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| AP8/AE8 | |
|---|---|
| Name | AP8/AE8 |
| Type | Radiation belt models |
| Developer | National Aeronautics and Space Administration; United States Air Force |
| First release | 1960s |
| Latest release | 1990s |
| Language | English |
| Domain | Space environment |
AP8/AE8
AP8/AE8 are legacy empirical models of the Earth's trapped proton and electron radiation belts used for spacecraft design and mission planning. These models synthesize measurements from satellite missions and instrument campaigns to provide omnidirectional flux maps and spectral fits for protons and electrons in low Earth orbit and geostationary environments. They have influenced radiation hardening, mission planning, and standards across agencies and contractors.
AP8 and AE8 were developed to characterize the Van Allen radiation belts observed by early satellites such as Explorer 1, Vanguard 1, Luna 1, and later spacecraft including Sputnik 3 and Pioneer 3. AP8 describes trapped proton fluxes while AE8 describes trapped electron fluxes; both provide flux as functions of spatial coordinates typically expressed in L-shell and magnetic local time-averaged conditions. The models were promulgated for engineering use by organizations such as the National Aeronautics and Space Administration, the United States Air Force, and the European Space Agency and were incorporated into standards used by contractors like Lockheed Martin, Boeing, and Raytheon.
Development traces to data synthesis efforts in the 1960s and 1970s after discoveries by missions including Explorer 3, Ion-Sonde experiments, and Orbiting Geophysical Observatory series. Consolidation occurred at laboratories and centers such as the NASA Goddard Space Flight Center, Air Force Geophysics Laboratory, and universities associated with the National Academy of Sciences. Major datasets from missions like Ogo, Ariel 3, HEOS-2, and ERBS were aggregated; later reanalysis included contributions from CRRES and GOES satellites. The AP8/AE8 releases formalized earlier empirical fits and influenced later models such as AE9/AP9 and modeling efforts at institutions like the Naval Research Laboratory.
AP8 produced omnidirectional integral fluxes for protons in multiple energy bins derived from energy-dependent channel data from instruments aboard platforms including Explorer 12, Explorer 15, and Ariel 1. AE8 produced electron fluxes across energy thresholds using satellite measurements from platforms like IMP probes, Vela series, and DMSP sensors. Both models parameterize flux versus L-shell, geomagnetic latitude, and energy, offering solar-minimum and solar-maximum variants reflecting datasets tied to specific solar cycles documented by observatories such as Sunspot Index and Long-term Solar Observations and mission-era records from NOAA and USAF archives. Data reduction involved instrument cross-calibration methods practiced at centers including Los Alamos National Laboratory and Johns Hopkins University Applied Physics Laboratory.
AP8/AE8 served as inputs for shielding design by contractors including Northrop Grumman and General Dynamics, spacecraft component testing at facilities like Sandia National Laboratories and Brookhaven National Laboratory, and mission dose budgeting for NASA missions including International Ultraviolet Explorer and early Hubble Space Telescope planning. They informed standards and handbooks from agencies such as MIL-STD publications and influenced avionics design in programs run by European Space Agency and national agencies like JAXA and Roscosmos. Satellite operators for constellations like GOES, Iridium, and GPS historically used these models for risk assessment, anomaly analysis, and orbit selection.
Validation campaigns compared AP8/AE8 outputs against in situ measurements from missions including CRRES, SAMPEX, ACE, THEMIS, and Van Allen Probes. Limitations include static averaging that neglects rapid temporal dynamics associated with events such as geomagnetic storms, coronal mass ejections, and solar proton events documented by SOHO and STEREO; poor representation of outer zone variability driven by magnetospheric substorms and wave–particle interactions studied by Cluster and RBSP. Instrument biases, limited spatial-temporal sampling, and epoch-dependent baselines constrained accuracy, prompting successors like AE9/AP9 and physics-based simulations implemented at NASA Goddard and the Naval Research Laboratory to incorporate stochastic variability, improved cross-calibration, and assimilation of modern datasets from Van Allen Probes and POES.
AP8/AE8 implementations exist in software libraries and engineering tools such as those distributed by NASA's community and legacy toolkits in agencies like USAF and laboratories including Los Alamos National Laboratory. They are embedded in flight software and ground analysis tools at organizations such as Ball Aerospace, Airbus Defence and Space, and Thales Alenia Space. While maintained for legacy support, users are encouraged to migrate to modern models used by ESA and NOAA programs; archives and model code are available through institutional repositories at NASA Goddard, university data centers like Columbia University's Lamont-Doherty, and government archives operated by National Archives and Records Administration.
Category:Space physics models