Greetings. National Space Day celebrations are being held significantly across the country. Joining us is Mr. M. Mohan, head of the Liquid Propulsion Systems Centre in Thiruvananthapuram. We know that M. Mohan became the head of LPSC after Dr. V. Narayanan, who was the ISRO Chairman, moved on. Welcome, sir.So National Space Day is a celebration of Chandrayaan-3's success. Chandrayaan-3 is over. What all is happening now?Chandrayaan-3's landing on the South Pole happened on August 23, 2023, around 6 PM in the evening. It was the world's first such mission to land on the South Pole. Chandrayaan-3 accomplished this very successfully. LPSC's role in this was in the last phase of landing - below about 2 kilometers, its thrusters worked to bring it to a condition where it landed very slowly. This was done by throttleable thrusters specifically designed by LPSC. The electronics for this were also developed by LPSC itself.So very successfully, as a continuation of that, we now have Chandrayaan-4, Chandrayaan-5 programs - Chandrayaan follow-on programs. Ultimately, looking at the Prime Minister's Vision 2047, our target is to have a moon landing by an Indian human by around 2040. Work for that is currently ongoing.Sir, so Chandrayaan-3 is over, and preparations for Chandrayaan-4 and 5 are happening behind the scenes. What all is LPSC preparing for other Chandrayaan missions now?Chandrayaan-4 is planned as a sample return mission. When we say sample return mission, last time we landed Chandrayaan-3 there. Then the rover Pragyan descended there and traveled a few meters. After that, we had a 14-day mission - one lunar day. But after that, due to lack of power, we couldn't revive the rover or operate it.But in our next mission, we're planning not just to land a rover there, but to bring back a sample from there - we'll scoop up some material, or drill and extract samples, then bring that sample back to a module, then dock it with an orbiter and bring it back together. So it's a sample return mission. So the mission is to go down to the moon, take samples of soil, rocks, stones - whatever is there - and bring them back. This is Chandrayaan-4.Chandrayaan-5 is also a similar mission, but we're doing it in collaboration with the Japanese Space Agency JAXA. Its launch will be through Japanese launch vehicles. The propulsion systems for the satellite are new because the payload mass is 6500 kg. Previously, we had spacecraft of around 3000-4000 kg. This is a 6500 kg spacecraft. So we're now developing new thrusters for that. The qualification phase is currently ongoing.Yes sir, more powerful engines. We're in an era where this has become essential for spacecraft going to space as well as our Earth-based rockets. To increase LVM-3's capacity, semi-cryogenic engine development has been led by LPSC for quite some time. A small test of semi-cryo was conducted successfully some time ago - a test run. So at what stage is the semi-cryo engine development now?The semi-cryo engine - we have very successfully developed cryogenic engines in two categories. One is the cryogenic upper stage for GSLV with about 12 tons or 8 tons cryogenic thrust, and then for Mark-3, we developed a 20-ton cryogenic engine stage. But this one has very high capability - its propellant capability itself is 200 tons. So its thrust will be around 100 tons.So it's a very heavy launcher we're planning for the future. In this semi-cryo engine, as we know, we use liquid oxygen and kerosene - purified kerosene called ISROSENE. But when using this combination, engine manufacturing is extremely challenging because the temperatures and materials used are very different. So there have been difficulties in qualifying those materials and manufacturing.But now overcoming all that, we're in power head test activity - that is, a part that's like the brain of the engine. We've made it and completed four tests very successfully. Now we're taking the remaining series to the engine level. By the end of this year, we plan to make the first thrust chamber engine, and by the end of next year, make the stage, and the year after that, launch Mark-3 with semi-cryo.When that's done, we'll have a 110-ton liquid engine. There's already a liquid stage - L110 stage that comes as the core in GSLV Mark-3. At its bottom are two S200 strap-ons. In the middle is the L110. We're replacing that 1:1. But its thrust will be much higher. Based on that, what we can get now - if we're getting 4 tons propellant spacecraft mass, we can increase it to 5.5 tons. That's our first target. We intend to attempt that by the end of 2026, early 2027.Certainly, besides the semi-cryo engine, development of another powerful engine is also ongoing at LPSC. The LOX-methane engine for the upcoming New Generation Launch Vehicle. Where has that work reached now?For LOX-methane Next Generation Launch Vehicle (NGLV), we have two missions now. We know we have the Bharatiya Antariksh Space Station project ahead of us. Starting from 2028, we'll begin with Mark-3 vehicle itself. We plan to complete commissioning of its five modules by 2035. But if we need heavier payloads - now about 4 tons or 20 tons to low Earth orbit - especially when we look at the capability needed for a human to go to the moon and return, that requires much more capability - about 100-120 tons to low Earth orbit.For that, we're making NGLV and adding an extra stage to NGLV, or in a modular concept, making a stage with more powerful engines. We plan to use seven or nine engines in the first stage for LOX-methane engine. Now we've started with approval for development of a single 110-ton LOX-methane project. Its testing has begun - started last week. Even today there's a test.Very soon, I think within about three months, we can start testing at engine level. But its development completion - we'll complete development by next year's mid-point. Then we'll start stage activities separately as part of NGLV.Certainly, the country is waiting for NGLV. It's a rocket that will greatly increase our launch capacity. Certainly, we talked about rocket engines. Equally important is advanced technology used in satellites. LPSC has been approaching the great potential of electric propulsion for some time. We understand the first satellite using electric propulsion system is ready for launch. What are its features?Yes, very correct. We're now outsourcing a PSLV to an industry consortium. That mission is called PSLV N1. The satellite used in PSLV N1 is called TDS-01 (Technology Development Satellite).One specialty is that normally when we launch a spacecraft to 36,000 km geosynchronous or geo orbit, it would be 180 km perigee (closest distance) and 36,000 km apogee (farthest distance). But this is different - we'll launch this satellite by taking it to 240-18,000 km using PSLV. But after that, orbit raising to 36,000 km circular orbit will use electric propulsion.One advantage of electric propulsion is that propellant mass in a normal spacecraft is about 70-80%. If we say 4 tons, about 3200 kg would be propellant. But with electric propulsion, we can reduce that to about 100-150 kg total.It needs battery power, electric propulsion thrusters, and electronics. For thrusters, we've completely succeeded - developed and qualified them. We've already delivered for the next satellite, TDS-01. We're now working on electronics, which after qualification will be given for flight testing this month-end. Launch of N1 is planned for year-end.Once electric propulsion is demonstrated, we'll move to all-electric propulsion systems. Now we're doing 300 millinewton thrust. Instead, we plan to increase capacity to 1 newton. For 1 newton thrust, we need about 20 kilowatts power. If we're using 4 kilowatts now, for 1 newton thruster we need 20 kilowatts, requiring batteries and different technology.But as a first step, we developed a 300 millinewton thruster, developed its electronics, completed combined testing. We're now waiting for the next launch.Certainly, when electric propulsion comes fully, satellite weight will reduce. But there won't be compromise in capability, right?Never should be. Safety is most important. We usually talk about quality. Even a small quality lapse can cause mission loss. But here, safety comes before quality. So its certification board and certification level are much higher. Like aircraft safety clearance board, we have a national level board. Only with that board's clearance can we have human-rated conditions. We're already doing discussions, meetings, and approvals for that, so we'll be fully ready when the crewed mission comes.We mentioned TV-D2. TV-D2 is a mission we're all waiting for. Will there be an attempt this time to precisely land the rocket booster back at a location?Not this time. We're doing that as a separate project - Vertical Take-off and Landing experiment with the same TV thrust test vehicle configuration. But we need to make a throttleable engine - throttleable Vikas engine.We use Vikas engines in PSLV second stage, Mark-3's L110 stage, or GSLV second stage. We'll make this Vikas engine throttleable - we can throttle down to about 30% of current thrust development using electronics and valves, reducing performance gradually to minimize thrust before ground landing, making it soft landing when it comes at high velocity.We've completed that engine test - throttleable Vikas engine test. Now we need to make a stage like TV stage for vertical take-off and landing, with landing legs. It needs landing legs for landing, not parachutes. Similarly, it needs grid fins to reduce acceleration and increase drag.With all this, we can certainly do it. I think work will start next year, and the landing experiment will happen within two years. But we need to go to some altitude and return. Later, we plan to make the first stage of future NGLV reusable - recover and reuse. We'll demonstrate all that technology here.So big goals are waiting. There's still a long way to go. ISRO is advancing with experiments and various goals. All the best to LPSC, ISRO, and you all. Thank you very much for cooperating with us."This interview covers India's ambitious space program including lunar missions, advanced propulsion systems, reusable rocket technology, and the goal of human moon landing by 2040.