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

! Spacecraft Systems Engineering - Fortescue, Swinerd & Stark > Ch 2: The S/C Environment and its Effect on Design 2/2 > Flashcards

Flashcards in Ch 2: The S/C Environment and its Effect on Design 2/2 Deck (27):
1

aluminium wrt shielding

rubbish -> composites encased in Al sheets

2

single event upset

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

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

3

single event latch-up

[leaving that for now]

4

total dose events

caused by the deposition of energy by many particles

5

radiation damage to semiconductors

- lower energy conversion effectiveness in solar cells -> coverglass

- ??

6

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

7

solutions to parts below rad hardness requirement from 1D calc

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

8

steps in calculating the radiation dose inside SC

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

9

metallic whiskers

radiation -> cadmium, zinc etc might form whiskers

10

UV exposure damages

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

11

embrittlement

material damage caused by UV exposure

esp. polymers

12

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

13

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

14

low- and high- erosion materials

low: Al-coated Kapton, FEP teflon, silicones

high: PE, Kapton

15

interactions between oxygen atoms and spacecraft surfaces

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

16

why is atomic oxygen in LEO dangerous?

- momentum (@8 km/s)
- chemical reactions (esp. silver)

17

major atmospheric species in LEO?

atomic oxygen

18

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)

19

outgassing

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

20

Io's influence on Jupiter MF

SO2 dissociation products from volcanic activity -> ion

maybe has its own MF, maybe nota

21

how does ionosphere form

solar radiation -> photoionisation

22

space debris shielding

double-walled bumper

! critical size estimation depending on SC

23

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)

24

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

25

solar energetic particle events

solar cosmic, proton, electron, cap absorption events

ground level events

26

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

27

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