Looks like a good start! Very industrial design, I can definitely see the DA Wanzer influence. Definitely needs some colour (I've been told before never to use purely unsaturated greys and whites - always have some colour, even if it's extremely light). The guns are nice and look well-enough scaled... Although I hate to think what kind of weapon that giant spark plug is. 
Otherwise, the outlines are extremely bold and possibly don't need to be, especially internal ones, and you're completely missing any sense of depth. Have a go at smoothing the black lines and adding some lighting/shadow effects - it can make a flat 2D sprite really pop into life, even a small one.
I just went with this on Paint to draw the basic design. Gonna transfer to another program later. Though I'm kinda split which one should I use. I haven't made a sprite in ages and the ones I'm accustomed to was GBA and SNES sprites. As for the color, the unit was originally intended to be used by Independent factions/Civilian fleets thus the grey color scheme.
The "spark plug" looks like a flamethrower to me. Devious fighter, isn't it.
The "spark plug" is actually my take on the British army's Sten and Sterling submachine guns.
You've fallen a bit into the same problem I had; don't necessarily think you have to feel restricted to a bitmap like you might for an older game. you can use in-betweens and smudges to excellent effect You can go even further into detail.
For instance:
At 13 right now, and I'm currently trying to detail it (similar to vanilla hammerhead). With difficulty. It's like if you add detail to it, it ruins the lines of the ship, which is supposed to be smooth and sleek. Any ideas?
So here is my take on this ship:

And while I was at it, I recorded the process:
Yeah its an old habit I have to deal with sooner or later. I'm gonna gather some more info on how make the sprite look more "starsector" friendly.