What separates Sea Ceptor from Aster 15?

What is the difference between Sea Ceptor and Aster 15?

Aster 15 is being phased out in favor of Sea Ceptor, having covered an interim role during the transition from Sea Wolf.

Aster 15 is being phased out in favor of Sea Ceptor. Its role is described as covering the transition from Sea Wolf to Sea Ceptor.