Robert Michael Hornstein , 57, a scientist who had worked since 1968 for the National Aeronautics and Space Administration and directed its worldwide network of antennas used to communicate with orbiting spacecraft, died of a brain tumor March 11 at a hospital in Lancaster, Calif.

He moved from Falls Church to Lancaster in 1996 to be chief information officer of NASA's Dryden Flight Research Center. He had been deputy research systems director there since last year.

Mr. Hornstein, a Washington native, joined NASA during the heyday of the Apollo manned space flight program to design programs for ground tracking systems. He was recognized for helping save the Apollo 9 mission from being aborted shortly after launch when he modified tracking software to compensate for a computer malfunction in the launch vehicle.

Later, as ground networks director, he helped administer NASA's network tracking facilities during space shuttle orbits, the Voyager exploration of the solar system, the Galileo recovery effort and mission to Jupiter, the Magellan exploration of Venus and the international Halley's Comet tracking program. He was NASA's principal representative in arranging cooperative tracking efforts with other countries and was awarded membership in the Soviet Union's Federation of Cosmonautics.

Mr. Hornstein was awarded NASA's Outstanding Leadership Medal for his work to extend the tracking network from North Pole to South Pole. He also helped manage the renovation and upgrade of deep space network facilities in Australia, California and Spain. He was presented with NASA's Exceptional Service Medal shortly before his death.

Mr. Hornstein was raised in College Park and was a graduate of High Point High School and the University of Maryland. He received a master's degree in the technology of management from American University's business school.

He was a member of the Senior Executive Association, the Institute of Electrical and Electronics Engineers and the American Institute of Aeronautics and Astronautics. His interests included wildlife photography and scuba diving.

His marriages to Rhoda Shaller Hornstein and Joan McLaughlin ended in divorce.

Survivors include his wife of three months, Michele Bordier-Hornstein of Lancaster; his father, Irwin Hornstein of Silver Spring; and a brother, Charles David Hornstein of Adelphi.