Space Radiation Environment

GSFC's experts in this area are E.G. Stassinopoulos & Janet Barth in the Radiation Physics Office, NASA/GSFC. Please check out the Radiation Physics Office Home Page.

The following was taken from the SEECA (Single Event Effects Criticality Analysis).

The main sources of energetic particles that are of concern to spacecraft designers are:
1) protons and electrons trapped in the Van Allen belts,
2) heavy ions trapped in the magnetosphere,
3) cosmic ray protons and heavy ions, and
4) protons and heavy ions from solar flares.

The levels of all of these sources are affected by the activity of the sun. The solar cycle is divided into two activity phases: the solar minimum and the solar maximum. The cycle lasts about eleven years, with approximately four years of solar minimum and seven years of solar maximum.

There are also extremely large variations in the levels of SEE inducing flux that a given spacecraft encounters, depending on its trajectory through the radiation sources. Missions flying at Low Earth Orbits (LEOs), Highly Elliptical Orbits (HEOs), and Geostationary Orbits (GEOs), and Planetary and Interplanetary missions have vastly different environmental concerns.

Summary of Radiation Sources

Format for following data:
Radiation Source
- Models
- Effects of Solar Cycle
- Variations
- Types of Orbits Affected

Trapped Protons
- AP8-MIN AP8-MAX
- Solar Min - Higher; Solar Max - Lower
- Geomagnetic Field; Solar Flares; Geomagnetic Storms
- LEO, HEO, Transfer Orbits

Trapped Electrons
- AE8-MIN AE8-MAX
- Solar Min - Lower; Solar Max - Higher
- Geomagnetic Field; Solar Flares; Geomagnetic Storms
- LEO, GEO, HEO, Transfer Orbits

Galactic Cosmic Ray Ions
- CREME CHIME Badhwar & O'Neill
- Solar Min - Higher; Solar Max - Lower
- Ionization Level; Orbit Attenuation
- LEO, GEO, HEO, Interplanetary

Solar Flare Protons
- KING JPL92
- During Solar Max Only
- Distance from Sun; Outside 1 AU Orbit Attenuation Location of Flare on Sun
- LEO (I>45), GEO, HEO, Interplanetary

Solar Flare Heavy Ions
- CREME; JPL92; CHIME
- During Solar Max Only
- Distance from Sun Outside 1 AU, Orbit Attenuation; Location of Flare on Sun
- LEO, GEO, HEO, Interplanetary

Experience has shown that the most effective means of reducing uncertainty factors and design margins in particle predictions, is to define for the mission:

1. when the mission will fly,
2. where the mission will fly,
3. when the systems will be deployed,
4. what systems must operate during worst case environment conditions
5. what systems are critical to mission success, and
6. the amount of shielding surrounding the SEE sensitive part(s).

Estimates that include only worst case conditions lead to overdesign and should be used only in the concept design phase of a mission when the actual launch date and length have not been defined. After the launch date and duration are defined, it is possible to estimate how long the spacecraft will be in each phase of the solar cycle. These estimates should consider the impact of a launch delay of one year. Mission scenario definition is especially important for solar flare particles where the number of events is highly dependent on the amount time that the satellite spends in solar maximum conditions.

Greater detail is available in the environment section of the SEECA document, by Janet Barth & E.G. Stassinopoulos, NASA/GSFC/Code 900.

A few useful links:

Radiation Physics Group, NASA/GSFC.
Environment - related papers, documents still being added
NASA/Lewis Space Environment Effects Branch (SEEB)
National Oceanic and Atmospheric Administration (NOAA)
National Center for Atmospheric Research
Space Environment Lab (SEL)
Today's Solar Images from SEL
Solar Sites Index from SEL

...Radiation Effects & Analysis Home Page

Curator: Martha O'Bryan
Last Revised December 1, 1998