how rockets get thrust once they are out of our Atmosphere??

[shintu]

Hi all ,<br /><br />This is my first post here ..Always wondering about this ...I mean the rocket propels up because of the thrust its burning fuel causes ... I mean how does this concept ( also known as the newtons third law ) works in space as there is no air there to obtain the thrust from ???<br /><br /> I have heard that satellites have small thruster rockets which bring them back to orbits if they slightly drift away from orbits .. <br /><br />can somebody please explain me about this please ???<br /><br />with love ,shintu

 

[derekmcd]

Newton's third law states for every action there is an equal and opposite reaction. In rocket engines, the action is the propellant combusing inside the combustion chamber and pushing against the chamber wall. The reaction is the rocket and its payload being propelled or pushed in the desired direction.<br /><br />The propellent or exhaust is not pushing against the ground or against the air causing thrust... it is thrusting against the rocket itself. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[fingle]

shintu: how does this works in space as there is no air there to obtain the thrust from ? <br /><br />me: rockets bring their own air/oxidizer with them. like the shuttle uses liquid ozygen (LOX) as the oxidizer. <br /><br />fingle<br /><img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[shintu]

thanx for the reply guys ... Never knew that the thrust is gained by the fuel against the rocket walls itself thought it was gained by the burning fuel against the ground and air ...<br />thanx dudes <br /><br />well that clears it up <img src="/images/icons/smile.gif" />)<br /><br />and the oxidisers are for burning the fuel in the space i think dude as there is no oxygen there to burn the fuel ..<br /><br />and one more question <br /><br />How does the satellite drift from its orbit sometimes ??? What forces are acting on it ...Is it earths gravitation still or some other force ???<br /><br />Thought in space there woule be no force from earth to cause the drifting then thought well if moons gravitation can cause waves in earths sea then ....Should be some forces acting on our satellite too ... and the forces are simply compensated by the rotation of the satellite and thus it is in position or ???<br /><br />thanx in advance dudez....

 

[lukman]

Similar question, why rocket needs escape velocity? why not escape acceleration? or, is it impossible for rocket to get into orbit if it travels vertically at a slow speed, say, 10m/s? Or, if a plane, jet plane or something else, not rocketing upward, but steadily incline at a good speed, can it gets into orbit?<br /><br />I may understand if meteor were burned out by our atmosphere because of the entry speed. But why a shuttle ship re-enter always experience the same thing, cant they slow it down or enter the earth atmosphere slowly or circle the earth instead of rapid decline? <div class="Discussion_UserSignature"> </div>

 

[derekmcd]

<i>"Never knew that the thrust is gained by the fuel against the rocket walls itself"</i><br /><br />A good analogy is firing a gun. The jolt you pushing against you is from the gas combusting inside the chamber wall pushing against the gun.<br /><br /><i>"How does the satellite drift from its orbit sometimes ??? What forces are acting on it ...Is it earths gravitation still or some other force ??? "</i><br /><br />What you are refering to is orbital decay and is mainly due to atmopheric drag. The earths atmosphere actually extends quite far although not very dense at the distance satellites orbit. This drag slows the satellite down very gradually and the earth's gravitation will slowing decrease its altitude thus needing periodic corrections. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[derekmcd]

There's a difference between escape velocity and orbital velocity and there is some pretty hardcore math involved i'm not capable of. I think you are more referring to orbital velocity.<br /><br />Orbital velocity is a velocity required to keep equilibrium between the satellite's motion moving in a straight path and the earth's gravitational field 'pulling' it back down. Orbital velocity is much less than escape velocity which is the speed required for an object to escape the gravitation field WITHOUT using propulsion. That's a key point here. <br /><br />Could a rocket (or a jet plane ignoring the fact that jet engines operate different than rocket engines) achieve an orbit a slower speeds? Certainly they could, but they would need an enormous amount of fuel to maintain the desired altitude. <br /><br />The key to orbital and escape velocities are the speeds required to achieve after the engines are shut off.<br /><br /><i>"I may understand if meteor were burned out by our atmosphere because of the entry speed. But why a shuttle ship re-enter always experience the same thing, cant they slow it down or enter the earth atmosphere slowly or circle the earth instead of rapid decline?"</i><br /><br />The space shuttle's speed in orbit is over 17k mph. The enormous amount of extra fuel needed to slow it down enough to avoid burn during reentry would make launching the space shuttle quite difficult. Using the atmosphere to slow the shuttle down (aerobraking) is much, much more cost effective. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[shintu]

thanx again for the reply dudes the gun example was pretty amazing ... well i just wonder if this drag just slowly pulls the satellites towards our earth ... and certainly we have abandoned many satellites in space after their use right ??? I just know two years before or so they just bought one satellite back to the earth but its not usually done right ? So the abandoned satellites always can fall back to the earth or ?? is it a risk or not ??

 

[MeteorWayne]

For most satellites it is not a risk since they burn up in the atmosphere. An exception is especially large satellites, such as when SKylab had pieces fall to the surface, and there was also one Russian one whose name escapes me.<br />Of the current objects in orbit only a few would be of concern, the ISS and the Hubble, for example. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[qso1]

The large Russian station that re-entered earths atmosphere was Mir. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[MeteorWayne]

I'm not sure that's the one I was thinking of. MIR had a controlled descent into the Pacific (?) The object I'm thinking of had plutonium power and spread radioctivity over Canada (?)<br /><br />As you can see by the ?'s above, I can't reacll the details at this time. Tired Neurons <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[CalliArcale]

All of the Soviet space stations have deorbited, and all were large enough for pieces to reach the ground. The others were the Salyuts. As their deorbits were controlled, there was no hazard to personnel on the ground.<br /><br />Occasionally, large unmanned satellites have deorbited and had bits survive reentry. There was at least one Russian one powered by a nuclear reactor which deorbited. (AFAIK, only the Russians have ever used nuclear fission reactors to power spacecraft. It has the advantage of enormous power availability, but the disadvantages of being very heavy and complicated -- plus being politically troublesome should they deorbit uncontrolled over hostile territory.)<br /><br />The most common space debris to reach the ground has never reached orbit in the first place: spent rocket stages. Kazakh and Russian citizens have been known to form "rocket mafias" to collect these spent stages for their enormous scrap metal value -- they contain a lot of titanium. And American rocket parts have been known to fall on Africa, though in smaller pieces as American rockets launched from the Eastern Range are much higher up by the time they pass over land. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>