Editing Ranger 4 (section)

==Spacecraft design==
[[File:Atlas Agena B with Ranger 4 (Apr. 23, 1962).png|thumb|left|100px|Launch of Ranger 4]]

Ranger 4 was a Block II Ranger spacecraft virtually identical to [[Ranger 3]]. The basic vehicle was {{convert|331|kg|abbr=on}}, {{convert|3.1|m|abbr=on}} high and consisted of a lunar capsule covered with a balsawood impact-limiter, {{convert|0.65|m|in|abbr=on}} in diameter, a mono-propellant mid-course motor, a {{convert|22.6|kN|lb-f|-1|abbr=on}} thrust retrorocket, and a gold- and chrome-plated hexagonal base {{convert|1.5|m|abbr=on}} in diameter. A large high-gain dish antenna was attached to the base. Two wing-like solar panels ({{convert|5.2|m|abbr=on}} across) were attached to the base and deployed early in the flight.

Power was generated by 8,680 solar cells contained in the solar panels which charged an {{convert|11.5|kg|abbr=on}} 1&nbsp;kWh capacity [[Silver zinc battery|AgZn]] launching and backup battery. Spacecraft control was provided by a solid-state computer and sequencer and an Earth-controlled command system. Attitude control was provided by [[Sun]] and [[Earth]] sensors, [[gyroscope]]s, and pitch and roll jets. The telemetry system aboard the spacecraft, consisting of two 960&nbsp;[[Megahertz|MHz]] transmitters, one at 3&nbsp;[[Watt (unit)|W]] power output and the other at 50&nbsp;mW power output, the [[high-gain antenna]], and an omnidirectional antenna. White paint, gold and chrome plating, and a silvered plastic sheet encasing the retrorocket furnished thermal control.<ref name="nssdc1962-012A" />

Because heat sterilization was suspected to have caused the malfunction of [[Ranger 3]]'s computer, this procedure was dropped on Ranger 4. The seismometer capsule was also painted with a sawtooth pattern for better thermal protection.<ref name="nssdc1962-012A" />

The experimental apparatus included: (1) a vidicon television camera, which employed a scan mechanism that yielded one complete frame in ten seconds; 2) a gamma-ray spectrometer mounted on a {{convert|1.8|m|abbr=on}} boom; (3) a radar altimeter; and (4) a seismometer to be rough-landed on the lunar surface. The seismometer was encased in the lunar capsule along with an amplifier, a 50-milliwatt transmitter, voltage control, a [[turnstile antenna]], and six [[Silver-cadmium battery|silver-cadmium batteries]] capable of operating the lunar capsule transmitter for 30 days, all designed to land on the Moon at {{convert|130|to|160|km/h|mph|round=5|abbr=on}}. The radar altimeter would be used for reflectivity studies, but was also designed to initiate capsule separation and ignite the retro-rocket.<ref name="nssdc1962-012A" />