Attitude control was provided by six Sun and one Earth sensor, gyroscopes, and pitch and roll cold nitrogen gas jets.

[1] The experimental apparatus included: (1) a vidicon television camera, which employed a scan mechanism that yielded one complete frame in 10 s; (2) a gamma-ray spectrometer in a 300 mm sphere mounted on a 1.8 m boom; (3) a radar altimeter; and (4) a seismometer to be rough-landed on the lunar surface.

After Mariner 1 ended its mission in the Atlantic Ocean instead of interplanetary space, the agency started coming under increased scrutiny from Congress due to its apparent inability to have any kind of success with planetary probes.

Republican Congressman James Fulton confronted NASA Director of the Office of Programs J.J. Wyatt, noting that Mariner 1 had cost U.S. taxpayers $14 million and that there was no excuse at this point for failures every launch.

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.

Rolf Halstrup, who was in charge of the sterilization program, had vocally objected to this procedure as he was convinced that subjecting the probes to a heat dosage was damaging the sensitive electronics in them.

He convinced JPL in Pasadena management that sterilization of Ranger 4 had "very likely" damaged the main computer sequencer and timer and that the procedure needed to be stopped to ensure reliability of the spacecraft.

On August 20, Ranger 5 began the long cross-country trip from state of California to Florida and arrived there the day of Mariner 2's launch.

The Atlas-Agena combination malfunctioned four out of the six times that NASA had launched it and every booster that was delivered to Cape Canaveral required modifications or repair work before it could fly.

JPL technicians thought that they could still partially salvage the mission by firing the midcourse correction engine to ensure impact with the Moon, but they had to do it quickly before power ran out.

Ground controllers sent commands to unfurl the high-gain antenna and align the probe for the midcourse burn, but during this time more electrical shorts apparently occurred because there was a momentary dropout from the telemetry transmitter.