The Mariner IV spacecraft, which took the world's first closeup pictures of Mars last year, is once again in contact with Earth reporting on the space environment and its own operating performance after 18 months of flight.
The National Aeronautics and Space Administration said today that telemetry from the Mariner, received Saturday (May 21) over a 197.5-million-mile radio link with the Deep Space Network's Goldstone Space Communications Station in California, indicated that all spacecraft systems are operating properly.
Although Mariner was transmitting over its low-gain antenna, the signal was gathered in, amplified and recorded by the combination of a super-sensitive receiver and Goldstone's huge, new 210-foot-diameter antenna. (The spacecraft's highgain antenna, used during the Mars fly-by last July 14, is no longer pointing at the Earth.)
Mariner IV and the Deep Space Network have broken, set and re-broken all existing space communications records.
On October 1, 1965, Mariner's orbital path around the sun finally exceeded the telemetry range of the DSN's 85-foot antennas at the previously unprecedented distance of 191 million miles. Prior to that time, the spacecraft's radio signal was beamed at the Earth by a directional dish antenna.
Periodic tracking of Mariner's signal for the past eight months indicated that the transmitter was operating, but no telemetry could be received with the smaller ground antennas.
The "210", one of the world's largest and most sensitive automatic tracking antennas, gives the DSN the capability to track future spacecraft to the farthest reaches of the solar system.
Telemetry data recorded Saturday during Mariner's sevenhour pass over Goldstone, was processed by computers at the Jet Propulsion Laboratory in Pasadena, Calif. JPL built the Mariner and operates the Deep Space Network for NASA.
Some of the information derived from a preliminary analysis shows that:
..Mariner IV has exceeded its design life by more than 100 per cent. Designed for a 6000-hour mission, the spacecraft has operated continuously for more than 13,000 hours.
..The attitude control system has a 3.22-pound supply of nitrogen gas--enough to keep the spacecraft stabilized until sometime in 1968.
..After nearly one complete revolution of the sun, Mariner's solar panel remains the primary power source. The spacecraft has not lost sun-lock since sun acquisition occurred following the midcourse maneuver on December 5, 1964.
..Temperatures and voltages of all systems including the scientific instruments are normal.
..Mariner IV's star sensor probably is pointing at the star Denab instead of the star Canopus. This is indicated by the spacecraft's "look angle" and the light intensity reading from the Canopus sensor.
This assumption is supported by another telemetry reading from the Mariner's command system. One of 12 ground commands sent "blind" to the spacecraft since October 1, 1965, was not received or was received and not acted upon. Commands issued blind were those which the Mariner could not verify because of the extreme communications range.
Each of the 12 identical commands was addressed to the star tracker to change its look angle which compensates for the changing angular relationship of the spacecraft, the sun and Canopus and enables the tracker to keep the star in view throughout the solar orbit.
Canopus lock is necessary when Mariner's exact orientation in space must be known. This is needed when the television camera is operating, when the high-gain antenna is in use and at the initiation of a trajectory correction maneuver.
Mariner Project officials believe the "lost" command was one of six transmitted last month when the Earth and the spacecraft were on nearly opposite sides of the sun. The ground commands were carried by a radio signal that penetrated the solar corona very near the surface of the sun itself.
The signal from Mariner was received at the time that the spacecraft was nearly on the opposite side of the sun from the earth. This was the first time in history that an earth station has received a spacecraft radio signal after it had passed deep into the solar corona. This differs from the frequent reception by radio telescopes of star noise sources through the solar corona.
Mariner IV was launched November 28, 1964, from Cape Kennedy. It completed its primary mission on August 2, 1965,
after transmitting to Earth 21 full pictures and a fraction of a 22nd picture of the Martian surface recorded July 14 when it flew within 6118 miles of the planet.
For 307 days--launch day through October 1, 1965-Mariner IV radioed scientific data to Earth on interplanetary magnetic fields, radiation and micrometeorites. More than 50 million scientific and engineering measurements were obtained.
Mariner Project and Deep Space Network officials plan to use the 210-foot antenna to track the spacecraft and record telemetry about once each month during the next year. In mid1967, when the Mariner IV and the Earth are much closer, the spacecraft may be tracked more frequently. Plans are being made to send commands for re-exercising some of its systems.
Mariner IV has traveled nearly 750 million miles around the sun and will complete its first solar revolution on June 18, 1966.
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