Very little has emerged from the Strategic Defense Initiative days revealing *actual* weapons designs. With the exception of some of the Brilliant Pebbles and Zenith Star designs, almost nothing apart from unreliable artwork has been released. On occasion, though, bits have come out. Three neutral particle beam satellite weapon concepts were shown, in low-rez and frustrating detail, in a report on power systems for SDI use.

The Martin-Marietta NPB concept:

The Ge/Lockheed NPB concept:

The TRW concept:

The drawings are too small to glean details such as full-scale dimensions, or even get a really good handle on layouts. The GE/Lockheed design seems to come equipped with large  panels, presumably radiators, held within a triangular cross-section framework.  The Martin and TRW concepts appear to be roughly cylindrical. And unlike the majority of the artwork produced for public consumption, here you can make out the nuclear reactors meant to power the systems.

While dimensions are either unavailable or illegible in these illustrations, two show the SP-100 reactor and associated radiator system.  The radiators change from illustration to illustration of the SP-100, so cannot be firmly relied upon as a scale reference, and the Sp-100 reactor itself is little more than a dot, but this illustration of the SP-100 should help to give a rough idea how big it, and by extension the NPB concepts, were going to be.