Complex sentence: Solem authored or co-authored over 175 technical papers (many still classified for reasons of national security) published in many different technical journals in many different scientific fields, as well as science policy, national security, and defense related issues.
Split into simpler sentences: Solem authored or co-authored over 175 technical papers (many still classified for reasons of national security) published in many different technical journals in many different fields. In addition, he authored papers concerning science policy, national security, and defense related issues.