Crew Escape System and the first Gaganyaan test flight

On October 21, the Indian Space Research Organisation (Isro) will launch the first developmental flight under its Gaganyaan mission from the Satish Dhawan Space Centre in Sriharikota.

The demonstrator Test Vehicle Abort Mission or TV-D1 is the first milestone in the run-up to India’s ambitious human space flight programme – now set for a 2025 launch – as it will test the mission’s Crew Escape System in field conditions.

R Krishnakumar looks at what constitutes the CES and how TV-D1 will set the tone for Isro’s plan of sending an Indian to space in an Indian spacecraft.

What is a Crew Escape System (CES)?

The crew escape system (also known as Launch Abort System or Launch Escape System) is an emergency exit option critical to manned space missions. It is designed to pull away the crew module – which carries the astronauts – from the launch vehicle, take it to a safe altitude and bring it safely back on the earth in the event of a launch abort or during the vehicle’s ascent.

The CES for TV-D1 carries the crew module in its rear portion. It is 15.5 metres long and is mounted at the front-end of the liquid-propelled, single-stage, 19.5 metres-long test vehicle. The TV-D1 CES has five types of solid motors – crew escape system jettisoning motor, high-altitude escape motor (four of them), low-altitude escape motor, low-altitude pitch motor and high-altitude pitch motor. These motors generate the thrust needed for various mission requirements.

When did Isro test the CES for the first time?

In July 2018, Isro carried out the successful flight testing of CES, demonstrating safe recovery of the crew module in the event of an emergency. In the test that lasted 259 seconds, the CES along with a simulated 12.6-tonne module lifted off from the spaceport and reached an altitude of about 2.7 km before it separated from the test vehicle for a safe touchdown.

How will the Crew Module (CM) for the unmanned test flight function?

In the first Gaganyaan mission, the space agency plans to send a three-member crew to an orbit of 400 km for a three-day mission. The crew module will carry the astronauts in a pressurised, earth-like condition. For the uncrewed test flight on October 21, the space agency has developed an unpressurised version of the module. It is a single-walled aluminium structure with a simulated thermal protection system. It matches the size (3.1 m x 2.97 m) and mass (4,520 kg) of the module that will be developed for the manned mission. Ahead of its final integration to the test vehicle, it has undergone a series of electrical and vibration tests. The module comes with avionics systems and all the deceleration and recovery systems including 10 parachutes. It is designed to record flight data that will be used to analyse the performance of the subsystems.

The TV-D1 will be the first test of the mission’s CES. What does it entail?

The flight will simulate an abort condition while the test vehicle is in ascent. The vehicle’s ascent trajectory will correspond to a Mach-1.2 velocity path (about 400 metres per second) which is in line with the ascent trajectory projected for the manned mission. At an altitude of about 17 km, the crew escape system and crew module will be separated from the test vehicle. This will mark the start of the abort sequence leading to the separation of the two systems. The parachutes will be deployed for the crew module’s final descent and touch down on the sea, about 10 km from the coast of Sriharikota. The touchdown velocity is estimated to be about 8.5 metres per second. A diving team of the Indian Navy will attach a buoy to the module, hoist it using a ship crane and bring it to the shore.

TV-D1 will be the first of the four such test flights scheduled ahead of Gaganyaan. It is a significant capability demonstration as it involves the integration of a “near-complete system” for a test flight. Its results will shape Isro’s preparations for the subsequent qualification tests.