Aftermath of Ranger 6 and preparation for Ranger 7
Although NASA had attempted to put a positive spin on Ranger 6 on the grounds that everything except the camera system had worked well, William Coughlin, editor of the publication Missiles and Rockets, called it a "one hundred percent failure" and JPL's record thus far was "a disgrace". The mission had not been a complete failure, but Coughlin was not alone in his opinion that Jet Propulsion Laboratory in Pasadena, a nonprofit laboratory and extension of the California Institute of Technology (Caltech), was a "soft" academic environment without the drive or ambition needed to make the missions succeed. He considered Ranger a "loser" and for a while, anyone at NASA involved in the Ranger program tried to conceal it. It was also being said that sending probes up for the sole purpose of returning images was pointless and accomplished nothing that Apollo could not also achieve.
Shortly after Ranger 6's mission concluded, a review board was convened to resolve the cause of the TV camera failure. This was determined quickly; the inadvertent activation of the camera telemetry system during ascent had been caused by an electrical short that crippled the power supply for the cameras. But why it had happened was as yet a mystery, especially as telemetry data sent back from the probe could only provide a limited amount of information. On February 14, 1964, JPL released a report noting that an internal command switch could have activated prematurely or that arcing had occurred in the umbilical connector on the payload fairing. However, there was no evidence of the latter happening or any obvious way that it could occur and several modifications were proposed to the camera system and/or the payload fairing.
The NASA review board found that Ranger 6's systems were not as redundant as JPL had claimed, that prelaunch testing was inadequate, and there had been instances of the cameras turning themselves on at the RCA plant in New Jersey. If the cameras had to be completely redesigned from scratch, the next Ranger mission could be delayed almost a full year.
The full report as submitted to U.S. Congress came under criticism from several people at NASA, noting that, although the cameras lacked redundancy, any one of dozens of failure modes in the booster or spacecraft could also result in failure to return any TV images. In regards to the lack of adequate prelaunch testing, they brought up the incident back in 1961 with Ranger 1 deploying its solar panels during a ground test and that ground tests with full 60 W power had been discontinued on the Block II probes for fear of accidentally igniting the midcourse correction engine on the pad and destroying the entire launch vehicle in the process.
RCA also promised to look into workmanship standards at their main plant in Hightstown, New Jersey, when examination of a sealed Ranger module discovered a plastic bag with screws and washers inside. Although there was suspicion that this had been done by a disgruntled employee, it was far more probable that someone had done it by accident.
Since no obvious reason for the malfunction could be found in the cameras themselves, investigation next shifted to the electrical umbilical on the payload fairing. This umbilical connector would normally be attached on the ground to permit testing of the Ranger's subsystems and only a thin hinged door covered it during launch. One of the pins on the connector was "hot" and could easily be bridged, transferring a voltage to the adjacent pins and activating the TV camera system during launch. As for the cause of it, one possibility was electrostatic discharge, the other was a shock wave of some sort.
Alexander Bratenahl, a physicist at JPL's Space Sciences Division, suggested that the electrical short was caused by venting propellant during Atlas booster section jettison. There was no tracking camera footage of this event on Ranger 6's launch, which had occurred on an overcast day, but film of other Atlas launches showed that a large white plume enveloped the launch vehicle after staging. Convair technicians confirmed that 112 pounds (51 kg) of LOX was vented from the Atlas after staging, but although the shock wave theory seemed tempting, James Kendall, another JPL physicist, dismissed it out of hand. The idea of an electrostatic discharge was also unlikely given the thinning air and high altitude of the Atlas when staging occurred.
Bratenahl persisted and studied more film of Atlas launches with the frames enlarged, which revealed light flashes in the post-staging plume. Another phone call to Convair revealed that 67 pounds (30 kg) of RP-1 were also dumped during staging and that the Atlas's sustainer engine exhaust ignited the propellant cloud, producing these flashes. Since the umbilical door on the payload shroud was only held in place with a thin latching mechanism, hot gases from igniting propellant could have contacted the electrical connector and caused a short. The inadvertent activation of the telemetry system during launch had occurred almost simultaneous with booster jettison at T+140 seconds. With that, the book could be closed on the cause of Ranger 6's failure.
Among the changes made for Ranger 7 included new procedures to apply full power testing to the spacecraft off of the launch pad, where there was no risk of the midcourse correction engine activating on top of a fully fueled Atlas-Agena.
Jet Propulsion Laboratory had originally wanted to have Ranger 7 impact in the same general area as Ranger 6 so the impact crater could be imaged, but lighting conditions during July would not be favorable so they instead decided to go for a little-known area 11 degrees south of the Moon's equator near the Sea of Storms. The probe was shipped to Cape Canaveral in mid-June along with Atlas 250D and Agena 6009.