Mariner 4

After Mariner 3 was a total loss due to failure of the payload shroud to jettison, JPL engineers suggested that there had been a malfunction caused during separation of the metal fairing exterior from the fiberglass inner lining due to pressure differences between the inner and outer part of the shroud and that this could have caused the spring-loaded separation mechanism to become tangled and fail to detach properly.

Testing at JPL confirmed this failure mode and an effort was made to develop a new, all-metal fairing. The downside of this was that the new fairing would be significantly heavier and reduce the Atlas-Agena's lift capacity. Convair and Lockheed-Martin had to make several performance enhancements to the booster to wring more power out of it. Despite fears that the work could not be completed before the 1964 Mars window closed, the new shroud was ready by November.[13]

After launch from Cape Canaveral Air Force Station Launch Complex 12,[14] the protective shroud covering Mariner 4 was jettisoned and the Agena-D/Mariner 4 combination separated from the Atlas-D booster at 14:27:23 UTC on November 28, 1964. The Agena's first burn took place from 14:28:14 to 14:30:38. The initial burn put the spacecraft into an Earth parking orbit and the second burn from 15:02:53 to 15:04:28 injected the craft into a Mars transfer orbit. Mariner 4 separated from the Agena at 15:07:09 and began cruise mode operations. The solar panels deployed and the scan platform was unlatched at 15:15:00. Sun acquisition occurred 16 minutes later.[15]

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:[7] a stray light pattern from the near Earth, Alderamin, Regulus, Naos, and Gamma Velorum were acquired before Canopus.[3][11]

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.[7][11]

The 7½ month flight of Mariner 4 involved one midcourse maneuver on December 5, 1964. The maneuver was initially scheduled for December 4, but due to a loss of lock with Canopus, it was postponed. The maneuver was successfully completed on December 5; it consisted of a negative pitch turn of 39.16 degrees, a positive roll turn of 156.08 degrees, and a thrusting time of 20.07 seconds. The turns aimed the motor of the spacecraft back in the general direction of Earth, as the motor was initially pointed along the direction of flight. Both the pitch and roll changes were completed with better than 1% accuracy, the velocity change with about 2.5% accuracy. After the maneuver, Mariner 4 was on course for Mars as planned.[7]

On January 5, 1965, 36 days after launch and 10,261,173 km (6,375,997 mi) from Earth, Mariner 4 reduced its rate of transmission of scientific data from 33 1/3 to 8 1/2 bits per second. This was the first autonomous action the spacecraft had taken since the midcourse maneuver.[16]

The Mariner 4 spacecraft flew by Mars on July 14 and 15, 1965. Its closest approach was 9,846 km (6,118 mi) from the Martian surface at 01:00:57 UT July 15, 1965 (8:00:57 p.m. EST July 14), its distance to Earth was 216 million kilometres (134 million miles), its speed was 7 km/s (4.3 mi/s) relative to Mars, 1.7 km/s (1.1 mi/s) relative to Earth.[17]

Planetary science mode was turned on at 15:41:49 UT on July 14. The camera sequence started at 00:18:36 UT on July 15 (7:18:49 p.m. EST on July 14) and 21 pictures using alternate red and green filters, plus 21 lines of a 22nd picture were taken. The images covered a discontinuous swath of Mars starting near 40° N, 170° E, down to about 35° S, 200° E, and then across to the terminator at 50° S, 255° E, representing about 1% of the planet's surface. The images taken during the flyby were stored in the on-board tape recorder. At 02:19:11 UT, Mariner 4 passed behind Mars as seen from Earth and the radio signal ceased. The signal was reacquired at 03:13:04 UT when the spacecraft reappeared. Cruise mode was then re-established. Transmission of the taped images to Earth began about 8.5 hours after signal reacquisition and continued until August 3. All images were transmitted twice to ensure no data was missing or corrupt.[2] Each individual photograph took approximately six hours to be transmitted back to Earth.[18]

The spacecraft performed all programmed activities successfully and returned useful data from launch until 22:05:07 UT on October 1, 1965, when the long distance to Earth (309.2 million kilometres (192.1 million miles)) and the imprecise antenna orientation led to a temporary loss of communication with the spacecraft until 1967.[2]

Mariner 4 tape recorder

The on-board tape recorder used on Mariner 4 was a spare, not originally intended for the Mariner 4 flight. Between the failure of Mariner 3, the fact that the Mariner 4 recorder was a spare, and some error readings suggesting an issue with the tape-recorder, it was determined that the team would test the camera function definitively. This eventually led to the first digital image being hand-drawn. While waiting for the image data to be computer processed, the team used a pastel set from an art supply store to hand-color (paint-by-numbers style) a numerical printout of the raw pixels. The resulting image provided early verification that the camera was functioning. The hand-drawn image compared favorably with the processed image when it became available.[19]

• 
  The first digital image from Mars hand-colored like a paint-by-numbers picture
• 
  Processed first digital image from Mars

Data acquisition resumed in late 1967. The cosmic dust detector registered 17 hits in a 15-minute span on September 15, part of an apparent micrometeoroid shower that temporarily changed the spacecraft attitude and probably slightly damaged its thermal shield. Later it was speculated that Mariner 4 passed through debris of D/1895 Q1 (D/Swift), and even made a flyby of that comet's possibly shattered nucleus at 20 million kilometres (12 million miles).[20]

On December 7 the gas supply in the attitude control system was exhausted, and between December 10 and 11, a total of 83 micrometeoroid hits were recorded which caused perturbation of the spacecraft's attitude and degradation of the signal strength. On December 21, 1967, communications with Mariner 4 were terminated. The spacecraft is now derelict in an exterior heliocentric orbit.[21][22]