NGLV -The modular launch vehicle of ISRO.

PSLV is not immortal as said by ISRO Chief Dr. S Somnath. PSLV was designed in 80s and cannot serve requirements of 2020s. After completing the government approved missions PSLV will be retired. Dr. S Somnath spoke these above words at “Engineers conclave 2022” at LPSC, Tirvananthapuram. The propellant used in some stages are toxic, the manufacturing processes of some components are too tedious to be scaled up and with new advancements in space technologies elsewhere, people can launch payloads in space more efficiently and at a cheaper costs. In an industry where the sizes of satellites and launch vehicles are getting smaller PSLV worked as workhorse but would soon be outdated by the quick “launch on demand” type Launch vehicles being developed by startups. Clearly ISRO has made SSLV for that and for high capacity govt, military and exploration satellites ISRO is developing a new modular launch vehicles that takes some inspiration from Spacex and some innovation from their own skills. Few years back ISRO presented a concept named ULV (unified launch vehicle) which showed multiple variants of GSLV mk3 like Launch Vehicle, I even made an article about it. The NGLV takes the same modularity approach so that standardised systems and subsystems could be manufactured en-masse and stored to keep the Launch Vehicles ready. standardised common parts amongst various systems and stages could mean more volume of order of these parts that should bring down procurement costs.

​ISRO scientists took painstaking efforts to make upper stage cryogenic engine of GSLV mk2, the case of Shri Nambi Narayan is infront of us already. These efforts led to development of CUS/CE20 engine that is used in GSLV mk3 today and is being uprated currently. Despite all this time has come to replace these launch vehicles for good so that we could become an advanced level space power from an entry level position that we are at right now.

We have compiled information scattered on internet here and there to give a general idea about the technological development happening for NGLV. Unlike ULV many technologies are currently being developed in that pursuance. Since the future is unpredictable any future disruptive technology might put the NGLV concept in doldrums just like ULV. ULV terminology itself is outdated now.

​BASIC CONFIGURATION 3 stage and 2 stage modular

Out of all the presentations given by Dr. S Somnath the previous designs were all 3 stage and talked about expendable Super Heavy Launch Vehicle. But in one of the presentations a two stage variant was seen. This two stage variant was seen with just SC400/LM400 as first stage and LM40 as second stage. For NGLV claims are being made for carrying 10 Tonnes to GTO which make it the first heavy class SLV being made in India. It also has bold plans to bring launch cost to LEO at just 1900USD/kg. 

​This configuration shows from what I understand an optional second stage that could be used only for heavier payloads. The upper stage is all methelox while first two stages have optional kerelox or methelox propulsion systems. Contrary to the outside appearance I expect the methelox and kerelox stages to be completely different. They would also need different volumes of fuel and oxidiser which would influence the fuel tank sizing. In an ISRO RTI reply it was revealed that the SCE200 engine which will be clustered to form the core SC400 stage is not restartable hence not reusable. This means that ISRO will use methelox based propulsion systems on expendable stages and kerelox based systems on recoverable booster stage. I personally think NGLV when and if made will look quite different from what is being shown in presentations. This entire article is our speculation from a space enthusiast point of view.

RLV A DIFFERENT VERTICLE THAN NGLV

ISRO is still pursuing development of RLV. Technologies are being tested, mentions are done in presentations and press conferences. Their are three configurations of RLV, one is where first stage is VTVL recoverable booster plus winged second stage. Second is winged first stage with parachute recoverable upper stage and third is that whacky spaceplane first stage and RLV second stage. I putting pictures below for reference all are taken from presentations. Very recently LEX was performed with a model RLV dropped from a helicopter. In next test they will send an RLV model in space from atop a GSLV mk2 and attempt de orbit and landing. I personally wish this test should use the ADMIRE test vehicle instead of GSLV mk2 I don’t know weather ADMIRE could impart enough delta V to a standard sized RLV model or not but it would look like a 100 percent reusable launch vehicle.

​TSTO with RLV upper stage can be seen in this snapshot from a presentation slide below. We have hypothesised that SC400 is not recoverable so this configuration might only be for test purpose.

​There is also another configuration of the same vehicle. Here they planned to use RLV as first stage and parachute recoverable second stage. The entire concept can be seen in the video below.

Pegasus RLV video

​PROBLEMS WITH RLV

The RLV as a space shuttle inspired vehicle seems good as concept. It is not absolutely reusable like an aircraft but it is refurbishable. But the limitations are also similar tp space shuttle. The RLV aims to bring down the cost required to build a brand new SLV to launch a payload by making the SLV reusable. But unlike other SLVs RLV has wings, it has heat resistant tiles and an engine that would barely have any use in space. For the same amount of fuel spent a normal SLV can carry larger payload compared to RLV, because RLV has to bear extra weight of the wings and tiles, etc while launching. Space Shuttle faced this same problem. Instead of brining costs down it actually increased the costs. The Soviets cancelled Buran exactly for this reason. With technological advancements that happened during development of Spacex falcon 9 and starship after retirement of space shuttle, refurbishment has actually become simpler. Inclusion of new technologies might bring refurbishment cost and complexity to a level where launch cost per kg would be competitive. The RLV can be used for a military application. We will surely find out in future let’s focus on NGLV for now.

Watch this video for points discussed on RLV.

CURRENT DEVELOPMENTS.

100 tonne Methelox engine clustered to form LM400 stage.

​100 tonne methelox engine is being pursued by ISRO as confirmed by Dr. S Somnath in a presentation and an RTI response by ISRO.

An RTI filed by some space enthusiasts responded that the 100KN metheox engine being developed by ISRO is throttleable and reusable. ISRO presentations by Dr S Somnath has shown first stage of NGLV have “LM400” engine. All these things hint at the methelox engine being clustered and used in LM400. The SC400 will be used in expendable NGLV I guess. The same RTI replied that SCE200 isn’t reusable.

A news article appeared in a local TV news channel about ISRO’s development of 100 KN LOX Methane engine. 

Single SCE-200 used to form SC-120 stage.

This development is being pursued for GSLV itself. The L110 core stage will be replaced by SC120 and the CUS/C-25 upper stage will be modified into C-32 stage having a higher propellant loading. The C-32 will also be restartable. This feature helps in achieving the Delta V in an economical way by coasting the upper stage for some time. ISRO also plans to use advanced composite materials, miniaturised avionics and iso-grid structures in interstages for weight reduction.

​As per presentation slides the payload capacity of LVM3 would dramatically increase upto 5.5 to 6 tonnes in GTO, just imagine what could be the capacity for LEO I wish it could go upto 20 tonnes in LEO. In some old presentations about HLV a GSLV mk3 uprated version is seen SC200 core stage with 2 S250 boosters and C-34 upper stage having a whopping 28 tonnes payload capacity to LEO.

Conversion of CUS/C25 stage into a methelox engine clustered to form LM40 stage.

​I found this slide in an old presentation last year which talked about a 5 to 10 tonne thrust Methelox engine. The slide clearly used words like “restarting abiltiy” and “throttling capability” showing prospects of reusability. Since CE20 produces around 20 tonnes of thrust I think they will have to cluster two such engine to produce equivalent thrust.

LM20 Methelox engine clustered to form LM40 stage.

​Last year ISRO conducted a hot test of 20 tonne thrust engine. The engine said to use similar gas generator cycle that is used in CE20. As per the same slide, ISRO is trying it’s hands on Fuel Rich Staged Combustion Cycle or an Expander-Bleeder cycle in the upper stage methelox engine development. 

LM20 Methelox upper stage engine hot test.

Interview of LPSC Director Dr. V Narayanan, watch from 10.00 He mentions LOX Methane engines.

Clustered SCE200 to form SC400 stage.

Throttleable Vikas Engine Development

CLICK ON THE IMAGE TO VIEW TEST NEWS BY ISRO

​Liquid engines that support throttling of the engine thrust facilitate booster stage recovery in launch vehicles. In order to enable booster stage recovery in future launch vehicle configurations, the first Throttling demonstration hot test of the Vikas engine was successfully accomplished on January 30, 2023 for a targeted 67% thrust level throttling for a duration of 43 s. Throttling of the engine was achieved by a closed loop thrust regulation system and the engine had been successfully throttled from the chamber pressure of 58.5 bar in steps of 50 bar, 45 bar & 40 bar, with dwelling at each pressure level for 7 s. In addition, the Vikas engine was also throttled down to 45% for the last 3 s before the engine shut down. The results of the first hot test of Throttleable Vikas Engine indicate stable combustion and subsystem performed in accordance with the prediction. The overall performance of engine sub-systems, control systems & test facility systems were as expected.

ISRO’s strategy for design and development.

​ISRO if currently focused on achieving fundamental levels of technological capacities like supersonic retro propulsion with deep throttling and restart capability for it’s upcoming VTVL mission. Other developments like Landing gear and grid fins are also going on. Once completed the ADMIRE test vehicle will be used to test the technologies to validate ISRO’s ability to develop a reusable vertical landing Launch vehicle. ISRO is planning to modify the L40H strap on boosters used on GSLV mk2 that produce 760KN of thrust using Vikas engine. Once this development completes ISRO will start development of throttleable 100 Tonne methelox and kerelox engines as well as clustering of 800 tonne engine.

All these technologies will go in making a recoverable SC400/LM400 stage which will be the core stage of all variants of NGLV. For this development Core Booster Recovery Experiments will be performed. The development of engine clustered upper stages will commence afterwards. The new initiatives being undertaken by ISRO is development of miniaturised and weight optimised avionics, advanced light weight composite materials, additive manufacturing and 3D printing of critical components for ease of production, minimal turnaround time and bulk manufacturing.

Prospective requirement.

​The primary objective will be similar to GSLV mk3 which is launch Communication and Earth Observation satellites for Civil and Military purposes. ISRO has plans for deep space missions on Mars, Venus, Moon and Sun. With increase in interest and Govt spending ISRO might attempt an asteroid study mission as well. In some old presentation of Dr. S Somnath a similar looking vehicle using SC400 first stage and C32 second stage was seen, named as HLV-HSP. ISRO will definitely use the NGLV technologies to make a Spacex Falcon 9 type reusable first stage crewed launch vehicle. SInce ISRO has concrete plans to build a space station for permanent Indian orbital human presence the components of Indian Space station and cargo supply missions can also be launched from an NGLV. 

ISRO will also launch interplanetary missions in future. Chandrayaan 3 has a payload that detects earthlike exo planets.

​Finally, despite the success of one web. If ISRO or some other company decides to launch a large constellation of satellites for earth observation or communication purpose NGLV would be an amazing low cost carrier option.

Sources :-
https://www.youtube.com/watch?v=XFWfSo256js
https://www.youtube.com/watch?v=eHGoNnCVMzY
https://www.youtube.com/watch?v=eUULKeFaLXY&list=PLsSEX5MtEwoFeOPijoAWCssaW9imPgOOC&index=2&t=2355s
https://www.youtube.com/watch?v=BL2OJqa-SbI&list=LL&index=179&t=1s