International Space Station information

[alpamht]

Hi I have zero knowledge about space and solar system. I just read the news about the STS-116 and viewed some photographs of ISS. Can you please tell me what is the main purpose of ISS and how it works. When it flys with around 17215 miles per hour how STS-116 crew member gets into it. How their space shuttle is parked (don't know technical word) on space. Why ISS is flying so fast? What fuel is used to fly and how it is refilled?<br /><br />Thanks,

 

[MeteorWayne]

Welcome to Space.com!<br /><br />Main purpose? Well giving us some kind of presence in space, pretty much.<br />There's much discussion of the why, I'm sure there will be plenty of comments on that.<br /><br />The ISS has to fly that fast to stay in orbit. If it was flying slower, gravity would pull it into the atmosphere.<br />If it were going 50% faster, it would leave earth orbit and wander among the solar system.<br /><br />Since it is in orbit, travelling at that speed, it would stay there forever except for the fact that does rub up against the outer fringes of the atmosphere, and therefore slows down a little bit every orbit.<br /><br />It's speed is boosted when Russian vehicles or the shuttle are attached since they have liquid hydrogen and oxygen propellant aboard, at least for the shuttle.<br />I'm not 100% sure what propellant the russian vehicles use.<br /><br />Again, I believe, but am not sure, that the ISS has some ability to reboost itself in an emergency, I would assume that would be from tanks refilled when other craft visit, but there are several experts here who will answer that question. <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>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>shuttle are attached since they have liquid hydrogen and oxygen propellant aboard<p><hr /></p></p></blockquote><br />Actually, as I recall, the shuttle only uses LH and LOX for ascent. Once in orbit, they use hypergolics. You should confirm that with ShuttleGuy. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[alpamht]

Thanks for your prompt response. Still waiting to get more info from other experts.<br /><br />I saw the Video of ISS when crew were working to install P5. We can't say that ISS is flying with speed of more than 17000 miles per hour. When we drive car in speed of 100 miles we can feel shaky. But video was showing that the astruanaut who was walking flying in slow motion. So it seems that because of gravity you don't feel that speed or what? (Again I zero in this science). But I will have to know so that I can tell my little kids if they ask me any questions.<br /><br />Again greatly appreicated for your prompt response.

 

[MeteorWayne]

It's really because there's almost no air there. If you were doing 17.000 mph here on earth, you'd burn up in an instant. And since the astronauts are moving at the same speed as the station, they don't drift apart.<br /><br />What gravity does, is keep an object travelling at that speed in orbit around the earth. Basically, the ISS is falling toward the earth, just as it would in your back yard, but since the earth is round, the surface is falling away at the same rate since it's moving at that speed, it stays at the same altitude.<br /><br />Hence, an orbiting object! <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>

 

[brellis]

It's like when you ride on a train, you don't feel like you're moving, because you're not accelerating. It's not shaky for them, because there's no air up there. <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[alpamht]

Thanks guys for your prompt response.

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>they don't drift apart.<p><hr /></p></p></blockquote><br />Actually, they do. Just not very much. The drifting that is there is why they have tethers and other safety gear.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>it stays at the same altitude.<p><hr /></p></p></blockquote><br />Not quite the same. All orbits are elliptical. Hence the orbit varies by at least a few miles. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

Actually, I took the Amtrak Cascades from Portland, Oregon to Seattle once. You could feel the train moving, but only side to side. Walking was about as close as I get to walking drunk (I don't touch alcohol). <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[MeteorWayne]

Yes, they do drift apart, but it is more due to the forces that they exert against surfaces. Their relative speed is zero. The atmopsheric effect would not cause any such drifting in the time of an EVA, AFAIK. In any case, that is not relevant to the original posters question.<br /><br />Again, you are correct about the elliptical orbit, but from the original poster's stated level of knowledge, that's more detaail than he needs to absorb at one time <img src="/images/icons/smile.gif" /><br />Orbital mechanics can come later ! <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>

 

[SpeedFreek]

The purpose of ISS could be said to be to promote international cooperation in a scientific project for the benefit of mankind.<br /><br />The ISS is in orbit around the Earth. When a spaceship wants to fly into space, it needs enough power (called thrust) to gain the speed needed to lift it out of Earths atmosphere, against the pull of Earths gravity. If it doesn't have enough speed, gravity will pull it back to Earth. If it has enough speed to break free from Earths gravity and does so, it can turn off its engines and will cruise in space at that speed until it encounters another source of gravity (the Moon, for instance) which will start pulling on the spaceship, altering its course. Spacecraft don't need to thrust for the whole journey, they only need thrust to alter their speed when they are dealing with the pull of gravity, when they are moving through something that slows them down by friction (like the Earths athmosphere) or to change their course.<br /><br />When a spaceship blasts off from Earth, uses enough thrust not to fall back, but not enough to escape the gravity completely, it goes into what is called an orbit. The mathematics of putting a spaceship into a stable orbit (where it keeps orbiting for a long time without need to use any extra thrust) are complex. Often, small course corrections (achieved by small thrusts in certain directions relative to what they are orbiting) are required to keep the orbit stable.<br /><br />A spaceship in orbit can indeed be described as falling around the planet!<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[alpamht]

Thanks for your response.

 

[qso1]

willpittenger:<br />Actually, as I recall, the shuttle only uses LH and LOX for ascent. <br /><br />Me:<br />I think you forgot the other element in use during ascent...the SRBs (Ammonium perchlorate/powdered aluminum). But your right about the shuttle using LH2 and LOX during ascent and hypergols once on orbit. <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>

 

[qso1]

Purpose of ISS:<br />Conduct microgravity research. Study the effects of space on humans. Provide a permanent platform for human activity in space.<br /><br />Speed:<br />Both station and shuttle travel around earth at approximately 17,500 mph. The reason the crew is able to get into ISS is the shuttle can dock with it by maintaining low relative speed. Think of one of those auto chase scenes where someone jumps into another car while both cars travel down the highway at 80 mph. One car may be doing 79 mph while the other does 80 mph. There is only 1 mph difference so the person can jump to the other car. Same with ISS and shuttle.<br /><br />Why so fast:<br />Newtonian physics, 17,500 mph happens to be the speed at which a stable orbit is maintained at ISS altitude of around 400 Km. The moon travels around Earth at approximately 2,200 mph but is 240,000 miles out.<br /><br />Fuel:<br />The station is reboosted on occasion by shuttle and Progress vehicles. AFAIK, the station is not refilled with any propellants which is why the reboost flights are necessary. <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>

 

[willpittenger]

Actually, you collided (hopefully not fatally) with one of the problems with the English language. It wasn't clear what I was applying the word "only" to (ascent or where LH/LOX are used). For that, I apologize. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>the station is not refilled with any propellants which is why the reboost flights are necessary.<p><hr /></p></p></blockquote><br />What a pain. We launch some engines for it -- and ignore them after a while. They are now reducing the amount we can boost ISS. (Extra mass means less boost.)<br /><br /><br />Qso1, since you brought up the fuel not being resupplied, how does the station orient itself? Does a Progress or Soyuz have the oomph for that? <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[erioladastra]

"The station is reboosted on occasion by shuttle and Progress vehicles. AFAIK, the station is not refilled with any propellants which is why the reboost flights are necessary. "<br /><br />No, the SM tanks can be filled from a progress and used for reboost. ATV will also transfer fuel.

 

[erioladastra]

"What a pain. We launch some engines for it -- and ignore them after a while. They are now reducing the amount we can boost ISS. (Extra mass means less boost.) "<br /><br />???????<br /><br /><br />"Qso1, since you brought up the fuel not being resupplied, how does the station orient itself? Does a Progress or Soyuz have the oomph for that? "<br /><br />For attitude control the control moment gyros (CMGs). For attitude manuvers the SM/progress thrusters are used. Soyuz could be used but would be VERy inefficient and would make you nervous since that is your emergency vehicle so you would have to use spareingly.<br />