Heat tiles...

[l3p3r]

The heat tiles seem to be one of the (many) major weak points of the current space shuttle. <br /><br />Can a solid single piece heat shield be produced to replace the tiles? Not to be used on the shuttle, obviously, but will a new reusable launch vehicle use something like that rather than many failure prone individual tiles? <div class="Discussion_UserSignature"> </div>

 

[docm]

They're called "Thermal Protection Systems" and there is a decent starter article here.<br /><br />NASA's Orion TPS is still in development and the final report is (supposedly) due in 2009.<br /><br />Because the shuttle re-enters at 7.5 km/sec from Earth orbit and Orion will re-enter at 11 km/sec from a lunar trajectory their TPS systems will be very, <i>very</i> different. <br /><br />Tiles are <i>way</i> out and some kind of advanced ablative shield will be in. <div class="Discussion_UserSignature"> </div>

 

[deapfreeze]

Can a solid single piece heat shield be produced to replace the tiles?<br /><br />I would look at this like a side walk or similar to this. I would think they use the tiles because they would have a small gap between them for when they heat up they can expand. I would think if it is a solid piece it would be more likely to crack when it heats up.. I could be wrong here but I think this makes sense to me. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font size="2" color="#0000ff"><em>William ( deapfreeze ) Hooper</em></font></p><p><font size="1">http://deapfreeze-amateur-astronomy.tk/</font></p><p> </p> </div>

 

[docm]

SIRCA (Silicone Impregnated Reuseable Ceramic Ablator) can be machined so it can be applied as tiles, leading edges, nose caps or in any number of other custom shapes/sizes. <br /><br />The problem is weight; the amount required to retro-fit the shuttle would reduce the payload capacity by not a little. That of course depending on if the shuttles structure could handle it <i>or</i> if heat penetration to its skin would be too great.<br /><br />A better solution for re-entry vehicles is to use a TPS, SIRCA or otherwise, that is a spherical section or cone. This minimizes its area and therefore its weight. This is a big advantage of capsules. <div class="Discussion_UserSignature"> </div>

 

[jaxtraw]

The whole thing is Isaac Newton's fault. The problem is that spacecraft in orbit have to go too fast, in order to prevent falling back to Earth, at least 100 miles an hour or more I think. So they hit the atmosphere very fast and have to slow down by friction.<br /><br />It's amazing to me as a layman that NASA engineers didn't think of a way around this, it smacks of gross incompetence. Clearly they could get rid of all these heat shields and tiles if they simply fitted the Shuttle with some brakes. I presume that that there are "special interests" in the Big Heat Shield Industry that sustain this "high speed re-entry" situation.<br /><br />I think Congress need to set a maximum re-entry speed and force NASA engineers to adhere to it, and insist on compulsory brakes on all spacecraft. If ordinary automobiles can have safety standards requiring brakes, it's time they applied to spacecraft too.<br /><br />They would also be useful on aeroplanes, to prevent casualties in high speed collisions with the ground.

 

[billslugg]

You are overlooking an obvious solution. One that would cost very little. We could simply restate the orbital velocity in units that are much smaller. Instead of the shuttle traveling at 100 miles per hour (I think it is actually 150) we could convert it to Astronautical Units. An astronautical unit is the distance from the sun to the moon or 93 billion miles. Thus the shuttle would only be going .000001 AU/hr. Being so slow it would be much easier to stop. You could get by with a tinfoil parachute which actually attracts ions in outer space plus it could produce electricity to power a wind farm. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[ianke]

Hi jaxstraw,<br /><br />Correct me if I am wrong, but doesn't the present day spacecraft reenter at a speed more in the thousands of kilometers per hour? If they slowed to 100s of kph they wouldn't need heat sheilds at all. My car does 100 kph without a heat sheild in the densest part os the atmosphere. <br /><br />Also, it seems to me that slowing a craft to low enough speeds to not need such heat protection would need nearly as much fuel (but not quite) as the take-off. The craft would not only have to slow down but maintain altitude while doing it so that its velocity is reduced before it hits the atmosphere. <br /><br />I am certainly no rocket scientist, so I might be way off base. If wrong here, feel free to tell me so.<img src="/images/icons/wink.gif" /> <br /><br />Ianke <div class="Discussion_UserSignature"> </div>

 

[ianke]

Hi billslug,<br /><br />Doesn't the shuttle orbit at speeds somewhere around 17,000 mph? Also, I think you have the Sun a thousand times farther away. It is 93 million miles away.<img src="/images/icons/smile.gif" /><br /><br />Ianke <div class="Discussion_UserSignature"> </div>

 

[mvp347]

Well since the heat tiles are needed when taking off, they're going to be there when coming back down. So as long as they check to make sure that they are intact when they reach orbit, it is better to just come back at the speed they usually do instead of having to carry more fuel for them to use to slow down, which would mean using more fuel to get the added weight off the ground from the beginning..........

 

[nexium]

billslug is teasing: Your car brakes slow the car because the tires touch on the pavement. We can brake the shuttle by facing it to the rear of it's direction of motion and running the main engine, but it takes a lot of fuel to slow from 17000 miles per hour to 16000 miles per hour or any lesser speed, by this method.<br />The average distance to the sun from either the earth or moon is about 92 million miles. Neil edited to change break to brake

 

[ianke]

I thought so thanks.<img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> </div>

 

[l3p3r]

Nice one billslug <img src="/images/icons/smile.gif" /><br /><br />What I never understood about reentry, especially in the case of the shuttle, is why they don't just perform it at a much shallower angle and gradually aerobrake into a standard-ish flight IAS very very high, then work their way down. Is it not feasible to perform the entire operation without generating so much heat? <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

I don't believe the tiles are needed during ascent, only on return. The thermal load just isn't that high.<br />Not 100% sure though.<br />MW <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>

 

[MeteorWayne]

Braking the shuttle is good. Breaking is bad <img src="/images/icons/wink.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>

 

[jaxtraw]

billslug, you're definitely onto something here. A good example is Mars Climate Orbiter, where NASA successfully completely changed the orbit simply by changing from using Newtons to foot-pounds, which proves your idea works.<br /><br />The big thing to change is that at the moment so-called space "experts" insist on space orbits where the space boat is going slowest when it's farthest away from the Earth at "apologee", and fastest when it's near the earth at "periscope". They just need to swap these around. That would probably mean then they could use smaller Astrological Units as well.

 

[MeteorWayne]

I know (hope) you're being sarcastic but it is time to stop fooling around here.<br />People who don't go better might not get the joke and be seriously mislead. This is Space Science and Astronomy (for facts <img src="/images/icons/wink.gif" /> ), after all.<br />Just MHO.<br />I hate to see people's legs being pulled with facts when they might not realize it.<br />MW <br /><br />Edited to correct forum, and clarify <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>

 

[l3p3r]

Interesting article docm thanks! <br />Especially interesting was the page on the MOOSE system:<br /><blockquote><font class="small">In reply to:</font><hr /><p>falling from orbit protected by nothing more than a spacesuit and a bag of foam was unlikely to ever become a particularly safe - or enticing - maneuver.<p><hr /></p></p></blockquote>quite amusing <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[nexium]

In theory the hot part of re-entry could be spead over a few hours instead of a few minutes. This would make the tiles red hot instead of white hot. I believe the total number of BTU's that need to be radiated or carried away by the very thin air would remain the same. If you saw the movie Space Camp you saw that spreading the re-entry time over enough minutes required skilful piloting due to the air turbulence. Neil

 

[ianke]

He got me.<img src="/images/icons/blush.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[l3p3r]

Hmm yes I can see that trying to maintain a consistently low drag in the tenuous upper atmosphere would be difficult... <br /><br />What if something like a big parachute were deployed to perform the majority of the acceleration in the very high atmosphere? Or would that then mean that the shuttle would simply drop in to thicker air even faster and exacerbate the problem? <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

If you are being serious, if you deployed a parachute at interface it would be shredded so fast, your head would spin.<br /><br />Remember, we're doin' at least 17,000 mph here, almost 5 miles a second.<br /><br />MW <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>

 

[jaxtraw]

Well to be fair to me <img src="/images/icons/smile.gif" /> the only <i>fact</i> I've actually posted was that the Shuttle travels at at least 100mph, which is true...<br /><br /><img src="/images/icons/smile.gif" /><br /><br /><br />Bear with me. I've got whooping cough, and I'm feeling a bit strange right now <img src="/images/icons/frown.gif" />

 

[billslugg]

Good point Wayne!<br /><br />Let's review the errors in my post:<br /><font color="yellow">You are overlooking an obvious solution. One that would cost very little. We could simply restate the orbital velocity in units that are much smaller.</font><br />All scientific and engineering calculations are independent of units. That is to say that if you use a consistent set of units in the calculation, then the results will be identical, provided that the correct conversion factors are used to compare answers. The Mars spacecraft is a tragic example of what can happen when inconsistent units are used.<br /><br /><font color="yellow"> Instead of the shuttle traveling at 100 miles per hour (I think it is actually 150)</font><br />The shuttle travels at 17,000 miles per hour on orbit.<br /><br /><font color="yellow"> we could convert it to Astronautical Units.</font><br />There is no such thing as an Astronautical unit. There is an astronomical unit.<br /><br /><font color="yellow"> An astronautical unit is the distance from the sun to the moon</font><br />An astronomical unit is the average distance between the sun and the earth.<br /><br /><font color="yellow"> or 93 billion miles.</font><br />93 million miles<br /><br /><font color="yellow"> Thus the shuttle would only be going .000001 AU/hr. Being so slow it would be much easier to stop. </font><br />False, no matter what units you use, the shuttle is still going the same speed.<br /><br /><font color="yellow">You could get by with a tinfoil parachute </font><br />Tinfoil would be instantly shredded<br /><br /><font color="yellow">which actually attracts ions in outer space</font><br />Any charged object will attract ions of the opposite charge. A current WILL flow. Uncharged tinfoil would attract nothing.<br /><br /><font color="yellow"> plus it could produce electricity</font><br />False, see above.<br /><br /><font color="yellow"> to power a wind farm</font> <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[ianke]

Nobody told us there would be a test.<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

I thought it sounded very strange for a post coming from you.<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>