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

3.6.21 · D1 · Physics › Spacecraft Structures & Systems Engineering › Spacecraft bus — structure, power, thermal, ADCS, C&DH, comm

Parent note mein koi bhi formula padhne se pehle, tumhe woh alphabet chahiye jisme wo formulas likhe gaye hain. Yeh page har letter define karta hai — plain words mein uska matlab, woh kaunsi picture represent karta hai, aur kyun topic uske bina kaam nahi kar sakta. Upar se neeche padho; har idea sirf upar wale ideas use karta hai.

Part 0 — The stage: "space" kya remove karta hai

Yeh ek fact — no air — hi reason hai kyun thermal section sirf radiation ki baat karta hai, aur kyun parent note baar baar "no convection" kehta rehta hai. Ise yaad rakho.

Figure — Spacecraft bus — structure, power, thermal, ADCS, C&DH, comms, propulsion

Figure s01 — Woh picture jo Part 0 fix karti hai: warm box heat sirf orange radiation arrows se shed kar sakta hai; crossed-out "no air" yaad dilata hai ki convection aur conduction-to-air simply unavailable hain. Baad ke har thermal equation mein yeh restriction inherit hoti hai.

Part 1 — Numbers jo amounts describe karte hain

Mass — $m$

Area — $A$

Figure s02 — Kyun topic do alag areas alag rakhta hai: sunlight power plum projected (shadow) area $A_{proj}$ pe depend karti hai, bade teal panel pe nahi. Panel ko tilt karo aur uski shadow shrink ho jaati hai chahe panel khud unchanged ho — woh shrinking shadow exactly wahi hai jo $A_{proj}$ measure karta hai.

Length & density — $L$ , $ρ$

Part 2 — Numbers jo pushes aur pulls describe karte hain

Acceleration — $a_{acc}$ , aur launch $g$

Force — $F$ (aur Newton ka rule)

Stress aur yield strength — $σ$ , $σ_{y}$

Part 3 — Efficiency $η$ (kisi bhi $η$ -ratio se pehle define karo)

Hum Greek letter $η$ se pehle milte hain kisi bhi specialised ratio mein use karne se pehle, kyunki Part 4 mein structural "strength-per-weight" ratio usi letter se likha gaya hai.

Part 4 — Do amounts combine: efficiency ratios

Structural efficiency — $η_{struct} = σ_{y} / ρ$

Intuition Strength-per-weight, aur kyun units yahi kehte hain

Agar tum strength chahte ho lekin mass carry karna nahi chahte, to tumhe aisi material chahiye jismein high strength $σ_{y}$ ho lekin low density $ρ$ ho. Unka ratio $η_{struct} = σ_{y} / ρ$ hai "bang per kilogram" — exactly Part 3 ke $η$ sense mein ek goodness ratio (jo tum chahte ho ÷ jo cost hota hai).

Kyun units yeh "strength per weight" banate hain: stress $σ_{y}$ pascals $= N / m^{2}$ mein hai, aur force newtons mein $kg \cdot m / s^{2}$ hai, isliye $\frac{σ _{y}}{ρ} = \frac{N / m ^{2}}{kg / m ^{3}} = \frac{N \cdot m ^{3}}{m ^{2} \cdot kg} = \frac{N \cdot m}{kg} .$ Yeh hai force-carrying-capacity times length, divided by mass — literally kitna load-times-reach tum buy karte ho per kilogram jo tumhe orbit mein lift karna hai. Aluminium aur carbon-fibre yahan high score karte hain, aur yahi poora reason hai ki spacecraft inse banaye jaate hain.

Part 5 — Numbers jo energy, power, aur time describe karte hain

Energy $E$ aur Power $P$ — crucial difference

Is topic mein use hone wale power symbols — $P_{load}$ aur $P_{SA}$

Orbit mein time symbols — $T_{orbit}, T_{sun}, T_{eclipse}$

Figure s03 — Orbit-timing symbols kahan rehte hain: spacecraft dotted loop pe ride karta hai, arc $T_{sun}$ pe orange sunlight mein nahaya hua aur $T_{eclipse}$ ke liye plum shadow cone mein swallowed. Poora lap $T_{orbit}$ hai. Yeh woh physical stage hai jis par neeche ka power-balance derivation play out hota hai.

Array-sizing formula ko balance se build karna

Formula Kyun array oversized hona chahiye — full chain

Step 1 — WHAT battery ko survive karna hai. Eclipse ke waqt arrays dead hain, isliye battery akele load $P_{load}$ chalati hai time $T_{eclipse}$ ke liye. Lekin energy bahar nikalna leaky hota hai, isliye battery ko actually load se zyada release karna padta hai: $E_{discharge} = \frac{P _{load} \cdot T _{eclipse}}{η _{discharge}} .$ $η_{discharge} < 1$ se divide karna ise bada banata hai — leak cover karne ke liye extra store karna padta hai.

Step 2 — WHAT daylight mein bank karna padta hai. Sunlight ke waqt, load se upar extra array power $P_{SA} - P_{load}$ , battery ko time $T_{sun}$ ke liye charge karti hai, lekin charging bhi leaky hoti hai, isliye sirf ek fraction stick karta hai: $E_{charge} = (P_{SA} - P_{load}) \cdot T_{sun} \cdot η_{charge} .$

Step 3 — WHY yeh equal hone chahiye. Ek steady orbit mein battery wahan khatam hoti hai jahan shuru hui thi (no net drain), isliye banked = spent: $(P_{SA} - P_{load}) T_{sun} η_{charge} = \frac{P _{load} T _{eclipse}}{η _{discharge}} .$

Step 4 — $P_{SA}$ solve karo. $T_{sun} η_{charge}$ se divide karo, phir $P_{load}$ add karo: $P_{SA} = P_{load} + \frac{P _{load} T _{eclipse}}{T _{sun} η _{charge} η _{discharge}} = P_{load} (1 + \frac{T _{eclipse}}{T _{sun} η _{charge} η _{discharge}}) .$ Yeh exactly parent note ka sizing formula hai. Bracket oversizing factor hai: dark jitna lamba ( $T_{eclipse}$ upar), ya battery jitni leaky ( $η$ 's neeche), array utna bada hona chahiye.

Part 6 — Numbers jo heat aur light describe karte hain

Temperature $T_{temp}$ (Kelvin)

Definition Temperature in kelvin

Temperature measure karta hai koi cheez kitni hot hai. Spacecraft engineers kelvin (K) use karte hain: Celsius jaisi hi size ke steps, lekin absolute zero se shuru hoti hai, isliye $K = ° C + 273$ . Room temperature $20° C = 293 K$ . Letter ke baare mein note: parent note temperature ko plain $T$ likhta hai, lekin is page pe $T$ ka matlab pehle se ek time duration hai (Part 5). Isliye is Part mein hum temperature ko $T_{temp}$ tag karte hain dono ko alag rakhne ke liye; jab tum parent ka thermal formula padho, uska $T$ yahi temperature hai. Kelvin kyun, Celsius nahi? Kyunki neeche ka radiation law $T_{temp}^{4}$ se multiply karta hai, aur yeh sirf tab kaam karta hai jab temperature true zero se shuru ho — ek $0° C$ object abhi bhi bahut glow karta hai, isliye tumhe ise "no glow" mean nahi karne de sakte.

Solar constant $S$ , albedo $a$ , Earth IR $E_{Earth}$

Absorptivity $α$ , emissivity $ϵ$ — surface ki do personalities

Heat inputs $Q_{in}$ aur output $Q_{out}$ — ek sign convention

Radiation law — Stefan–Boltzmann $σ$ aur $T_{temp}^{4}$

Figure s04 — Woh cheez jo $T^{4}$ law add karta hai jo words nahi kar sakte: rejected heat ki orange curve tezi se aur tezi se upar uthti hai, isliye "heat jo mujhe dump karni hai" ki horizontal line (teal) exactly ek temperature pe cross karti hai (plum dot). Woh crossing HI spacecraft ki settling temperature hai — heat load thoda upar karo aur crossing barely move karti hai, isliye vehicle self-stabilise karta hai.

Sab kuch topic ko kaise feed karta hai

Parent Spacecraft Bus topic dekho in letters ko full subsystem story mein assemble hote dekhne ke liye.

Equipment checklist

Right side cover karo aur khud test karo — tab ready ho jab har jawab instantly aaye.

Launch par

F = m a_{acc}

se tum kya compute kar sakte ho?

Woh axial force jo structure ko carry karni padegi: mass times launch acceleration.

Acceleration ko is page par

a_{acc}

tag kyun kiya?

Ise plain italic

a

se alag rakhne ke liye jo Earth ke albedo ke liye use hota hai.

Stress

σ

aur force

F

mein kya difference hai?

Stress force divided by area hai; same force thin part par high stress deta hai, fat part par low stress.

σ_{y}

kya mark karta hai?

Yield strength — woh stress jiske upar material permanently jhuk jaata hai.

Efficiency

η

kya hai, ek phrase mein?

Ek goodness ratio — jo tum chahte ho divided by jo cost hota hai (often kept-fraction, 0 to 1).

σ_{y} / ρ

ke units "strength per weight" kyun mean karte hain?

Yeh newton·metre per kilogram tak reduce hote hain — load-times-reach jo per kilogram lifted khareeda jaata hai.

Ek wall ka mass

m = A L ρ

kyun hai?

Volume = cross-section area × length, phir mass = volume × density.

P_{load}

aur

P_{SA}

ka matlab kya hai?

P_{load}

woh rate hai jis par sab equipment power khaate hain;

P_{SA}

(SA = Solar Array) woh rate hai jis par panels power generate karti hain.

Power

P

aur energy

E

ko confuse kyun nahi karna chahiye?

P

ek rate hai (watts);

E

ek total hai (joules);

E = P T

jahan

T

ek time duration hai.

Array oversizing factor

1 + T_{eclipse} / (T_{sun} η_{charge} η_{discharge})

kahan se aata hai?

Daylight mein banked energy ko eclipse mein spent energy ke equal set karne se, dono battery leaks ke liye corrected.

Heat options se convection ko kya remove karta hai spacecraft ke liye?

Space ka vacuum — koi air nahi, isliye bahar jaane ka ek hi tarika radiation hai.

Radiation law ke liye temperature kelvin mein kyun likhi jaati hai?

Kyunki

Q_{out} \propto T^{4}

ko ek aise scale ki zarurat hai jo absolute zero se shuru ho.

α

aur

ϵ

har ek kya control karta hai?

α

= sunlight ka absorbed fraction;

ϵ

= surface kitna well heat glow karta hai.

Heat flows ko kaunsa sign convention ek saath jodta hai?

Sab warming flows positive inputs hain

Q_{in}

mein summed; ek hi exit

Q_{out}

hai, aur balance set karta hai

Q_{in} = Q_{out}

Effective radiating area geometric

A

se kam kyun ho sakti hai?

View factors — surface ka har part cold space nahi dekhta; kuch warm Earth ki taraf face karta hai ya block hota hai.

T^{4}

law ek stable operating temperature kyun deta hai?

Thodi si temperature rise rejected heat ko sharply multiply karti hai, balance wapas push karti hai.

Kaun si do unrelated quantities dono

σ

symbol use karti hain?

Mechanical stress (pascals) aur Stefan–Boltzmann constant (

5.67 \times 1 0^{- 8}