Ch 2: The S/C Environment and its Effect on Design 2/2 Flashcards
aluminium wrt shielding
rubbish -> composites encased in Al sheets
single event upset
heavy ion -> circuit -> charge -> change in logic state
soft error - no permanent damage (apart from when caused by bad data)
single event latch-up
[leaving that for now]
total dose events
caused by the deposition of energy by many particles
radiation damage to semiconductors
- lower energy conversion effectiveness in solar cells -> coverglass
- ??
transport of primary particles through SC structure - issues
increasing shielding δ isn’t always good:
- heavy ion crossing though material of sufficient thickness -> increased linear energy transfer -> ability to ionise
- secondary particles production during interaction with the shielding material atoms
solutions to parts below rad hardness requirement from 1D calc
- more detailed 3D modelling
- spot shielding
- find a different part
steps in calculating the radiation dose inside SC
- find the fluence spectrum of the external (unshielded) particles [particles/cm^2 @ specific energy]
- calculate 1D dose assuming spherical aluminium shell
//typical δ = 2.5 ÷ 3.8 mm //typical n = 1.3 ÷ 2
metallic whiskers
radiation -> cadmium, zinc etc might form whiskers
UV exposure damages
- embrittlement
- electrical changes (in resistivity)
- optical changes (in thermal properties and opacity) - esp. solar cell coverglass + adhesive darkening
embrittlement
material damage caused by UV exposure
esp. polymers
which material property improves in space and why?
fatigue life in a high vacuum
- influence of absorbed gases on crack propagation
- influence of oxidation and gas diffusion on the material (?)
GLASS: 3x strength @ e-3 p_atm
PURE NICKEL, INCONEL 550: not so much
effects of oxygen atoms on SC in LEO
- erosion -> material properties degradation
- stable oxide formation -> material properties change through oxidation, dimensional changes, spalling
- indirect impingement -> surface erosion
- O + NO -> NO2 -> glow
low- and high- erosion materials
low: Al-coated Kapton, FEP teflon, silicones
high: PE, Kapton
interactions between oxygen atoms and spacecraft surfaces
- erosion
- formation of stable oxide
- scattering and reflection
- chemiluminescence
why is atomic oxygen in LEO dangerous?
- momentum (@8 km/s)
- chemical reactions (esp. silver)
major atmospheric species in LEO?
atomic oxygen
problems caused by outgassing
- deposited material might damage optical and electronically sensitive components
- mass loss
- modified emissive properties
- special lubricants necessary (usually solid, also low-volatility oils)
outgassing
vaporization of surface atoms when ambient pressure comparable to material’s vapour pressure
Io’s influence on Jupiter MF
SO2 dissociation products from volcanic activity -> ion
maybe has its own MF, maybe nota
how does ionosphere form
solar radiation -> photoionisation
space debris shielding
double-walled bumper
! critical size estimation depending on SC
SC electrostatic charging
SC charging occurs in near-Earth environment both in and outside of radiation fields.
!! differential charging
prevention:
- conductive surfaces
- low-res coating (solar arrays)
solar proton events
- parameters vary
- 7 years during a solar cycle starting from 2 yrs before solar maximum - hazardous for SC
- protons accelerated during solar flares -> indicated by X-ray, radio and optical emissions
solar energetic particles will also produce heavy ions
solar energetic particle events
solar cosmic, proton, electron, cap absorption events
ground level events
primary cosmic radiation
cosmic rays propagate through Earth atmosphere -> nuclear collisions -> secondary rays consisting of all known nuclear and sub-nuclear species (?)
propagation -> ~1% isotropy (?)
composition: 83% p, 13% α, 1% nuclei Z>2, 3% e
interaction with ISM -> fragmentation, heavy charge rays depletion, more lighter nuclei
Galactic cosmic radiation
Galactic Cosmic Rays (GCR) are the slowly varying, highly energetic background source of energetic particles that constantly bombard Earth. GCR originate outside the solar system and are likely formed by explosive events such as supernova /but who knows/. These highly energetic particles consist of essentially every element ranging from hydrogen, accounting for approximately 89% of the GCR spectrum, to uranium, which is found in trace amounts only. These nuclei are fully ionized, meaning all electrons have been stripped from these atoms. Because of this, these particles interact with and are influenced by MFs. The strong MF of the Sun modulate the GCR flux and spectrum at Earth.
flux - mostly isotropic outside heliosphere
