Editing Explorer 2 (section)

== Instruments ==
=== Geiger counter ===
An Anton 314 omnidirectional Geiger tube detector was used to measure the flux of energetic [[charged particle]]s (protons E>30 MeV and electrons E>3 MeV). The instrument consisted of a single [[Geiger–Müller tube|Geiger-Mueller tube]], a scaling circuit to reduce the number of pulses, and a telemetry system to transmit the data to ground receiving stations. The Geiger-Mueller tube was a type 314 Anton halogen quenched counter with stainless steel (approximately 75% iron, 25% chromium) wall of approximately {{cvt|0.12|cm}} thickness. The instrument was mounted within the spacecraft hull, which had {{cvt|0.58|mm}} thick stainless steel walls. The counter was {{cvt|10.2|cm}} long by {{cvt|2.0|cm}} diameter and the internal wire was {{cvt|10|cm}} in length. The tube had a very small variation in counting efficiency over the range -55° to +175&nbsp;°C. It had approximately 85% counting efficiency for [[cosmic ray]]s, and about 0.3% counting efficiency for [[photon]]s of energy 660 keV. The "dead time" (time to reset to record the next count) of the counters was about 100 microseconds. The counter was connected to a [[Amplifier|current amplifier]], which directly fed a scaler stage, a bistable transistor multivibrator that could operate over a wide range of voltages and a temperature range of -15° to +85&nbsp;°C, limited primarily by the supply batteries. The scaler resolving time was 250 microseconds. For pulse counts higher than 4000 per second, the scaler indicated a count of 4000. Results were sent to the ground through the telemetry system in real time. The experiment had no onboard data storage device, and could only send telemetry to the ground when it was passing over an Earth receiving station, so some regions had no coverage during the flight.<ref name="Instrument1">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1958-001A-01|title=Experiment: Geiger counter|publisher=NASA|date=14 May 2020|access-date=13 February 2021}} {{PD-notice}}</ref>

=== Micrometeorite Detector ===
Direct measurements of [[micrometeorite]]s were made on Explorer 1 using two separate detectors: a wire grid detector and a crystal transducer. The parameters determined were the influx rates of each size interval, the impinging velocity, the composition, and the density of the micrometeorite.<ref name="Instrument2">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1958-001A-02 |title=Experiment: Micrometeorite Detector|publisher=NASA|date=14 May 2020|access-date=14 February 2021}} {{PD-notice}}</ref>

The wire grid detector consisted of 12 cards (connected in parallel) mounted in a [[fiberglass]] supporting ring which in turn was mounted on the satellite's cylindrical surface. Each card was wound with enameled 17-micron-diameter nickel alloy wire. Two layers of wire were wound on each card to ensure that a total area of {{cvt|1|xx|1|cm}} completely covered. A micrometeorite of about 10 microns would fracture the wire upon impact, destroy the electrical connection, and thus record the event.<ref name="Instrument2"/>

The acoustic detector (transducer and solid-state amplifier) was placed in acoustical contact with the middle section skin where it could respond to meteorite impacts on the spacecraft skin such that each recorded event would be a function of mass and velocity. The effective area of this section was 0.075 m<sup>2</sup>, and the average threshold sensitivity was 0.0025 g-cm/s.<ref name="Instrument2"/>

=== Satellite Drag Atmospheric Density ===
Because of its symmetrical shape, Explorer 2 was selected for use in determining upper atmospheric densities as a function of altitude, latitude, season, and [[Solar activity and climate|solar activit]]y. Density values near [[Apsis|perigee]] were deduced from sequential observations of the spacecraft position, using optical ([[Schmidt camera|Baker-Nunn camera network]]) and radio and/or radar tracking techniques.<ref name="Instrument3">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1958-001A-03|title=Experiment: Satellite Drag Atmospheric Density|publisher=NASA|date=14 May 2020 |access-date=14 February 2021}} {{PD-notice}}</ref>

=== Resistance Thermometers ===
The Explorer 2 satellite was equipped with four [[resistance thermometer]]s that made direct temperature measurements, three external and one internal. The primary purpose of the experiment was to study the efficacy of passive thermal control (in this case, insulation and exterior coatings) on the exterior and interior of a satellite, and to document the temperature of the instrumentation to study its effect on instrument operation.<ref name="Instrument4">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1958-001A-04|title=Experiment: Resistance Thermometers|publisher=NASA|date=14 May 2020 |access-date=14 February 2021}} {{PD-notice}}</ref>

==== Thermometers ====
The thermometer designated external temperature gauge no. 1 was mounted on the outer hull at the bottom of the upper (instrumentation) section of the satellite. This measured the cylinder skin temperature over a range of -50&nbsp;°C to +110&nbsp;°C, with an accuracy of 4&nbsp;°C over the range -10&nbsp;°C to +80&nbsp;°C. External temperature gauge no. 2 was mounted along the bottom of the nose cone to measure the nose cone skin temperature. It could cover a range of -50&nbsp;°C to +220&nbsp;°C. The accuracy was 16&nbsp;°C at a temperature of 50&nbsp;°C and 18&nbsp;°C at 0&nbsp;°C. External temperature gauge no. 3 was mounted at the top of the nose cone and measured the stagnation-point temperature. It covered from -50&nbsp;°C to +450&nbsp;°C with an accuracy of approximately 20&nbsp;°C.<ref name="Instrument4"/>

The internal temperature gauge was mounted in the high powered transmitter at the base of the instrumentation section. It could cover a range of -60&nbsp;°C to +110&nbsp;°C. The accuracy was 2&nbsp;°C at temperatures from 0&nbsp;°C to +30&nbsp;°C and fell off to an accuracy of 20&nbsp;°C at a temperature of 90&nbsp;°C. External temperature gauges no. 2 and no. 3 transmitted on the low-powered (10 mW, 108.00-MHz) transmitter, and the other two gauges transmitted on the high-powered (60 mW, 108.03-MHz) transmitter. Additionally, the nose cone internal temperature could be indirectly estimated by measuring the frequency of the cosmic ray channel. Calibrations of the oscillator indicate the internal nose cone temperature could be known within 12&nbsp;°C from 0 to +25&nbsp;°C, and to 6&nbsp;°C for 25 to 50&nbsp;°C.<ref name="Instrument4"/>