That sounds cool, are there any links you'd suggest reading up on that? Are you talking about mass-> energy conversion in general or something specific which has already been theorized successfully?

And I was thinking not just exploration, but sustained energy intensive missions. Chemical energy will be enough for entry to space, but solar energy might not be sufficient for long term missions.

If heavy machinery needs to be operated (like space mining) we need nuclear energy, and this can happen soon enough that humans haven't yet figured out complex energy production measures like the 'total mass conversion' you mentioned.