If there is no air in space, how do they use rockets to position the space shuttle?

Originally posted by Manasseh
reply to post by Phage

 

So, since the space shuttle weighs 165,000 lbs empty on earth, what is it's mass in space, and how much thrust would it take to move such a mass, considering there in no air for resistance?

When you say "in space" I'll assume you mean in orbit (gotta be careful around here). Its mass would not change except for the mass of the fuel expended getting into orbit. Since in orbit it is in free fall, it is weightless.

Any thrust at all will move it. Tell me how fast you want it to accelerate and I can give you a number. Better yet, you can figure it out yourself. The formula is a=m/F.

reply to post by Phage


So another words, if a 2 mile wide asteroid is headed towards earth, Superman could get up close to it, and sneeze, and that sucker would high tail it in the opposite direction?

reply to post by Phage


You can call me a troll, and laugh at me with your buddies, yet when the questions get tough, you don't have the time to play.

If the shuttle is closing in on the space station at 200ft per second, and they need to slow down, how many bursts from those 38 steering rockets would they need. And how much thrust per burst from those giant holes they have in the nose?


www.sti.nasa.gov...

reply to post by Manasseh


I don't know.

According to you it wouldn't do any good anyway since there's nothing for the rockets to "push against".

reply to post by Phage

Newton's Third Law of motion: For every action there is an equal and opposite reaction.

Nothing needs to "push against" anything to move. Rockets send gasses backward, moving the vehicle forward. The propeller of an airplane sends air backward, moving the aircraft forward. When you swim in water you move water backward, moving your body forward. Here's a real tough one (this ought to be good): when you walk, you move the earth backward, moving your body forward.

You are the one who chimed in as an expert.

Remember Newton's third law???

Originally posted by Manasseh
reply to post by Phage

 

Newton's Third Law of motion: For every action there is an equal and opposite reaction.

Nothing needs to "push against" anything to move. Rockets send gasses backward, moving the vehicle forward. The propeller of an airplane sends air backward, moving the aircraft forward. When you swim in water you move water backward, moving your body forward. Here's a real tough one (this ought to be good): when you walk, you move the earth backward, moving your body forward.

You are the one who chimed in as an expert.

Remember Newton's third law???

Try this experiment: get something heavy and a wheeled chair. Sit on it then throw this object. What will happen next? It can't be any clearer than that.

[edit on 15-8-2008 by Deaf Alien]

Originally posted by Phage

Originally posted by Manasseh
reply to post by Phage

 

So, since the space shuttle weighs 165,000 lbs empty on earth, what is it's mass in space, and how much thrust would it take to move such a mass, considering there in no air for resistance?

When you say "in space" I'll assume you mean in orbit (gotta be careful around here). Its mass would not change except for the mass of the fuel expended getting into orbit. Since in orbit it is in free fall, it is weightless.

Any thrust at all will move it. Tell me how fast you want it to accelerate and I can give you a number. Better yet, you can figure it out yourself. The formula is a=m/F.

There is atmosphere (and therefore drag) in LEO and the correct formula would be a=F/m.

reply to post by Manasseh
I admit I didn't read all posts so if this has already been said, sorry. Who said there is no air in space. There is, "air in space." Space is not a vacuum.

Ok here is an experiment for you.

Take two 45 lb weights, one in each hand. Hold them tight against your chest.
Then push these weights as hard and as fast as you can forward.

Do not feel bad if you hit your head hard on the ground or drop a weight on your testicles. I'm guessing you have little use for either.


I do believe in Jesus, I saw him this morning in front of Home Depot. He does tile work.

[edit on 15-8-2008 by mother_jung]

reply to post by mother_jung


Now that was funny.

Since I am 225ish lbs, that WOULD be a funny site.

Jesus is your grocery clerk, and your judge.

But you laugh it up, sucker, since them testicles would be on your chin.

By the way, since 20,000 people have seen this, they will have no excuses either.

Manassehaahaa



[edit on 15-8-2008 by Manasseh]

reply to post by Manasseh


Mannasseh, You have every right to be offended.

Back on point.....

Let's continue to examine this concept of the need for air to 'push against' in order for a rocket to work.

The point most are trying to impart here is, when one mass is ejected, it imparts a force in the opposite direction.

I used a balloon example, and the firehose example.

Please try to refute them.

Thanks.

reply to post by weedwhacker


weedwhacker,

without taking the resistance of air out of the picture, I don't see how we can take your examples as a good point of reference.

People fail to realize the density of air. It will hold up that 165,000 lb shuttle (sorta) as it re-enters the atmosphere.

But, I appreciate your participation, and look forward to your interesting rebuttles to our little debate.

What does resistance of air have to do with your initial question of producing thrust?

I'm not getting the connection. The "resistance of air" impedes forward movement caused by thrust, so why do you act as if the first must be available for the second?

reply to post by Manasseh


Manasseh....allow me to change tactics.

Imagine a jet airplane....(I flew them for more that two decades)

The air doesn't 'hold up' an airplane in flight. It is the motion THROUGH the air, and the airfoil shape of the wing, that provide lift...lift counter-acts weight.

This is the way of airplanes, designed to operate in air.

If you could magically transport a jet into space it would be useless.

No air to run the engines, nor the APU (which is really just a smaller jet engine) You'd have some electricity for a short while, from the batteries (maybe...they might explode in a vacuum)

Point is, a spacecraft is designed to operate in a vacuum....AND, in the case of the STS, also in the atmosphere.

You see, after re-entering, the Shuttle is simply a glider. It IS aerodynamic, and controllable in ways similar to airplanes....but it is a very, very non-efficient 'glider' (some have called it a brick with wings)....hence, it's rate of descent is far, far higher than a 'real' glider....the ones with the long wings.

The Shuttle has NO engines, once it re-enters.

There are basically four forces that act on a regular airplane....Lift, Weight (gravity), Thrust and Drag.

LIFT is provided by an airfoil...a wing. Gravity is obvious. THRUST, from the engine/engines....and DRAG is the resistance of the object through the air (see a Physics text). OR, just wave your hand through the air, then through some water. Which provides more resistance?? BTW, air, although it's a gas, is in an aerodynamic sense, similar to fluid in its dynamics.

OK, the Four Forces....I know the next question....the Shuttle (or any other glider) has no THRUST. True. In this instance, gravity and forward momentum provide the 'thrust'....at the expense of, a loss of altitude. Basically, Kinetic and Potetential energy, when combined, will allow the vehicle to continue forward. Sometimes you will hear a term called 'Conservation of Energy' when applied to the Shuttle. It refers to the 'potential energy' (altitude above the ground) and 'kinetic energy' is the speed, or better, the velocity.

Velocity can be sacrificed, to reduce descent rate....but only up to a point. Altitude can be sacrificed, in increase velocity. THIS is conservation of energy, since we do NOT have the other energy source, in this example....THRUST! (and drag, in an atmosphere, is always there....)

Take an object....expel a mass away from it, and the motion of THAT mass will result in an opposite motion.....simple as pie!!!! The masses react to each other!!!

reply to post by weedwhacker


Lift is created by air. Less pressure on top than on the bottom

As far as the APU, (auxilary power unit) which powers the aircraft
when on the ground, what does that have to do with the discussion?

Air has everything to do with the conversation. Hot air rises, but to what point does it stop rising.

reply to post by Manasseh


Have you tried the experiment? Or at least think about it conceptually?

Originally posted by Manasseh
reply to post by Phage

 

So, since the space shuttle weighs 165,000 lbs empty on earth, what is it's mass in space, and how much thrust would it take to move such a mass, considering there in no air for resistance?

The mass will be 74, 800 + kg. No matter what the elevation, attitude or air resistance. So again I ask, what difference does it make about the air resistance? That has nothing to do with thrust other than to be an impedance in a post-impulse environment.???

I'll jump back in on this thread...why not? I thought of another way to express this.

A rocket in space does have "air" to push against...in a sense...and what is that air? The "air" is the rocket exhaust itself. The force or thrust is from accelerating that exhaust relative to the rocket engine.