Indian Space Program: News & Discussion

[a_bharat]

AgniKul Cosmos
@AgnikulCosmos
Humbled to share that we successfully test fired 3 semi-cryogenic rocket engines simultaneously, as a cluster. All the 3 engines are 3d printed as single pieces of hardware - designed and manufactured in-house at AgniKul Cosmos Rocket Factory - 1. As with all our propulsion systems, these 3 engines are also powered by electric motor driven pumps.

This test involved calibrating 6 pumps, 6 motors and tuning 6 speed control algorithms to work together in perfect sync to achieve uniform startup, steady state and shutdown performance across the entire system.

To the best of our knowledge, this is the first time such a test has been performed in India with semi cryogenic engines. We are extremely grateful to have the opportunity to be building world class, original space technology from India, for the world with the support of
@isro and @INSPACeIND

[uddu]

Dhawan-III | Static Test Fire | Skyroot Aerospace
National Science Day marks the discovery of the Raman Effect, encouraging young people across the country to continue pursuing their passions in STEM. Today feels like the right moment to share what we've been building to fuel further innovation at Skyroot.

Dhawan-III, our upgraded cryogenic rocket engine, just completed a 145-second endurance test on an indigenous mobile test stand built in-house.

This engine has been developed under the Aatmanirbhar Bharat ARISE-ANIC initiative with a focus on reusability and greener propulsion.

Happy National Science Day.

[sanjaykumar]

What do those shock diamond thingees signify?

[drnayar]

What do those shock diamond thingees signify?

Rocket engine exhaust often contains a distinctive pattern known as shock diamonds or Mach diamonds. These are a series of shock waves and expansion fans that increase and decrease, respectively, the supersonic exhaust gases’ pressure until it equalizes with atmospheric pressure. The bright glowing spots visible to the naked eye are caused by excess fuel in the exhaust igniting. As awesome as shock diamonds look, they’re actually an indication of inefficiencies in the rocket: first, because the exhaust is over- or underexpanded, and second, because combustion inside the engine is incomplete. Both factors reduce a rocket engine’s efficiency (and both are, to some extent, inescapable).

https://fyfluiddynamics.com/2015/10/roc ... stinctive/

[sanjaykumar]

Thanks. Often wondered.

[drnayar]

and they have use in assessing calibration of rocket engines and assessing performance

Pressure Matching: They appear when the exhaust pressure doesn't match the surrounding air. If an engine is designed for high altitude, it will show these diamonds at sea level because it is over-expanded.

Flow Verification: Engineers use high-speed schlieren photography to see these waves, confirming the exhaust is supersonic.

Performance Tuning: The angle and length of the diamonds allow engineers to calculate the exhaust Mach number and pressure ratios.

Combustion Efficiency: If diamonds are visible to the naked eye, it often means unburned fuel is reigniting in the shock waves, signaling incomplete combustion.

how they form :

Imbalance: Exhaust leaves the nozzle at a different pressure than the atmosphere.
Compression: The outside air "squeezes" the exhaust, creating a shock wave.
Expansion: The gas bounces back, expanding past the ideal point.
Repetition: This "bouncing" repeats, forming the diamond chain until the pressures eventually equalize

How nozzle shapes affect shaping [ or not]

Nozzle shape fundamentally changes how exhaust interacts with the atmosphere, which determines if and how shock diamonds appear. While traditional bells create fixed patterns, advanced shapes like aerospikes are designed to "self-correct" and minimize them.

1. Traditional Bell Nozzles (Static Patterns)
Bell nozzles are optimized for a single altitude. At any other altitude, the pressure mismatch creates visible shock diamonds.
Over-expanded (Low Altitude): The nozzle is "too big" for the high air pressure at sea level. The air "pinches" the exhaust inward as it leaves the nozzle, creating a series of inward-pointing shock waves that form the first diamond.
Under-expanded (High Altitude): The exhaust leaves at a higher pressure than the thin air and "billows" outward. It then snaps back inward due to expansion fans, creating diamonds that appear larger and further downstream.

2. Aerospike Nozzles (Minimal/Dynamic Patterns)
An aerospike engine is essentially a bell nozzle turned inside out.

Altitude Compensation: Instead of a fixed metal wall, it uses the ambient air pressure as one "wall" of the nozzle.
Diamond Suppression: Because the exhaust is always exposed to the atmosphere, it constantly adjusts its expansion to match the outside pressure. This means the exhaust is almost always "perfectly expanded," which theoretically eliminates or significantly reduces the pressure imbalances that cause shock diamonds.
Visual Difference: If diamonds do appear in an aerospike (such as in linear variants), they are often less distinct or only visible when viewed from specific angles (e.g., from the end of a linear spike).

3. Dual-Bell and E/D Nozzles
These are "hybrid" shapes designed to have two optimal points.

Dual-Bell: These have a "kink" in the nozzle wall. At low altitudes, the flow separates at this kink, creating a smaller effective nozzle and smaller, sharper shock diamonds. As the rocket climbs, the flow "attaches" to the full bell, and the diamonds shift to a larger pattern.

Expansion-Deflection (E/D): Uses a center pintle to push exhaust outward. This creates a hollow exhaust plume where shock diamonds might form in a ring or complex internal structure rather than a solid center chain.

[Zynda]

^^This is great post. Thanks