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OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA. TELEPHONE 354-5011
FOR RELEASE AM's OF FRIDAY, SEPTEMBER 24, 1965.
The Mariner IV spacecraft, having achieved its mission
objectives and now in its 300th day of flight, will receive a
command from Earth next week, concluding--but possibly only
temporarily--the National Aeronautics and Space Administration's
longest and most complex deep space mission.
Since launch November 28, 1964, Mariner IV has transmit-
ted to Earth nearly 50 million engineering and scientific
measurements on the environment of interplanetary space and in
the vicinity of Mars. It flew past Mars last July 14 at an
altitude of 6118 miles, recording the first close-up pictures of
the planet's surface.
After October 1, when the ground command switches the
spacecraft transmitter from Mariner's high-gain directional
antenna to an omnidirectional antenna, telemetry from Mariner IV
will cease.
Although next week will mark the end of useful
telemetry between Mariner IV and Earth during 1965, project
officials at the Jet Propulsion Laboratory said the spacecraft
will continue transmitting and may renew its radio link with
Earth in 1967.
During the next two years, it will be possible to track
Mariner IV only with a new 210-foot antenna, which will begin
operation in April, 1966, at the Goldstone Space Communication
Station in California. No telemetry will be received during this
-2-
period, but periodic tracking of the spacecraft as it orbits the sun
will determine whether or not its transmitter is still operating.
Tracking data during the long cruise will help in the
evaluation of the new giant antenna system and hopefully will
allow trajectory analysts to increase the accuracy of the known
relative positions of Earth and Mars.
In June, 1967, Mariner IV and the Earth will be about
30 million miles apart, a distance over which communications can
be resumed with the low-gain antenna. JPL engineers said several
months of useful telemetry may be obtained at that time if the
transmitter and other critical systems continue to operate.
Next Friday's antenna switchover command will be sent by
a 100 kilowatt transmitter and beamed at the spacecraft from one
of Goldstone's three 85-foot antennas. Some 17 minutes later, the
command will reach Mariner, more than 191 million miles away.
Another 17 minutes will pass before engineers in the operations
center at JPL receive the final bits of information.
In addition to acting upon on-board commands from its
central computer and sequencer, Mariner IV has received to date 84
ground commands from Goldstone and the four other stations of
NASA's Deep Space Network, located in Johannesburg, South Africa;
Madrid, Spain; and near Woomera and Canberra, both in Australia.
At 5 p.m. Pacific Daylight Time today, Mariner IV will be
187,152,860 miles from Earth and 17,606,438 miles from Mars. It has
travelled more than 410 million miles in its orbit around the sun.
-0-
359-9/24/65