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March 13, 1987

       The Voyager 2 spacecraft, en route to the planet Neptune, today successfully executed mid-course alteration of its flight path to the eighth planet. Voyager will encounter Neptune and its large moon Triton on Aug. 25, 1989.

       Acting on commands radioed from antennas on Earth, Voyager 2 fired its hydrazine thrusters for 70 minutes, 30 seconds, resulting in change of velocity of 9.2 meters per second (20.5 miles per hour). The firing lasted from 5:06:28 until 6:l6:55 a.m. Pacific Standard Time. (The time given is the Earth-received time. At the spacecraft, the event happened 3 hours, 6 minutes earlier -- the time it takes Voyager's signal to reach Earth.)

       The trajectory correction was made to cause the spacecraft to arrive at Neptune system 12 hours earlier than it would have if it continued on its previous course. Other, smaller trajectory corrections will take place before the encounter to more precisely aim the spacecraft. The adjusted arrival time will allow Voyager to fly very close to Triton (within 40,000 kilometers or 25,000 miles), and also put the spacecraft in position to perform important measurements as Voyager's radio signal passes through Triton's atmosphere.

       The arrival time of 4 a.m. on Aug. 25, 1989, Greenwich Mean Time, or 9 p.m. Pacific Daylight Time on Aug. 24, 1989, will also allow critical radio science measurements of the atmospheres of both Neptune and Triton to be received at Australian complex of antennas operated by NASA's Deep Space Network. Several large DSN antennas and the Australian government's Parkes Radio Astronomy antenna will be electronically connected to allow more and higher quality data to be received at this time as well as throughout the Neptune encounter. The same technique was used to optimize the data return from Voyager 2 during its flyby of Uranus in January 1986. The National Science Foundation's Very Large Array in Las Cruces, N.M., will also be arrayed with the DSN's complex at Goldstone, Calif., to enhance data return.

       The trajectory chosen for Voyager 2's flight past Neptune will send the spacecraft within 5,000 kilometers (3,100 miles) above the planet's north pole. The trajectory was chosen to maximize the probable science return while keeping the spacecraft beyond the region where ring arcs, or partial rings, have been reported.

       Voyager 2 was launched from Earth on Aug. 20, 1977. It flew past Jupiter on July 9, 1979, Saturn on Aug. 25, 1981, and Uranus Jan. 24, 1986. An identical spacecraft, Voyager 1, was launched Sept. 5, 1977, and flew past Jupiter on March 5, 1979 and Saturn on Nov. 12, 1980. Voyager 1 is searching for the heliopause, the boundary where the Sun's influence ends.

       The Voyager Neptune/Interstellar Mission is conducted by JPL for NASA's Office of Space Science and Applications.