Gaganyaan: What Is TV-D1 Mission? Know How ISRO Will Conduct It, Its Significance, And Challenges

Gaganyaan Test Flight: The Indian Space Research Organisation (ISRO) is set to launch the first developmental test flight mission of the Gaganyaan programme on October 21, 2023, at 8:00 am IST, from the First Launch Pad at Satish Dhawan Space Centre, Sriharikota. Gaganyaan's first developmental test flight mission is known as the TV-D1 mission, or the Flight Test Vehicle Abort Mission-1. The mission is important because it will demonstrate the performance of the Crew Escape System, and is the first mission of Gaganyaan's uncrewed flight tests.  As part of the Gaganyaan TV-D1 mission, in-flight abort of the Crew Escape System will be demonstrated. This means that while the Crew Module is in the air, the Crew Escape System will be jettisoned, so that ISRO will be able to check certain flight metres, and whether the Crew Escape System can be effectively jettisoned to save the lives of astronauts during crewed missions in case a mishap occurs. ISRO expects to conduct more test flight missions in the future.  <h3>What is Mach number 1.2? Why will TV-D1 be aborted at Mach number 1.2?</h3> The TV-D1 mission will be aborted at Mach number 1.2. Mach number refers to the ratio of the velocity of an object to the velocity of sound in the surrounding medium. This parameter has been named after Austrian physicist and philosopher Ernst Mach. The fact that the Crew Escape System will be jettisoned at Mach number 1.2 means that at that time, the velocity of the Crew Module has to be 1.2 times the velocity of sound in air.  "In aerospace engineering, the speeds of different objects can be defined as subsonic, transonic, supersonic, and hypersonic. Subsonic is below the speed of the sound. If something's speed is 1.2 times the speed of sound, it is considered transonic," a senior ISRO scientist, who did not wish to be named, told ABP Live.  So, in the case of TV-D1, the abort demonstration will occur at transonic speed. Mach 0.8 to 1.2 is considered transonic speed. The ISRO scientist also said that anything above 1.2 times the speed of sound to 5 times the speed of sound is supersonic, and anything above 5 times the speed of sound is hypersonic.  "The significance of Mach number 1.2 is that this is the stage at which the launch vehicle is expected to experience the greatest challenge, in terms of vibration and other parameters. So, if some anomalies are likely to occur, they will most probably occur during this stage. Mach 1.2 is about 360 metres per second. The vehicle will be taken to that speed. Once this speed is achieved, the abort command will be given. The Crew Escape System's role is to safely pull out the Crew Module from the launch vehicle, so that the Crew Module and the Crew Escape System go in different directions," said the ISRO scientist. <h3>Why is an unpressurised crew module being used for TV-D1?</h3> During TV-D1, an unpressurised crew module will be used. However, in the case of the crewed flight test of Gaganyaan, a pressurised crew module will be used, inside which Earth-like atmospheric pressure conditions will be simulated.  Both the pressurised and unpressurised versions of the Crew Module have the same mass and size. Also, both versions have the same systems for deceleration and recovery, including complete sets of parachutes.  While the Crew Module used for TV-D1 will simulate all the conditions that will be prevalent during the crewed flight of Gaganyaan, the one used for the former will be unpressurised. Explaining the reason behind this, the ISRO scientist said, "Ideally, we should have the pressurised module. But this Crew Escape System will not differentiate between pressurised and unpressurised modules. The TV-D1 is conducted essentially to evaluate or measure the performance of the Crew Escape System. Possibly, in the next flight, a pressurised module will be used. Right now, the focus is the command of abort. ISRO wants to see if the Crew Escape System does its job correctly when it receives the command of abort." <h3>Why are the avionics of the Crew Module in dual redundant mode?</h3> According to ISRO, the avionics systems (electronics applicable to aviation) are in a dual redundant mode. Explaining what dual redundancy means, the ISRO scientist said, "Suppose the main system is not working, an alternate or redundant system should work. If one system is not working, the other system should take over. Two sets of systems are built inside the Crew Module for functions such as navigation, sequencing, telemetry, instrumentation, and power. The Crew Escape System may work properly, but we may not know if navigation fails. Therefore, dual redundancy is there. In case the navigation system I am depending on undergoes some problem, the second navigation system, which is identical, will take over. So, there are two sets of systems corresponding to navigation, frequency, telemetry, instrumentation, and power." <h3>What achievements have been made so far?</h3> A single-stage liquid rocket will be used to launch the Crew Module, as part of the Gaganyaan TV-D1 mission. However, in case of the crewed flight, LVM-3 (Launch Vehicle Mark III) is likely to be used, the ISRO scientist said. "LVM3 is human-rated. The Crew Module is designed and fabricated, but there is a long way to go. Propulsion systems are developed under advanced stages of qualification." <h3>How the TV-D1 mission will be conducted, and the challenges</h3> As part of the TV-D1 mission, the Crew Module will reach an altitude of 11.7 kilometres in about 60 seconds. After reaching that altitude, an abort condition will be simulated. At that time, the speed of the Crew Module will be 1.2 times the speed of sound.  The Crew Escape System will jettison and pull the Crew Module to an altitude of about 17 kilometres, the ISRO scientist said. "After this, the Crew Escape System will be released. The Crew Escape System will fall on its own, under the influence of gravity. The Crew Module has an apex cover. The cover will be removed, and at an altitude of 16.7 kilometres, the parachutes will be deployed so that the velocity of the Crew Module is reduced from about 150 metres per second to 50 to 60 metres per second. When the Crew Module comes down to an altitude of 2.5 kilometres, the main parachutes will be deployed. At the last second of touching the surface of the sea, where the altitude will be about nine metres, the velocity will be about 8.5 metres per second. In this way, the Crew Module will touch down. It has a buoyant system because of which it will float on the sea. Colleagues from the Indian Navy will rescue the Crew Module from a location about 10 kilometres from the coast of Sriharikota." The critical aspect of the Gaganyaan TV-D1 mission is the performance of the Crew Escape System, the scientist said.  At an altitude of 17 kilometres, the Crew Escape System and Crew Module will be separated. The Crew Escape System's engines will be fired. The abort sequence will be executed autonomously. After the Crew Escape System is separated, drogue parachutes will be deployed from the Crew Module, when it is at an altitude of 16.7 kilometres. The main parachute will be deployed when the altitude is less than 2.5 kilometres. Finally, the Crew Module will splash down in the sea, about 10 kilometres from the coast of Sriharikota.  <h3>What is the significance of the Gaganyaan TV-D1 mission?</h3> The Gaganyaan TV-D1 mission is important because if it is successful, ISRO will be able to conduct further missions that will decide whether the Crew Module, Crew Escape System, and propulsion systems are qualified to perform the uncrewed as well as crewed flight missions. <h3>When will Gaganyaan’s human spaceflight mission be launched?</h3> The ISRO scientist also said that if everything goes fine, then by the first quarter of 2025, the first crewed flight of the Gaganyaan programme will be launched.

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Gaganyaan: What Is TV-D1 Mission? Know How ISRO Will Conduct It, Its Significance, And Challenges

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