Systems engineering — V-model, requirements traceability: Foundations

3.6.26 · D1 · Physics › Spacecraft Structures & Systems Engineering › Systems engineering — V-model, requirements traceability

Pehle aapko parent note V-Model & Traceability padhna hai, toh uske liye zaruri hai ki aap us note ke words aur symbols mein fluent ho jaao. Neeche, har idea ko bilkul zero se build kiya gaya hai, ek picture di gayi hai, aur justify kiya gaya hai. Upar se neeche padho — har item pichle wale pe lean karta hai.

1. Requirement — har cheez ka atom

Ise picture karo. Ek requirement ek checkbox jaisi hai jiske saath ek rule likha hai: "☐ Battery shall survive 5 years." Baad mein, koi ya toh ise tick karta hai (proven) ya nahi.

Topic ko yeh kyun chahiye. Parent note mein har cheez — V, matrix, flow-down — sirf aise sentences ke pile ko manage karne ke liye hai, bina koi kho jaaye. Agar ek requirement testable nahi hai, toh aap kabhi uska box tick nahi kar sakte, isliye "testable" optional nahi hai.

2. Abstraction level — aap kitne zoomed-in hain

Figure — Systems engineering — V-model, requirements traceability

Ise picture karo (upar wali figure): ek telescope ke zoom ki tarah sochiye. Bilkul zoom out karo toh "the mission" dikhta hai. Ek baar zoom in karo: "subsystems" (power, thermal, camera). Phir zoom in karo: "components" (ek battery, ek lens). Same object, alag detail.

Topic ko yeh kyun chahiye. Parent note mein letter $n$ ("level $n$ left pe hai toh verify hoga level $n$ par right pe") bas ek zoom setting ko label karne wala number hai. Levels ke idea ke bina, V-model ke koi rungs nahi hote.

3. Decomposition aur flow-down — ek promise ko todna

Ise picture karo. Ek arrow ek box mein enter karta hai, kaafi saare arrows neeche bahar jaate hain — ek promise fan out ho jaata hai sub-promises mein. Requirements Derivation dekho.

Do naaye symbols aaye hain. Abhi inhe earn karo.

Symbol $\land$ — "AND"

Ise picture karo. Do switches ek hi wire pe series mein lagate hain: current tabhi flow karta hai jab dono closed hoon. Ek open switch → koi current nahi.

AND kyun, OR kyun nahi? Ek spacecraft ek chain hai: agar battery fail hoti hai ya solar panel fail hota hai ya electronics fail hota hai, mission khatam. Aapko sab kuch succeed karna hai, isliye sub-promises ko AND se jodo, kabhi OR se nahi. (OR ka matlab hoga "koi ek kaafi hai" — serial systems ke liye galat.)

Symbol $⟹$ — "guarantee deta hai / le jaata hai"

Ise picture karo. Ek domino: agar domino $A$ girta hai, toh domino $B$ zarur girega. Lekin $B$ kisi aur wajah se bhi gir sakta hai, isliye aap arrow ko ulta nahi chala sakte.

Topic ko yeh kyun chahiye. Flow-down ka pura point yahi guarantee hai: agar har subsystem apna promise rakhta hai, toh system ka promise bhi rakha jaata hai. Woh arrow hi reason hai ki chhote parts ko verify karne se hum bade system par trust kar sakte hain.

Shorthand $⋀$ — "sab ka AND"

Ise picture karo. Series switches ki ek row, $n$ pieces ki, aur aapko har ek closed chahiye.

4. V-model — decomposition mirrored by verification

Ab letters ka matlab samajh aaya, toh shape draw ho sakti hai.

Ise picture karo (upar wali figure): ek bada letter V. Top-left mission hai; aap neeche-left slide karte ho aur zyada detailed hote jaate ho; bottom par pahunchte ho (hardware build karte ho); phir upar-right climb karte ho, bade aur bade chunks ko assemble aur test karte hue, jab tak top-right par, pura mission check nahi kar lete.

V kyun, straight line kyun nahi? Dono arms matching heights par hain purpose se: height abstraction level hai. Ek component-level promise (low, bottom ke paas) check hota hai ek component test se (woh bhi low). Yeh "same height = same level" pairing hi horizontal rungs ka matlab hai, aur isliye problems sabse saste possible level par pakdi jaati hain. Top-right rung (validation) aur lower rungs (verification) ke crucial difference ke liye Verification vs Validation dekho.

5. Verification vs Validation — do alag sawaal

Ise picture karo. Verification = apna homework rubric se check karna. Validation = check karna ki rubric sahi assignment thi bhi ya nahi. V ke lower rungs verification hain; bilkul top-right rung validation hai. Puri detail Verification vs Validation mein hai.

ConOps (Concept of Operations) simply ek plain-language story hai ki mission din-pratidin kya karta hai — yeh dono arms ke upar baitha hai.

6. Traceability aur traceability matrix — koi promise mat kho

Ise picture karo (upar wali figure): har requirement ek moti hai; strings har moti ko upar uske parent se aur neeche uske design item aur test se connect karti hain. Kisi bhi moti ko kheencho aur aap puri string trace kar sakte ho.

Topic ko yeh kyun chahiye. Do reasons jo parent stress karta hai: completeness (ek empty cell = bina proof wala promise, ek launch risk) aur impact analysis (ek requirement change karo aur usse touch karne wali har string light up ho jaati hai — aapko turant pata chal jaata hai kya redo karna hai). Yeh bookkeeping Configuration Management (in documents ke versions track karna) aur Interface Control Documents (subsystems ke beech ke promises record karna) ke close cousins hain.

7. Examples mein engineering symbols

Parent ke worked examples physics shorthand use karte hain. Har ek earn karo:

Definition Power/thermal budgets mein use hone wale symbols

$S$ — solar constant, sunlight power jo space mein ek square metre par padti hai, $S \approx 1361 W/m^{2}$ . Picture: space mein ek 1 m² ki khidki jo sunlight soak up kar rahi hai.
$A$ — solar array ki area $m^{2}$ mein. Picture: panel ki size.
$η$ (Greek "eta") — efficiency, sunlight ka woh fraction jo electricity mein convert hota hai, e.g. $η = 0.30$ matlab 30%. Picture: ek leaky bucket jo sirf 30% rakhta hai jo pour kiya gaya.
$P_{BOL}$ , $P_{EOL}$ — power at Beginning- aur End-Of-Life. Picture: panel factory se bilkul naya vs. space radiation ke saath kaafi saalon baad.
$d$ — yearly degradation fraction (e.g. $d = 0.025$ = har saal 2.5% kho deta hai).
$t$ — time saalon mein.
$Δ v$ ("delta-vee") — change in velocity jo ek propulsion system supply kar sakta hai; orbital manoeuvres ki currency.

Ise picture karo (upar wali figure): BOL power ek bhara hua glass hai; har saal aap current level ka fraction $d$ nikal dete ho, toh curve bend ho jaata hai aur flat hone lagta hai, seedha drop hone ki jagah. Yahi bending reason hai ki yeh $(1 - d)^{t}$ hai na ki $1 - d t$ .

Recall

$(1 - d)^{t}$ kyun, $1 - d t$ kyun nahi? Har saal baaki bachi power ka ek share remove hota hai, original ka nahi. Repeated multiplication → ek power. Yeh compound decay hai. ::: Straight-line version $1 - d t$ loss ko over-predict karta aur negative bhi ja sakta tha.

Prerequisite map

Equipment checklist

Khud test karo — sirf answer dene ke baad reveal karo.

Har requirement kya honi chahiye, nahi toh worthless hai?

Testable — aap ek aisi measurement point kar sako jo true/false decide kare.

"Abstraction level

n

" physically kya matlab hai?

Aap kitne zoomed-in ho; dono V arms par same number ka matlab same detail level hai.

Subsystem promises ko AND (

\land

) se kyun join karo, OR se kyun nahi?

Spacecraft ek serial chain hai — sab hold karne chahiye ya mission fail ho jaata hai.

A ⟹ B

ko plain words mein padho, aur kya aap arrow ko ulta chala sakte ho?

"Agar A toh B guaranteed hai"; nahi, implication one-way hai.

V par har rung ka promise kahan prove hota hai?

Same height (same abstraction level) par opposite arm par.

Verify aur validate mein kya fark hai?

Verify = sahi banaya (requirements meet karta hai); validate = sahi cheez banayi (mission/ConOps meet karta hai).

Traceability-matrix row "closed" kab hoti hai?

Jab uska test result PASS likhta hai, requirement → design → test evidence ko link karte hue.

Solar degradation

(1 - d)^{t}

kyun hai,

1 - d t

kyun nahi?

Har saal jo bacha hai uska fraction kho jaata hai — compound (multiplicative) decay.

BOL power formula likho aur har symbol ka naam batao.

P_{BOL} = A S η

: area × solar constant × efficiency.