Environmental testing — thermal vacuum (TVAC), vibration, acoustic, EMC - EMI: Question bank

3.6.33 · D5 · Physics › Spacecraft Structures & Systems Engineering › Environmental testing — thermal vacuum (TVAC), vibration, ac

Related vault topics jo saath mein open rakhne layak hain: Spacecraft Thermal Control Systems, Structural Mechanics, Launch Vehicle Dynamics, Electromagnetic Wave Propagation, Reliability Engineering, Quality Assurance in Aerospace.

Definition Is page par use kiye gaye symbols

Inhe ek baar padho, phir neeche ke traps self-contained hain.

$T_{s}$ = spacecraft surface ka absolute temperature kelvin (K) mein; $T_{\infty}$ = aaspaas deep space ka absolute temperature ( $\approx 3$ K); akela $T$ matlab "jis bhi body ki baat ho rahi hai uska temperature" jab sirf ek present ho. $σ = 5.67 \times 1 0^{- 8} W/(m^{2} K^{4})$ = Stefan–Boltzmann constant; $ε$ = emissivity, 0 (shiny mirror, kuch radiate nahi karta) se 1 (perfect black radiator) tak ka number; $α$ = absorptivity, aane wali sunlight ka woh fraction jo surface absorb karti hai (0 = sab reflect, 1 = sab absorb); $A$ = radiating area; $S$ = solar flux, sunlight power jo per unit area padti hai ( $\approx 1368 W/m^{2}$ Earth ke paas).
$ω$ = drive frequency jis par shaker push karta hai (rad/s); $ω_{n} = k / m$ = structure ki natural frequency, woh rate jis par woh khud hilna pasand karta hai; $f_{n} = ω_{n} /2 π$ wahi cheez hertz mein hai.
$r = ω / ω_{n}$ = frequency ratio — drive natural frequency se compare karke kaisa hai. $r < 1$ = natural se slower drive, $r = 1$ = exactly resonance par, $r > 1$ = tez.
$ζ$ (zeta) = damping ratio, ek number jo batata hai free wobbles kitni jaldi khatam hote hain (0 = kabhi nahi, bada = jaldi); spacecraft structures $ζ = 0.02$ – $0.05$ ke paas hote hain.
$Q$ = quality factor $= 1/ (2 ζ)$ = resonance par shaking input se kitni zyada ho jaati hai. Kam damping → bada $Q$ → dangerous amplification.
$Tr$ = transmissibility = component par bahar aane wali shaking ka base par andar daali gayi shaking se ratio (ek pure number, temperature nahi). Poore page mein $Tr$ likha hai taaki temperature $T_{s}$ se kabhi confuse na ho.
dB (decibel) sound ke liye $20 lo g_{10} (p / p_{ref})$ hai jahan $p_{ref} = 20 μ Pa$ standard reference pressure hai (sabse quiet audible pressure); toh 140–150 dB ek pressure ratio hai us reference ke against, force nahi.

Neeche wali picture vibration traps ke liye sabse important plot hai: $r$ badalne par shaking kitni amplify hoti hai.

Aur yeh wali har thermal trap ko anchor karti hai — jahan absorbed sunlight $α S A$ aur radiated power cross karke equilibrium temperature set karti hai.

True or false — justify karo

Ek sealed (hermetic) box vacuum se unaffected hota hai.

False — sealing andar ko vacuum se rokti hai, lekin box ka convective cooling path phir bhi chala jaata hai; andar generate hoti heat ab sirf mounts ke through conduction aur radiation se nikal sakti hai, isliye internal parts zyada hot ho jaate hain.

Space roughly 3 K hai, toh sunlight mein ek spacecraft surface 3 K ke paas rahegi.

False — surface ek equilibrium tak pahunchti hai jahan absorbed sunlight

α S A

radiated power ke barabar hoti hai (doosri figure mein crossing point); woh balance room temperature ke paas ya zyada hot hoti hai, aur thanda 3 K sky sirf (tiny)

T_{\infty}^{4}

sink term set karta hai.

Kyunki radiated power

T_{s}^{4}

ki tarah jaati hai, ek hot object per degree bahut tez thanda hota hai cold object ke mukable.

True — derivative

d q / d T_{s} = 4 σ ε T_{s}^{3}

temperature ke saath badhta hai, isliye 350 K ke paas har extra kelvin 250 K ke paas se kahin zyada watts shed karta hai, yahi wajah hai ki hot components zyada strongly self-limit karte hain.

Random vibration aur sine vibration ek hi cheez test karte hain, toh ek karna kaafi hai.

False — sine vibration individual resonances ko ek frequency at a time hunt aur characterise karta hai, jabki random vibration saare modes ko simultaneously excite karta hai fatigue reproduce karne ke liye; dono alag failures reveal karte hain.

High natural frequency

f_{n}

wala component automatically launch ke dauran safer hota hai.

True in spirit —

f_{n}

ko launcher ke strong low-frequency content se upar push karna ("frequency separation") resonant amplification se bachata hai, yahi wajah hai ki designers structures ko stiffen karte hain

f_{n}

raise karne ke liye.

Agar shaker ka input 1 g hai, toh component kabhi 1 g se zyada nahi dekh sakta.

False — resonance par transmissibility quality factor

Q = 1/ (2 ζ)

ke barabar hoti hai, toh light damping (

ζ \approx 0.03

) ke saath 1 g input part par ~15 g ban jaata hai.

Acoustic testing aur vibration testing redundant hain.

False — shaker load mounting feet ke through drive karta hai, jabki acoustic pressure large lightweight panels (solar arrays, antennas) ki poori exposed surface area ko load karta hai jo shaker achhe se excite nahi kar sakta.

EMC aur EMI ek hi cheez hain.

False — EMI unwanted emission ya susceptibility hai (problem); EMC bina interference ke coexist karne ka goal hai (emissions kaafi low, immunity kaafi high).

Acceptance-level testing pass karna prove karta hai ki design qualified hai.

False — acceptance tests ek specific flight unit ko workmanship ke liye flight levels par screen karte hain; qualification tests prove karte hain ki design higher (margined) levels par survive karta hai, usually ek dedicated qual unit par.

150 dB ke roop mein quoted sound level matlab panel par 150 units of force hai.

False — dB ek logarithmic pressure ratio hai

p_{ref} = 20 μ Pa

ke against; 150 dB ek pressure

p = 20 \times 1 0^{- 6} \cdot 1 0^{150/20} \approx 632 Pa

correspond karta hai, aur sirf us pressure ko area se multiply karne par force milti hai.

Error dhundho

"Outgassing sirf isliye matter karti hai kyunki thoda sa material waste hota hai."

Mass loss toh trivial hai; asli khatre ki baat yeh hai ki released vapour cold surfaces par condense hoti hai — optics, radiators, star trackers — unhe degrade karti hai, aur yahi TVAC bake-out dhundha karta hai.

"Net radiated heat

Q = A σ ε T_{s}^{4} - T_{\infty}

hai."

Galat — tum ek bare temperature

T_{\infty}

ko power se subtract nahi kar sakte. Dono sink terms ko same factors ke under fourth powers mein hona chahiye:

Q = A σ ε (T_{s}^{4} - T_{\infty}^{4})

, jahan

A

= radiating area,

σ

= Stefan–Boltzmann constant,

ε

= emissivity,

T_{s}

= surface temperature,

T_{\infty}

= space temperature — har term ab watts mein hai.

"Resonance par,

r = ω / ω_{n} = 0

Resonance

r = 1

hai (drive frequency natural frequency ke barabar);

r = 0

ek static load hai jahan transmissibility

Tr \approx 1

hai.

"Resonance ke upar component aur bhi zyada amplify hota hai."

Ulta —

r > 2

ke liye transmissibility 1 se neeche drop hoti hai, toh mount actually part ko isolate karta hai (pehli figure ki right tail dekho); amplification sirf

r = 1

ke paas peak karti hai.

"Hum low-level sine sweep skip kar ke seedha full random vibration par ja sakte hain."

Sweep pehle low, safe level par resonances dhundhi; full level par blindly jump karne se overtesting ka risk hai ya article destroy ho sakta hai is se pehle ki tumhe pata ho kaun si frequencies weak hain.

"Higher damping ratio

ζ

resonant peak

Q

badhata hai."

Q = 1/ (2 ζ)

, toh zyada damping peak ko ghataata hai; yahi reason hai ki designers resonance survive karne ke liye dampers add karte hain.

"Worked example mein solar panel ek face se radiate karta hai, toh hum power ko 1 se divide karte hain."

Thin panel dono faces se radiate karta hai, isliye radiating term mein 2 ka factor hota hai; ise ignore karne par equilibrium temperature overestimate ho jaati hai.

Why questions

Orbit mein convection absent kyun hai lekin ground TVAC setup ke dauran present hai?

Convection ko heat carry karne ke liye fluid (air) chahiye; chamber ko

1 0^{- 5}

–

1 0^{- 7}

Torr tak pump kiya jaata hai toh almost koi gas nahi rehti, faithfully space reproduce karta hai jahan sirf conduction aur radiation operate karte hain.

TVAC cycling kyun use karta hai sirf sabse hot temperature par ek hold ke bajaye?

Baar baar hot–cold cycling thermal fatigue drive karta hai — materials ke beech expansion mismatch solder joints crack karta hai aur boards delaminate karta hai — jo ek single steady soak kabhi reveal nahi karta.

Thermal extremes ke dauran har subsystem powered aur functional kyun rakhte hain?

Bahut se failures tabhi appear hote hain jab stress aur operation dono saath hote hain (ek marginal oscillator cold mein drift karta hua, ek regulator hot mein sag karta hua); har extreme par ek powered functional checkout inhe intermittent faults pakadta hai.

Launch acoustic environment

20 μ Pa

ke against decibels mein kyun quote kiya jaata hai newtons mein nahi?

Sound ek pressure field hai jo area par distribute hoti hai, aur dB ek logarithmic pressure ratio hai

p_{ref} = 20 μ Pa

se referenced; yeh large surfaces par padne wale huge broadband pressure range ko compactly capture karta hai, jo ek single force number nahi kar sakta.

Spacecraft ki first natural frequency usually ek launcher-specified minimum se zyada kyun honi chahiye?

Structure ko itna stiff rakhne ke liye ki uske resonances launcher ke dominant low-frequency loads se upar rahein, dangerous coupling rokne ke liye — Launch Vehicle Dynamics se ek frequency-separation requirement.

EMC testing kyun zaroori hai even agar har box individually apni emission limit meet karta ho?

Compatibility ek system property hai — kai "compliant" emitters saath mein, plus shared harnesses aur grounding loops, milke phir bhi itna couple kar sakte hain ki ek sensitive receiver upset ho jaaye; sirf integrated testing coexistence prove karta hai.

Ek component ka temperature 300 K se 350 K tak raise karne par uski radiated power almost double kyun ho jaati hai?

Kyunki power

T_{s}^{4}

ki tarah scale karti hai, ratio

(350/300)^{4}

hai; step by step

350/300 = 1.1667

, phir

1.166 7^{2} = 1.361

, aur

1.36 1^{2} = 1.85

, toh ek modest absolute-temperature rise rejected power almost double kar deti hai — passive thermal self-regulation ka basis yahi hai.

Edge cases

Agar spacecraft ki natural frequency random-vibration band ke andar fall hoti hai (maan lo 300 Hz), toh kya hota hai?

Woh mode full spectral level par driven hota hai aur apne quality factor

Q

se amplify hota hai, toh us mode par koi bhi weak joint ya fastener sabse zyada shake hota hai aur typically fail karta hai — yahi poore band ko cover karne ka point hai.

Kya hota hai agar emissivity

ε \to 0

(ek perfect mirror surface)?

Surface almost kuch radiate nahi kar sakti, toh absorbed heat radiation se nahi nikal sakti aur equilibrium temperature badhti rehti hai; yahi wajah hai ki radiators high- $ε$ coatings use karte hain, shiny metal nahi.

Kya hota hai transmissibility ko jab damping

ζ \to 0

exactly resonance par?

r = 1

ke saath, transmissibility

Tr = Q = 1/ (2 ζ) \to \infty

ho jaati hai, toh ek ideal undamped structure bina bound ke amplify karta rahega — real structures sirf isliye survive karte hain kyunki kuch damping hamesha exist karti hai.

Frequency ratio

r = ω / ω_{n} = 2

par transmissibility kya hai?

Force-transmissibility form

Tr = \frac{1 + ( 2 ζ r ) ^{2}}{( 1 - r ^{2} ) ^{2} + ( 2 ζ r ) ^{2}}

use karte hue,

r^{2} = 2

plug karo: numerator

1 + 8 ζ^{2}

hai aur denominator

(1 - 2)^{2} + 8 ζ^{2} = 1 + 8 ζ^{2}

— dono equal hain, toh

Tr = 1

exactly, damping se independent. Yahi wajah hai ki

r = 2

amplification se isolation tak ka universal crossover hai.

Agar chamber temperature cycling se pehle specified vacuum tak nahi pahunch sakta toh kya hota hai?

Residual gas ek convection path restore kar deta hai, toh parts true space se zyada thande chalte hain aur outgassing suppress hoti hai — test tab article ko under-stress karta hai aur ek aisi design falsely pass kar sakta hai jo orbit mein overheat ho jaati.

Shock (pyrotechnic separation) test kya capture karta hai jo random vibration miss karta hai?

Shock ek bahut short, bahut high-g transient hai (milliseconds ke liye hundreds to thousands of g) jo brittle/fastener failures ko apne sharp high-frequency content ke through excite karta hai, woh sustained fatigue nahi jo random vibration produce karta hai.

Kya radiative exchange sirf do surfaces ke temperatures par depend karta hai, ya geometry par bhi?

Geometry par bhi — view factor (ek surface ki radiation ka woh fraction jo actually doosri par land karta hai) exchange scale karta hai, toh deep space face karne wala component kahin zyada reject karta hai ek warm neighbour mein ghire hue component se; multi-surface layouts ko view-factor bookkeeping chahiye, simple two-surface formula nahi.

Ek spacecraft jahan absorbed solar power fixed rahe, agar radiating area double kar do toh equilibrium temperature ka kya hoga?

Equilibrium

T_{s}

girta hai, kyunki fixed input ke liye

T_{s}^{4} \propto 1/ A

, deta hai

T_{s} \to T_{s} / 2^{1/4}

— bade radiators thande chalte hain, passive Spacecraft Thermal Control Systems ka core lever yahi hai.

Recall Quick self-check

Damping ke terms mein resonance par transmissibility do ::: $Tr = Q = 1/ (2 ζ)$ , toh lighter damping matlab ek taller, zyada dangerous peak. Do heat paths ke naam do jo vacuum mein survive karte hain ::: Structure ke through conduction aur space mein radiation — convection chali gayi. EMI aur EMC ke beech difference ek phrase mein batao ::: EMI interference ki problem hai; EMC woh achieved state hai jisme interfere nahi hota. $r$ kya stand karta hai ::: Frequency ratio $r = ω / ω_{n}$ , drive frequency over natural frequency.