Gaganyaan mission: After success of crew module abort test, ISRO eyes uprighting system in 2024

The first test of the crew module and crew escape system in the TV D1 mission, where an abort sequence in the launch phase of a human mission was simulated, has been deemed a complete success after receiving all the data from the systems tested in the mission, Sivakumar said.

“All three elements of the mission are new. The test vehicle is new, the crew escape system is new and the crew module is new. Developing each of the systems was one of the challenges. The mission planning and mission design is very, very important here,” the scientist said. “We have got data from all the three systems and everything is nominal,” he added.

One of the biggest outcomes in the TV-D1 mission was the success of the tricky component of the deployment at a desired angle of the drogue chutes (which bring the crew module from a height of 17 km at a speed of 150 metres per second to a height of 2.5 km from the surface of the sea at a speed of 63 m/sec) after the release of crew module from the crew escape system in this mission, the 58-year-old mission director said. “The drogue chute deployment at the desired angle was a really tricky problem,” he added.

“Our mission profile was that we took the crew escape system to a particular Mach number (1.2 times the speed of sound) using the newly developed test vehicle and from there the crew escape system took the crew module it to a particular altitude and flight path angle. When the crew module comes out, we have to monitor its orientation and at the appropriate angle we have to deploy the apex cover and drogue parachutes. This was the mission design challenge,” Sivakumar said.

The mission was about understanding how to put the crew module in the appropriate position and orientation since the crew module in the TV-D1 flight did not have its own control system unlike the final crew module which will have its own onboard control system, he said.

“At 17 km altitude – when the crew module is coming out – in a real crew module, we would have a control system that is controlling the attitude such that the parachute deployment angle is controlled. Here, it is coming out in unfavorable orientation and must be deployed before the crew module starts tumbling or getting locked in an unfavorable orientation. So, we have to monitor the exact orientation and angle because only at a favourable angle can we deploy the drogue parachute. This is the real crux of the problem. The second crucial part is that we have never tested the parachute behaviour at such a high altitude,” Sivakumar pointed out.

“We don’t have the data either of our own or from literature. The drogue chutes which is the first set of parachutes deployed to reduce the descending velocity of the crew module…have been tested so far only up to an altitude of 15 km,” he said.

“At a higher altitude, the air density is very low and we had to see if the chutes would really deploy or collapse. We were trying to look at this aspect because we do not have this data,” he added.

Since an aircraft or a chopper cannot be taken to a height of 17 km altitude in the sky to conduct the parachute deployment experiment and massive balloons would be needed to test the deployment for a system weighing 4.5 tonnes, the newly designed Test Vehicle was used. “A new rocket was made,” Sivakumar said.

“We have tried to generate some fundamental data. All the parachutes and crew escape system are newly designed for the Gaganyaan programme,” said Sivakumar, who has a Master’s degree from IIT Mumbai and has been with ISRO for 38 years after joining initially with a diploma in engineering.

While the TV-D1 mission used a basic capsule that is similar in weight and mass properties to the final crew module for the Gaganyaan mission, a second demonstration flight next year will involve a crew module closer to the final one.

“We will be simulating the crew seats, control and floatation syxtem etc close to the final version. In the present experiment, these things were not simulated. In this mission, only an equivalent mass and inertia is used. These will all be part of the test vehicle D2 flight next year,” Sivakumar said.

The crew module uprighting system

One of the elements that will be tested in the crew module for the D2 mission is a crew module uprighting system that will keep the crew module upright after splashdown in the sea, unlike the TV-D1 splashdown which got inverted after landing upright.

“The two stable positions are upright and upside down. Now, to avoid the upside-down situation in the real crew module, there will be an uprighting system that will be like gaseous balloons – something like the airbags in cars that deploy on impact – which will inflate at the time of touchdown,” Sivakumar said.

Test vehicle graphic from TV-D1.

“If the crew module is trying to topple, the balloon system will bring it back to the upright position. In this particular crew module, we have not put that and that is why it has gone down to the inverted position after splashdown. We wanted to see if it could remain stable and we found that when there is a lateral wind and disturbance due to sea waves it goes to an unstable point and that is why it was near an upside-down position,” he said.

“This was anticipated and was not a surprise as we did not include the system in this mission,” the TV-D1 mission director said. The crew module will also have redundancy systems in place to compensate for the failure of the primary crew module uprighting system, he said.

“The recovery aids like the beacons had to work well underwater and the sea water dye should get ejected to mark the region of the landing. These are the other parameters that have to be considered,” he said. However, in TV D1 the module landed upright and then it toppled presumably due to disturbance from sea conditions.

Even if the crew module was in the water in an upside-down position, the communication systems was not affected since antennas are on the sidewall and “they were radiating”, Sivakumar said.

According to a recent paper on a crew module uprighting system being developed for the Orion crew module to be used on National Aeronautics and Space Administration’s (NASA) Artemis 1 mission to the moon, 47 per cent of all landings during the Apollo, Skylab, and Apollo-Soyuz programmes were in an inverted orientation “with the nose of the crew module submerged – creating a risk to crew egress”.

“Inverted or sideways stable configurations for the CM [crew module] would result in submergence of the hatch doors and communications antennae and an undesirable crew orientation. The CMUS [crew module uprighting system] provides the CM with additional buoyancy to reorient itself into the upright configuration post-splashdown and maintain this orientation for at least 24 hours,” says the paper on ‘Dynamic Characterization of the Crew Module Uprighting System for NASA’s Orion Crew Module’ authored by NASA scientist Ivan Rodrigues Bertaska and others.

“We are targeting the next test vehicle mission sometime in the first quarter of next year. The crew module made with the control systems and simulate the crew seat systems and suspension systems, the uprighting system etc. Also in the crew escape system we will use both low and high altitude escape motors unlike in D1 where we have used only the high altitude escape motors. All these elements will be tested in the TV-D2 mission,” Sivakumar said.

The Gaganyaan project plans to demonstrate human spaceflight capability by launching a crew (of around three members) to an orbit of 400 km in space on a three-day mission. The mission aims to bring the human crew back to earth safely by landing in Indian sea waters.