Explorer 15

Explorer 15
	Explorer 15 satellite
Names	EPE-C; Energetic Particles Explorer-C; NASA S-3B
Mission type	Space physics
Operator	NASA
Harvard designation	1962 βλ1
COSPAR ID	1962-059A
SATCAT no.	00445
Mission duration	12 months (planned); 3 months (achieved)
Spacecraft properties
Spacecraft	Explorer XV
Spacecraft type	Energetic Particles Explorer
Bus	S-3
Manufacturer	Goddard Space Flight Center
Launch mass	44.4 kg (98 lb)
Power	4 deployable solar arrays and batteries
Start of mission
Launch date	27 October 1962, 23:15:01 GMT
Rocket	Thor-Delta A (Thor 346 / Delta 014)
Launch site	Cape Canaveral, LC-17B
Contractor	Douglas Aircraft Company
Entered service	27 October 1962
End of mission
Last contact	30 January 1963
Decay date	19 December 1978
Orbital parameters
Reference system	Geocentric orbit
Regime	Highly elliptical orbit
Perigee altitude	300 km (190 mi)
Apogee altitude	17,438 km (10,835 mi)
Inclination	18.0°
Period	311.40 minutes
Instruments
	Angular Distribution; Directional and Omnidirectional Energetic Protons and Electrons; Electron and Proton Solid-State Detectors; Fluxgate Magnetometers; Proton-Electron Scintillation Detector
	Explorer program ← Explorer 14 Explorer 16 →

Last updated September 15, 2022

Explorer 15, also called EPE-C or Energetic Particles Explorer-C, was a NASA satellite launched as part of the Explorer program. Explorer 15 was launched on 27 October 1962, at Cape Canaveral Air Force Station, Florida, United States, with a Thor-Delta A .

Spacecraft

Explorer 15 was a spin-stabilized, solar cell-powered spacecraft instrumented to study the artificial radiation belt produced by the Starfish high-altitude nuclear burst of July 1962. The backup payload for Explorer 14 was modified and used for Explorer 15.^[1]

Instruments

The instrumentation included three sets of particle detectors to study both electrons and protons, and a two-axis fluxgate magnetometers to determine magnetic aspect. A 16-channel PFM/PM time-division multiplexed telemeter was used. The time required to sample the 16 channels (one frame period) was 0.323 seconds. Half of the channels were used to convey eight-level digital information, and the others were used for analog information. During ground processing of the telemetered data, the analog information was digitized with an accuracy of 1/100 of full scale. One analog channel was subcommutated in a pattern 16 frames long and was used to telemeter spacecraft temperatures, power system voltages, electric currents, etc. A digital solar aspect sensor measured the spin period and phase, digitized to 0.041 seconds, and the angle between the spin axis and the Sun direction to about 3° intervals. During launch the spacecraft failed to despin. The spin rate ranged from 72.9 to 73.2 rpm during the life of the spacecraft. The spin axis pointed at right ascension 80.97° and declination 20.9°.^[1]

Experiments

Directional and Omnidirectional Energetic Protons and Electrons

The UCSD Particle Experiment consisted of two plastic scintillator detectors. There was a two-level pulse-height discriminator associated with each detector. One detector was oriented perpendicular to the spacecraft spin axis and had a 16° full-angle aperture. Counting rates from the two discrimination levels of this detector yielded information on directional fluxes of electrons with energies above 0.5 MeV. The second detector was omnidirectional, and it separately measured fluxes of protons with energies from 40 MeV to 110 MeV and of electrons with energies above about 4 MeV. Counts in each of the four discrimination states were accumulated for 9.3 seconds once each 69-seconds telemetry sequence. In connection with the directional fluxes, it is significant that 9.3 seconds is about 11.3 times the spacecraft spin period. The detectors functioned normally from 27 October 1962, until 30 January 1963, after which no further data were obtained.^[5]

Electron and Proton Solid-State Detectors

Six diffused silicon p-n junction semiconductor diodes were used to measure the energy spectrum of electrons and protons in the artificial radiation belt. Detector A was sensitive to electrons in the energy range 0.5 to 2.8 MeV and to protons in the range 2.1 to 4.0 MeV. Detectors B through F were sensitive to electrons in the range 0.5 to 2.9 MeV and to protons in the range 2.1 to 22 MeV. The detectors were operated in high and low bias modes, enabling discrimination of protons from electrons. Detectors B and C were located on protruding omnidirectional mounts with a look angle of about 2 pi sr. The other four detectors looked perpendicular to the spin axis of the satellite. The detectors fed through prescalers and log rate meters to 16 analog telemetry channels. Counts were accumulated for 0.15 seconds every 0.3 seconds. All data transmission was in real time. Useful data were obtained from the experiment from launch through 23 December 1962.^[6]

Fluxgate Magnetometers

The purpose of this experiment was to measure the magnitude and direction of the earth's magnetic field between 1.7 and 3.5 Earth radii. The instrument was a two-axis, saturable-core fluxgate magnetometer. Each axis had a range of plus or minus 4000 nT and an accuracy of 40 nT. The magnetometer was mounted at the end of a boom to minimize the effects of spacecraft fields. Owing to the failure of the spacecraft to despin and the large uncertainty in the field measurements, the data were of little or no value for studies of the geomagnetic field.^[7]

Proton-Electron Scintillation Detector

This experiment was designed to measure the directional fluxes and spectra of low-energy trapped and auroral protons and electrons. It employed a 5-mg-thick powder phosphor scintillator covered with a 1000-A aluminum coating. Additional absorbers were inserted in the detector aperture by a 16-position stepped wheel. The aperture was pointed at 45° to the spin axis. Due to the thinness and type of phosphor, the detector in the pulse mode would respond only to low-energy ions, and, therefore, essentially measured the flux of protons that penetrated the absorbers and stopped in the phosphor. Both the pulse counting rate and the phototube current were telemetered once each frame period. Sixteen readings were telemetered in each wheel position, and thus one complete set of data was obtained every 256 frames (one wheel revolution=80 seconds). Protons in seven energy ranges were measured. The high-energy limit was about 10 MeV for all ranges, and the low-energy cutoffs were 105, 140, 177, 254, 512, 971, and 1668 keV. The energy fluxes of electrons in three ranges were measured separately using scatter geometry, absorbers, and the phototube current. The low-energy cutoffs were 15, 21, and 27 keV, and the high-energy cutoff was about 100 keV for all three ranges. The experiment worked well throughout the life of the spacecraft. However, the directional resolution was poor because the spin rate was higher than planned.^[8]

Related Research Articles

Explorer 4 was an American satellite launched on 26 July 1958. It was instrumented by Dr. James van Allen's group. The Department of Defense's Advanced Research Projects Agency (ARPA) had initially planned two satellites for the purposes of studying the Van Allen radiation belts and the effects of nuclear explosions upon these belts, however Explorer 4 was the only such satellite launched as the other, Explorer 5, suffered launch failure.

<span class="mw-page-title-main">Explorer 35</span> NASA satellite of the Explorer program

Explorer 35,, was a spin-stabilized spacecraft built by NASA as part of the Explorer program. Designed for the study of the interplanetary plasma, magnetic field, energetic particles, and solar X-rays, from lunar orbit.

Explorer 6, or S-2, was a NASA satellite, launched on 7 August 1959, at 14:24:20 GMT. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the upper atmosphere, and the flux of micrometeorites. It also tested a scanning device designed for photographing the Earth's cloud cover. On 14 August 1959, Explorer 6 took the first photos of Earth from a satellite.

<span class="mw-page-title-main">Explorer 5</span> United States satellite launched in 1958

Explorer 5 was a United States satellite with a mass of 17.43 kg (38.4 lb). It was the last of the original series of Explorer satellites built, designed, and operated by the Jet Propulsion Laboratory.

<span class="mw-page-title-main">Explorer 33</span> NASA satellite of the Explorer program

Explorer 33, also known as IMP-D and AIMP-1, was a spacecraft in the Explorer program launched by NASA on 1 July 1966 on a mission of scientific exploration. It was the fourth satellite launched as part of the Interplanetary Monitoring Platform series, and the first of two "Anchored IMP" spacecraft to study the environment around Earth at lunar distances, aiding the Apollo program. It marked a departure in design from its predecessors, IMP-A through IMP-C. Explorer 35 was the companion spacecraft to Explorer 33 in the Anchored IMP program, but Explorer 34 (IMP-F) was the next spacecraft to fly, launching about two months before AIMP-E, both in 1967.

<span class="mw-page-title-main">Explorer 18</span> NASA satellite of the Explorer program

Explorer 18, also called IMP-A, IMP-1, Interplanetary Monitoring Platform-1 and S-74, was a NASA satellite launched as part of the Explorer program. Explorer 18 was launched on 27 November 1963 from Cape Canaveral Air Force Station (CCAFS), Florida, with a Thor-Delta C launch vehicle. Explorer 18 was the first satellite of the Interplanetary Monitoring Platform (IMP). Explorer 21 (IMP-B) launched in October 1964 and Explorer 28 (IMP-C) launched in May 1965 also used the same general spacecraft design.

Explorer 14, also called EPE-B or Energetic Particles Explorer-B, was a NASA spacecraft instrumented to measure cosmic-ray particles, trapped particles, solar wind protons, and magnetospheric and interplanetary magnetic fields. It was the second of the S-3 series of spacecraft, which also included Explorer 12, 14, 15, and 26. It was launched on 2 October 1962, aboard a Thor-Delta launch vehicle.

Explorer 10 was a NASA satellite that investigated Earth's magnetic field 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.

The ISEE-2 was an Explorer-class daughter spacecraft, International Sun-Earth Explorer-2, was part of the mother/daughter/heliocentric mission. ISEE-2 was a 165.78 kg (365.5 lb) space probe used to study magnetic fields near the Earth. ISEE-2 was a spin-stabilized spacecraft and based on the design of the prior IMP series of spacecraft. ISEE-1 and ISEE-2 were launched on 22 October 1977, and they re-entered on 26 September 1987.

Explorer 12, also called EPE-A or Energetic Particles Explorer-A and as S3), was a NASA satellite built to measure the solar wind, cosmic rays, and the Earth's magnetic field. It was the first of the S-3 series of spacecraft, which also included Explorer 12, 14, 15, and 26. It was launched on 16 August 1961, aboard a Thor-Delta launch vehicle. It ceased transmitting on 6 December 1961 due to power failure.

Explorer 26 was a NASA satellite launched on 21 December 1964, as part of NASA's Explorer program. Its primary mission was to study the Earth's magnetic field.

Explorer 28, also called IMP-C, IMP-3 and Interplanetary Monitoring Platform-3, was a NASA satellite launched on 29 May 1965 to study space physics, and was the third spacecraft launched in the Interplanetary Monitoring Platform program. It was powered by chemical batteries and solar panels. There were 7 experiments on board, all devoted to particle studies. Performance was normal until late April 1967, when intermittent problems began. It stayed in contact until 12 May 1967, when contact was lost. The orbit decayed until it re-entered the atmosphere on 4 July 1968. The spacecraft design was similar to its predecessors Explorer 18 (IMP-A), launched in November 1963, and Explorer 21 (IMP-B), launched in October 1964, though this satellite was a few kilograms lighter. The successor Explorer 33 (IMP-D) began the use of a new design.

Explorer 21, also called IMP-B, IMP-2 and Interplanetary Monitoring Platform-2, was a NASA satellite launched as part of Explorer program. Explorer 21 was launched on 4 October 1964, at 03:45:00 GMT from Cape Canaveral (CCAFS), Florida, with a Thor-Delta C launch vehicle. Explorer 21 was the second satellite of the Interplanetary Monitoring Platform, and used the same general design as its predecessor, Explorer 18 (IMP-A), launched the previous year, in October 1964. The following Explorer 28 (IMP-C), launched in May 1965, also used a similar design.

Explorer 25, was a NASA magnetically aligned satellite launched simultaneously with Explorer 24 (AD-B) using a Scout X-4 launch vehicle. This was NASA's first dual-satellite launch. The satellite's primary mission was to make measurements of the influx of energetic particles into the atmosphere of Earth and to study atmospheric heating and the increase in scale height which have been correlated with geomagnetic activity. Studies of the natural and artificial trapped Van Allen radiation belts were also conducted. A biaxial fluxgate magnetometer was used to monitor the orientation of the spacecraft with respect to the local magnetic field.

Explorer 34, was a NASA satellite launched as part of Explorer program. Explorer 34 as launched on 24 May 1967 from Vandenberg Air Force Base, California, with Thor-Delta E1 launch vehicle. Explorer 34 was the fifth satellite launched as part of the Interplanetary Monitoring Platform program, but was known as "IMP-4" because the preceding launch was more specifically part of the "Anchored IMP" sub-program. The spacecraft was put into space between the launches of Explorer 33 in 1966 and Explorer 35 in July 1967, but the next satellite to use Explorer 34's general design was Explorer 41, which flew in 1969.

Explorer 41, also called as IMP-G and IMP-5, was a NASA satellite launched as part of Explorer program. Explorer 41 as launched on 21 June 1969 on Vandenberg AFB, California, with a Thor-Delta E1 launch vehicle. Explorer 41 was the seventh satellite launched as part of the overall Interplanetary Monitoring Platform series, though it received the post-launch designation "IMP-5" because two previous flights had used the "AIMP" designation instead. It was preceded by the second of those flights, Explorer 35, launched in July 1967. Its predecessor in the strict IMP series of launches was Explorer 34, launched in May 1967, which shared a similar design to Explorer 41. The next launch was of an IMP satellite was Explorer 43 in 1971.

Explorer 43, also called as IMP-I and IMP-6, was a NASA satellite launched as part of Explorer program. Explorer 43 was launched on 13 March 1971 from Cape Canaveral Air Force Station (CCAFS), with a Thor-Delta M6 launch vehicle. Explorer 43 was the sixth satellite of the Interplanetary Monitoring Platform.

Explorer 45 was a NASA satellite launched as part of Explorer program. Explorer 45 was the only one to be released from the program Small Scientific Satellite.

Explorer 47, was a NASA satellite launched as part of Explorer program. Explorer 47 was launched on 23 September 1972 from Cape Canaveral, Florida, with a Thor-Delta 1604. Explorer 47 was the ninth overall launch of the Interplanetary Monitoring Platform series, but received the launch designation "IMP-7" because two previous "Anchored IMP" flights had used "AIMP" instead.

Explorer 50, also known as IMP-J or IMP-8, was a NASA satellite launched to study the magnetosphere. It was the eighth and last in a series of the Interplanetary Monitoring Platform.

References

1 2 3 "Display: Explorer 15 1962-059A". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .
↑ "Launch Log". Jonathan's Space Report. 21 July 2021. Retrieved 6 November 2021.
↑ "EPE". Encyclopedia Astronautica. Archived from the original on 27 December 2016. Retrieved 9 June 2018.
↑ "Trajectory: Explorer 15 1962-059A". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .
↑ "Experiment: Directional and Omnidirectional Energetic Protons and Electrons". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .
↑ "Experiment: Electron and Proton Solid-State Detectors". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .
↑ "Experiment: Fluxgate Magnetometers". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .
↑ "Experiment: Proton-Electron Scintillation Detector". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

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[Display-1] 1 2 3 "Display: Explorer 15 1962-059A". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

[JSR-2] "Launch Log". Jonathan's Space Report. 21 July 2021. Retrieved 6 November 2021.

[astronautix-3] "EPE". Encyclopedia Astronautica. Archived from the original on 27 December 2016. Retrieved 9 June 2018.

[Trajectory-4] "Trajectory: Explorer 15 1962-059A". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

[Experiment2-5] "Experiment: Directional and Omnidirectional Energetic Protons and Electrons". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

[Experiment1-6] "Experiment: Electron and Proton Solid-State Detectors". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

[Experiment6-7] "Experiment: Fluxgate Magnetometers". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

[Experiment5-8] "Experiment: Proton-Electron Scintillation Detector". NASA. 28 October 2021. Retrieved 6 November 2021.This article incorporates text from this source, which is in the public domain .

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