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ISRO achieved a major milestone with the successful hot testing of liquid rocket engine manufactured through Additive Manufacturing (AM) technology for a duration of 665 s on May 9, 2024. The engine used is the PS4 engine of PSLV upper stage.

The PS4 engine manufactured in the conventional machining and welding route has been in use for the fourth stage of PSLV which has a thrust of 7.33 kN in vacuum condition. The same engine is also used in the Reaction Control System (RCS) of the first stage (PS1) of PSLV. The engine uses the earth-storable bipropellant combinations of Nitrogen Tetroxide as oxidizer and Mono Methyl Hydrazine as fuel in pressure-fed mode and was developed by the Liquid Propulsion Systems Centre (LPSC), ISRO.

LPSC redesigned the engine making it amenable to the Design for Additive Manufacturing (DfAM) concept thereby gaining considerable advantages. The Laser Powder Bed Fusion technique employed has brought down the number of parts from 14 to a single-piece, and eliminated 19 weld joints, saving significantly on the raw material usage per engine (13.7 kg of metal powder compared to the 565 kg of forgings and sheets for conventional manufacturing process) and reduced 60% in the overall production time. The manufacturing of the engine was done in the Indian industry (M/s WIPRO 3D), and the engine was hot tested at ISRO Propulsion Complex, Mahendragiri.

As part of the development programme, the injector head of the engine was realised and successfully hot tested earlier. Detailed flow and thermal modelling, structural simulation, and cold flow characterisation of the proto hardware were carried out to gain confidence for the hot test. Consequently, four successful developmental hot tests of integrated engine were conducted for a cumulative duration of 74 s which validated the engine performance parameters. Furthermore, the engine was successfully tested for the full qualification duration of 665 s and observed that all the performance parameters were as expected. It is planned to induct this AM PS4 engine into the regular PSLV program.

The performance of the engine during the long-duration test is shown in the following graph.