The successful launch of Mariner 2 on August 27 momentarily blunted criticism of NASA and Jet Propulsion Laboratory and also seemed to verify the soundness of the Ranger design. Meanwhile, JPL engineers were still trying to figure out what had caused the computer failure on Ranger 4, which had occurred during a period when the probe was out of range of ground tracking. The malfunction was especially puzzling because the probe had been given very thorough ground testing without any anomalies occurring. Examination of telemetry records seemed to suggest that the failure had occurred during separation of Ranger 4 from the Agena, at the point where the electrical interface between the two was disconnected and Ranger 4 would have switched to internal power. The behavior of the probe indicated a transformer or inverter malfunction, probably a short circuit caused by loose metal coatings contacting the pins on the power umbilical attaching the probe to the Agena. Modifications to Ranger 5 included a backup timer to ensure continued operation of the telemetry system if the main computer failed, an additional nitrogen bottle to the attitude control system to reduce gas pressure, and an additional pyrotechnic igniter for the midcourse correction engine. Most importantly, extra diodes and fuses were added to the electrical lines to prevent another short from occurring.