Ch 2: The S/C Environment and its Effect on Design 1/2 Flashcards Preview

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Flashcards in Ch 2: The S/C Environment and its Effect on Design 1/2 Deck (34):
1

Main sources of noise and vibration during launch

- LV engines
- aerodynamic buffeting in lower atmosphere

2

aerodynamic buffeting

Buffeting is a high-frequency instability, caused by airflow separation or shock wave oscillations from one object striking another. It is caused by a sudden impulse of load increasing. It is a random forced vibration.

3

Peak vibration/acoustic levels during launch

1. LIFT-OFF: rocket motor + ground reflection of exhaust products -> primary vibration to PL through structural elements and secondary through the launch shroud

2. TRANSONIC FLIGHT

4

peak acceleration depending on LV

HIGH PEAK ACC - low-mass LVs (obvs), air-launched

multistage - peak at seperation

5

what is the thermal environment during launch determined by?

launch shroud temperature

after ejection - friction, but by then low atmospheric density

6

determining the temperature reached during launch

specific heat of the shroud material
friction heating vs radiative + convective heat loss

7

depressurisation rate

venting ports in shrouds

8

venting ports esp. required where in PL?

electronic boxes

9

EMI

EM interference; huge hazard during launch

-> PL prop ignition etc

10

Sun mass

~2e30 kg

11

Sun radiated light peak λ

~460 nm

12

Interstellar gas density

~3 atoms/cm^3

13

Sun surface temperature

~5800 K

14

Sun radiation - regions causing dips from the BB curve

CHROMOSPHERE: lower atmosphere, few thousand kms above the photosphere, increasing temperature to ~10e3 K -> enhanced UV emission

CORONA: upper atmosphere, extends to a few solar radii, 2e6 K -> X-rays emission

15

solar wind - what, where from, physical properties @ Earth

flow of plasma expelled at high velocity; outermost layer of solar atmosphere

@ Earth: ~450 km/s, ~9 protons/cm^3, kinetic temp ~100e3 K

16

sunspots

regions of the solar disk cooler than the rest

large number of sunspots -> enhanced solar activity primarily @ radio, X and γ - solar flares usually occur near sunspots

17

Zürich sunspot number Rz

quantifies overall number of sunspots at given time

Rz = K (10g + f)

K - normalisation factor depending on observing instrument
g - number of sunspot groups present
f - number of sunspots exhibiting umbrae

18

sunspot regions

umbra - middle, darkest
penumbra - around, lighter
pores - small dark spots around

19

components of solar flux @ Earth

1. ~20 minutes after the flare: first heightened EM emissions

2. ~1 day after the flare: enhanced solar wind components, ~1e3 km/s

20

lower atmosphere - approx boundary, difference to higher

~86 km

sufficiently turbulent to be homogeneous (bc gas mixture)

above that, the homogeneity is disturbed by photochemical processes

21

upper atmosphere processes

the homogeneity of atmosphere starts being disturbed by photochemical processes from ~86 km

-> solar UV radiation causes dissociation of oxygen

-> by ~120 km all atmospheric species decoupled from others

//txtbook - eq of the diffusive equilibrium (number density, molecular weight, altitude, vertical transport velocity, molecular and thermal diffusion coeff, atmospheric temperature, R, g);

can be simplified assuming no vertical transport and negligible thermal diffusion -> hydrostatic equilibrium; number density profile(atmospheric temp)

22

exospheric temperature T_inf

increase in solar activity -> rise in T_inf

also geomagnetism

23

how does solar activity cause lower lifespan for SC in LEO?

solar activity -> lower atmospheric density (~T^-1)

//txtbook - models to estimate orbit decay

24

ratio of atmosphere/interplanetary medium at GEO

~1

25

SC - atomic/molecular collisions

v rare above 200 km (mean free path 240 m and rises fast)

-> heat exchange virtually only through radiation - primary: solar radiation ~1371 W/m^2, secondary: Earth albedo, Earthshine ~200 W/m^2

-> aerodynamics based on free molecular flow (Ch. 4)

26

ionosphere

>86 km

increased plasma density caused by photoionisation by incident UV photons

27

plasma influence on wave propagation

waves with frequency lower than plasma frequency fp~9000*sqrt(ne) cannot propagate (units???)

Faraday rotation - polarisation of EM wave passing through plasma due to an EM field when EMF present

28

sources of Earth MF

1. core currents -> dominant MF at surface

2. differential motion of electrons and ions in the magnetosphere -> MF at higher altitudes

also solar wind

29

Earth MF constant or?

- decreases by ~0.05% pa
- weakest @ the equator

30

Van Allen belts structure

primary: protons and electrons following Earth MF lines

secondary: fluxes of heavy ions (He, N, O) - atmospheric density dependant on solar and geomagnetic activity

31

what are heavy ions?

in nuclear physics, any particle with one or more units of electric charge and a mass exceeding that of the helium-4 nucleus (alpha particle). 

32

South Atlantic Anomaly

region of enhanced radiation in which parts of the radiation belt are brought to lower altitudes

cause: geomagnetic =/= rotation axis (offset, tilt)

33

radiation belt - dangers to SC

-> collision with semiconductor lattice causes displacement causes local ionisation and energy structure disruption -> arrays energy conversion efficiency

-> ionisation -> impulsive charge release -> SEU (single-upset event)

34

influence of electrons and protons depending on orbit

<800 km - mostly protons
>800 km - mostly electrons

protons - much higher mass -> more effective