WHEN METEOROIDS ENTER the earth’s atmosphere and burn up, they are called meteors (those that survive become meteorites). Meteors are almost entirely vaporised and the bright trails they leave are called shooting stars. Being an eye-catching phenomena, shooting stars have become the subject of much superstition―like the belief that seeing them can bring good luck.
Luckily for astronauts, scientists do not set much store by luck. They rely on precision and cutting-edge technology to complete the challenging task of entering the earth’s atmosphere from orbit.
A series of carefully calculated manoeuvres ensure that the spacecraft/crew module is at the perfect angle to re-enter the atmosphere to use atmospheric drag to slow down the craft. The friction generated when it collides with air molecules creates intense heat―more than 1,000 degrees Celsius. “The sophisticated heat shields are typically made of materials designed to absorb and dissipate heat,” said space expert Girish Linganna. “A common method is ablation. Ablative shields are designed to burn away in a controlled manner. The outer layer vaporises, leaving a cooler layer beneath. This process protects the craft and the crew inside.”
As the craft decelerates, crew experiences g-force several times the earth’s gravity.
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“At specific speeds, a series of parachutes will deploy,” said Linganna. “First, small pilot parachutes will stabilise the module, followed by larger drogue parachutes that will further slow it down. Finally, the main parachutes will open, ensuring a gentle descent and then the splashdown in the sea.” Many modern spacecraft are designed for touchdowns on land. They might use additional systems like engines that fire in the direction opposite to motion to ensure a soft landing.
Linganna said the Gaganyaan crew module will have sophisticated systems that will guide the module during re-entry, ensuring it follows the correct trajectory and lands in the designated area.
Mylswamy Annadurai, programme director of Chandrayaan-1, Chandrayaan-2 and Mangalyaan, said that any technical issue hampering the safe return of the gaganauts need to be avoided. “The level of redundancies that need to be in place should ensure safe human return,” he told THE WEEK. “The key is foolproof technology. Common wisdom is the real need to attain that goal.”