Spacecraft bus — structure, power, thermal, ADCS, C&DH, comms, propulsion: Question bank

3.6.21 · D5 · Physics › Spacecraft Structures & Systems Engineering › Spacecraft bus — structure, power, thermal, ADCS, C&DH, comm

True or false — justify karo

Spacecraft bus science karta hai, payload sirf usse support karta hai.

False — ulta hai. Payload hi mission hai (camera, telescope, sensor); bus woh skeleton-plus-life-support hai jo payload ko alive, pointed, aur heard rakhta hai.

Ek CubeSat jiska load-bearing wall area 1.63 mm² hai woh safe hai kyunki yield-stress calculation satisfy ho raha hai.

False — yield strength sirf yeh check karta hai ki metal permanently deform nahi karega. Real walls 1–2 mm ki hoti hain kyunki stiffness (vibration modes) aur safety factors dominant hote hain, raw strength nahi.

Agar koi structure axial launch load survive kar le toh poora launch survive kar lega.

False — steady axial g-force sirf ek load hai. Vibration, acoustic, aur shock loads resonant modes excite karte hain aur aksar static load se zyada structure ko size karte hain.

Structural efficiency

σ_{y} / ρ

batata hai kaunsa material sabse strong hai.

False — yeh batata hai strength per unit density. Ek denser material stronger ho sakta hai phir bhi spacecraft ke liye worse hoga, kyunki har kilogram launch mass cost karta hai.

Space mein ek spacecraft heat radiation, convection, aur surrounding gas mein conduction se lose karta hai.

False — koi surrounding gas nahi hai, isliye space mein convection zero hai. Radiation (

ϵ σ A T^{4}

) vehicle se heat bahar jaane ka ek hi rasta hai; conduction sirf heat ko andar move karta hai.

Black surface (high

α

) satellite ke liye hamesha buri choice hoti hai.

False — high absorptivity tabhi buri hai jab solar input problem ho. Ek thande, sun-starved orbit mein aap sunlight absorb karna chahenge, isliye "sahi" coating thermal environment par depend karti hai.

Emissivity

ϵ

badhana spacecraft ko hamesha thanda karta hai.

False —

ϵ

radiated output aur absorbed Earth-IR input (

ϵ A E_{Earth}

) dono mein appear karta hai. Ise badhane se rejection aur intake dono boost hote hain, toh net effect is baat par depend karta hai ki kaunsa term dominant hai.

Solar array power end of mission par launch ke waqt jitni hoti hai utni hi hoti hai.

False — cells degrade hote hain (~2.5%/yr LEO mein radiation se). Aapko Beginning of Life ke liye size karna padta hai taaki degradation ke baad bhi End of Life par kafi power bachi rahe.

Agar battery round-trip efficiency 100% hoti, toh solar array ko sirf average load supply karna padta.

False — perfect batteries ke baath bhi array ko poori orbit ki energy sirf sunlit fraction ke dauran generate karni padti hai, isliye woh phir bhi

P_{load}

se eclipse/sun time ratio ke anusaar zyada hoga.

Error dhundo

Q_{out} = ϵ σ A T

heat radiate karta hai."

Temperature fourth power mein hona chahiye:

Q_{out} = ϵ σ A T^{4}

. Radiated power

T^{4}

ke scale par hoti hai, isliye thoda sa temperature rise bahut zyada heat dump karta hai.

T

Stefan–Boltzmann equation mein degrees Celsius mein hai."

Galat — yeh Kelvin mein absolute temperature honi chahiye. 293 K ki jagah 20 use karne se radiated power hazaron guna underestimate ho jaati hai.

"Solar input equals

α \cdot A_{total} \cdot S

jahan

A_{total}

poori surface area hai."

Sirf Sun ki taraf facing projected area sunlight absorb karti hai, total surface nahi. Ek cube Sun ke saamne ek face present karta hai, chhe nahi.

"95-min orbit ka 35% eclipse fraction matlab eclipse 35 min tak chalta hai."

0.35 \times 95 = 33.25

min, toh lagbhag 33 min, 35 nahi. 35 ek percentage hai, duration nahi.

"Kyunki

A \geq \frac{m a}{σ _{y}}

hai, safe rehne ke liye sabse bada area use karo."

Inequality ek minimum deti hai; oversizing mass waste karta hai. Engineering goal sabse chhota area hai jo strength aur stiffness dono meet kare, kyunki mass dushman hai.

"Albedo heating Sun se aati hai, isliye eclipse ke dauran disappear ho jaati hai."

Albedo Earth se reflect hua sunlight hai, toh day side par yeh exist karta hai — lekin eclipse ke dauran spacecraft Earth ki shadow ke peeche hota hai, isliye albedo wahan vanish ho jaata hai. Trap yeh hai ki ise Sun-independent term kehna; yeh neeche Earth ki surface ki illumination track karta hai.

Why questions

Structure ko on-orbit environment se nahi, launch environment se kyun size kiya jaata hai?

Kyunki launch sabse harsh mechanical loads deliver karta hai — high g-forces, vibration, aur acoustic shock — jabki orbit almost force-free hota hai. Launch survive kar lo toh orbit aasaan hai.

Hum solar array ko average load ke exactly size ka kyun nahi bana sakte?

Array sirf sunlight mein power produce karta hai, lekin load poori orbit chalti hai. Ise eclipse ke liye energy bank karne ke liye sunlit part ke dauran overproduce karna padta hai, saath mein battery losses bhi cover karne padti hain.

Hum

α / ϵ

ke ratio ki care kyun karte hain, na ki har value ki alag-alag?

Equilibrium temperature solar-in (via

α

) aur radiated-out (via

ϵ

) ke balance par depend karti hai. ==Low

α / ϵ

== sunlight mein thanda rehta hai; high wala warm — toh ratio running temperature set karta hai.

Safety factor structural requirement ko 2× nahi, 10–20× kyun multiply karta hai?

Kyunki kai independent unknowns stack up hote hain: material scatter, vibration/resonance, handling, thermal cycling, aur modelling uncertainty — har ek margin demand karta hai, aur yeh add nahi multiply hote hain.

Battery ki zarurat hi kyun hai agar solar array load meet kar sakta hai?

Array sirf sunlight mein kaam karta hai; eclipse ke dauran zero generation hota hai, isliye battery ko poora load carry karna padta hai. Storage har orbit ke dark half ko bridge karta hai.

Thermal balance mein emissivity ke do alag roles kyun hain?

Wahi surface spacecraft ki apni heat bahar radiate karta hai (

ϵ σ A T^{4}

) aur Earth ki infrared glow absorb bhi karta hai (

ϵ A E_{Earth}

). Ek coating property IR exchange ke dono directions drive karti hai.

Edge cases

Zero eclipse wale spacecraft (jaise dawn–dusk sun-synchronous orbit) ke power budget ka kya hoga?

T_{eclipse} = 0

, toh sizing term

\frac{T _{eclipse}}{T _{sun} η _{c} η _{d}}

vanish ho jaata hai aur

P_{SA} \to P_{load}

— array ko sirf load cover karna hai, aur battery almost idle rehti hai.

Deep space mein, Sun aur Earth se bahut door, spacecraft ke liye thermal balance kya predict karta hai?

Solar, albedo, aur Earth-IR inputs sab zero ki taraf drop ho jaate hain, sirf internal dissipation radiate karne ke liye bachti hai. Equilibrium temperature girta hai, toh design problem cooling se warm rakhne (heaters) ki taraf flip ho jaati hai.

Agar internal dissipation

Q_{dissip}

akela heat source hota (fully shaded orbit)?

Tab

Q_{out} = ϵ σ A T^{4} = Q_{dissip}

akela hoga, aur equilibrium temperature purely waste heat aur radiating area se set hogi — koi

α

term appear nahi karega.

Eclipse duration ek poori orbit ke karib pahunchne par (

T_{sun} \to 0

) required array power ka kya hoga?

Ratio

T_{eclipse} / T_{sun} \to \infty

, toh

P_{SA} \to \infty

— ek unphysical demand jiska matlab hai koi realistic array near-permanently-eclipsed orbit survive nahi kar sakta; aapko ek alag power source chahiye hoga.

α = ϵ

wali surface (grey body) ke liye, sunlight mein equilibrium temperature Earth ke coating-driven tuning se kaise compare karta hai?

α = ϵ

ke saath ratio 1 hai aur coating koi thermal tuning leverage nahi deti; temperature sirf geometry aur flux se fix hoti hai, isliye engineers deliberately aise coatings choose karte hain jahan

α \neq = ϵ

Agar launch acceleration zero hota (imaginary gentle launch) toh minimum wall area kya hogi?

Static formula

A \geq 0

deta hai, yaani strength koi constraint nahi impose karta — lekin structure ko phir bhi stiffness, handling, aur thermal loads ke liye finite thickness chahiye, jo dikhata hai ki yield calc akele real minimum kabhi set nahi karta.

Recall Quick self-test

Woh ek property jo space mein zero hai aur isliye spacecraft thermal balance mein kabhi appear nahi karti ::: Convection (heat carry karne ke liye koi surrounding gas nahi). Woh environment jo usually primary structure ko size karta hai ::: Launch — g-forces, vibration, acoustic, aur shock loads. Solar array average load se hamesha bada kyun hota hai ::: Ise eclipse energy bank karni hoti hai aur battery losses cover karne hote hain jabki sirf sunlight mein generate kar sakta hai.