9.3              Preparation of a radiation environment specification

a.              A specification of the expected radiation environment of a space system shall be established.

b.              The specification of a mission environment shall include:

1.              Mission­average proton and electron energy spectra from trapped radiation issued from the chosen models (according to mission orbit and time).

2.              The fluence spectrum of solar protons for the complete mission with geomagnetic shielding applied.

3.              Maximum instantaneous energy spectra of trapped electrons, trapped protons and solar energetic protons (geomagnetically shielded) for the mission, for internal charging and sensor interference analysis.

4.              The ion LET flux spectrum derived from the GCR flux spectra for the appropriate solar cycle phase, together with the worst 5 minute solar energetic particle LET spectrum, including:

(a)            Contributions from all ions from Z = 1 to Z = 92.

(b)           Geomagnetic shielding.

(c)            Material shielding. If no justification is available for another value, 1 g cm-2 of aluminium shielding is used.

5.              The ion LET fluence spectrum derived from the GCR fluence spectra for the appropriate solar cycle phase, together with the fluence spectra from a number of events at worst day CREME96 solar energetic particle LET spectrum, including:

(a)            Contributions from all ions from Z = 1 to Z = 92.

(b)           Geomagnetic shielding.

(c)            Material shielding. If no justification is available for another value, 1 g cm-2 of aluminium shielding is used.

NOTE              For solar cycle 23 the number of CREME96 worst days was 5-7.

6.              Orbital time­behaviour of radiation­belt (if any), cosmic ray and solar energetic particle fluxes if the mission has a susceptibility to radiation background in sensors.

7.              Additional contributions from on­board nuclear/radioactive sources.

8.              Uncertainties of the radiation models as applied for the given mission.

c.               The uncertainties in results from the models shall be included in the risk assessment.

NOTE              For all the models, it is of the responsibility of the mission manager to specify the margins for the project.

d.              The specification shall include the evolution of the mission orbit whether caused naturally or by deliberate orbit manoeuvres.

NOTE              This can have significant effects on radiation­belt exposure (e.g. due to natural perigee rise and apogee fall).

e.               The effects of operations that result in geo­synchronization of the orbit shall be included in the assessment

NOTE 1      For example: geostationary, apogee longitude maintenance of near­synchronous HEO orbits.

NOTE 2      In such missions radiation belt exposures are not averaged out.