3.2.27 · D1 · Physics › Orbital Mechanics & Astrodynamics › Pork chop plots — Δv vs launch - arrival date
Ek pork chop plot ek hi sawaal ka jawaab deta hai: "Agar main Earth se is din niklunga aur Mars pe us din pahunchna chahta hoon, toh trip kitna fuel khaayegi?" Kyunki dono planets hamesha move karte rehte hain, yeh cost dono dates ke saath badlati hai — aur har date-pair pe cost draw karne se ek contour map banta hai jiske sabse saste islands pork chops ki tarah dikhte hain.
Uss map pe ek bhi contour padhne se pehle, hume parent note mein aane waale har symbol pe poora command hona chahiye. Neeche, har idea usse pehle waale idea pe build hota hai — kuch borrow nahi, kuch assume nahi. Ek samajhdaar 12 saal ka baccha line one se shuru kar sakta hai.
Yahan sab kuch solar system mein hai, jo ek 3-D space hai. Yeh kehne ke liye ki koi cheez kahan hai ya kitni tezi se move karti hai, ek number kaafi nahi — direction bhi chahiye.
Definition Vector aur arrow notation
Ek vector ek arrow hai: iska ek length hota hai (kitna) aur ek direction hoti hai (kidhar). Hum vector ko upar ek chhoti arrow ke saath likhte hain, jaise r ya v .
r (Sun se kisi planet tak ka arrow) = ek position .
v (motion dikhane wala arrow) = ek velocity .
Arrow ke bina plain letter, r ya v , sirf us arrow ki length hai (ek single positive number, koi direction nahi).
Intuition Kyun arrows chahiye, sirf numbers nahi
Do spacecraft ek hi speed (same length v ) pe move kar sakte hain lekin opposite directions mein. Earth ke liye ek door bhaag raha hai, doosra paas aa raha hai. Fuel cost direction ke difference pe depend karti hai, isliye hum arrows throw away nahi kar sakte.
Ek vector ki length vertical bars se likhi jaati hai: ∣ v ∣ matlab "arrow v ki length". Agar v 3 units right aur 4 units upar point kare, toh right triangle se, ∣ v ∣ = 3 2 + 4 2 = 5 . (Length hamesha arrow ke sideways aur upward parts se bane box ka diagonal hota hai — yeh sirf Pythagoras hai.)
Parent note mein baar baar v 1 − V E jaisi cheezein likhi hain. Hume exactly pata hona chahiye ki do arrows subtract karne ka matlab kya hai aur, sabse important, yeh kaise dikhta hai .
Definition Vector subtraction = "B ki tip se A ki tip tak ka arrow"
A − B woh arrow hai jo B mein add karne pe A pe pahunche. Picture: dono arrows ko ek hi starting point se draw karo; difference woh arrow hai jo B ki tip se A ki tip tak jaata hai.
Intuition Kyun subtraction "relative velocity" ka dil hai
Socho tum ek train (Earth) mein ho jo V E pe move kar rahi hai, aur ek chidiya (spacecraft) v 1 pe ud rahi hai. Tumhe train ke andar chidiya v 1 − V E pe move karti lagegi — tum apni khud ki motion subtract karte ho kyunki tum use apne saath carry karte ho aur use "still" feel karte ho. Yahi exact idea hai ki spacecraft ki speed Earth ke relative v 1 − V E hai, v 1 nahi.
Yeh single picture parent ki ek "common mistake" already khatam kar deta hai: cost kabhi raw speed v 1 nahi hoti, yeh difference v 1 − V E hai.
Ab hum parent ke use kiye har arrow ko naam de sakte hain.
Definition Position aur velocity symbols
r 1 = launch ke waqt Earth ki position (Sun se Earth tak ka arrow). Heliocentric = "Sun se measure kiya hua".
r 2 = arrival pe target planet ki position .
r 1 , r 2 = unki lengths (Sun se distances).
V E = Earth ki orbital velocity (jis tarah Earth khud Sun ke around sweep karti hai).
V t a r g e t = target planet ki orbital velocity.
v 1 = woh velocity jo spacecraft ko uske transfer orbit ki shuruat mein chahiye.
v 2 = transfer ke end mein spacecraft ki velocity.
Poori trip yeh hai: r 1 pe v 1 pe shuru karo, curved path pe coast karo, r 2 pe v 2 pe pahuncho.
c
c = ∣ r 2 − r 1 ∣
Chord woh straight-line distance hai jahan tum shuru karte ho aur jahan khatam — woh arrow ki length jo dono planet positions ko connect karta hai. Yeh Lambert's problem mein appear karta hai kyunki start aur end ke beech straight line "kitni door apart" hain uska sabse simple measure hai.
Definition Time of flight
Δ t = TOF = ( arrival date ) − ( launch date )
Greek capital delta, Δ , hamesha "change in" ya "difference of" ka matlab hota hai. Toh Δ t sirf journey kitne din chalti hai woh number hai. Pork chop plot pe, constant Δ t ki lines diagonally chalti hain (kyunki unke saath arrival − launch fixed hoti hai).
Intuition Kyun TOF freely choose nahi kar sakte
Ek baar launch date aur arrival date choose ho jaayein, dono planet positions r 1 , r 2 lock ho jaati hain , aur unke beech ka time Δ t bhi. Physics tab sirf ek hi coasting curve allow karti hai jo fit hoti hai — tumhe shape bhi choose karne ka mauka nahi milta. Yeh "ek curve dhundhna" ka kaam Lambert's Problem hai.
==Δ v == ("delta-vee") woh total speed change hai jo rocket ko apne engines se produce karni padti hai , km/s mein measure kiya hua. Yeh space travel ki sachchi currency hai: zyada Δ v chahiye = zyada fuel = bhaari, mehenga rocket.
Δ v aur directly "fuel in kg" nahi
Fuel ki zaroorat rocket ke design pe depend karti hai (engine, mass). Lekin Δ v design-independent hai — yeh ek pure "yeh trip kitni mushkil hai" number hai jo sirf orbits se set hota hai. Tsiolkovsky Rocket Equation phir Δ v ko fuel mass mein convert karti hai. Toh mission designers Δ v plot karte hain: yeh fair, universal cost hai.
Parent ki ek cell ke liye total cost hai
Δ v t o t = Δ v d e p + Δ v a r r
— jo tum Earth chodne ke liye jalate ho plus jo tum target pe arrive/capture karne ke liye jalate ho.
Definition Gravitational parameter
μ
μ = GM
M ek body ka mass hai, G universal gravitational constant hai. Milke, μ ("mew") measure karta hai woh body kitni strongly pull karti hai . Earth ke liye μ E = 398600 km 3 / s 2 ; subscript batata hai kaunsi body. Hum μ use karte hain G aur M alag alag ki jagah kyunki yahi actually orbits control karta hai, aur yeh dono factors mein se kisi ek se kahin zyada precisely jaana jaata hai.
μ se bane do speeds har jagah aate hain:
Intuition Kyun square root
Dono energy se aate hain. Kinetic energy speed squared (2 1 v 2 ) se badhti hai, jabki gravity ka pull 1/ r se kamzor hota hai. Energy-in ko energy-needed ke barabar set karne se v 2 ∝ μ / r milta hai, isliye speed khud square root hai. Square root ek trick nahi — yeh energy bookkeeping ko wapas speed mein convert karna hai.
Yeh sabse subtle symbol hai, isliye hum ise ek picture ke saath build karte hain.
v ∞ ki kahani
Ek departing spacecraft Earth ke gravity well se bahar chadh raha hai, poore raste speed khota hua (gravity peeche kheenchti rehti hai). Agar uske paas exactly escape speed hoti, toh woh infinitely door pahunchta with zero speed bacha ke. Agar woh escape se tez shuru kare, toh infinity pe bhi kuch speed bachti hai. Woh bachi hui cheez hyperbolic excess speed hai.
v ∞ aur C 3
v ∞ ("vee-infinity") = woh speed jo spacecraft ke paas Earth ke relative tab bhi hai jab woh itna door ho ki Earth ki gravity aur matter nahi karti. Subscript ∞ literally "infinite distance pe" matlab hai.
C 3 ≡ v ∞ 2
==C 3 == ("characteristic energy") simply v ∞ squared hai. Iske units energy-jaise hain km 2 / s 2 . Rockets ko us C 3 se rate kiya jaata hai jo woh deliver kar sakte hain, isliye yeh natural launch-side cost number hai. Dekho Hyperbolic Excess Velocity & C3 .
C 3 mein square karo?
Energy speed squared ke saath scale hoti hai. v ∞ ko square karna ek speed ko energy-per-unit-mass mein convert karta hai, jo exactly wahi hai jis mein launch vehicle ka performance curve stated hota hai. Toh C 3 "woh interplanetary energy hai jo rocket inject karni padti hai". Ek rocket jo "C 3 = 12 " deliver kar sakta hai, woh kisi bhi trip mein zyada mass bhej sakta hai jisme v ∞ ≤ 12 = 3.46 km/s chahiye.
Parent ka boxed formula upar ki sab cheezein bundle karta hai. Aao ise symbol by symbol padhein.
v p er i kahan se aata hai (energy, ek line mein)
Departure path pe specific energy = (kinetic) − (gravity ka dip) = 2 1 v p er i 2 − r p μ E . Door jaake, gravity ka dip khatam ho jaata hai aur sirf 2 1 v ∞ 2 bachta hai. Energy conserved hoti hai, toh woh dono barabar hain:
2 1 v p er i 2 − r p μ E = 2 1 v ∞ 2 ⇒ v p er i = v ∞ 2 + r p 2 μ E .
Isliye tum v c subtract karte ho, v ∞ nahi: tum sirf wahan se burn karte ho jo tumhare paas hai wahan tak jo tumhe chahiye , right there parking orbit pe. Gravity well mein gehre fire karna efficient hai — woh bonus Oberth Effect hai.
Arrival burn Δ v a r r ka ek jaisa hi shape hai, bas target ke μ T , uski capture radius r a , aur v ∞ , a r r ke saath.
Definition Period aur synodic period
T E , T T = orbital periods — har planet ko Sun ke around ek chakkar laane mein kitne din lagte hain.
Synodic period T sy n = kitne time mein dono planets same relative geometry pe wapas aate hain (Sun se dekhe jaane pe unke beech wahi angle).
T sy n 1 = T E 1 − T T 1
Intuition Kyun yeh formula, ek picture mein
Socho do runners circular tracks pe hain. 1/ T ek "laps per day" rate hai. Tez runner slow runner se difference of their rates, 1/ T E − 1/ T T , pe aage nikal jaata hai. Jab woh lead ek full lap tak pahunche, toh acha aiming geometry wapas aa jaata hai — woh waiting time T sy n hai. Absolute value ∣ ⋯ ∣ sirf jawaab positive rakhta hai chahe koi bhi planet tez ho. Isliye fresh pork chops Earth–Mars ke liye har 26 mahine mein appear hote hain. Zyada: Synodic Period .
Vector subtraction = relative velocity
Hyperbolic excess v-infinity
Gravitational parameter mu
Circular and escape speeds
Departure and arrival burns
Transfer velocities v1 v2
Related deep tools jo aage milenge: Hohmann Transfer (sabse sasta, sabse slow case), Patched Conic Approximation (kyun hum Earth-escape aur Sun-transfer alag alag treat kar sakte hain), aur Tsiolkovsky Rocket Equation (Δ v ko fuel mein convert karna).
Right side cover karo; kya tum har ek ka jawaab reveal karne se pehle de sakte ho?
r pe chhoti arrow ka kya matlab hai, versus plain r ?r ek arrow hai (length
aur direction dono);
r sirf uski length hai, ek single positive number.
A − B draw karo — woh arrow kahan jaata hai?B ki tip se
A ki tip tak, jab dono same point se shuru hoon.
Spacecraft ki cost v 1 − V E pe kyun based hai, v 1 pe nahi? Earth tumhe pehle se
V E pe free mein carry karti hai; relative velocity apni khud ki motion subtract karti hai.
Plot pe Δ t kya hai, aur kaunsi lines use constant rakhti hain? Time of flight = arrival − launch; constant TOF ki diagonal lines.
μ kya hai aur G aur M ki jagah ise kyun use karte hain?μ = GM , ek body ki pull strength; yeh kahin zyada precisely jaana jaata hai aur directly orbits control karta hai.
v c aur v esc symbols mein do aur unka ratio batao.v c = μ / r ,
v esc = 2 μ / r ; escape
2 times circular hai.
Ek sentence mein, v ∞ kya hai? Woh leftover speed jo kisi planet ke relative tab bachti hai jab tum itne door ho ki uski gravity aur matter nahi karti.
C 3 aur v ∞ kaise related hain, aur kyun square karte hain?C 3 = v ∞ 2 ; square karne se speed energy-per-mass mein convert hoti hai, woh unit jisme rockets rate kiye jaate hain.
Departure burn mein v c kyun subtract karte hain (v ∞ nahi)? Tum parking orbit mein already jo speed hai us se jo perigee speed chahiye us tak burn karte ho.
Synodic period formula batao aur yeh kya count karta hai. 1/ T sy n = ∣1/ T E − 1/ T T ∣ ; woh time jisme tez planet relative angle mein ek full lap gain kar le.