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originally posted by: Soylent Green Is People
a reply to: anonentity
So, you think it is fishy that a vehicle experiencing the heat due to atmospheric friction can have parachutes that don't melt? What about the Russian Soyuz capsule, then, which has a few atmospheric entries every year without its parachute melting?
In the case of the MSL (the Curiosity Rover), most of the speed of the craft was diminished due to the friction of atmospheric entry -- not due to the parachute. The friction of atmospheric entry of the craft caused it to slow down to about 1000 mph prior to the chutes deploying. 1000 mph is not enough speed for the friction to cause the nylon to melt.
Granted, the MSL craft did heat up quite a bit during entry -- about 3,800 F at 15 miles up moving at 11,000 mph (maximum combination of speed and atmospheric thickness), but that is long before the chute deploys. The atmosphere has slowed down the craft quite a bit by then, and the speed no longer produces great frictional heat.
Going back to the Russian Soyuz: obviously, vehicles such as the Soyuz capsule DO IN FACT re-enter Earth's atmosphere after orbiting at 17,000+ mph, and they also use parachutes. The earth's atmosphere is even thicker, and cause more heat friction, yet the Russian's parachutes don't melt; that's because (just like the mars MSL) the friction of re-entry has slowed the craft down quite a bit BEFORE the chute is deployed.
Erik was citing surface conditions, but thin air can slow down things a lot more than you think, in fact most truck sized meteors entering Earth's atmosphere already heat up so much where the air is quite thin that they explode high in Earth's atmosphere.
originally posted by: anonentity
I can understand the re-entry to Earths atmosphere but into a near vacuum ? at more than 10 feet per second per second. It doesn't seem to my thinking that this would do diddly squat to a mass around 800 kilos.
The air is pretty thin 70 km up. Look at the density curve on this graph which is so close to zero at 37 km that you can't even see it without going to another more sensitive plot:
Meteors become incandescent – or glow – almost as soon as they hit Earth’s atmosphere. Some meteors such as the Perseids in August burn up in the atmosphere at about 100 kilometers – or 60 miles – above Earth’s surface.
Other meteors such as the Draconids in October fall to 70 kilometers – or about 40 miles – before they heat up enough to glow and vaporize. The difference is that the Draconids are much slower meteors than the Perseids. So the height in the atmosphere at which a meteor begins to glow depends on its arrival speed.
originally posted by: Chamberf=6
a reply to: Rob48
I know you're being kind and diplomatic...but I'll say it........so many ways to learns basic facts found from missions, calculations, etc...a person just has to be too lazy to open a book or look at verified information to say some things on ATS.
originally posted by: eriktheawful
a reply to: anonentity
Yes the atmosphere on Mars is thin, however drag on space craft begins at about 80 km from the surface.
As a craft with a heat shield that is blunt in shape enters the atmosphere, it does so at hypersonic speeds. The air in front of the shield can not get out of the way in time and becomes compressed (oop! There it is! "how to make a thin atmosphere thicker on your way down"). Even at 0.00636 kPa is more than enough to have enough drag to slow a space craft down.
And it will slow it down very quickly.
Here are some links you can look at on the subject:
Mars Atmospheric Entry
Curiosity's parachute, which was a parachute 52 feet wide and did not deploy until it had slowed down to Mach 1.7
The parachute was designed to handle speed up to Mach 2.2.
The parachute was located opposite of where the heat shield was (duh), the heat shield takes the brunt of the heat of re-entry...NOT the rest of the space craft/rover. That's what it's for.
Mach 1.7 (or 2.2 for that mater) is not fast enough to produce high heat from friction.
So yes, based on how the physics of drag works, and also how gases react when a blunt object tries to move through it at hypersonic speeds, it's more than enough to slow an object from orbital speeds (tens of thousand kilometers per hour) to under Mach 2 in just a few minutes.
This works exactly the same on Mars as it does no Earth. The only difference is that our atmosphere reaches out further, and is thicker at the surface.
ETA - almost forgot:
Curiosity's parachute was a Ribbon and Ring Parachute, designed for supersonic speeds and is normally made of kevlar.
Concord travelled at Mach 2 approx. the airframe increased the length of the aircraft by 6 to 8 inches.
Why are you arguing that the people who designed the braking system didn't know their job?