continued from here.
My last post about rockets left evoked lots of responses:-D. I think Arunpk was the only one who gave an overall idea about the whole issue, all the rest had pieces of information & this made me determined to find out more (I also have to admit that I was so relieved to find out that there are others like me:-P), so here are 2 answers....
The Question No. 1 answer sort of just skims the surface whereas Answer No 2 goes into more details. Both were lifted from the net. Choose the one you want to read:-D
Question No 1: Where do rockets and spacecraft normally land when they return to Earth?
Answer: Expendable rocket boosters typically just fall into the ocean a few miles offshore from where they were launched and are left there to make new homes for bottom-dwelling sea creatures.
USA's NASA Space shuttle solid rocket boosters parachute into the Atlantic Ocean where they are picked up and reused.The shuttles themselves land at one of a few identified landing strips - I believe only Edwards AFB in California and a strip in Florida have actually been used.
Former Soviet and now Russian capsules parachute to a ground landing in either Russia or Ukraine.
Payloads from unmanned missions that return to Earth come down wherever the controlling organization plans (typically in or near the country that launched them).
Question No. 2 : I am not a young student, but a medical doctor. I have been teaching some stuff about space to my young daughter. However, I am unable to tell her how a rocket lands, reason being I myself don't exactly know. Could you please enlighten me? How do rockets land? Do they land at all or do they all burn up? Why do we see pictures of astronauts jumping from parachutes?
Answer: A major problem of an airliner returning to Earth is how to get rid of its energy of motion--kinetic energy--while still getting enough "lift" from the motion of air across its wings. If your daughter ever sat by the window of a landing airliner, she would see all sorts of auxiliary extensions of the wing sliding into place at the back of the wing--increasing air resistance and slowing down the airplane, and at the same time creating extra "lift" to hold the airplane up. The lift is much less efficiently produced than in ordinary flight, but that is all right, this unusually slow flight lasts only a short time and then the airplane is rolling on the ground.
A satellite in low Earth orbit must move at 24 times the speed of sound (or faster), which means its kinetic energy, the energy of motion, is at least 24 x 24 = 576 times the energy of something moving at the speed of sound, which is already more than the speed of an airliner. Weight for weight, a satellite has about 20-50 times the energy of a rifle bullet, enough to melt it, even boil it away. Getting rid of that energy safely is the main challenge in landing.
The astronauts returning from the Moon (at even greater speed) could not save their spacecraft but had to abandon it, and return in a "capsule" designed to stand a lot of heating, and meanwhile creating a powerful shock wave ahead of it, containing very hot air whose glow dissipated the energy. Then in the thicker atmosphere, at low speed, they used a parachute, and splashed down into the ocean.
Like the Apollo Moon ship, many research rockets are abandoned when their job is done--it would be too hard to bring them back intact. The space shuttle enters the upper atmosphere (which is very rarefied) sideways, with its bottom forward: the bottom has heat-resistant ceramic tiles, and creates a great shock wave (in the "Columbia" some tiles broke away and the heat destroyed the shuttle). By the time it reaches the denser atmosphere, it has slowed down to about half the speed of sound, and it can land like an airplane--still, much faster than a jetliner, requiring accurate computer control.
Burt Rutan's "Spaceship One" similarly used wings, first as brakes (turning them to create air resistance), then to land as an ordinary airplane. However, since it only reached about 3.5 times the speed of sound, this was not as great a challenge.
p.s: I guess it doesnt need Rocket Science to figure out why my pictures show rockets taking off & not landing;-P.
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