From an email posted to Baen's Bar BuShips dated November 12, 2004:

Single-drive fusion-powered missiles

    Is anyone going to build a single-drive missile with a fusion power plant?

    Almost certainly not. A fusion plant is larger than the capacitors required to store the energy required by a single-drive missile. It's smaller than the multiple capacitors required to power the multiple drive systems of an MDM. In addition, adding the necessary hardware to kickstart the fusion plant before launch would require a substantial up-sizing of the launchers firing them. The only real argument in favor of putting a fusion plant aboard a single-drive missile would be that it would provide both the power density and the endurance required to take full advantage of the EW capabilities provided by Ghost Rider. That isn't a minor consideration, but for a ship which would be firing single-drive missiles, that's not likely to be as significant a concern. Those vessels are going to be smaller and less capable, whatever they do. If the idea is that somehow switching to a fusion-plant drive and single-drive missile would produce a smaller single-drive weapon, that wouldn't happen.