Phoenix Integration recently repackaged ModelCenter into 3 products: Integrate, Explore, and MBSE Pak. The differences between the products are described on their website:
To integrate ModelCenter with STK, the minimum you need is ModelCenter Integrate and the STK plug-in that is included with STK / Analyzer. ModelCenter Integrate gives you the capability to create a ModelCenter workflow containing STK and any other tool (Excel, MATLAB, CAE tools, CAD tools, etc.). ModelCenter Integrate also includes basic trade studies such as parametric studies and design of experiments (DOE).
ModelCenter Explore contains more advanced trade studies such as Monte Carlo and optimization.