A series of commands were radioed 16-1/2 million miles to NASA's Mariner IV spacecraft early today by JPL engineers from the Mariner spaceflight operations center to check out spacecraft equipment that will be used if Mariner is still operating normally when it reaches Mars next July 14. The Goldstone station of the DSN was used to transmit the commands.
The twelve commands that were sent during an 8-1/2 hour period dropped the lens cover off the television camera, turned on a scanning platform that carries the camera and two Mars sensors, turned on portions of the television system (intentionally no pictures were taken), and checked out the capability of Mariner to perform the encounter sequence.
Commands to turn off the encounter equipment after the checkout were timed to preset the scan platform in a position to be pointing at Mars during the fly-by should the scan platform later fail to function and to set the camera shutter in a desired position.
The lens cover was dropped at this time rather than at planet encounter to shake loose any possible dust particles that might interfere with the Canopus sensor, a light sensing device that locks on the star Canopus to prevent the spacecraft from rolling.
Early in the mission, dust particles had reflected light into the sensor causing a response that ordered the spacecraft to break lock on Canopus and begin rolling in a new search for the star. If this occurred at encounter with Mars it would have been necessary to send commands to counteract the roll. At encounter, the Earth-spacecraft distance will be 134 million miles and it would take 12-1/2 minutes for a signal to reach Earth from the spacecraft to inform engineers that Canopus had been lost and another 12-1/2 minutes to reach the spacecraft with a command to counteract loss of Canopus. This time lag could seriously affect accomplishing mission objectives.
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