Editing Explorer 3 (section)

==Spacecraft==
[[File:Explorer 3 Flight Recorder.jpg|thumb|upright=1.0|right|Explorer 3 Tape Recorder]]

The objective of this spacecraft was a continuation of experiments started with Explorer 1. The [[Payload (air and space craft)|payload]] consisted of a [[micrometeorite]] detector (a wire grid array and acoustic detector) and the same [[cosmic ray]] counter (a [[Geiger-Müller tube]]) experiment included on Explorer 1, but this time with an on-board [[tape recorder]] to provide a complete [[radiation]] history for each orbit, Ludwig having had time to accommodate for the [[spin-stabilized satellite|spin-stabilization]] of the satellite.<Vanguard/>{{rp|241}}<ref name="Trajectory">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1958-003A|title=Trajectory: Explorer-3 1958-003A|publisher=NASA|date=14 May 2020|access-date=15 February 2021}} {{PD-notice}}</ref>

Its total weight was {{cvt|14.1|kg}}, of which {{cvt|8.4|kg}} was instrumentation. The instrument section at the front end of the satellite and the empty scaled-down [[MGM-29 Sergeant|fourth-stage rocket casing]] orbited as a single unit, to be spun around its long axis at 750 [[revolutions per minute]]. Data from these instruments would be transmitted to the ground by a 60 [[Watt|milliwatt]] transmitter operating on 108.03 [[hertz|MHz]] and a 10 milliwatt transmitter operating on 108.00 MHz.<ref name="Trajectory"/>

Transmitting [[antenna (radio)|antennas]] consisted of two [[fiberglass]] slot antennas in the body of the satellite itself. The four flexible whip antennas of Explorer 1 were removed from the design.<ref>{{cite web|url=https://ntrs.nasa.gov/search.jsp?R=19650073999|title=Vehicle Motions as Inferred from Radio-signal – Strength Records|author=Pilkington, W. C.|date=September 5, 1958|publisher=NASA|access-date=October 18, 2018}} {{PD-notice}}</ref> The external skin of the instrument section was painted in alternate strips of white and dark green to provide passive temperature control of the satellite. The proportions of the light and dark strips were determined by studies of shadow-sunlight intervals based on firing time, [[trajectory]], orbit, and [[orbital inclination]].<ref name="Trajectory"/>

Electrical power was provided by Mallory type RM Mercury batteries that made up approximately 40% of the payload weight. These provided power that operated the high power transmitter for 31 days and the low-power transmitter for 105 days. Because of the limited space available and the requirements for low weight, the Explorer 3 instrumentation was designed and built with simplicity and high reliability in mind.<ref name="Trajectory"/>