Gaganyaan: Why multiple landing site options are critical for manned missions

The country's first manned space mission, Gaganyaan, may have two landing site choices for astronauts after their return from the week-long mission. The calmer Arabian Sea may be the primary choice, while the Bay of Bengal is being considered as a backup option.

Usually space missions have a minimum of two re-entry sites. At times when the ocean or landing terrain become unfavourable due to weather conditions, it is important to have a backup site. Although ISRO has launched hundreds of satellites into space and a few to the moon and Mars, they are meant to remain in space and not designed to return to earth. However, in a manned mission, the crew must return safely to earth. Several precisely executed maneuvers have to be made for the craft to re-enter and touch down without harm.

“Re-entry is very crucial for every mission. Environmental parameters should satisfy the smooth re-entry of the crew. The site chosen should be more stable with a predictable weather condition and a diverse choice of concrete and spacious dry lake bed runways. The re-entry is generally very fast—in just about three to four hours the astronauts are on earth. The crew will face up to 8-9g force upon re-entry and if the weather is harsh then it might make it difficult. Hence, choosing the right re-entry site is very important for any mission. NASA’s favourite touch down point is Florida though its backup is in California. The Russian Soyuz predominately touches down on the flat steppe of Kazakhstan in central Asia,” remarked Srimathy Kesan, founder and CEO of Space Kidz India.

Space experts point out that in such missions, determination of landing site location is a thorough process taking in account all the mission parameters, nominal and abortion scenarios. “Different landing site locations are worked out against re-entry phase initiation starting with the de-boost burn. My understanding is that, based on the status of the mission, crew and external parameters, experts will decide if the de-boost needs to be initiated now or in the next orbit, resulting in two different landing locations, each of which should have astronaut recovery facility readiness. There is one astronaut recovery facility being planned in Gujarat coast for landing in the Arabian Sea. In case of any unlikely scenario, if it needs to abort and land in a site other than their designated site on other country's soil or waters, appropriate permission will be taken in accordance with the international space treaty,” said Rohan M. Ganapathy, CEO and the CTO of Bellatrix Aerospace.

Experts point out that re-entry of the spacecraft is one of the most critical stages of the mission and has to be executed with precise acumen. Having multiple landing sites can help in keeping the astronauts safe in case of any challenge while landing at the designated site.

“When the time comes for landing, the spacecraft must de-orbit from 400 km to about 120 km altitude using the propulsion system in the service module. The craft should also de-boost. Once the orbiter module drops down to a determined height, the solar panels and service module are to be jettisoned. The crew module must orient at an exact angle and speed. If not, the life of the crew is in danger. Operations like aero-braking, deployment of parachutes must take place sequentially at the appointed time. Shooting stars are small space rocks that fall on earth. While traversing the atmosphere, due to friction, they heat up and burst into flame. In a similar manner, the crew capsule will turn into a ball of flame while re-entering the Earth’s atmosphere during the landing maneuver. The temperature will soar to thousands of degrees. To prevent burning of the craft with the crew, thermal shield tiles made with unique materials are affixed on the exterior of the capsule,” explained Girish Linganna, a space and aerospace expert and the Director of ADD Engineering Components India Limited.

Linganna pointed out that after re-entry, the crew module will fall towards the earth like a stone. “The Aerial Delivery Research and Development Establishment, one of the research and development labs under the Defence Research and Development Organisation (DRDO), has developed a robust and sturdy parachute which when deployed, reduces the vertical speed of the crew module from a breakneck pace of 216 meters per second to safe levels of 11 meters per second on touchdown. The ISRO crew module, upon re-entry, is designed to splashdown in a predetermined spot in the sea. Once the crew module touches the water, the parachutes must disengage and separate. Flotation must inflate and keep the module from sinking under the sea. The module must then broadcast a tracking signal beacon for the rescue and recovery ship to swiftly approach and take away the crew,” added Linganna.

The crew module is a double-walled system and the habitat of astronauts, who would be part of the manned mission. It has an ablative Thermal Protection System (TPS) to protect it during the intense aerodynamic heating during the flight. The crew module is fitted with a set of small propellants that will be fired in a controlled manner during re-entry into the atmosphere.

After landing, the coordinates of the crew module will be shared with the recovery teams waiting on board various ships. The crew module will have life-saving packets for each astronaut, which will be sufficient for two days. However, ISRO is sure that the crew module will be traced within two hours of its landing in the sea.