Ch 2: The S/C Environment and its Effect on Design 2/2

Question 1

aluminium wrt shielding

Answer 1

rubbish -> composites encased in Al sheets

Question 2

single event upset

Answer 2

heavy ion -> circuit -> charge -> change in logic state

soft error - no permanent damage (apart from when caused by bad data)

Question 3

single event latch-up

Answer 3

[leaving that for now]

Question 4

total dose events

Answer 4

caused by the deposition of energy by many particles

Question 5

radiation damage to semiconductors

Answer 5

• lower energy conversion effectiveness in solar cells -> coverglass
• ??

Question 6

transport of primary particles through SC structure - issues

Answer 6

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

Question 7

solutions to parts below rad hardness requirement from 1D calc

Answer 7

• more detailed 3D modelling
• spot shielding
• find a different part

Question 8

steps in calculating the radiation dose inside SC

Answer 8

1. find the fluence spectrum of the external (unshielded) particles [particles/cm^2 @ specific energy]
2. calculate 1D dose assuming spherical aluminium shell

//typical δ = 2.5 ÷ 3.8 mm
//typical n = 1.3 ÷ 2

Question 9

metallic whiskers

Answer 9

radiation -> cadmium, zinc etc might form whiskers

Question 10

UV exposure damages

Answer 10

• embrittlement
• electrical changes (in resistivity)
• optical changes (in thermal properties and opacity) - esp. solar cell coverglass + adhesive darkening

Question 11

embrittlement

Answer 11

material damage caused by UV exposure

esp. polymers

Question 12

which material property improves in space and why?

Answer 12

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

Question 13

effects of oxygen atoms on SC in LEO

Answer 13

• erosion -> material properties degradation
• stable oxide formation -> material properties change through oxidation, dimensional changes, spalling
• indirect impingement -> surface erosion
• O + NO -> NO2 -> glow

Question 14

low- and high- erosion materials

Answer 14

low: Al-coated Kapton, FEP teflon, silicones
high: PE, Kapton

Question 15

interactions between oxygen atoms and spacecraft surfaces

Answer 15

• erosion
• formation of stable oxide
• scattering and reflection
• chemiluminescence

Question 16

why is atomic oxygen in LEO dangerous?

Answer 16

• momentum (@8 km/s)

- chemical reactions (esp. silver)

Question 17

major atmospheric species in LEO?

Answer 17

atomic oxygen

Question 18

problems caused by outgassing

Answer 18

• deposited material might damage optical and electronically​ sensitive components
• mass loss
• modified emissive properties
• special lubricants necessary (usually solid, also low-volatility oils)

Question 19

outgassing

Answer 19

vaporization of surface atoms when ambient pressure comparable to material’s vapour pressure

Question 20

Io’s influence on Jupiter MF

Answer 20

SO2 dissociation products from volcanic activity -> ion

maybe has its own MF, maybe nota

Question 21

how does ionosphere form

Answer 21

solar radiation -> photoionisation

Question 22

space debris shielding

Answer 22

double-walled bumper

! critical size estimation depending on SC

Question 23

SC electrostatic charging

Answer 23

SC charging occurs in near-Earth environment both in and outside of radiation fields.

!! differential charging

prevention:
- conductive surfaces
- low-res coating (solar arrays)

Question 24

solar proton events

Answer 24

• 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

Question 25

solar energetic particle events

Answer 25

solar cosmic, proton, electron, cap absorption events

ground level events

Question 26

primary cosmic radiation

Answer 26

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

Question 27

Galactic cosmic radiation

Answer 27

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