Ch 2: The S/C Environment and its Effect on Design 1/2 Flashcards
Main sources of noise and vibration during launch
- LV engines
- aerodynamic buffeting in lower atmosphere
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.
Peak vibration/acoustic levels during launch
- LIFT-OFF: rocket motor + ground reflection of exhaust products -> primary vibration to PL through structural elements and secondary through the launch shroud
- TRANSONIC FLIGHT
peak acceleration depending on LV
HIGH PEAK ACC - low-mass LVs (obvs), air-launched
multistage - peak at seperation
what is the thermal environment during launch determined by?
launch shroud temperature
after ejection - friction, but by then low atmospheric density
determining the temperature reached during launch
specific heat of the shroud material
friction heating vs radiative + convective heat loss
depressurisation rate
venting ports in shrouds
venting ports esp. required where in PL?
electronic boxes
EMI
EM interference; huge hazard during launch
-> PL prop ignition etc
Sun mass
~2e30 kg
Sun radiated light peak λ
~460 nm
Interstellar gas density
~3 atoms/cm^3
Sun surface temperature
~5800 K
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
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
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
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
sunspot regions
umbra - middle, darkest
penumbra - around, lighter
pores - small dark spots around
components of solar flux @ Earth
- ~20 minutes after the flare: first heightened EM emissions
- ~1 day after the flare: enhanced solar wind components, ~1e3 km/s
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
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)
exospheric temperature T_inf
increase in solar activity -> rise in T_inf
also geomagnetism
how does solar activity cause lower lifespan for SC in LEO?
solar activity -> lower atmospheric density (~T^-1)
//txtbook - models to estimate orbit decay
ratio of atmosphere/interplanetary medium at GEO
~1
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)
ionosphere
> 86 km
increased plasma density caused by photoionisation by incident UV photons
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
sources of Earth MF
- core currents -> dominant MF at surface
- differential motion of electrons and ions in the magnetosphere -> MF at higher altitudes
also solar wind
Earth MF constant or?
- decreases by ~0.05% pa
- weakest @ the equator
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
what are heavy ions?
in nuclearphysics, any particle with one or more units ofelectric charge and a mass exceeding that of thehelium-4 nucleus(alpha particle).
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)
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)
influence of electrons and protons depending on orbit
<800 km - mostly protons
>800 km - mostly electrons
protons - much higher mass -> more effective
