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Explorer 50
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.
Explorer 50 was a drum-shaped spacecraft, 135.6 cm (53.4 in) across and 157.4 cm (62.0 in) height, with propulsion Star-17A, instrumented for interplanetary medium and magnetotail studies of cosmic rays, energetic solar particles, plasma, and electric and magnetic fields. Its initial orbit was more elliptical than intended, with apogee and perigee distances of about 45.26 Earth radii and 22.11 Earth radii. Its orbital eccentricity decreased after launch. Its orbital inclination varied between 0 deg and about 55° with a periodicity of several years. The spacecraft spin axis was normal to the ecliptic plane, and the spin rate was 23 rpm. The data telemetry rate was 1600 bit/s. The spacecraft was in the solar wind for 7 to 8 days of every 11.99 days orbit. Telemetry coverage was 90% in the early years, but only 60-70% through most of the 1980s and early 1990s. Coverage returned to the 90% range in the mid to late 1990s.
Explorer 50 was launched on 23 October 1973 at 02:26:03 UTC, by a Thor-Delta 1604 launch vehicle from Cape Canaveral (CCAFS), Florida. The spacecraft functioned nominally until 7 October 2006. The satellite orbited the Earth once every 12 days, at an inclination of 28.67°. Its perigee was 25 Earth radii and apogee was 45 Earth radii.
Three solid-state detectors in an anticoincidence plastic scintillator observed electrons between 0.2 and 2.5 MeV; protons between 0.3 and 500 MeV; alpha particles between 2.0 and 200 MeV; heavy particles with Z values ranging from 2 to 5 with energies greater than 8 MeV; heavy particles with Z values ranging between 6 and 8 with energies greater than 32 MeV; and integral protons and alphas of energies greater than 50 MeV/nucleon, all with dynamic ranges of 1 to 1E+6 particles per (cm2-second-sr). Five thin-window Geiger–Müller tubes observed electrons of energy greater than 15 keV, protons of energy greater than 250 keV, and X-rays with wavelengths between 2 and 10 A, all with a dynamic range of 10 to 1E+8 per (cm2-second-sr). Particles and X-rays, primarily of solar origin, were studied, but the dynamic range and resolution of the instrument also permitted observation of cosmic rays and magnetotail particles.
This experiment used two telescopes to measure the composition and energy spectra of solar (and galactic) particles above about 0.5 MeV/nucleon. The main telescope consisted of five collinear elements (three solid state, one Caesium iodide (CsI), and one sapphire Cherenkov) surrounded by a plastic anticoincidence shield. The telescope had a 60°, full-angle acceptance cone with its axis approximately normal to the spacecraft spin axis, permitting eight-sectored information on particle arrival direction. Four elements of the main telescope were pulse-height analyzed, and low- and high-gain modes could be selected by command to permit resolution of the elements Hydrogen (H) through Nickel (Ni) or of electrons and the isotopes of Hydrogen (H) and Helium (He) and light nuclei. A selection-priority scheme was included to permit sampling of less abundant particle species under normal and solar-flare conditions. The low-energy telescope was essentially a two-element shielded solid-state detector with a 70° full-angle acceptance cone. The first element was pulse-height analyzed, and data were recorded by sectors.
This experiment was designed to measure the differential energy spectra of the isotopes of hydrogen through oxygen from 2 to 40-MeV/nucleon, and of electrons from 0.2 to 5-MeV. The instrument consisted of a stack of 11 fully depleted silicon solid-state detectors surrounded by a plastic scintillator anticoincidence cup. The outer two solid-state detectors were annular, permitting measurements in both narrow-geometry (typical geometrical factor was 0.2 cm2-sr) and wide-geometry (typical geometric factor was 1.5 cm2-sr) coincidence modes. Anisotropy data (45° angular and 20 seconds temporal resolution) were obtained.
The instrument was designed to measure ambient electric fields in the solar wind and the Earth's magnetosheath up to 1 kHz in frequency. The sensor consisted of a pair of 70 m (230 ft) wire antennas (140 m (460 ft), tip-to-tip), which were held rigid by centrifugal force due to satellite spin (about 24 rpm). The wires were insulated from the plasma, except for their short outer sections, to remove the active probe area from the spacecraft sheath. The antenna served as a double floating probe, and measurements were obtained every 1/4 spacecraft revolution (about 0.75 second). Ultra low frequency (ULF) and Very low frequency (VLF) measurements were obtained using seven 60% bandwidth filters with center frequencies logarithmically spaced from 1-Hz to 1000-Hz. These frequency channels had an intrinsic sensitivity of 1.0E-5 V/m, and a peak range of 1.0E-2 V/m. However, the effective low-frequency filter threshold was determined by interference due to harmonics of the spacecraft spinning within an asymmetric sheath. The other major limitation was also due to sheath effect. Whenever the electron plasma density was less than about 10 particles/cc, the sheath overlapped the active antenna portions and precluded meaningful measurements of ambient conditions.
A wide-band receiver was used to observe high-resolution frequency-time spectra, and a six-channel narrow-band receiver with a variable center frequency was used to observe wave characteristics. The receivers operated from three antenna systems. The first system contained a pair of long dipole antennas (one, extendable to about 124 m (407 ft), normal to the spacecraft spin axis and the other antenna, extendable to about 6.1 m (20 ft), along the spin axis). The second system contained a boom-mounted triad of orthogonal loop antennas. The third system consisted of a boom-mounted 0.51 m (1 ft 8 in) spin-axis dipole. The magnetic and electric field intensities and frequency spectra, polarization, and direction of arrival of naturally occurring radio noise in the magnetosphere were observed. Phenomena studied were the time-space distribution, origin, propagation, dispersion, and other characteristics of radio noise occurring across and on either side of the magnetospheric boundary region. The frequency range for electric fields was 0.3 Hz to 200 kHz, and for magnetic fields it was 20 Hz to 200 kHz.
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Explorer 50
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.
Explorer 50 was a drum-shaped spacecraft, 135.6 cm (53.4 in) across and 157.4 cm (62.0 in) height, with propulsion Star-17A, instrumented for interplanetary medium and magnetotail studies of cosmic rays, energetic solar particles, plasma, and electric and magnetic fields. Its initial orbit was more elliptical than intended, with apogee and perigee distances of about 45.26 Earth radii and 22.11 Earth radii. Its orbital eccentricity decreased after launch. Its orbital inclination varied between 0 deg and about 55° with a periodicity of several years. The spacecraft spin axis was normal to the ecliptic plane, and the spin rate was 23 rpm. The data telemetry rate was 1600 bit/s. The spacecraft was in the solar wind for 7 to 8 days of every 11.99 days orbit. Telemetry coverage was 90% in the early years, but only 60-70% through most of the 1980s and early 1990s. Coverage returned to the 90% range in the mid to late 1990s.
Explorer 50 was launched on 23 October 1973 at 02:26:03 UTC, by a Thor-Delta 1604 launch vehicle from Cape Canaveral (CCAFS), Florida. The spacecraft functioned nominally until 7 October 2006. The satellite orbited the Earth once every 12 days, at an inclination of 28.67°. Its perigee was 25 Earth radii and apogee was 45 Earth radii.
Three solid-state detectors in an anticoincidence plastic scintillator observed electrons between 0.2 and 2.5 MeV; protons between 0.3 and 500 MeV; alpha particles between 2.0 and 200 MeV; heavy particles with Z values ranging from 2 to 5 with energies greater than 8 MeV; heavy particles with Z values ranging between 6 and 8 with energies greater than 32 MeV; and integral protons and alphas of energies greater than 50 MeV/nucleon, all with dynamic ranges of 1 to 1E+6 particles per (cm2-second-sr). Five thin-window Geiger–Müller tubes observed electrons of energy greater than 15 keV, protons of energy greater than 250 keV, and X-rays with wavelengths between 2 and 10 A, all with a dynamic range of 10 to 1E+8 per (cm2-second-sr). Particles and X-rays, primarily of solar origin, were studied, but the dynamic range and resolution of the instrument also permitted observation of cosmic rays and magnetotail particles.
This experiment used two telescopes to measure the composition and energy spectra of solar (and galactic) particles above about 0.5 MeV/nucleon. The main telescope consisted of five collinear elements (three solid state, one Caesium iodide (CsI), and one sapphire Cherenkov) surrounded by a plastic anticoincidence shield. The telescope had a 60°, full-angle acceptance cone with its axis approximately normal to the spacecraft spin axis, permitting eight-sectored information on particle arrival direction. Four elements of the main telescope were pulse-height analyzed, and low- and high-gain modes could be selected by command to permit resolution of the elements Hydrogen (H) through Nickel (Ni) or of electrons and the isotopes of Hydrogen (H) and Helium (He) and light nuclei. A selection-priority scheme was included to permit sampling of less abundant particle species under normal and solar-flare conditions. The low-energy telescope was essentially a two-element shielded solid-state detector with a 70° full-angle acceptance cone. The first element was pulse-height analyzed, and data were recorded by sectors.
This experiment was designed to measure the differential energy spectra of the isotopes of hydrogen through oxygen from 2 to 40-MeV/nucleon, and of electrons from 0.2 to 5-MeV. The instrument consisted of a stack of 11 fully depleted silicon solid-state detectors surrounded by a plastic scintillator anticoincidence cup. The outer two solid-state detectors were annular, permitting measurements in both narrow-geometry (typical geometrical factor was 0.2 cm2-sr) and wide-geometry (typical geometric factor was 1.5 cm2-sr) coincidence modes. Anisotropy data (45° angular and 20 seconds temporal resolution) were obtained.
The instrument was designed to measure ambient electric fields in the solar wind and the Earth's magnetosheath up to 1 kHz in frequency. The sensor consisted of a pair of 70 m (230 ft) wire antennas (140 m (460 ft), tip-to-tip), which were held rigid by centrifugal force due to satellite spin (about 24 rpm). The wires were insulated from the plasma, except for their short outer sections, to remove the active probe area from the spacecraft sheath. The antenna served as a double floating probe, and measurements were obtained every 1/4 spacecraft revolution (about 0.75 second). Ultra low frequency (ULF) and Very low frequency (VLF) measurements were obtained using seven 60% bandwidth filters with center frequencies logarithmically spaced from 1-Hz to 1000-Hz. These frequency channels had an intrinsic sensitivity of 1.0E-5 V/m, and a peak range of 1.0E-2 V/m. However, the effective low-frequency filter threshold was determined by interference due to harmonics of the spacecraft spinning within an asymmetric sheath. The other major limitation was also due to sheath effect. Whenever the electron plasma density was less than about 10 particles/cc, the sheath overlapped the active antenna portions and precluded meaningful measurements of ambient conditions.
A wide-band receiver was used to observe high-resolution frequency-time spectra, and a six-channel narrow-band receiver with a variable center frequency was used to observe wave characteristics. The receivers operated from three antenna systems. The first system contained a pair of long dipole antennas (one, extendable to about 124 m (407 ft), normal to the spacecraft spin axis and the other antenna, extendable to about 6.1 m (20 ft), along the spin axis). The second system contained a boom-mounted triad of orthogonal loop antennas. The third system consisted of a boom-mounted 0.51 m (1 ft 8 in) spin-axis dipole. The magnetic and electric field intensities and frequency spectra, polarization, and direction of arrival of naturally occurring radio noise in the magnetosphere were observed. Phenomena studied were the time-space distribution, origin, propagation, dispersion, and other characteristics of radio noise occurring across and on either side of the magnetospheric boundary region. The frequency range for electric fields was 0.3 Hz to 200 kHz, and for magnetic fields it was 20 Hz to 200 kHz.
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