Although, why does it have anything other then graphite aerogel?
If something heavily optimized is made of aramid, nitrile rubber, PTFE or any variant of PE the answer is probably "lasers".
If it's a radshield, the answer might also be "I find ablative 6Li shielding unrealistic, unrealistically performant and/or fear gammas".
I usually don't armour big, moving components with just graphogel, because it doesn't seem like it wouldn't go hilariously wrong in more than one way at once (I do stuff my whipple shielding this way and I borderline accept graphogel barrel armour since we don't have barrel fins), so my engines have much lower TWR.
I also never use potassium or calcium for anything structural. It's just wrong (potassium should be added as liquid, just like sodium is - it's a decent potential coolant once melted).