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

Question 1

Main sources of noise and vibration during launch

Answer 1

• LV engines

- aerodynamic buffeting in lower atmosphere

Question 2

aerodynamic buffeting

Answer 2

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.

Question 3

Peak vibration/acoustic levels during launch

Answer 3

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

Question 4

peak acceleration depending on LV

Answer 4

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

multistage - peak at seperation

Question 5

what is the thermal environment during launch determined by?

Answer 5

launch shroud temperature

after ejection - friction, but by then low atmospheric density

Question 6

determining the temperature reached during launch

Answer 6

specific heat of the shroud material

friction heating vs radiative + convective heat loss

Question 7

depressurisation rate

Answer 7

venting ports in shrouds

Question 8

venting ports esp. required where in PL?

Answer 8

electronic boxes

Question 9

EMI

Answer 9

EM interference; huge hazard during launch

-> PL prop ignition etc

Question 10

Sun mass

Answer 10

~2e30 kg

Question 11

Sun radiated light peak λ

Answer 11

~460 nm

Question 12

Interstellar gas density

Answer 12

~3 atoms/cm^3

Question 13

Sun surface temperature

Answer 13

~5800 K

Question 14

Sun radiation - regions causing dips from the BB curve

Answer 14

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

Question 15

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

Answer 15

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

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

Question 16

sunspots

Answer 16

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

Question 17

Zürich sunspot number Rz

Answer 17

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

Question 18

sunspot regions

Answer 18

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

Question 19

components of solar flux @ Earth

Answer 19

1. ~20 minutes after the flare: first heightened EM emissions
2. ~1 day after the flare: enhanced solar wind components, ~1e3 km/s

Question 20

lower atmosphere - approx boundary, difference to higher

Answer 20

~86 km

sufficiently turbulent to be homogeneous (bc gas mixture)

above that, the homogeneity is disturbed by photochemical processes

Question 21

upper atmosphere processes

Answer 21

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)

Question 22

exospheric temperature T_inf

Answer 22

increase in solar activity -> rise in T_inf

also geomagnetism

Question 23

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

Answer 23

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

//txtbook - models to estimate orbit decay

Question 24

ratio of atmosphere/interplanetary medium at GEO

Answer 24

~1

Question 25

SC - atomic/molecular collisions

Answer 25

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)

Question 26

ionosphere

Answer 26

> 86 km

increased plasma density caused by photoionisation by incident UV photons

Question 27

plasma influence on wave propagation

Answer 27

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

Question 28

sources of Earth MF

Answer 28

1. core currents -> dominant MF at surface
2. differential motion of electrons and ions in the magnetosphere -> MF at higher altitudes

also solar wind

Question 29

Earth MF constant or?

Answer 29

• decreases by ~0.05% pa

- weakest @ the equator

Question 30

Van Allen belts structure

Answer 30

primary: protons and electrons following Earth MF lines
secondary: fluxes of heavy ions (He, N, O) - atmospheric density dependant on solar and geomagnetic activity

Question 31

what are heavy ions?

Answer 31

in nuclearphysics, any particle with one or more units ofelectric charge and a mass exceeding that of thehelium-4 nucleus(alpha particle).

Question 32

South Atlantic Anomaly

Answer 32

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

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

Question 33

radiation belt - dangers to SC

Answer 33

• > 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)

Question 34

influence of electrons and protons depending on orbit

Answer 34

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

protons - much higher mass -> more effective