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.

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.

[8] 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 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.

The charge state of energetic ions contains key information to unravel source temperatures, acceleration, fractionation, and transport processes for these particle populations.

SIS has two telescopes composed of silicon solid-state detectors that provide measurements of the nuclear charge, mass, and kinetic energy of incident nuclei.

SIS was specially designed to achieve excellent mass resolution under the extreme, high flux conditions encountered in large solar particle events.

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.

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.

[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.

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.

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.

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.

This shape unexpectedly occurs in the quiet solar wind; in disturbed conditions downstream from shocks, including CIRs; and elsewhere in the heliosphere.

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.

[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.

[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.