William Djinis, a nuclear physicist who served as coordinator of NASA’s orbital space debris program, which helped prevent rockets and satellites from colliding with other objects orbiting Earth, died Feb. 1 at Suburban Hospital in Bethesda. He was 91.

The cause of death was a heart attack. A son, Peter G. Djinis, confirmed the death.

Mr. Djinis spent his early career at Grumman Aerospace in Beth Page, N.Y., where he became chief scientist for space and aircraft systems. In the 1960s, he helped oversee the electronic and avionic systems of the Lunar Excursion Module used in the Apollo moon landings. He also assisted Mission Control in Houston in the safe return of the Apollo 13 astronauts in 1970, his family said.

In the late 1960s, he took a leave from Grumman to serve as a presidentially appointed scientific adviser to the Air Force. In the 1970s, he worked for companies such as Westinghouse before joining NASA in 1980. He retired in 1991.

William Djinis was a native of Poughkeepsie, N.Y. He attended Rensselaer Polytechnic Institute in Troy, N.Y., from which he received bachelor’s (1948) and master’s (1950) degrees in physics.

He served in India as a meteorologist with the Army Air Forces during World War II and retired from the Air Force Reserve in 1981 with the rank of colonel.

Mr. Djinis, a Potomac resident, was a past president and treasurer of the parish council at St. George Greek Orthodox Church in Bethesda. His other memberships included the Sigma Xi scientific research society and AHEPA, a Greek American organization.

Survivors include his wife of 64 years, Mary Telepas Djinis of Potomac; three children, Anthony W. Djinis of Potomac, Peter G. Djinis of Sarasota, Fla., and Chrysanthi Golden of Gilbert, Ariz.; a sister; five grandchildren; and a great-grandson.

— Adam Bernstein