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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Advanced Composition Explorer | 2/4 | https://en.wikipedia.org/wiki/Advanced_Composition_Explorer | reference | science, encyclopedia | 2026-05-05T12:47:43.911410+00:00 | kb-cron |
The Electron, Proton, and Alpha Monitor (EPAM) instrument on the ACE spacecraft is designed to measure a broad range of energetic particles over nearly the full unit-sphere at high time resolution. Such measurements of ions and electrons in the range of a few tens of keV to several MeV are essential to understand the dynamics of solar flares, co-rotating interaction regions (CIRs), interplanetary shock acceleration, and upstream terrestrial events. The large dynamic range of EPAM extends from about 50 keV to 5 MeV for ions, and 40 keV to about 350 keV for electrons. To complement its electron and ion measurements, EPAM is also equipped with a Composition Aperture (CA) which unambiguously identifies ion species reported as species group rates and/or individual pulse-height events. The instrument achieves its large spatial coverage through five telescopes oriented at various angles to the spacecraft spin axis. The low-energy particle measurements, obtained as time resolutions between 1.5 and 24 seconds, and the ability of the instrument to observe particle anisotropies in three dimensions make EPAM an excellent resource to provide the interplanetary context for studies using other instruments on the ACE spacecraft.
=== Magnetometer (MAG) ===
The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium. These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particle distributions. The experiment consists of a pair of twin, boom-mounted, triaxial flux gate sensors which are located 165 inches (419 cm) from the center of the spacecraft on opposing solar panels. The two triaxial sensors provide a balanced, fully redundant vector instrument and permit some enhanced assessment of the spacecraft's magnetic field.
=== Real-Time Solar Wind (RTSW) === The Real-Time Solar Wind (RTSW) system is continuously monitoring the solar wind and producing warnings of impending major geomagnetic activity, up to one hour in advance. Warnings and alerts issued by NOAA allow those with systems sensitive to such activity to take preventative action. The RTSW system gathers solar wind and energetic particle data at high time resolution from four ACE instruments (MAG, SWEPAM, EPAM, and SIS), packs the data into a low-rate bit stream, and broadcasts the data continuously. NASA sends real-time data to NOAA each day when downloading science data. With a combination of dedicated ground stations (CRL in Japan and RAL in Great Britain) and time on existing ground tracking networks (NASA DSN and the USAF's AFSCN), the RTSW system can receive data 24 hours per day throughout the year. The raw data are immediately sent from the ground station to the Space Weather Prediction Center in Boulder, Colorado, processed, and then delivered to its Space Weather Operations Center where they are used in daily operations; the data are also delivered to the CRL Regional Warning Center at Hiraiso Station, Japan, to the USAF 55th Space Weather Squadron, and placed on the World Wide Web. The data are downloaded, processed and dispersed within 5 minutes from the time they leave ACE. The RTSW system also uses the low-energy energetic particles to warn of approaching interplanetary shocks and to help monitor the flux of high-energy particles that can produce radiation damage in satellite systems.
=== Solar Energetic Particle Ionic Charge Analyzer (SEPICA) ===
The Solar Energetic Particle Ionic Charge Analyzer (SEPICA) was the instrument on the Advanced Composition Explorer (ACE) that determined the ionic charge states of solar and interplanetary energetic particles in the energy range from ≈0.2 MeV nucl-1 to ≈5 MeV charge-1. The charge state of energetic ions contains key information to unravel source temperatures, acceleration, fractionation, and transport processes for these particle populations. SEPICA had the ability to resolve individual charge states with a substantially larger geometric factor than its predecessor ULEZEQ on ISEE-1 and ISEE-3, on which SEPICA was based. To achieve these two requirements at the same time, SEPICA was composed of one high-charge resolution sensor section and two low-charge resolution, but large geometric factor sections. As of 2008, this instrument is no longer functioning due to failed gas valves.
=== Solar Isotope Spectrometer (SIS) ===
The Solar Isotope Spectrometer (SIS) provides high-resolution measurements of the isotopic composition of energetic nuclei from He to Zn (Z=2 to 30) over the energy range from ~10 to ~100 MeV/nucleon. During large solar events, SIS measures the isotopic abundances of solar energetic particles to determine directly the composition of the solar corona and to study particle acceleration processes. During solar quiet times, SIS measures the isotopes of low-energy cosmic rays from the Galaxy and isotopes of the anomalous cosmic ray component, which originates in the nearby interstellar medium. SIS has two telescopes composed of silicon solid-state detectors that provide measurements of the nuclear charge, mass, and kinetic energy of incident nuclei. Within each telescope, particle trajectories are measured with a pair of two-dimensional silicon strip detectors instrumented with custom very-large-scale integrated (VLSI) electronics to provide both position and energy-loss measurements. SIS was specially designed to achieve excellent mass resolution under the extreme, high flux conditions encountered in large solar particle events. It provides a geometry factor of 40 cm2 sr, significantly greater than earlier solar particle isotope spectrometers.
=== Solar Wind Electron, Proton and Alpha Monitor (SWEPAM) ===