Geosynchronous Satellite Launch Vehicle Simulator

Theory

LVM3 is ISRO's heavy-lift launch vehicle, configured as a three-stage vehicle with two solid strap-on motors (S200), one liquid core stage (L110) and a high-thrust cryogenic upper stage (C25). It is designed to place 4,000 kg-class communication satellites (GSAT series) into Geosynchronous Transfer Orbit in a cost-effective, fully self-reliant manner. Staging lets the vehicle discard empty structural mass and use propulsion suited to each phase of ascent.

Vehicle Specifications

Height	43.5 m
Vehicle diameter	4.0 m
Heat shield (payload fairing) diameter	5.0 m
Number of stages	3
Lift-off mass	640 tonnes
Payload to GTO	4,000 kg (180 × 36,000 km)
Payload to LEO	8,000 kg (about 600 km altitude)

Stage-by-Stage

S200 solid boostersStrap-ons ×2
Developed at Vikram Sarabhai Space Centre and among the largest solid boosters in the world. They give the huge thrust needed for lift-off.

Height / Diameter	25 m / 3.2 m
Propellant	about 205 t HTPB each (nominal)

L110 liquid core stageStage 2
Powered by two Vikas engines designed and developed at the Liquid Propulsion Systems Centre (LPSC). It ignites while the S200 boosters are still burning.

Height / Diameter	21 m / 4 m
Engines	2 × Vikas
Propellant	115 t of liquid propellant (UDMH-based fuel with N₂O₄ oxidiser)

C25 cryogenic upper stageStage 3
Powered by CE-20, India's largest cryogenic engine, developed by LPSC. It burns liquid hydrogen (fuel) and liquid oxygen (oxidiser), a high-performance combination suited to the final ascent.

Height / Diameter	13.5 m / 4.0 m
Engine	CE-20
Propellant	28 t of LOX + LH₂

Payload fairing and encapsulated assembly
The 5 m fairing protects the spacecraft from aerodynamic loads, heating and acoustics. The Encapsulated Assembly (EA) is the spacecraft + Payload Adaptor (PLA) + fairing, and sits above the Equipment Bay (EB) that houses avionics.

Nominal Flight Sequence (GTO mission)

Event	Time	Remark
Lift-off	T+0 s	Both S200 ignite together
L110 ignition	≈113 s	Air-lit during S200 burn
S200 burn-out	≈134 s	Tail-off phase follows
S200 separation	137 s	Boosters jettisoned
Fairing separation	≈217 s	At about 115 km altitude
L110 separation / C25 ignition	≈313 s	Cryogenic burn begins
GTO injection	≈974 s	180 × 36,000 km

The Simulator tab replays the CMS-03 mission telemetry, so its event times differ slightly from these nominal figures.

Core Relationships

Thrust: T = ṁ Vₑ + (pₑ - pₐ)Aₑ Net force: F = T - D - mg Acceleration: a = F / m Dynamic pressure: q = ½ ρ V² Ideal rocket equation: ΔV = Vₑ ln(m₀ / m_f) Specific impulse: Isp = Vₑ / g₀

Key Ideas

Why staging?
As propellant is consumed, empty tanks and engines become dead mass. Separating completed stages improves the mass fraction of what remains.

Why different propellants? Solids give very high thrust with simple hardware for lift-off. Storable liquids give controllable, restartable core thrust. Cryogenic LOX/LH₂ gives the highest specific impulse, which matters most when the stage is small and the velocity gain is large.

Propellant share of lift-off mass: about 2 × 205 + 115 + 28 ≈ 553 t out of 640 t, so roughly 86% of the vehicle at lift-off is propellant.

Max-Q: dynamic pressure rises with speed but falls with air density. It peaks in the lower atmosphere, then drops, which is why the fairing can be released only once the air is very thin.

GTO vs LEO: GTO perigee speed is about 10.3 km/s versus about 7.6 km/s for a 600 km circular orbit. That extra velocity is why LVM3 carries 4 t to GTO but 8 t to LEO.

Embedded LVM3 3D Simulator · 16:9 Auto-fit

Viva Questions

1. Why does LVM3 use multiple propulsion stages?

Staging discards depleted hardware and lets different propulsion systems operate efficiently during different phases of ascent.

2. What is the primary role of the S200 boosters?

They provide the very high thrust needed for liftoff and the initial atmospheric climb.

3. Why is a payload fairing required?

It protects the spacecraft from aerodynamic pressure, heating, acoustic loads and the external environment during early ascent.

4. What is special about a cryogenic upper stage?

It uses propellants stored at very low temperatures and provides high-performance propulsion suited to the upper ascent phase.

5. Why does vehicle mass decrease during flight?

Propellant is continuously consumed, and completed boosters/stages or the fairing may be separated.

6. What does dynamic pressure represent?

Dynamic pressure, q = ½ρV², represents the aerodynamic loading associated with atmospheric density and vehicle speed.

Tricky Questions

7. Why is the L110 core stage ignited while the S200 boosters are still burning?

Igniting L110 at about 113 s, before S200 burn-out at about 134 s, keeps thrust continuous so there is no thrust gap to lose velocity to gravity. It also lets the core engines start in thinner air, and the boosters' thrust already carries the vehicle while the engines settle into steady operation.

8. LVM3 lifts 8,000 kg to LEO but only 4,000 kg to GTO. Why exactly half?

The same vehicle must give a much larger velocity gain for GTO. A 600 km circular orbit needs about 7.6 km/s, while the 180 × 36,000 km GTO perigee speed is about 10.3 km/s. From the rocket equation, every extra km/s forces the payload mass down, and here the payload halves.

9. Why launch eastward from Sriharikota, and how much does it help?

Earth's rotation gives a free eastward speed of ωR·cos(latitude), about 465 m/s × cos 13.7° ≈ 0.45 km/s at Sriharikota. That is why the simulator starts with an inertial velocity of about 0.45 km/s. A westward launch would pay that amount as a penalty.

10. Vehicle speed keeps increasing, so why does dynamic pressure (q = ½ρV²) peak and then fall?

Speed increases roughly linearly, but air density drops roughly exponentially with altitude. Beyond Max-Q the density decrease wins over the V² increase, so q falls even as the vehicle accelerates. Max-Q is the structural design-critical moment.

11. Why is the fairing jettisoned at about 115 km, not earlier or later?

Earlier, residual air would cause aerodynamic heating and pressure on the exposed satellite. Later, carrying the fairing wastes performance because it is dead mass. About 115 km is the compromise where free-molecular heating on the spacecraft is acceptably low, and every kilogram dropped goes straight into payload capacity.

12. The vehicle is 4.0 m in diameter but the fairing is 5.0 m. Why the mismatch?

The fairing's diameter is set by the volume of the largest satellite it must hold, not by the stage underneath. The wider fairing gives room for big GSAT-class spacecraft with antennas folded, and a conical transition joins it to the 4 m stage.

13. What fraction of LVM3's lift-off mass is propellant, and what does it imply?

About 2 × 205 + 115 + 28 ≈ 553 t out of 640 t, or about 86%. The structure, engines, fairing and payload together are only about 14%. It shows why launch vehicles are essentially flying tanks, and why even a small saving in dead mass matters.

14. If you double the exhaust velocity, ΔV doubles. If you double the mass ratio, does ΔV double?

No. ΔV = Vₑ ln(m₀/m_f). Doubling Vₑ doubles ΔV, but doubling the mass ratio adds only Vₑ ln 2 ≈ 0.69 Vₑ. The logarithm gives diminishing returns, which is why high-Isp engines and staging are preferred over simply adding propellant.

15. S200 burns for about 134 s but separates at 137 s. Why wait for those 3 seconds?

After burn-out, the thrust of a solid motor decays slowly (tail-off). Separating while residual thrust remains could push the boosters back into the stack, so the sequence waits until thrust has fallen low enough before firing the separation devices.

16. Why use cryogenic LOX/LH₂ only on the upper stage and not for lift-off?

Liquid hydrogen is very light, so it needs huge, insulated tanks that add drag and mass at lift-off, and the thrust needed on the ground is better supplied by dense solids. Its very high Isp pays off at the top, where small stage size and high final velocity make efficiency matter most.