It would help if you could recall where you read this.

It sounds very much like fiction. The deepest anyone has drilled into the crust is about 10 km, while even the boundary of the outer core is about 3,000 km deep. We have no current technology to drill that deep, and the Nazis didn't either.

Besides, firing a rocket into the hole would be silly for a couple reasons:

• a rocket requires a pre-existing tunnel which would collapse unless reinforced. We have no reinforcing materials that can stand the pressure and temperature at depth.

• there's no need for a rocket anyway, just drop stuff in the hole and gravity will do the rest.

The only proposals that have even the remotest chance of succeeding involve no tunnels and no rockets. For example, drop an absolutely humungous amount of molten iron on the surface, and it will eventually melt its way to the core. Over thousands of years.