Shuttle Debris Protection Question.

[cybernomad]

Concerning debris impacting the Shuttle’s protective foam heat shields on take-off.<br /><br />My question is (it sounds so simple as to be a stupid question but I'm curious concerning your thoughts on this)<br /><br />Why don't they install a disposable debris shield (maybe made of titanium) over vulnerable surfaces (e.g. leading edge of wings) which then would be jettisoned before reentry?<br /><br /><br />I'll greatly appreciate your time taken to reply.<br /><br />Thank You<br /><br />

 

[najab]

><i>Why don't they install a disposable debris shield. . .which then would be jettisoned before reentry? </i><p>Because every pound of shielding would be a pound less payload capability. As it is, the RMS boom extension has cut half a ton from the payload they can take to the Station.</p>

 

[cybernomad]

A titanium shield over the leading wingtip would not add much mass. It is far more protective than the foam insulation which is designed mainly for reentry and not takeoff debris impacts. I’d bet an average man could carry the total weight of it.

 

[nacnud]

The foam insulation of the ET is to stop ice forming on the ET in case it falls off during launch and hits the orbiter. It also reduces boil-off of the cryogenic propellants.<br />

 

[cybernomad]

Yes but post testing (did not make headlines) indicated that some debris could and would still come off and impact the foam on the leading edges. (it was a suprise) It was determined that the same damage that downed the last could occur again.

 

[najab]

><i>A titanium shield over the leading wingtip would not add much mass.</i><p>Yes it would. It certainly would add many hundreds of pounds.<p>><i>It is far more protective than the foam insulation which is designed mainly for reentry and not takeoff debris impacts.</i><p>I'm not sure what you're talking about here. The only foam insulation used on the Shuttle stack is on the External Tank. By definition, it is not expected to survive re-entry.<p>><i>I’d bet an average man could carry the total weight of it.</i><p>I'm willing to take that bet.</p></p></p></p></p>

 

[najab]

><i>Yes but post testing (did not make headlines) indicated that some debris could and would still come off and impact the foam on the leading edges.</i><p>Once again.THERE IS NO FOAM ON THE ORBITER'S WING. The foam is on the External Tank.</p>

 

[cybernomad]

OK, I don't much about the Shuttle but what was it that led to the downfall of the last Shuttle?

 

[nacnud]

Foam from the External Tank hit the Carbon-Carbon leading edge of the orbiter.

 

[cybernomad]

and my question is why can't we place a disposable titanium shield over that fragile surface.? Surely a 2 millimeter thick shielding would not weigh hundreds of pounds and yet be many times more protective than the Carbon-Carbon material against debris it may encounter upon lift-off?

 

[nacnud]

OK here is a SWAG for the mass of titainum needed.<br /><br />Length of shuttle leading edges ~ 50m<br />Height of shuttle leading edges ~1.5m<br />Thickness of sheald ~ 0.002m<br />Density of titainium ~ 4500 kg/m3<br /><br />Mass of titanium needed ~ 50*1.5*0.002*4500 = 675 kg or 1485 lb<br /><br />Not including any supporting structure or methods of removing titainum from leading edges before re-entry.<br />

 

[najab]

><i>Surely a 2 millimeter thick shielding would not weigh hundreds of pounds and yet be many times more protective than the Carbon-Carbon material against debris it may encounter upon lift-off?</i><p>2mm of Titanium wouldn't be a strong as the current RCC. RCC isnt' fragile at all, it takes quite a bit of force to damage it.</p>

 

[cybernomad]

just the edges! not 50M X 1.5M of it. <br /><br />edited to add;<br /><br />it may be 1/10th of what you calc

 

[cybernomad]

I saw a discussion on it on TV, its not all that tough. Even so their primary purposes design it as a heat shield upon reentry and not for impact debris on take-off. Surely a more durable shield designed for debris impact in mind is better than the Carbon-Carbon material.

 

[nacnud]

That is just the leading edges!

 

[najab]

That <b>is</b> just the edges. Here's a pic of one RCC panel being installed. You're talking about covering all of them with Titanium.

 

[najab]

><i>Even so their primary purposes design it as a heat shield upon reentry and not for impact debris on take-off. Surely a more durable shield designed for debris impact in mind is better than the Carbon-Carbon material.</i><p>Better still is eliminating the source of large pieces of debris, which they have done.</p>

 

[cybernomad]

even so 2 mm is just a fig for discussion sake, 1 mm may still be much better than just what's there now. Also the substantial decreased risk far outweighs benefit of slightly less weight. Didn't they after all now mandate a larger arm on all flights that has greatly increased the weight?<br /><br />BRB

 

[cybernomad]

didn't you see the follow-up tests which indicate potentially damaging debris still exist?<br /><br />BRB in a couple hrs<br />

 

[najab]

><i>Even so 2 mm is just a fig for discussion sake, 1 mm may still be much better than just what's there now.</i><p>No. It wouldn't be. RCC really is pretty tough stuff. As long as you don't let <b>big</b> pieces of debris hit it, there's no problem. A piece of debris big enough to hurt a RCC panel would definitely hurt a piece of 1mm thick Ti sheet.</p>

 

[vogon13]

What if titanium doesn't come off before re-entry? How can adding more complexity to a complex vehicle make it more reliable? Reliability is the sum of the failure rates for ALL the equipment on the vehicle. I can just imagine melting shreds of titanium foil jamming rudder speed brake or wing/body flap mechanism. Or divoting silca tiles. Or if it comes partially loose and upsets aerodynamics of shuttle at mach 25? They believe molten/vaporized aluminum was cause of com disruption on Columbia, would titanium behaive same way? There are probably more unpleasant outcomes I haven't thought of. Many of these failures will result in loss of vehicle. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[cybernomad]

<blockquote><font class="small">In reply to:</font><hr /><p>" What if titanium doesn't come off before re-entry? "<p><hr /></p></p></blockquote><br /><br />the technology for ejection is extremely reliable, well known and used for decades.<br /><br />It will be done when in orbit or can even be detached with the arm.<br />

 

[najab]

><i>the technology for ejection is extremely reliable, well known and used for decades.</i><p>Which adds more mass. And further reduces the payload capacity.</p>

 

[cybernomad]

evidently not tough enough (ref latest tests of new and improved tanks which are not supposed to shed debris that can damage the shuttle but was found in fact to do so). It was chiefly designed as a heat shield not a debris shield. Any other more suitable material designed for debris protection would be better than the present heat shield.

 

[cybernomad]

didn't they already add a lot more mass with every shuttle req to carry the new longer arm - all in the name of increased saftey?