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1993-04-21
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OFFICE OF PUBLIC EDUCATION AND INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA. TELEPHONE 354-5011
FOR RELEASE AFTER 2:00 p.m. PST WEDNESDAY, MARCH 3, 1965
Los Angeles---Changes in the performance of two scien-
tific instruments aboard NASA's Mars-bound Mariner IV spacecraft
were reported here today by a Jet Propulsion Laboratory engineer.
Dan Schneiderman, JPL's Mariner Project manager, said
data from the solar plasma probe, which ceased normal function 10
days after Mariner was launched last November 28, now has become
understandable to scientists through analysis of the component
failure in the probe.
However, telemetry from a second instrument,
Schneiderman reported, indicates that a portion of the ionization
chamber experiment, which measures radiation in space, is not
operating properly. The new failure, he said, is in the Geiger-
Mueller tube which counts the number of charged particles in the
energy region measured by the ion chamber.
The chamber itself, which measures the total effect of
radiation in the region of energy of electrons greater than 0.5
million electron volts and protons greater than 10 million elec-
tron volts, continues to function normally. The malfunction of
the Geiger-Mueller tube portion of the experiment was ascertained
after several days of analyzing data that did not fall within pre-
dicted levels and could not be correlated with other measurements.
Schneiderman related the latest events in the Mariner IV
mission in an address before the Unmanned Spacecraft Meeting,
-2-
sponsored by the American Institute of Aeronautics and Astro-
nautics, at the International Hotel.
He said the malfunction in the solar plasma probe was
found to be the failure of a resistor in the instrument's high
voltage circuitry. By taking this failure into account, experi-
menters were able to recalibrate the instrument and interpret
data which otherwise would be unintelligible.
Schneiderman pointed out to the AIAA deligates that
this is the 95th day of Mariner IV's flight to Mars and that the
spacecraft is now 26 million miles from Earth and travelling at a
speed of 22,700 miles per hour relative to the Earth.
Mariner IV has received and acted upon 42 commands from
Earth, he said, and a number of others issued by the on-board
central computer and sequencer.
The latest CC&S-commanded event occurred last Saturday
morning when the spacecraft's Canopus tracker was updated to
compensate for the changing relationship between the spacecraft,
the sun and the star Canopus. This was accomplished without
changing the attitude of the spacecraft, but by electronically
changing the "look angle" of the tracker. Three more Canopus
updates are scheduled to occur before Mariner IV flys by Mars on
July 14.
Next Friday, Schneiderman said, Mariner's transmitter
will be switched automatically from the omni-directional antenna,
in use since launch, to the high-gain fixed directional antenna
which is needed for the spacecraft-to-Earth radio link as the
-3-
communications distance increases. Antenna-switching also is an
event controlled by the CC&S and backed up by ground command
capability.
Performance of the spacecraft's attitude control,
thermal control and power subsystems has been excellent,
Schneiderman said.
Based on nitrogen gas consumption to date, he estimated
there is enough gas available to keep Mariner IV stabilized for
about six years. Since last December 17, when a special command
was transmitted to the spacecraft, there has been no reoccurrence
of loss of lock with Canopus.
Telemetry readings, which report measurements of
voltages, currents and temperatures of various Mariner IV
subsystems, have been close to nominal throughout the mission,
Schneiderman said.
###
JPL No. 319
3/2/65