lux wrote:^ Looks like a friendly chap too.
Dmitry wrote:reichstag fireman wrote:Gentlemen,
how about a tiny school trigonometry problem?
AFAIK, no one ever claimed to having found any ionosphere at 2199.7 km or above: 600 km is the upper limit.
All that numbers show the same simple fact: the ionospheric mirror is just too low for reichstag fireman's model to be adequate.
simonshack wrote:Caption: "Astrounaut James Van Hoften repairing the LEASAT F3" :
Now, the SYNCOM Wiki page tells us that these LEASAT barrels weighed "1.3 tonnes each (over 7 tonnes with launch fuel)." So...we are actually asked to believe that : NASA dropped that thing off at about 400km altitude. It failed to ignite. They later docked with it again with another Space Shuttle, got it fixed, than got it fired up in mid-air - and remotely steered/navigated/and braked it - all the way up into a 35,678km orbit. How do they do it? My head hurts!
I warmly welcome any (possibly sensible) clarifications from any rocket scientist on board - thank you very much!
I am not really rocket scientist, but will do my best. Well, what do hurt your head?
Q: My understanding of space is that it is a vacuum, i.e., devoid of pretty much all matter, just empty space. Also from my amazingly limited knowledge of physics I understand that in order for a force to create movement it must act upon something. So if a spacecraft fires its rockets into space, a vacuum, what is this force is acting upon? If there is nothing there, what are the rockets pushing against to cause the ship to move?..
A: … The truth is that the rocket does have something to push against: namely, its own fuel. Let's illustrate with an example you kids can try at home. First, you need to get yourself into some sort of frictionless situation. Wearing ice skates on a slippery ice rink would be good, or maybe your office has a chair that rolls really well on a hard surface. Next, you'll need a medicine ball. You are the rocket and the medicine ball is your fuel. Toss the medicine ball. You'll notice that as you shove the medicine ball forwards, you yourself lurch backwards. Ta-da, the miracle of physics! (If you think this is because the medicine ball pushed on the air, then try the experiment without the medicine ball--just push on the air with your hands, see how far you lurch backwards.)
Newton's Third Law is usually expressed as, "For every action there is an equal and opposite reaction," and you can also think of it as "Forces always come in pairs." While you are pushing on the medicine ball, Newton's Third Law says that the medicine ball is also pushing on you. Thus, you are accelerated by the force acting (backward) on you by the medicine ball. Never mind that it was you who decided to start the pushing in the first place; you can't push on the ball without having the ball push back. Forces always come in pairs.
Of course, rockets work on more sophisticated principles than just tossing fuel out the back. First, the fuel is burned and its hot exhaust gases are expelled at very high velocity (if you toss the medicine ball faster, your body experiences greater backward force). And the rocket's exhaust nozzle has a narrowing so as to squirt the exhaust gasses out even faster, like putting your thumb over the end of a garden hose. Exhaust from chemical propulsion (i.e., fuel-burning propulsion) is typically expelled at 2 km/s (= 4500 mph), and your average rocket mass at launch is 80-85% propellant (fuel + oxidizer), most of which eventually gets squirted out.
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