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Old 21 July 2015, 08:06 AM
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Icon27 These Pluto Truthers Insist NASA Images Are Fake

http://gizmodo.com/these-pluto-truth...ake-1717828679
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It wouldn’t be a monumental achievement in human history without some truthers on the internet calling it fake. And NASA's historic Pluto flyby is no different. The conspiracy theory crowd has descended on the event as their too-good-to-be-true choice this week. Wake up sheeple! Pluto is just a dog at Disneyland!
Having followed the space program since I was a kid I knew this was inevitable. If you're feeling brave check out the comments from "Nolita," who not only believes that all space mission have been faked so have all ballistic missile flights.

Brian
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Old 21 July 2015, 02:10 PM
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Because why? Things like baseballs, golf balls, and footballs can follow ballistic trajectories but much larger objects on more controlled ballistic trajectories powered by something other than a bat, club, or someone's arm (or foot) couldn't possibly be real?

~Psihala
(*Trollin', trollin', trollin'...)
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Old 21 July 2015, 02:42 PM
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Because math is hard and if they can't figure it out, obviously it was made up.
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Old 21 July 2015, 03:00 PM
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Wow. That "Nolita" person really made an effort to sound reasonable. There were a few others who commented in agreement. How sad.

This all is exacerbated by folks like Alex Jones, a prominent conspiracy theory radio guy who says the Moon landings were faked to hide NASA's secret alien technology, airplane contrails are secret weather-control chemicals, fluoridation is a government cancer plot, and the Pentagon was hit by a sneaky missile instead of American Airlines Flight 77. Once a person begins to feel all paranoid like that, it's easy to begin adding to the list of things that fall under "the conspiracy".
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Old 21 July 2015, 06:45 PM
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At this point I wonder why we bother with a mandatory K-12 education with people like this (including anti-vaxers and climate deniers). It was clearly a complete and utter waste of time.
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  #6  
Old 22 July 2015, 12:17 AM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by Psihala View Post
Because why? Things like baseballs, golf balls, and footballs can follow ballistic trajectories but much larger objects on more controlled ballistic trajectories powered by something other than a bat, club, or someone's arm (or foot) couldn't possibly be real?

~Psihala
(*Trollin', trollin', trollin'...)
There is actually a huge difference between "ballistic" objects like baseballs versus ballistic rockets. The former operate just fine without any ability to steer, the latter absolutely requires the ability to steer. A trajectory for say a trip to the moon is easily calculable but completely impossible to actually realize with something like a baseball (even if you could launch it at a high enough velocity). Real rocket's "trajectory" is a mathematical construct that the rocket can't actually follow unless the rocket has the ability to constantly steer itself to try to get to the calculated trajectory. A "ballistic rocket", if it looses its guidance system, usually won't follow its intended trajectory and usually wont hit its target.
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  #7  
Old 22 July 2015, 12:38 AM
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Quote:
Originally Posted by jimmy101_again View Post
There is actually a huge difference between "ballistic" objects like baseballs versus ballistic rockets
Time for me to get a bit "technical" and dust off my old helmet...

If it steers, it is a missile. Rockets are purely ballistic once its fuel has been burnt.

There are ballistic missiles. As well, there are cruise missiles. But ballistic missiles are launched and less "guided" than "nudged" towards their target. The intent is that if the guidance system does not work, the missile will still hit the intended target. This is done by the missile not steering itself for the majority of its flight. It flies a purely ballistic trajectory (once fuel is burnt) and only in the descending branch of the trajectory will any attempt to manoeuvre it be made. It saves on power and also having the seeker jammed.

Meanwhile, cruise missiles fly their way to the target.

So, in summary, rockets "fly" like baseballs. Ballistic missiles "fly" like baseballs for most of their trip. Cruise missiles have nothing in common with baseballs.

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Old 22 July 2015, 01:15 AM
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I think they should put extendable, controllable fins on baseballs. It'd make the game a whole lot more interesting.

~Psihala
(*"And there's a high fly ball to left... No, no! Right!")
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  #9  
Old 22 July 2015, 11:32 AM
Troberg Troberg is offline
 
 
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Quote:
Originally Posted by UEL View Post
Time for me to get a bit "technical" and dust off my old helmet...

If it steers, it is a missile. Rockets are purely ballistic once its fuel has been burnt.
I think that, if it's not carrying a military payload, it's usually not called a missile. Even more so if it's manned.
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  #10  
Old 22 July 2015, 08:50 PM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by UEL View Post
Time for me to get a bit "technical" and dust off my old helmet...

If it steers, it is a missile. Rockets are purely ballistic once its fuel has been burnt.

There are ballistic missiles. As well, there are cruise missiles. But ballistic missiles are launched and less "guided" than "nudged" towards their target. The intent is that if the guidance system does not work, the missile will still hit the intended target. This is done by the missile not steering itself for the majority of its flight. It flies a purely ballistic trajectory (once fuel is burnt) and only in the descending branch of the trajectory will any attempt to manoeuvre it be made. It saves on power and also having the seeker jammed.

Meanwhile, cruise missiles fly their way to the target.

So, in summary, rockets "fly" like baseballs. Ballistic missiles "fly" like baseballs for most of their trip. Cruise missiles have nothing in common with baseballs.

I don't think that last part is quite right. A missile, like the space shuttle or any of the current orbital craft, steers pretty much the entire boost phase and any flight within the atmosphere. Rockets (and missiles, and bullets, and baseballs, and ...) are ballisticaly unstable, if they are not steered they will start to tumble. For a baseball, tumbling doesn't affect the flight too much, for a bullet or a rocket/missile tumbling makes the trajectory too unpredictable (in the atmosphere).
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Old 22 July 2015, 09:28 PM
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Interesting point, but there are plenty of methods to prevent tumbling in the atmosphere without the need for active steering. Spin is one of the simplest methods.

If what you are saying is entirely true, then the artillery (Ubique) would not exist as its ability to hurl projectiles beyond the horizon would be too unpredictable. As it stands now, 155 mm unguided projectiles can achieve ranges of about 40 km without sacrificing accuracy. Gerald Bull was looking to use unguided artillery technology to launch satellites...but that is another story.

Rockets do have fins (or some other spinning mechanism) that provides stability. This is not the same effect of spinning a bullet from a barrel, but it does provide enough stability to allow it relatively accurate flight. The MLRS used in the Persian Gulf wars was known to get within 50 metres of the target area over 26 km away (the maximum distance at the time).

Most ballistic missiles do spin as well. This provides stability until they get to the downward slope of their trajectory, at which time guidance systems then take over and use either control surfaces or thrusting to manoeuvre the missile onto the intended target. I will caveat, though, I don't have experience with ballistic missile intended to fly super far ranges, such as ICBM. I am only knowledgeable of the ones that fly shorter ranges, say, less than 500 km.

Now, space craft are a different beast than a missile for weaponry, I'll admit. For a space craft there is a very tiny window of velocity, angle, position and location that needs to be precisely hit. This may indeed be the reason for guidance along the entire course of the vehicle's trajectory. I just watched Soyuz launch, and was thinking about your point as I saw it soar. I am not a space vehicle guy, so I'm not entirely sure.

If we are talking cruise missiles, they are completely different. They fly low and are guided to avoid detection and then steer themselves to ideal attack positions.

But, from my experience studying and understanding the flight characteristics of missiles and rockets, ballistic is the key word. Rockets are ballistic and ballistic missiles are ballistic until descending towards their target.

I gotta hit the road right now, so I will check back in tomorrow.
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Old 22 July 2015, 09:31 PM
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I don't think that's steering though, so much as having a gyroscopic mechanism to keep the pointy end pointing forwards so that they actually follow a predictable ballistic trajectory... (ideally a parabola, but atmospheric resistance would be taken into account when aiming...)

(eta) Sorry, this was a reply to jimmy101_again. I accept UEL's expertise on this stuff, even though my own knowledge is basically A-level physics... (We didn't cover the more practical aspects later on because it turns into engineering!)
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  #13  
Old 23 July 2015, 12:52 AM
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Fins sometimes work but they have restrictions, in particular they only work when the air velocity is high enough. For many missiles there is an early phase when they are moving to slow for fins to have any effect. Rocket propelled grenades are often fin stabilized but they require a launch rail or tube to keep them going straight for the first couple feet until they get moving fast enough for fins to have an effect. If you launch an RPG without a launch tube you have zero idea where it is going and its flight will not be "ballistic".

Stability can also be obtained by having most of the weight in the nose. That is basically how an arrow works. With most rockets though the center of mass (weight) is coincident with the center of thrust (aka center of drag) at least at the time of launch when it is carrying a full load of fuel. So for many rockets/missiles having the weight forward isn't possible.

Spinning is of course how most rifles work. Indeed that is what the term "rifle" basically means, threads (rifling) in the barrel spin the projectile and that removes tumbling vie gyroscopic forces (at the expense of not actually aligning the front of the shell with the air flow over the shell, arrows are better at actually pointing into the wind than are bullets). On a spherical round the spin can be in any direction and as long as every round spins in the same direction then the trajectory will be reasonably predictable. Baseballs are thrown with spin in different directions and any spin makes the pitch more controllable and more predictable. A "knuckle ball" is a pitch purposely thrown with as little spin as possible, the result is that the trajectory is hard to predict (it is not sufficiently "ballistic") and batters don't know where to swing the bat because they can't predict where the ball is going go.

Big rockets, as in ships into space, are a special case where "ballistics" is really really misleading. This type of rocket, dynamically, is like trying to balance a pencil on its point... it is impossible. All rockets of this type have one or two types of steering. The first is gyroscopes that can twist the rocket about its center of mass and correct the direction it is pointing. This approach only works with relatively light rockets and the gyro need to have a mass that is significant relative to the rocket's mass, which is a huge problem with space craft since the fuel cost to lift the massive gyro becomes prohibitive. That leaves the true technological advance that the rocket scientists of the 40's, 50's and 60's had to figure out -- you must be able to gimbal (steer) the rocket engines so you can point the thrust in different directions allowing the engines themselves to keep the rocket pointed in the right direction (keep the pencil balanced on its point). The direction of pointing is often determined by comparison with a gyro, a gyro that is way to light to actually turn the rocket itself, or by reference to ground tracking data. Spin won't work since it is too hard to get the rocket spinning before lift off. Fins don't work because at launch the rocket is moving to slowly for aerodynamics to have much effect. Having the weight forward doesn't work because most of the weight is the fuel, which is in the bottom of the rocket.

So all the heavy lifters, from Gemini to Apollo (Saturn V) to the Space Shuttle to ICBMs have steerable engines. Below are some videos showing the Shuttle's gimbaled engines exercising right before lift off. The gimbal engines perform two tricks; they keep the "pencil balanced on its point" and they adjust the flight path to follow the precomputed trajectory. "Ballistics" is acquired by actively correcting the flight path, not by an intrinsic property of the rocket. These rockets intrinsically have no capability to follow a ballistic trajectory. (We've all seen the rocket failure videos from the 50's and 60's, many of those failure are failures of the steering system and the rocket behaves like all unsteered rockets will behave, they pivot, corkscrew, turn 180 degrees and generally do not behave "ballisticlly".)

The shuttle, at about 27 seconds you can see the nozzles get moved by the engine gimbals in preparation for lift off.
https://www.youtube.com/watch?v=cn4MVoIEJvU

In the video below, at about 10 seconds the gimbals are tested, if they don't work the launch will be aborted because no gimbals means dead astronauts about 3 seconds after liftoff because a rocket being propelled is aerodynamically unstable and not ballistic.
https://www.youtube.com/watch?v=v_jserW1Mbk

A rough idea just how far the Shuttle's engine's gimbals can swing the engine, it is a pretty long way considering how much thrust is going out the nozzle at launch (this is a test without the engine running);
https://www.youtube.com/watch?v=7Wtg_3Y4lFc

The massive Saturn 5 engines of the Apollo program were gimbaled, as were the engines for the 2nd and 3rd stages.

"Cruise missiles" use gyros, fins and vectored engine thrust to keep pointing in the right direction, all actively controlled to follow a particular trajectory. They are not ballistic and without active guidance would be hard pressed to hit a particular continent let alone a particular building.

That's probably more about missile stability than most care to hear.
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  #14  
Old 23 July 2015, 05:06 PM
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Quote:
Originally Posted by jimmy101_again View Post
"Cruise missiles" use gyros, ...
Now how are sandwiches supposed to help missiles? You are obviously part of the conspiracy.
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Old 23 July 2015, 05:27 PM
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Besides which, he's a vegetarian, so he would only have falafel.
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