which one of the following is difficult? entering into the space or returning down to earth?

Question

I wonder about the space ships entering and returning to earth, i was not able to come to conclusion about that.

Answer 1

Getting into space is probably easier than landing on the Earth or for that matter any planet with a substantial atmosphere, but not as easy as it looks. The biggest problem upon going into space is something going wrong and your booster or spacecraft blowing itself up or going off course into the sea. Even if you get into orbit, you're not home free yet. Many a space probe has exploded or been trapped in earth orbit when the upper stage suffers a catastrophic failure. Be that as it may, getting into space is easy compared to returning to Earth. The problem is the velocity of your craft, which for an orbital mission is at least 18,000 mph. If you're returing from deep space, it will be at least 25,000 mph. Either way, you have to bleed off all of that velocity, and you cannot do it all at once without the gee forces killing you. The way a returning spacecraft does this is to use drag from the atmosphere to brake itself to a landing. But all the kinetic energy has to go somewhere, and it goes into forming a shockwave of air ahead of the vehicle that cannot get out of the way due to the hypersonic speeds. It is compressed so rapidly it reaches temperatures at least 20,000 degrees or more. The radiant heat from this shockwave in turn heats the shell of the spacecraft. This heat can be dealt with with the use of materials that simply reject it, like the pure silica tiles of the Space Shuttle, or burn away and take the heat with it as with the Apollo, Gemini, Soyuz and Mercury spacecraft. Instead of diving straight down, you have to enter a trajectory that takes you through the upper atmosphere for hundreds or thousands of miles so first you slow down enough to avoid skipping off the atmosphere like a bullet off a pond and keeping both the gee forces and areodynamic forces from incinerating your spacecraft. The Apollo command modules experienced outer hull temperatures of up to 6,000 degrees, the Space Shuttle reaches 3,000 degrees in places. The Galileo entry probe that dove into Jupiter at more than 100,000 mph reached a temperature of more than 18,000 degrees on it's outer shell, hot enough to emit x-rays. If a spacecraft entered the atmosphere at too steep an angle, the heat shields would not protect it from the inferno of re-entry, and it would break up and disintegrate like the ill-fated Columbia back in 2003, or merely vanish as an especially bright fireball. It is possible for a robot probe or a re-entry vehicle carrying a nuclear warhead to plunge straight down into the atmosphere and survive fierce decelerations of 600 gees and outer hull temperatures of 20,000 degrees, but humans cannot take more than about 9 gees. Therefore the plunging trajectory is replaces with a gentle descent that keeps both the heat on the spacecraft's heatshield and the gee forces within human tolerance. Re-entry is a very precise manuver with little room for error or miscalculation. Apollo missions and the Space Shuttle have made it into space despite the failure of engines in flight, and even a lightning strike knocking out the electrical systems of Apollo 12 for a time. But any malfunction or mistake on the part of the pilot during re-entry will result in death for him and everyone else aboard.

Answer 2

>>Itis well known that to leave the earth's gravitational force the space shuttle needs to be sent up on a rocket at high speed.<< The shuttle does not leave Earth'd gravitational force. It is the balance between Earth's gravity and the shuttle's speed that allows it to remain in orbit. >>The question is when the space shuttle is re-entering the earth's gravitational influence and atmosphere, why does it have to do so at super high speed.<< Because slowing down is very hard. It takes both solid rocket boosters plus all the fuel in the external tank plus a little kick from the orbital manoeuvring engines to get the shuttle up to that speed. Slowing it significantly would require almost as much fuel again, and it can't carry that much. Even if it could, it can only stay up because it is going so fast. The moment it slows down even slightly it begins to drop back to Earth and hits the upper atmosphere. That's hw re-entry is achieved: the orbital manoeuvring engines fire to slow the shuttle slightly so it drops into the upper atmosphere. The rest of the speed is bled off by friction with the air. >>It is this super high speed that led to the burning up and disintegration of Columbia. What did the NASA people learn from it.<< They learned that you need to design a spacecraft that is not vulnerable to bits falling off and damaging the thermal protection system. >>In my opinion, such high speeds are NOT required to re-enter the earth's atmosphere.<< With the greatest respect, your opinion is irrelevant, and franlkly it is a bit arrogant to declare your iopinion in regard to a system designed and built by people who have been working on spacecraft systems for a long time and make their living doing it. Do you honestly think that if there was a viable way to bring a spacecraft back to Earth without hitting the upper atmosphere at high speed and generating huge temperatures and aerodynamic forces that they would not actually be using it by now? Yes, re-entry is dangerous, but it is still the best way to get home that there is.

Answer 3

Both have their own hardships.

With exiting, it's acheiving escape velocity. Can't get that, you don't leave the atmosphere.

With entering, it's encountering the friction of the atmosphere, as well as 'bouncing' on the atmosphere properly. One builds lots of heat, the other sends space ship off like a skipping stone.

Answer 4

They're both complicated, but the harder one is entering because as the ship enters the atmosphere it travels faster because of gravity, and the friction basically caused the ship to catch on fire.

Answer 5

Returning is said to be more difficult than leaving. To leave the atmosphere, you need to overcome gravity with thrust. To re-enter, you need to find and keep track of your re-entry spot, launch yourself through, then control the ship while it free-falls and heats up.

Answer 6

I'd say it's a lot harder going up than coming down. Going up, your rocket has to fight gravity the whole way. Coming down is merely falling. Both, of course, are dangerous, as demonstrated by the two shuttle accidents.

Answer 7

Entering DOWN because they have to land at a specific place and you have to go past a lot of magnetic feilds for exsample the ozone layer.

Answer 8

They are both filled with danger.

Answer 9

Well,both have their own hardships.