Why is it more difficult to bring people back from space than to take them there? But that's not quite accurate. Both launching and returning have their own challenges and dangers. To send people into space, the rocket has to overcome the gravitational force of the Earth, and in doing so a considerable amount of fuel has to be burned. And this process of launch works on recoil principle, in the same way as air leaks from the back of a balloon makes it spin round and round.
Although the rocket should not rotate in a circular motion, that is why it has thrusters that push the gas released from the rocket and propel the rocket in the right direction. A special navigation system keeps the rocket on its way, yet sometimes crashes do happen. In 2014, a few seconds after launch, the Antares rocket exploded and engulfed in flames, destroying the supply ship being sent to the ISS (International Space Station).
Once the capsule carrying the astronauts reaches Earth's orbit, then the next challenge is to get it to the ISS. For this, the capsule is taken to the correct height by making very accurate calculations using the onboard computer, as the slightest mistake can result in a collision. Then its speed is brought equal to the speed of ISS, and in case of emergency, this work has to be done by the astronauts themselves.
On their return trip, after being undocked from the ISS, the capsule carrying the astronauts starts moving at a speed of 28,000 kilometers per hour in space. The first challenge is to slow it down, and once it has come across some distance from the ISS, the thruster is turned on to reduce the speed so that it can get out of orbit. And to leave the orbit, the components that are no longer needed are discarded.
Next comes the most critical phase, re-entry into the Earth's atmosphere, which can only be done at a particular speed and angle. If the speed of the capsule is too slow and the angle is less, it will bounce at the atmosphere like a flat stone on the water and would propel back towards space. Whereas, if the speed remains fast and the angle is sharp, the heat shield will become hot and the crew in the capsule will burn.
At the time of entry into the earth's atmosphere, the speed of the capsule decreases very rapidly, due to which there is heavy friction, which produces heat up to 2000 ° C. After this, due to the opening of the parachute, the speed of the capsule decreases further. The Russian space capsules have such special thrusters that must ignite to bring the capsule safely to earth at a speed of just five km per hour. US space agency NASA's capsules do not require thrusters, because they can be lowered into the water, and water acts as a mattress for the capsule.
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