Editing Mariner 4 (section)

===Lock on Canopus===
After Sun acquisition, the Canopus star tracker went searching for [[Canopus]]. The star tracker was set to respond to any object more than one-eighth as, and less than eight times as bright as Canopus. Including Canopus, there were seven such objects visible to the sensor. It took more than a day of "star-hopping" to find Canopus, as the sensor locked on to other stars instead:<ref name=nasa3/> a stray light pattern from the near Earth, [[Alpha Cephei|Alderamin]], [[Regulus]], [[Zeta Puppis|Naos]], and [[Gamma Velorum]] were acquired before Canopus.{{r|Momsen1|Goss}}

A consistent problem that plagued the spacecraft during the early portion of its mission was that roll error signal transients would occur frequently and on occasion would cause loss of the Canopus star lock. The first attempt at a midcourse maneuver was aborted by a loss of lock shortly after the gyros began spinup. Canopus lock was lost six times within a period of less than three weeks after launch and each time a sequence of radio commands would be required to reacquire the star. After a study of the problem, the investigators concluded that the behavior was due to small dust particles that were being released from the spacecraft by some means and were drifting through the star sensor field-of-view. Sunlight scattered from the particles then appeared as illumination equivalent to that from a bright star. This would cause a roll error transient as the object passed through the field-of-view while the sensor was locked onto Canopus. When the object was bright enough that it exceeded the high gate limits at eight times the Canopus intensity, the spacecraft would automatically disacquire Canopus and initiate a roll search for a new star. Finally, a radio command was sent on December 17, 1964, that removed the high gate limit. There was no further loss of Canopus lock, although roll transients occurred 38 more times before encounter with Mars.{{r|nasa3|Goss}}