Slowing the Shuttle

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rogerinnh

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When Space Ship One (Rutan's winning entry in the X-Prize competition) returned from space, it's forward velocity was nearly zero. That is, it returned to Earth as if simply dropped from its maximum altitude. It therefore had a much easier flight path on the way back. Easier than the Shuttle, that is, which has to slow down from orbital velocity before it could then fly the rest of the way to Earth. The Shuttle uses atmospheric drag to slow it down, and hence the need for the tiles.<br /><br />So, I'm thinking, how much energy does it actually take to slow the Shuttle down from orbital velocity to zero? And how much propellant would have to be used to perform that slow-down, instead of using atmospheric drag? That is, it it conceivable for the Shuttle to carry along enough extra fueld to perofmr that slow-down operation, making it much easier to then return to Earth, as Space Ship One did?<br /><br />
 
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fangsheath

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It really isn't practical, the energy required is enormous. Keep in mind that the propellant required for de-orbit must itself be launched into orbit, so you must recalculate the energy cost from start to finish. Besides, notwithstanding the loss of Columbia, thermal protection systems work. Ablation shields have been used for 40 years. They work. The shuttle's TPS works just fine, although in my opinion the whole concept of the shuttle unnecessarily complicates getting to orbit and back. I would favor a more modular approach.
 
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rogers_buck

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Using the atmosphere for aerobraking from Mach 20+ is nice because you don't have to carry all that fuel with you. It's just too bad that fire bricks seem to be the best technology we can come up with to handle all that heat... <br /><br />The real problem is that you would have to "near - instantly" slow down because you would be headed for the atmosphere the moment you laid on the brakes. So a clever trick like using the ionosphere for electrical breaking wouldn't work unless you had a downward thrust to keep you in the sky while you were doing it...
 
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tom_hobbes

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There was quite a stir in the nineties about some plastic a British chemist had managed to create which could withstand simply amazing temperatures and he demonstrated this on a number of occasions. Then the man and the plastic disappeared off the radar completely and I never heard of it again. If anybody knows more on this I'd love to hear it. <br /><br />Apart from oven linings and many other mundane uses, an entire plastic hull could have been moulded out of this stuff with no breaks. A perfect heat shield. I always wondered what happened to him and his invention.<br /> <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>
 
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Saiph

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my guesses:<br /><br />1) A fraud<br /><br />2) Contracted by the Gov't (or a Gov't) for work on a black project. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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rogers_buck

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Heat paste seems to be hanging in there, but I have seen no mention of Nasa looking at the stuff...
 
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silylene old

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Actually any silicon-containing polymer with more than 15 wt% silicon is amazingly stable to oxygen plasmas and very high heat (25+ wt% works best).<br /><br />Silicon oxidizes to form a non-volatile material, SiO2. An organosilicon polymer oxidizes in oxygen plasma to form a tough non-volatile surface skin (about 0.1 um thick) which protects the underlying polymer from destruction. As such, organosilicon polymers are amazingly stable in hot active oxygen plasma. Polysilanes, certain silicones and polysilsequioxanes are examples. Other atoms which form non-volatile oxides, such as titanium, germanium, and tin also work if incorporated in a polymer. (I did my graduate work on organosilicon polymers used as plasma etch masks in the early 80's...and later received a nice research grant in the late '80s).<br /><br />Organosilicon polymers are used for this purpose of high oxygen plasma etch resistance in bilayer photolithography, and as coatings on some satellites. <br /><br />In contrast, the carbon in organic polymers oxidizes to form CO2, which are volatile. This is why organic materials are quite unstable in hot plasmas and etch away very rapidly.<br /><br /> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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Saiph

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yeah, but the silicon rich materials still ablate away due to sheer thermal energy right? <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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silylene old

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yes, but very slowly. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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Saiph

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makes sense. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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thalion

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That equation is pretty straightforward; just take the dry mass of the Shuttle (which I'm assuming is close to the actual mass of the orbiter on re-entry), use the average orbital speed (~17,500 mph) and solve a simple change-of-kinetic energy formula:<br /><br />W = 1/2 m*v^2(2) - 1/2m*v^2(1)<br /><br />m = mass<br />v = velocity<br />(2) = final velocity<br />(1) = initial velocity<br /><br />I've never bothered to use this little formula to figure out the numbers myself, but I'm sure the answer is *very* large.
 
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teije

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rogers_buck:<br />Heat paste seems to be hanging in there, but I have seen no mention of Nasa looking at the stuff... <br /><br /><br />are there any links to sites about this?<br />cheers,<br />Teije
 
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CalliArcale

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Maybe it's not very practical? After all, a substance must resist heat, be lightweight, be attached to the vehicle in such a way that it's not going to come off from launch vibrations, be cost-effective, and be manufacturable in sufficient quantities quickly enough that it doesn't delay launch.<br /><br />So creating the material is only part of the problem. We've got carbon nanotubes, for instance, but we can't build a space elevator. This is because carbon nanotubes can currently only be spun a few inches long, and are very expensive, I think mostly because they're labor-intensive. They exist, but are impractical right now. Maybe that's why these other heat-resistent materials aren't being used on Shuttle. <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>
 
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rogers_buck

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Not quite. If you started to put on the brakes you would wind up in the atmosphere. So you would need an increasing thrust in the downward direction ultimately equal to the weight of the vehicle.
 
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rogers_buck

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This thread discusses thermal protection and has a link to the Fire Paste...<br /><br />LINK
 
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rogerinnh

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Thalion wrote:<br /><br />----------------------------<br /><br />That equation is pretty straightforward; just take the dry mass of the Shuttle (which I'm assuming is close to the actual mass of the orbiter on re-entry), use the average orbital speed (~17,500 mph) and solve a simple change-of-kinetic energy formula: <br /><br />W = 1/2 m*v^2(2) - 1/2m*v^2(1) <br /><br />m = mass <br />v = velocity <br />(2) = final velocity <br />(1) = initial velocity<br /><br />----------------------<br /><br /><br />I can't quite figure out what you mean, regarding the two velocities. Can it be re-written like this:<br /><br /><br />W = 1/2 m*vf^2 - 1/2m*vi^2 <br /><br />w = kinetic energy<br />m = mass <br />vi = velocity, initial<br />vf = velocity, final <br /><br />And what are the units for w, m, vi, and vf ?<br /><br /><br />
 
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rogerinnh

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rogers_buck wrote:<br /><br /><br />--------------------------<br /><br />Not quite. If you started to put on the brakes you would wind up in the atmosphere. So you would need an increasing thrust in the downward direction ultimately equal to the weight of the vehicle. <br /><br />----------------------------------------<br /><br />I don't think so. The idea is to reduce the forward motion to zero so that the craft simply falls (approximately) straight down into the atmosphere, much like Space ShipOne did, so that heating effects are substantially reduced by passing through considerably less atmosphere at considerably less velocity.
 
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rogers_buck

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Momentum is what keeps an object in a set orbit. Reduce its momentum by reducing its forward velocity and the orbit lowers. To drop from orbit the shuttle fires its OMS engine to slow its orbital velocity.<br /><br />Think of a cannon that fires a cannon ball at progressively higher speeds. At -0- the cannon ball drops out the end like SS1. SS1 went straight up with little or no forward vector. As the cannon ball speed increases the cannon balls fall to earth progressively farther away after following parabolic trajectories. When the cannon ball is fired at around 18K,mph it will not only miss the lim of the earth its momentum will carry it up to the shuttle (the repair kit better work). Now run this example backwards. Slow down the cannon ball closing in on the shuttle until its speed is -0- and it drops from the barrel.<br /><br />To stop without lowering the orbit you would need either to apply the brakes instantly, sending crew and content out the wind screen, or provide thrust to effectively counter gravity.
 
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fangsheath

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When you apply retrograde thrust, it lowers the orbit primarily on the opposite side of the planet, not where the ship is. Initially you will not have to apply much downward thrust to maintain altitude. Of course, as the orbit deteriorates and the vehicle assumes more of a ballistic trajectory, you will have to apply increasing downward thrust to hold your altitude.
 
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