaris 600 years before the events of the game.
The name could be a reference to Mjolnir Recon number 54, the cyborg hero of the early Bungie first-person shooter game Marathon.
Mjolnir is romanized name for the Norse god Thor's hammer. In short, Mjolnir is very powerful and just.