How do I get at this crystal?

I'm exploring this sector, and run into an asteroid with a couple mineable crystals in it. Problem is, I can't seem to actually get to the crystals to mine them. The only way in that I can see is this shielded entrance, and I can't seem to figure out how to drop it.

How am I supposed to get into this cavern, so I can get at the crystal?

No matter where you see a shield in the game, there is always one or more shield generators near the shield creating it. Find the generators and shoot them down to deactivate the shield. The generators glows yellow like the G&B fuel or gas containers. Most times the shield generators are within the shield and can be shot down from that side, but sometimes the generators are behind the shield, where you can not shoot them. In that case, there is a second shielded entrance on the other side of the asteroid with reachable generators. Also there is often a small hidden entrance without a shield with which you can bypass the shields and fully loot the asteroid cavern without deactivating any shield.