Shuttle's re-entry into earth's atmosphere

[pmurgai]

I have a question about the Shuttle's re-entry into earth's atmosphere. As we know that entering the earth's atmosphere generates lot of heat due to friction of air. This primarily happens because of speed of the entering body.<br /><br />What if we make the vehicle enter earth's atmosphere very very slow ? This will greatly reduce heat produced due to friction and thus prevent any damage to the shuttle. <br /><br />This is a little difficult due to earth's pulling action and we have to device ways to counter that force. But I guess it is not impossible. For e.g. we can design shuttles with helicopter kind of technology or any such technology for that matter which can control the speed of the vehicle.<br /><br />What is wrong with the above theory ? I am sure NASA would have definitely gone in this direction if something like this was possible.

 

[glutomoto]

<font color="orange">Re: make the vehicle enter earth's atmosphere very very slow</font><br /><br />To slow down the shuttle a lot for reentry would cost more fuel, it would cost a lot more. Also the shuttle is the worst glider ever built, a very slow reentry might not be possible.<br /><br /><br /><font color="orange">Re: design shuttles with helicopter kind of technology</font><br /><br />A design like that has already undergone some flight testing, but has not gone into orbit yet. <br />Rotary Rocket is tested<br /><br /><br />Then there is the winner of the x-prize which glides back, but has not done it from orbit. I am not sure that the SpaceShipOne design is meant for use with an orbital vehicle but is at least work along the line you suggested.<br />Scaled Composites SpaceShipOne<br /><br /><br /><img src="/images/icons/smile.gif" /><br /><br />edited to fix link. <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>As we know that entering the earth's atmosphere generates lot of heat due to friction of air.<p><hr /></p></p></blockquote><br /><br />Actually, that's not true. It's a common misunderstanding, but the heat is not generated by friction. It's generated by compression. The sheer force of the Space Shuttle (or any other entering object) pushing through the atmosphere at fantastic speed causes the air to be compressed ahead of it, creating a shockwave. This shockwave is so compressed and so hot that it becomes a plasma -- the fourth state of matter. Plasma is electrically conductive, and in fact radio waves have a hard time penetrating it; this is why spacecraft can lose contact with the ground during reentry. (The Shuttle cheats; it doesn't talk directly to the ground, but rather to the TDRS satellites in geosynchronous orbit and thus not obscured by the plasma. But it's line-of-sight to the satellites isn't always good, so even the Shuttle's signal may drop out periodically during entry.)<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>What if we make the vehicle enter earth's atmosphere very very slow ? This will greatly reduce heat produced due to friction and thus prevent any damage to the shuttle.<p><hr /></p></p></blockquote><br /><br />There are a couple of problems. The first is that the vehicle is going the equivalent of about Mach 17 when its in orbit. It has to; your orbit is defined by your forward velocity, so if you go to slow, you actually fall and hit the Earth. (Orbiting means falling while you're going forward so fast that you actually miss the Earth and just fall around it forever. Isaac Newton's famous thought experiment for this concerned a canonball shot at greater and greater velocities. I can elaborate on that if you want.) No matter what, you have to slow down from Mach 17 to 0 MPH in order to land. That's a hell of a lot of energy. You have to do something with it.<br /><br />On <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>

 

[pmurgai]

Thanks Calli, that was a nice explanation.<br /><br />Just one more thing...<br /><br />-----------------------------------------------------------------------<br />< your orbit is defined by your forward velocity, so if you go too slow, you actually fall and hit the Earth. /><br />-----------------------------------------------------------------------<br /><br />May be I am missing some point here but what is wrong with reducing the speed of the shuttle in space and falling into the earth during re-entry. The shuttle has to land anyways. This way the only force that has to be opposed is earth's gravitation.<br /><br />Or is retrorockets the only way to reduce speed in space ?

 

[glutomoto]

<font color="yellow">Re: Or is retrorockets the only way to reduce speed in space ?</font><br /><br />Yes, only on the shuttle they are called the Orbital Manuevering System. Nasa's Return to Flight Web Site has some information. <br /><br /><i>"When it is time to return to Earth, the orbiter is rotated tail-first into the direction of travel to prepare for another firing of the Orbital Maneuvering System engines. This firing is called the deorbit burn. Time of ignition (TIG) is usually about an hour before landing. The burn lasts three to four minutes and slows the Shuttle enough to begin its descent."</i><br /><br /><font color="yellow">Re: what is wrong with reducing the speed of the shuttle in space and falling into the earth during re-entry.</font><br /><br />I guess by this you mean as you said before, to slow the shuttle to basically zero forward velocity ?? There are two reasons. 1) It would require alot of propellent to do that, almost as much as for take off. The Shuttle doesn't carry very much propellent, and the OMS engines are very small compared to the SSME's. 2) The shuttle flies like a brick or two, but it does fly if it is going about mach2. Which means that speed would need to be regained for the shuttle to land correctly.<br /><br /><br /><br /><img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[igorsboss]

<font color="yellow">Because if you stop all velocity gravity accelerates you and that added energy must be removed before impact !</font><br /><br />Well put!<br /><br />Remember all that impressive-looking rocket energy that was expended to launch the shuttle into orbit? Well, in order to bring the shuttle to stop on the ground again, all that pent-up energy needs to be released again.<br /><br />You can release it little-by-little, or all at once. The quicker you release the energy, the more impressive the explosion. The slower you release the energy, the less damage you do.<br /><br />This is why cometary impacts are so extremely devestating. Imagine the rocket power you would need to lift Manhattan Island to Pluto. Now, imagine all of that power being released in the span of about 1 second. That's a big-a-bada-boom!<br /><br />That's also why a tiny grain of sand can look as bright as a shooting star.

 

[joshbe]

BUZZZZZ! WRONG!! The shuttle does not generate heat due to friction, rather it compresses the gases of the Earth's atmosphere. Mass and Speed are the key factors. The Shuttle is big, and it's traveling at 17,500 mph. Thats whole lotta hot gas. In response to your question:<br />We are slowing down the orbiter, If it kept going at 17, 500 mph, It would keep orbiting. If NASA went any slower than it does, the orbiter would drop llike a rock. Plus, It has to have some speed so it can land.