A model of the Mk21 reentry vehicle on display at the Zero Gravity Summit in Salt Lake City.The Mk21 is used by the U.S. LGM-30G Minuteman III ICBM and carries the W87 nuclear warhead. It was originally designed and developed by AVCO Systems Division under the Advanced Ballistic Reentry Vehicle (ABRV) program. AVCO’s defense business was later incorporated into Textron Systems.