travestytrav, that just sounds wrong.
SPY-3 = the system of the zumwalt. and you about everything works together, as long as it is made for the job. for example: aegis can not guide aster because aster requires an different guidance system.
Actually, it sounds exactly right. The SPY-3 is a brand new design and is in no way related to the AEGIS SPY-1, which, as you say, cannot guide the ASTER missiles. Like I said, the SPY-3 isn't even in service yet, it doesn't even exist except in computer models and laboratories. The version of the SPY-3 that's going on the Zumwalt destroyers probably can't guide Asters because, as far as I know, the US has no plans to buy Aster missiles. But, if you're willing to pay Raytheon enough, I guarantee they could make it compatible with whatever weapon system you want to use. You would just wind up with SPY-3B Mod 1, or something like that, that's slightly different than US version of the SPY-3.
Or, Canopus, you can just come up with an indigenous radar system that's similar to the SPY-3, but can work with Aster missiles. It's an AU design, so you don't have to use something that actually exists. Just realize that an indigenous sytem would require all your own research and development, which would make it more expensive. Or, you can just use the off-the-shelf SAMPSON system that Aster-equipped ships use, but you may not like how that fits with your design.