Explorer 10 (also known as Explorer X or P14) was a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

satellite that investigated

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from structure of Earth, Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from ...

and nearby plasma. Launched on 25 March 1961, it was an early mission in the Explorer program and was the first satellite to measure the "shock wave" generated by a

solar flare A solar flare is a relatively intense, localized emission of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and ot ...

Mission

The objective was to investigate the magnetic field and plasma as the spacecraft passed through Earth's

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior Dynamo ...

and into cislunar space. The satellite was launched by a Thor DM-19 Delta (Thor 295) into a highly-

elliptical orbit In astrodynamics or celestial mechanics, an elliptical orbit or eccentric orbit is an orbit with an orbital eccentricity, eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. Some or ...

and was spin-stabilized with a spin period of 0.548 seconds. The direction of its spin vector was 71°

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

and −15°

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

Spacecraft

Explorer 10 was a cylindrical, battery-powered spacecraft instrumented with two fluxgate magnetometers and one

rubidium Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...

vapor magnetometer extending from the main spacecraft body, and a

Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English chemist and physicist who contributed to the study of electrochemistry and electromagnetism. His main discoveries include the principles underlying electromagnetic inducti ...

cup plasma probe. The magnetometers were produced by

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

, and the

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a Private university, private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of moder ...

(MIT) provided the plasma probe.

Experiments

Faraday Cup Plasma Probe

This experiment consisted of a

Faraday cup A Faraday cup is a metal (conductive) cup designed to catch charged particles. The resulting current can be measured and used to determine the number of ions or electrons hitting the cup. The Faraday cup was named after Michael Faraday who first ...

with four grids and a collector designed to provide data on the density of the solar plasma and the magnitude and direction of its bulk motion.

Proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

s were measured in the following energy ranges: 0 to 5, 0 to 20, 0 to 80, 0 to 250, 0 to 800, and 0 to 2300 eV. The experiment was mounted on the spacecraft so that the symmetry axis of the plasma probe was perpendicular to the spacecraft spin axis. The Faraday cup had its maximum response to particles incident at 0° to its symmeter axis. The response fell off rapidly until the instrument had a zero response to particles coming in at 63° and greater to its normal. The effective area of collection for normal incidence was 28-cm². The instrument had two outputs: a DC component related to photoelectric effects and the plasma flux, and an AC component related only to the plasma flux. The shift in the frequency of the AC output component was encoded to be proportional to the plasma flux. The upper energy limit of the plasma particles generating the AC component was determined by the value of a positive retarding voltage applied to one of the grids. This "modulating voltage" had six possible values, from 5 to 2300 eV, and it could also be set to 0. During each 148-second telemetry sequence, 5 seconds were used by the plasma probe. These 5-second intervals, subcommutated by an interval program, were used to transmit sequentially a marker signal, the DC output of the instrument, and the AC output of the experiment at one of the six modulating voltages. Thus, a complete plasma probe sequence, consisting of eight telemetering cycles, lasted 19 minutes and 44 seconds. No inflight calibration was provided, and no onboard processing was done. Because of the limited lifetime of the spacecraft battery, only 52 hours of data were acquired. The principal investigator was Herbert S. Bridge from the

, who worked together with Bruno Rossi.

Rb-Vapor and Fluxgate Magnetometers

A dual gas

alkali vapor instrument and two monaxial fluxgate magnetometers were designed to obtain vector magnetic field measurements of all three field components along a 1.8- to 42.6-Earth radii trajectory traversing the geomagnetic field and extending into the interplanetary medium. The fluxgate magnetometers were oriented at an angle of 57° 45' to the satellite spin axis and were placed on the ends of booms to reduce to less than 1 nT the possibility of spacecraft magnetic field contamination. Data were transmitted to ground stations in periods of 126 seconds from the rubidium magnetometer and 3 seconds for each of the fluxgate magnetometers, in sequence with the other experiment transmissions. Performance was excellent, and data were obtained for 52 hours. During launch, however, outgassing caused deposition of a film on the sphere containing the rubidium-vapor magnetometer. This increased the absorbency of the surface and raised the rubidium vapor magnetometer's temperature to 60°C after 2 hours in sunlight, which interrupted the continuous operation of the magnetometer at 18 Earth radii. Intermittent operation occurred for the next 6 hours and this permitted inflight vector calibration of the fluxgate magnetometers in weak fields.

Sun-Moon-Earth Aspect Sensor (Spacecraft)

The optical aspect sensor consisted of a

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

sensor and associated electronics. The Earth-Moon part of the sensor consisted of a fan field of vision, 3° wide and 120° long, which swept through the sky as the probe rotated in space. The appearance of the Moon or Earth in the sensor's field of view caused a step change in subcarrier frequency. The Sun part of the sensor consisted of a digital coded slit 2° wide and 100° long. The appearance of the Sun in the field of view of the slit caused a discrete frequency on the subcarrier which corresponded to the position of the Sun in the field of view.

Results

Because of the limited life of the spacecraft batteries, the only useful data were transmitted in real-time for 52 hours on the ascending portion of the first orbit. The distance from the Earth when the last bit of useful information was transmitted was 42.3 Earth radii, and the local time at this point was 22:00 hours. All transmission ceased several hours later.

References

External links

Explorer 10 NASA web page
{{Orbital launches in 1961 Explorers Program Observational astronomy Spacecraft launched in 1961 Spacecraft which reentered in 1968 Geospace monitoring satellites