Mathematics – Logic
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.338c&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Mathematics
Logic
Scientific paper
Thirty years after the first evidence of in-flight electrostatic discharges on synchronous spacecraft, they are still a threat. Analysis of anomalies will be always necessary for improving design guidelines and standards. A Ground Control Center dedicated to a Space System is monitoring for the nominal configuration of the spacecraft. An alarm or warning is triggered when the spacecraft gets out of its nominal working state. How to know what happens in flight? An electrostatic discharge is never observed itself but only its permanent consequences. Telemetry data is never designed for detecting unforeseen events, it is only defined for command purpose and good-health diagnosis. Probes are exceptionally implemented on commercial spacecraft to determine the state of environment at the location of the spacecraft at the time of the anomaly. The first step is the elimination of non-environmental causes: electromagnetic interference problem, equipment failure, corona discharge inside a high-voltage powered box, or man-made spurious command. Heavy ions or micrometeoroids are environmental causes with consequences that look like electrostatic discharges, so involving charging needs detailed and exhaustive analysis. The spacecraft-charging anomaly is at the end of a long chain of causes and consequences. Some regions of space have a radiation and particle content able to build up absolute and differential potentials at the surface or inside the spacecraft up to exceeding the breakdown voltage. Charges are released that induce electromagnetic fields in coupling current and voltage transients to cables. The pulses penetrate boxes and propagate along printed circuit board tracks, reaching active devices, upsetting logical devices, saturating amplifiers, or fusing lanes inside integrated circuits. Spacecraft event understanding is the conclusion of three convergent ways of analysis: environmental data, vacuum charging tests, electromagnetic immunity tests. When there is no borne particle detectors, we rely on Space Weather plots issued by the Space Environment Center of Boulder, CO, USA. It is only informative since measurements are not made at the same location of the orbit as the spacecraft of concern. A proton analyzer provides proton flux data from solar flares in three spectral bands: E>10 MeV, E>50 MeV, and E>100 MeV. Electron fluxes are plotted for two bands: E>600 keV and E>2 MeV. The geomagnetic field at GOES location and the planetary K-indices are also given. The photoemission from illuminated parts of the spacecraft prevents charging but large negative potentials can build up on shadowed parts. The sun direction is known from the spacecraft attitude in the geocentric axes, the sun seasonal inclination, and the local time. Bulk and surface resistivity, secondary emission yield to electrons and ions, photoemission efficiency responsible for charging characteristics are documented during the spacecraft development. Testing flight-representative items in a vacuum chamber under electron beams allows forecasting of in-flight potentials and assessment of the discharge risk. During the tests we identify the electromagnetic pulses to reproduce them in normal laboratory ambience testing the electromagnetic immunity of equipment.
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