Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/JPLNEWS1/0388.PR

Text File | 1993-04-21 | 6KB | 116 lines

OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.  TELEPHONE:  [phone]

FOR IMMEDIATE RELEASE -- May 26, 1966
          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 high-
gain 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.

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          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 seven-
hour 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 read-
ing from the Mariner's command system.  One of 12 ground commands

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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 through-
out the solar orbit.
          Canopus lock is necessary when Mariner's exact orienta-
tion 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 sta-
tion 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,

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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 mid-
1967, 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 travelled nearly 750 million miles
around the sun and will complete its first solar revolution on
June 18, 1966.




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