Advanced Composition Explorer

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Advanced Composition Explorer
Advanced Composition Explorer.jpg
An artist's concept of ACE
NamesExplorer 71
ACE
Mission type Solar research
Operator NASA
COSPAR ID 1997-045A OOjs UI icon edit-ltr-progressive.svg
SATCAT no. 24912
Website www.srl.caltech.edu/ACE/
Mission duration5 years (planned)
26 years, 7 months and 27 days
(in progress)
Spacecraft properties
SpacecraftExplorer LXXI
Spacecraft typeAdvanced Composition Explorer
Bus ACE
Manufacturer Johns Hopkins Applied Physics Laboratory
Launch mass757 kg (1,669 lb)
Dry mass562 kg (1,239 lb)
Dimensions2 m (6 ft 7 in) in diameter
1.9 m (6 ft 3 in) in length
wingspan of 8.3 m (27 ft)
Power444 watts
Start of mission
Launch date25 August 1997, 14:39:00 UTC
Rocket Delta II 7920-8
Launch site Cape Canaveral LC-17A
Contractor McDonnell Douglas
Entered service12 December 1997
End of mission
Deactivated2024 (planned)
Orbital parameters
Reference system Heliocentric orbit
Regime Lissajous orbit
Perigee altitude 145,700,000 km (90,500,000 mi)
Apogee altitude 150,550,000 km (93,550,000 mi)
Inclination ~0°
Period 1 year
Instruments
Cosmic-Ray Isotope Spectrometer (CRIS)
Electron, Proton, and Alpha-particle Monitor (EPAM)
Magnetometer (MAG)
Real-Time Solar Wind (RTSW)
Solar Energetic Particle Ionic Charge Analyzer (SEPICA)
Solar Wind Electron, Proton and Alpha Monitor (SWEPAM)
Solar Isotope Spectrometer (SIS)
Solar Wind Ion Composition Spectrometer (SWICS) and Solar Wind Ion Mass Spectrometer (SWIMS)
Ultra-Low-Energy Isotope Spectrometer (ULEIS)
ACE mission logo.png
ACE mission patch  
Explorer program
←  Fast Auroral SnapshoT Explorer (Explorer 70)
Student Nitric Oxide Explorer (Explorer 72) →
Animation of Advanced Composition Explorer's orbit viewed from the Sun .mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{} Earth * Advanced Composition Explorer Animation of Advanced Composition Explorer's orbit viewed from the Sun.gif
Animation of Advanced Composition Explorer's orbit viewed from the Sun
  Earth ·  Advanced Composition Explorer
ACE in orbit around the Sun-Earth L1 point. Advanced Composition Explorer in space.jpg
ACE in orbit around the Sun–Earth L1 point.

Advanced Composition Explorer (ACE or Explorer 71) is a NASA Explorer program satellite and space exploration mission to study matter comprising energetic particles from the solar wind, the interplanetary medium, and other sources.

Contents

Real-time data from ACE are used by the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) to improve forecasts and warnings of solar storms. [1] The ACE robotic spacecraft was launched on 25 August 1997, and entered a Lissajous orbit close to the L1 Lagrange point (which lies between the Sun and the Earth at a distance of some 1,500,000 km (930,000 mi) from the latter) on 12 December 1997. [2] The spacecraft is currently operating at that orbit. Because ACE is in a non-Keplerian orbit, and has regular station-keeping maneuvers, the orbital parameters in the adjacent information box are only approximate.

As of 2023, [3] the spacecraft is still in generally good condition, and is projected to have enough propellant to maintain its orbit until 2024. [4] NASA Goddard Space Flight Center managed the development and integration of the ACE spacecraft. [5]

History

The Advanced Composition Explorer (ACE) was proposed in 1986 as part of the Explorer Concept Study Program. ACE is designed to make coordinated measurements of the elemental and isotopic composition of accelerated nuclei from H (Hydrogen) to Zn (Zinc) spanning six decades in energy per nucleon, from solar wind to galactic cosmic ray energies, with sensitivity and with charge and mass resolution much better than heretofore possible. Following a Phase-A definition study, ACE was selected for development in 1989, and began construction in 1994. On 25 August 1997, ACE was successfully launched from Cape Canaveral Air Force Station by a Delta II launch vehicle. The August 1997 launch was originally scheduled back in 1993. [6]

Science objectives

ACE observations allow the investigation of a wide range of fundamental problems in the following four major areas: [7]

Elemental and isotopic composition of matter

A major objective is the accurate and comprehensive determination of the elemental and isotopic composition of the various samples of "source material" from which nuclei are accelerated. These observations have been used to:

Origin of the elements and subsequent evolutionary processing

Isotopic "anomalies" in meteorites indicate that the Solar System was not homogeneous when formed. Similarly, the Galaxy is neither uniform in space nor constant in time due to continuous stellar nucleosynthesis.

ACE measurements have been used to:

Formation of the solar corona and acceleration of the solar wind

Solar energetic particles, solar wind, and spectroscopic observations show that the elemental composition of the solar corona is differentiated from that of the photosphere, although the processes by which this occurs, and by which the solar wind is subsequently accelerated, are poorly understood. The detailed composition and charge–state data provided by ACE are used to:

Particle acceleration and transport in nature

Particle acceleration is ubiquitous in nature and understanding its nature is one of the fundamental problems of space plasma astrophysics. The unique data set obtained by ACE measurements have been used to:

Instruments

Cosmic-Ray Isotope Spectrometer (CRIS)

The Cosmic-Ray Isotope Spectrometer covers the highest range of the Advanced Composition Explorer's energy coverage, from 50 to 500 MeV/nucleon, with an isotopic resolution for elements from Z ≈ 2 to 30. The nuclei detected in this energy interval are predominantly cosmic rays originating in our Galaxy. This sample of galactic matter investigates the nucleosynthesis of the parent material, as well as fractionation, acceleration, and transport processes that these particles undergo in the Galaxy and in the interplanetary medium. Charge and mass identification with CRIS is based on multiple measurements of dE/dx and total energy in stacks of silicon detectors, and trajectory measurements in a scintillating optical fiber trajectory (SOFT) hodoscope. The instrument has a geometrical factor of 250 cm2 (39 sq in)-sr for isotope measurements. [8]

Electron, Proton, and Alpha-particle Monitor (EPAM)

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 (CIR's), 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. [9]

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. [10]

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. [11]

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. [12]

As of 2008, this instrument is no longer functioning due to failed gas valves. [4]

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. [13]

Solar Wind Electron, Proton and Alpha Monitor (SWEPAM)

The Solar Wind Electron Proton Alpha Monitor (SWEPAM) experiment provides the bulk solar wind observations for the Advanced Composition Explorer (ACE). These observations provide the context for elemental and isotopic composition measurements made on ACE as well as allowing the direct examination of numerous solar wind phenomena such as coronal mass ejection, interplanetary shocks, and solar wind fine structure, with advanced, 3-D plasma instrumentation. They also provide an ideal data set for both heliospheric and magnetospheric multi-spacecraft studies where they can be used in conjunction with other, simultaneous observations from spacecraft such as Ulysses. The SWEPAM observations are made simultaneously with independent electron (SWEPAM-e) and ion (SWEPAM-i) instruments. In order to save costs for the ACE project, SWEPAM-e and SWEPAM-i are the recycled flight spares from the joint NASA/ESA Ulysses mission. Both instruments had selective refurbishment, modification, and modernization required to meet the ACE mission and spacecraft requirements. Both incorporate electrostatic analyzers whose fan-shaped fields of view sweep out all pertinent look directions as the spacecraft spins. [14]

Solar Wind Ion Composition Spectrometer (SWICS) and Solar Wind Ion Mass Spectrometer (SWIMS)

The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments optimized for measurements of the chemical and isotopic composition of solar and interstellar matter. SWICS determined uniquely the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from H through Fe at all solar wind speeds above 300 km/s−1 (protons) and 170 km/s−1 (Fe+16), and resolved H and He isotopes of both solar and interstellar sources. SWICS also measured the distribution functions of both the interstellar cloud and dust cloud pickup ions up to energies of 100 keV/e−1. SWIMS measures the chemical, isotopic and charge state composition of the solar wind for every element between He and Ni. Each of the two instruments are time-of-flight mass spectrometers and use electrostatic analysis followed by the time-of-flight and, as required, an energy measurement. [15] [16]

On 23 August 2011, the SWICS time-of-flight electronics experienced an age- and radiation-induced hardware anomaly that increased the level of background in the composition data. To mitigate the effects of this background, the model for identifying ions in the data was adjusted to take advantage of only the ion energy-per-charge as measured by the electrostatic analyzer, and the ion energy as measured by solid-state detectors. This has allowed SWICS to continue to deliver a subset of the data products that were provided to the public prior to the hardware anomaly, including ion charge state ratios of oxygen and carbon, and measurements of solar wind iron. The measurements of proton density, speed, and thermal speed by SWICS were not affected by this anomaly and continue to the present day. [4]

Ultra-Low-Energy Isotope Spectrometer (ULEIS)

The Ultra-Low-Energy Isotope Spectrometer (ULEIS) on the ACE spacecraft is an ultra-high-resolution mass spectrometer that measures particle composition and energy spectra of elements He–Ni with energies from ~45 keV/nucleon to a few MeV/nucleon. ULEIS investigates particles accelerated in solar energetic particle events, interplanetary shocks, and at the solar wind termination shock. By determining energy spectra, mass composition, and temporal variations in conjunction with other ACE instruments, ULEIS greatly improves our knowledge of solar abundances, as well as other reservoirs such as the local interstellar medium. ULEIS combines the high sensitivity required to measure low particle fluxes, along with the capability to operate in the largest solar particle or interplanetary shock events. In addition to detailed information for individual ions, ULEIS features a wide range of count rates for different ions and energies that allows accurate determination of particle fluxes and anisotropies over short (few minutes) time scales. [17]

Science results

The spectra of particles observed by ACE

An oxygen fluence observed by ACE (Figure 1) ACE O Fluence.png
An oxygen fluence observed by ACE (Figure 1)

Figure 1 shows the particle fluence (total flux over a given period of time) of oxygen at ACE for a time period just after solar minimum, the part of the 11-year solar cycle when solar activity is lowest. [18] The lowest-energy particles come from the slow and fast solar wind, with speeds from about 300 to about 800 km/s. Like the solar wind distribution of all ions, that of oxygen has a suprathermal tail of higher-energy particles; that is, in the frame of the bulk solar wind, the plasma has an energy distribution that is approximately a thermal distribution but has a notable excess above about 5 keV, as shown in Figure 1. The ACE team has made contributions to understanding the origins of these tails and their role in injecting particles into additional acceleration processes.

At energies higher than those of the solar wind particles, ACE observes particles from regions known as corotating interaction regions (CIRs). CIRs form because the solar wind is not uniform. Due to solar rotation, high-speed streams collide with preceding slow solar wind, creating shock waves at roughly 2–5 astronomical units (AU, the distance between Earth and the Sun) and forming CIRs. Particles accelerated by these shocks are commonly observed at 1 AU below energies of about 10 MeV per nucleon. ACE measurements confirm that CIRs include a significant fraction of singly charged helium formed when interstellar neutral helium is ionized. [19]

At yet higher energies, the major contribution to the measured flux of particles is due to solar energetic particles (SEPs) associated with interplanetary (IP) shocks driven by fast coronal mass ejections (CMEs) and solar flares. Enriched abundances of helium-3 and helium ions show that the suprathermal tails are the main seed population for these SEPs. [20] IP shocks traveling at speeds up to about 2,000 km/s (1,200 mi/s) accelerate particles from the suprathermal tail to 100 MeV per nucleon and more. IP shocks are particularly important because they can continue to accelerate particles as they pass over ACE and thus allow shock acceleration processes to be studied in situ.

Other high-energy particles observed by ACE are anomalous cosmic rays (ACRs) that originate with neutral interstellar atoms that are ionized in the inner heliosphere to make "pickup" ions and are later accelerated to energies greater than 10 MeV per nucleon in the outer heliosphere. ACE also observes pickup ions directly; they are easily identified because they are singlely charged. Finally, the highest-energy particles observed by ACE are the galactic cosmic rays (GCRs), thought to be accelerated by shock waves from supernova explosions in our galaxy.

Other findings from ACE

Shortly after launch, the SEP sensors on ACE detected solar events that had unexpected characteristics. Unlike most large, shock-accelerated SEP events, these were highly enriched in iron and helium-3, as are the much smaller, flare-associated impulsive SEP events. [21] [22] Within the first year of operations, ACE found many of these "hybrid" events, which led to substantial discussion within the community as to what conditions could generate them. [23]

One remarkable recent discovery in heliospheric physics has been the ubiquitous presence of suprathermal particles with common spectral shape. This shape unexpectedly occurs in the quiet solar wind; in disturbed conditions downstream from shocks, including CIRs; and elsewhere in the heliosphere. These observations have led Fisk and Gloeckler [24] to suggest a novel mechanism for the particles' acceleration.

Another discovery has been that the current solar cycle, as measured by sunspots, CMEs, and SEPs, has been much less magnetically active than the previous cycle. McComas et al. [25] have shown that the dynamic pressures of the solar wind measured by the Ulysses satellite over all latitudes and by ACE in the ecliptic plane are correlated and were declining in time for about 2 decades. They concluded that the Sun had been undergoing a global change that affected the overall heliosphere. Simultaneously, GCR intensities were increasing and in 2009 were the highest recorded during the past 50 years. [26] GCRs have more difficulty reaching Earth when the Sun is more magnetically active, so the high GCR intensity in 2009 is consistent with a globally reduced dynamic pressure of the solar wind.

ACE also measures abundances of cosmic ray nickel-59 and cobalt-59 isotopes; these measurements indicate that a time longer than the half-life of nickel-59 with bound electrons (7.6 × 104 years) elapsed between the time nickel-59 was created in a supernova explosion and the time cosmic rays were accelerated. [27] Such long delays indicate that cosmic rays come from the acceleration of old stellar or interstellar material rather than from fresh supernova ejecta. ACE also measures an iron-58/iron-56 ratio that is enriched over the same ratio in solar system material. [28] These and other findings have led to a theory of the origin of cosmic rays in galactic superbubbles, formed in regions where many supernovae explode within a few million years. Recent observations of a cocoon of freshly accelerated cosmic rays in the Cygnus superbubble by the Fermi gamma-ray observatory [29] support this theory.

Follow-on space weather observatory

On 11 February 2015, the Deep Space Climate Observatory (DSCOVR)—with several similar instruments including a newer and more sensitive instrument to detect Earth-bound coronal mass ejections—successfully launched by NASA and National Oceanic and Atmospheric Administration aboard a SpaceX Falcon 9 launch vehicle from Cape Canaveral, Florida. The spacecraft arrived at L1 by 8 June 2015, just over 100 days after launch. [30] Along with ACE, both will provide space weather data as long as ACE can continue to function. [31]

See also

Related Research Articles

<i>Ulysses</i> (spacecraft) 1990 robotic space probe; studied the Sun from a near-polar orbit

Ulysses was a robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990 and made three "fast latitude scans" of the Sun in 1994/1995, 2000/2001, and 2007/2008. In addition, the probe studied several comets. Ulysses was a joint venture of the European Space Agency (ESA) and the United States' National Aeronautics and Space Administration (NASA), under leadership of ESA with participation from Canada's National Research Council. The last day for mission operations on Ulysses was 30 June 2009.

<i>Nozomi</i> (spacecraft) Failed Mars orbiter

Nozomi was a Japanese Mars orbiter that failed to reach Mars due to electrical failure. It was constructed by the Institute of Space and Astronautical Science, University of Tokyo and launched on July 4, 1998, at 03:12 JST with an on-orbit dry mass of 258 kg and 282 kg of propellant. The Nozomi mission was terminated on December 31, 2003.

<span class="mw-page-title-main">Mars 96</span> Failed Mars mission

Mars 96 was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a 320 km (200 mi) long portion of the Pacific Ocean, Chile, and Bolivia. The Mars 96 spacecraft was based on the Phobos probes launched to Mars in 1988. They were of a new design at the time and both ultimately failed. For the Mars 96 mission the designers believed they had corrected the flaws of the Phobos probes, but the value of their improvements was never demonstrated due to the destruction of the probe during the launch phase.

<span class="mw-page-title-main">Heliosphere</span> Region of space dominated by the Sun

The heliosphere is the magnetosphere, astrosphere, and outermost atmospheric layer of the Sun. It takes the shape of a vast, tailed bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the Milky Way. As part of the interplanetary magnetic field, the heliosphere shields the Solar System from significant amounts of cosmic ionizing radiation; uncharged gamma rays are, however, not affected. Its name was likely coined by Alexander J. Dessler, who is credited with the first use of the word in the scientific literature in 1967. The scientific study of the heliosphere is heliophysics, which includes space weather and space climate.

<i>Wind</i> (spacecraft) NASA probe to study solar wind, at L1 since 1995

The Global Geospace Science (GGS) Wind satellite is a NASA science spacecraft designed to study radio waves and plasma that occur in the solar wind and in the Earth's magnetosphere. It was launched on 1 November 1994, at 09:31:00 UTC, from launch pad LC-17B at Cape Canaveral Air Force Station (CCAFS) in Merritt Island, Florida, aboard a McDonnell Douglas Delta II 7925-10 rocket. Wind was designed and manufactured by Martin Marietta Astro Space Division in East Windsor Township, New Jersey. The satellite is a spin-stabilized cylindrical satellite with a diameter of 2.4 m and a height of 1.8 m.

<span class="mw-page-title-main">Solar energetic particles</span> High-energy particles from the Sun

Solar energetic particles (SEP), formerly known as solar cosmic rays, are high-energy, charged particles originating in the solar atmosphere and solar wind. They consist of protons, electrons and heavy ions with energies ranging from a few tens of keV to many GeV. The exact processes involved in transferring energy to SEPs is a subject of ongoing study.

An electrostatic analyzer or ESA is an instrument used in ion optics that employs an electric field to allow the passage of only those ions or electrons that have a given specific energy. It usually also focuses these particles into a smaller area. ESAs are typically used as components of space instrumentation, to limit the scanning (sensing) energy range and, thereby also, the range of particles targeted for detection and scientific measurement. The closest analogue in photon optics is a filter.

<span class="mw-page-title-main">Solar Anomalous and Magnetospheric Particle Explorer</span> NASA satellite of the Explorer program

The Solar Anomalous and Magnetospheric Particle Explorer was a NASA solar and magnetospheric observatory, and was the first spacecraft in the Small Explorer program. It was launched into low Earth orbit on 3 July 1992, from Vandenberg Air Force Base aboard a Scout G-1 launch vehicle. SAMPEX was an international collaboration between NASA and the Max Planck Institute for Extraterrestrial Physics of Germany. The Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) is the first of a series of spacecraft that was launched under the Small Explorer (SMEX) program for low cost spacecraft.

<span class="mw-page-title-main">Energetic neutral atom</span> Technology to create global images of otherwise invisible phenomena

Energetic Neutral Atom (ENA) imaging is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere.

<span class="mw-page-title-main">Solar particle event</span> Solar phenomenon

In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in the Sun's atmosphere during a solar flare or in interplanetary space by a coronal mass ejection shock. Other nuclei such as helium and HZE ions may also be accelerated during the event. These particles can penetrate the Earth's magnetic field and cause partial ionization of the ionosphere. Energetic protons are a significant radiation hazard to spacecraft and astronauts.

<span class="mw-page-title-main">Heliophysics Science Division</span>

The Heliophysics Science Division of the Goddard Space Flight Center (NASA) conducts research on the Sun, its extended Solar System environment, and interactions of Earth, other planets, small bodies, and interstellar gas with the heliosphere. Division research also encompasses geospace—Earth's uppermost atmosphere, the ionosphere, and the magnetosphere—and the changing environmental conditions throughout the coupled heliosphere.

<span class="mw-page-title-main">ISEE-1</span> NASA satellite of the Explorer program

The ISEE-1 was an Explorer-class mother spacecraft, International Sun-Earth Explorer-1, was part of the mother/daughter/heliocentric mission. ISEE-1 was a 340.2 kg (750 lb) space probe used to study magnetic fields near the Earth. ISEE-1 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.

<span class="mw-page-title-main">Pickup ion</span>

In solar physics, heliospheric pickup ions are created when neutral particles inside the heliosphere are ionized by either solar ultraviolet radiation, charge exchange with solar wind protons or electron impact ionization. Pickup ions are generally characterized by their single charge state, a typical velocity that ranges between 0 km/s and twice the solar wind velocity (~800 km/s), a composition that reflects their neutral seed population and their spatial distribution in the heliosphere. The neutral seed population of these ions can either be of interstellar origin or of lunar-, cometary, or inner-source origin. Just after the ionization, the singly charged ions are picked up by the magnetized solar wind plasma and develop strong anisotropic and toroidal velocity distribution functions, which gradually transform into a more isotropic state. After their creation, pickup ions move with the solar wind radially outwards from the Sun.

<span class="mw-page-title-main">Cosmic Ray Subsystem</span> Instrument aboard the Voyager 1 and Voyager 2 spacecraft

Cosmic Ray Subsystem is an instrument aboard the Voyager 1 and Voyager 2 spacecraft of the NASA Voyager program, and it is an experiment to detect cosmic rays. The CRS includes a High-Energy Telescope System (HETS), Low-Energy Telescope System (LETS), and The Electron Telescope (TET). It is designed to detect energetic particles and some of the requirements were for the instrument to be reliable and to have enough charge resolution. It can also detect the energetic particles like protons from the Galaxy or Earth's Sun.

<span class="mw-page-title-main">Interstellar Mapping and Acceleration Probe</span> Planned NASA heliophysics mission

The Interstellar Mapping and Acceleration Probe(IMAP) is a heliophysics mission that will simultaneously investigate two important and coupled science topics in the heliosphere: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. These science topics are coupled because particles accelerated in the inner heliosphere play crucial roles in the outer heliospheric interaction. In 2018, NASA selected a team led by David J. McComas of Princeton University to implement the mission, which is currently planned to launch in late April to late May 2025. IMAP will be a Sun-tracking spin-stabilized satellite in orbit about the Sun–Earth L1 Lagrange point with a science payload of ten instruments. IMAP will also continuously broadcast real-time in-situ data that can be used for space weather prediction.

<span class="mw-page-title-main">Explorer 43</span> NASA satellite of the Explorer program

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.

<span class="mw-page-title-main">Explorer 47</span> NASA satellite of the Explorer program

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.

<span class="mw-page-title-main">Explorer 50</span> NASA satellite of the Explorer program

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.

<span class="mw-page-title-main">Pluto Energetic Particle Spectrometer Science Investigation</span> Instrument on the New Horizons space probe

Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), is an instrument on the New Horizons space probe to Pluto and beyond, it is designed to measure ions and electrons. Specifically, it is focused on measuring ions escaping from the atmosphere of Pluto during the 2015 flyby. It is one of seven major scientific instruments aboard the spacecraft. The spacecraft was launched in 2006, flew by Jupiter the following year, and went onto flyby Pluto in 2015 where PEPSSI was able to record and transmit back to Earth its planned data collections.

Antoinette (Toni) Galvin is space physicist at the University of New Hampshire. She is known for her research on the solar wind.

References

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  2. ↑ "Operations Day -- 346/1997 (12 December 1997)". srl.caltech.edu. 31 December 1997. Retrieved 28 October 2021.
  3. ↑ "ACE (Advanced Composition Explorer) - Mission Status". ESA eoPortal Directory. 15 June 2021. Retrieved 29 October 2021.
  4. 1 2 3 Christian, Eric R.; Davis, Andrew J. (10 February 2017). "Advanced Composition Explorer (ACE) Mission Overview". California Institute of Technology. Retrieved 14 December 2017.
  5. ↑ "Display: Advanced Composition Explorer (1997-045A)". NASA. 28 October 2021. Retrieved 28 November 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .
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