B.2.2 LEO orbits with high inclination

LEO orbits with inclination of 55 degrees and above can frequently intercept auroral arcs. Here, the spacecraft experiences a higher energy electron environment similar to that of geostationary orbit. Requirements concerned with the following are intended to be adopted by spacecraft in these high-inclination orbits:

• Surface charging (clause 6). However, an electrostatic discharge does not occur unless the charging process is sufficiently rapid to reach dangerous potential values within the time taken to cross the oval (about 90s). Hence there may be a relaxation in requirements, in that dielectrics and floating metallic parts with capacitance above 50pF per cm² of area exposed to the environment do not charge up dangerously in the time available and so may be retained, even if unfavourable in terms of secondary yield, conductivity etc. As a result of this relaxation, large areas of ungrounded MLI may be permissible if assessed to have high capacitance.

NOTE The capacitance is that of the whole structure, not that of a single layer i.e. for MLI with N layers, the total capacitance is the result of the combination in series of N capacitors.

Analysis or simulation may take into account the neutralising current from LEO ambient plasma. However, surfaces in a wake do not see this current and the analysis resembles that for GEO.

• Solar array ESD effects on the array itself (clause 7).

• High voltage interactions (clause 8).