John Rheinstein ’51, a widely respected physicist who was a major contributor to the development of ballistic missile defense technology, died on January 10 in Bedford, Massachusetts. John was born in Germany and emigrated to the United States with his parents as a young child. At Dartmouth he was a math major, member of Phi Sigma Kappa and active in WDBS, the College radio station. After service as a lieutenant commander in the U.S. Navy, he earned an MS in physics at the University of Chicago and a Ph.D. at the Technische Hochschule in Munich, Germany. He spent 30 years as an associate division head in the systems analysis group of Lincoln Laboratory’s re-entry systems program. His research and scientific writings were cited by the Journal of Defense Research. From 1969 to 1973 he was active as a consultant. John traveled widely with his first wife, Betty, who predeceased him. He was an avid reader, HAM radio operator and dog lover, as well as a volunteer tax consultant for the elderly. He is survived by his second wife, Eve, three children and three grandchildren.