This is a defend mission. You now get scout terradynes so you can start doing some serious customization of your troops if you wish. I usually find their base units are quite fine for getting the job done.

Defend for a while - it's not too hard - and then get told to head to the top right for the artifact. Work your way along, with the infantry on the sides and tanks in the imddle, until you get to the opening of their base. This is really just a patience mission - if you move slowly enough, it's easy to win without any losses.

When you get there you get an interesting video of you sneaking in thief-style to see the artifact. Maybe they should throw some first-person action into this game ...

Ground Control Walkthrough