Starship heat shield

[sebk]

Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.

SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.

No, please. I understand SS will not reenter nose first. Reread the my post with the assumption of a realistic AoA.

AIUI, SS is intended to reenter with an AoA of ~70deg. This moves the point of first contact from the centerline of the barrel up onto the ogive. At this point there are two radii to consider. Up/down and left/right, and it gets complicated.

At the edge where the tippy tip tile is missing a new up/down radius is introduced along the centerline. Flow will 'flow' over the lip and most likely down to the newly exposed surface. The shock will most probably also make an adjustment around the lip but my dedicated CFD computer is down right now (/s) and I can't tell if there will be any shock impingement. Greatest danger might be the side face of the tile opposite the flow.

Down on the barrel, let's assume an AoA of 90deg. It makes the visualization easier. The shock front is closest along the centerline and compressive force and it's heating are greatest. Surface flow is from the centerline to the sides. Remove one centerline tile.

The compressive forces stay the same but are now on the skin, not a tile. AIUI, the shock front would dimple in at a rate determined by the radius of curvature of the tile edge. Here it gets interesting. With the shock front dimpling in and the missing tile forming a pocket, there may be a Venturi effect with the semi trapped flow excessively heating the adjacent tile edges. This effect decreases as the missing tile distance from the centerline increases.

This is admittedly all a mind experiment. The only number I have is 42, and Elon's already used it on SS.

Actually, on the center-spot (or center line at 90° AoA) behind the stagnation point there would be no local shock even if a tile fell off. The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement. There will be turbulence and stuff (unless things are so smooth the flow is laminar) but they will be subsonic.

But as you'd start moving to the side, you'd start getting air movement again. If you'd move totally to the side you'd actually get supersonic flow (in the order of Mach 2.5 if I remember correctly; I could be badly wrong, though). So somewhere on the side of the barrel, likely at some point between 30° and 60° to the side you actually get supersonic flow behind the bow shock too. So that's the place where there's potential for shock impingement onto the skin if a tile is missing. OTOH heating would be less there, because bow shock standoff is significantly larger back there, and the flow has lower pressure (so it's colder and contains less heat to transfer).

You could (extremely roughly!) think about the skin of the vehicle and bow shock forming a kind of a nozzle through which the stagnation point air expands to escape behind the sides of the reentering vehicle.

The CFD system is still down <g> so I'm trying to use my head and model this one air particle at a time. Again assume a 90deg. AoA for simplicity.


The heatshield is in vacuum so there are no aerodynamics. Then it encounters one particle of air directly on the centerline. The particle hits and that is one tiny bit of compressive heating to both the heatshield and the particle. The energetic particle is now conceptually sharing a frame of reference with the ship and being hot and energetic, rebounds.


A key concept here is 'mean free space' between air particles. As the air gets denser the mean free space goes down and a rebounding particle has an increasing chance of impacting an incoming* particle of air. When a rebounding particle hits an incoming particle a nascent shock wave forms.


That first partial that impacts an incoming particle would bounce back towards the ship and contribute again to compressive heating. The particle it impacted would also rebound and have some chance of hitting yet another incoming particle and the process would cascade. This is all at the stagnation point.


To one side or the other the process would follow this pattern but with a radial component. This is what forms the flow under the shock. Particles are always bleeding in from the shock and adding to the flow. Particles are always piling up and entering the ships frame of reference. This pileup is the shockwave.


Not sure where this is going. Gotta think on it some more. Somebody point me in the right direction if I'm off base.


* Really just unlucky enough to be in the way.

Your understanding is pretty good.

Just few additions:

To actually have a shock formed, its standoff distance must be incomparably larger than the mean free path of air molecules. Otherwise it will be "too blurred", i.e. the variance of actual free paths of actual particles will be too large. Once would hit another just after a millimeter while another would fly freely for half a meter.

So the bigger the reentering object and lower its curvature, the earlier will the shock form. That's why you could have the bow shock of our solar system forming in a gas so rarefied that human scale objects could fly through thousands km per second without forming anything.

Another part is that those molecules will emit thermal photons, i.e. they will lose energy via radiation. And to make things even more interesting depending on their states they may be also absorb or not photons which fly around them.

The interactions are complex, you get multiple blurry layers differing by temperature and actual chemical species present (the temperatures are high enough to cause ionization not to even mention chemical reactions which would be rare in calmer conditions). For example, simplifying air to just nitrox, you'd have O2, N2, O, N, O+, N+, O3-, O3,  various species of NOx, (NO2, N2O4, NO+, N2O, etc...), even some O+2 and N+2, etc...

The net effect is that the bow shock itself is about 8000K hot, but between it and the vehicle nose things get a lot cooler, so the skin could be for example at 1260K.

NB, there's an interesting phenomenon that if the air is rarefied enough that the bow shock doesn't form, you get extremely high temperatures very close to the skin. The effect is that the skin will absorb much higher fraction of the heat when there's no bow shock, than when there's the cushion formed by the bow shock and the layers behind. So for example in Shuttle you'd already get high heating and plasma visible behind the windows while the braking force was like 0.1g or so.

[OTV Booster]

Re: sebk and one particle at a time.


Yeah, was trying to keep it simple and add complexities one at a time. The early example of a single partial impact is what happens before a bow shock forms. All heating is applied directly to the skin.


I was thinking about the various species. They're there, they're important but ISTM, irrelevant in assessing the flow impact of a missing tile. Thermal and chemical, but not flow.


Something I'm chewing on is charges. That first partial, it's gonna hit hard. Not only will it break apart into constituent atoms, it will also most probably shed an electron or two. In the grand scheme of things charge will be conserved but are there local effects?  If there are, this might affect flow.


You also touched on stand-off distance and shock development. For argument, let's assume particles are evenly distributed and there is no issue with 'mushiness' in the shock structure. At a high mean free space (thin atmosphere) that first secondary impact would stand off quite a bit. From here several things happen simultaneously an I'm unclear on what dominates, and how much everything contributes to shock stand-off throughout reentry.


1) As secondary rebounds increase with decreasing MFS (Mean Free Space) the density of the stagnation gasses increase which would increase the stand-off distance.


2) As the above happens and MFS is decreasing, more particles are interacting with the rebounds, increasing the density (correct word?) and energy of the shock. My first thought is that would press the shock closer but on rethink, I'm not so sure.


3) As velocity bleeds off into denser air the MFS decreases but the MFS itself interacts with the slowing ship such that the TIME between between particle impacts may be lower and the stand-off distance affected. My brain hurts.


You mentioned a tentative mach 2.5 on the stagnation layer velocity. Is this in relation to the ship surface or the surrounding medium? Would it be an overall velocity or differential through its thickness? Slow at the ship and fast at the shock or visa versa? I'm sure it's something you read and half remember, so maybe I'm just being cruel in asking

[john smith 19]

Re: sebk and one particle at a time.


Yeah, was trying to keep it simple and add complexities one at a time. The early example of a single partial impact is what happens before a bow shock forms. All heating is applied directly to the skin.


I was thinking about the various species. They're there, they're important but ISTM, irrelevant in assessing the flow impact of a missing tile. Thermal and chemical, but not flow.


Something I'm chewing on is charges. That first partial, it's gonna hit hard. Not only will it break apart into constituent atoms, it will also most probably shed an electron or two. In the grand scheme of things charge will be conserved but are there local effects?  If there are, this might affect flow.

"Real gas effects" is the general term for this stuff.  Historically they used a 7 element model for reentry from orbital velocity, about 7900m/s.  At this speed ionization was not considered but you do get dissociation where O2 -> O + O and N2 -> N + N. This absorbs substantial energy and as was noted there is also photon emission. Whether they make to the skin or are aborbed in the gas layer can have significant effects.  Given that temperature is a measure of a particles velocity an O2 "particle" is heavier than an O, so it's temperature will be lower. This is why the early ICBM warhead studies about enormous temperatures (able to melt tungsten for example) were so misleading.

An analytical model for this was developed in the late 50's by Lighhill, but it only dealt with a single gas. This has recently been extended to cope with air. I've added a file on it. It claims to be within 4% of the full calculated solution up to 12000k. Good luck.

[Nomadd]

 I found a 16 square ft. piece of white, 5/8" thick, lined fuzzy insulation that I think is heat tile underlayment. The storm last week was kind enough to blow it onto public land.
 I'm trying to think of a few tests to do.

[eriblo]

The easiest that come to mind (if you have a decent scale) is to weight it to get the density. Soak it in water to see how hydrofilic/fobic it is. Bake it for a bit in an oven - weight changes might be to small to measure but any smoke or changes in texture/color would suggest some organic components/treatments. Repeat water testing after baking.
Obviously: seeing what it takes to melt/burn it.

These results will of course be mostly boring "nothing happens" if it is a good TPS material.

[john smith 19]

These results will of course be mostly boring "nothing happens" if it is a good TPS material.

Should be "nothing happens."

If something does then things become more interesting and you'd wonder why SX went with a material that displayed those properties.

But 16Sq Ft is kind of a large thing to be blowing round. So either a)It's really light (like it's mostly air) or b)That storm was very serious 

TBH I could believe either.

[RamsesBic]

I have been thinking about the way the TPS tiles are made and how they are attached to the hull.
If I understand the way the tiles are made, they are baked (sintered) with a Y shaped frame on the back that has 3 holes for the studs that are welded to the hull by robots.

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

To do that the studs on the tile need to be electrically wired to make the welding possible. Then as much of that wiring as possible could be pulled away (or left in place). I was thinking the frame would include the wires.

I have seen how studs are welded, but I don't know if that can be done while a stud is behind a tile.

If a tile is cracked it will have to be removed as they do now, but the studs have to also be cut off to make place for a new tile.

Just a thought that maybe others can improve...or debunk.

[OTV Booster]

I have been thinking about the way the TPS tiles are made and how they are attached to the hull.
If I understand the way the tiles are made, they are baked (sintered) with a Y shaped frame on the back that has 3 holes for the studs that are welded to the hull by robots.

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

To do that the studs on the tile need to be electrically wired to make the welding possible. Then as much of that wiring as possible could be pulled away (or left in place). I was thinking the frame would include the wires.

I have seen how studs are welded, but I don't know if that can be done while a stud is behind a tile.

If a tile is cracked it will have to be removed as they do now, but the studs have to also be cut off to make place for a new tile.

Just a thought that maybe others can improve...or debunk.

Cabling large enough to carry welding current for the pins would leave holes or gaps in the tiles that would negate the tiles purpose. Leaving the cables in place would create a thermal path to the pins and underlying surface. If the cables stay in place the weight increase would most likely at least double the weight of each tile.

[john smith 19]

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

[RamsesBic]

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

The studs would not be welded to the tile, but be part of the frame just as the holes are now.

When it comes to removing tiles I have noted they drill holes, then use those to break the tile in pieces then they remove the frame that was holding the tile last. With the tiles I am thinking of it would only add one step - grind off 3 studs.

The system I am envisioning would also be automated but instead of just welding studs the robot arm would place the tile, with its 3 built in studs, in its exact position then run the current through the frame on the back which would weld the tips of the studs to the hull, then pick up the next tile and repeat.

What I am not sure about is if to weld any stud there is a minimum thickness of the electrical wire used for the welding? Would it be possible to use the metal of the frame itself as a section of such a wire?

This system would also make it easier to leave all tiling until the ship is fully stacked. Then the robot would run all over the ship in one go. It can be mounted on a frame that can move it vertically and horizontally. Rotating the ship would also help.

The point of doing the tiling last is there will be no need to glue tiles at the junctions between sections the way they must at present. That would leave gluing to the tip of the nose cone and parts of the flaps. Maybe also the perimeter of the tiling surface. (Tiles are glued between sections because there is no way the studs on one side will perfectly aligned with studs on an adjacent section.)

But it all depends on the welding of the studs when installing the tile. If that for some reason can't be done then my idea is dead in the water. The wire needed for the welding has to be narrow enough to fit between any two tiles without causing damage. An alternative is to have 3 holes on the surface of each tile that connects the wires needed to the built in studs. When they have been welded the wire would be removed as the robot arm moves off the tile. Those holes would not be much more than the gaps between tiles - maybe less. They could even be at a slight angle to reduce exposure on reentry. Robots are good at doing that kind of exact movements and accurate placement.

If SpaceX wants to produce a ship every 3 days doing tiles by hand the way they are installed today will be very hard in the long run.

[OTV Booster]

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

IIRC, we've seen a bot welding the pins but I don't think we saw in enough detail to know exactly what technique was being used - or did we?


There was something recent about laser welding but I think that was about the rings. Does anybody have a handle on this?

[OTV Booster]

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

The studs would not be welded to the tile, but be part of the frame just as the holes are now.

When it comes to removing tiles I have noted they drill holes, then use those to break the tile in pieces then they remove the frame that was holding the tile last. With the tiles I am thinking of it would only add one step - grind off 3 studs.

The system I am envisioning would also be automated but instead of just welding studs the robot arm would place the tile, with its 3 built in studs, in its exact position then run the current through the frame on the back which would weld the tips of the studs to the hull, then pick up the next tile and repeat.

What I am not sure about is if to weld any stud there is a minimum thickness of the electrical wire used for the welding? Would it be possible to use the metal of the frame itself as a section of such a wire?

This system would also make it easier to leave all tiling until the ship is fully stacked. Then the robot would run all over the ship in one go. It can be mounted on a frame that can move it vertically and horizontally. Rotating the ship would also help.

The point of doing the tiling last is there will be no need to glue tiles at the junctions between sections the way they must at present. That would leave gluing to the tip of the nose cone and parts of the flaps. Maybe also the perimeter of the tiling surface. (Tiles are glued between sections because there is no way the studs on one side will perfectly aligned with studs on an adjacent section.)

But it all depends on the welding of the studs when installing the tile. If that for some reason can't be done then my idea is dead in the water. The wire needed for the welding has to be narrow enough to fit between any two tiles without causing damage. An alternative is to have 3 holes on the surface of each tile that connects the wires needed to the built in studs. When they have been welded the wire would be removed as the robot arm moves off the tile. Those holes would not be much more than the gaps between tiles - maybe less. They could even be at a slight angle to reduce exposure on reentry. Robots are good at doing that kind of exact movements and accurate placement.

If SpaceX wants to produce a ship every 3 days doing tiles by hand the way they are installed today will be very hard in the long run.

Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.

[RamsesBic]

Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.

I know that those welding wires are thick (I have done some DIY welding), that is why I am asking those who might know more than me. But don't forget that the gaps between tiles are a few mm (I can only compare the size of the gaps on photos to those of a tile).
My alternative is to use holes in the tiles that connect directly to the studs. Their small size would be of the same order as the gaps and could easily be tested in a lab to show if they would add to the risks.

You mention replacing tiles in space. I would counter that with the cases when workers have had to use crowbars and chisels to remove tiles. Doing that in space will be a challenge to say the least.

I know that the installation of tiles has improved a great deal and am pretty sure they will do fine. But what I was looking at was how to automate and simplify the process (and reduce the number of tiles cracked during installation). SpaceX's tile experts could I am sure find better modifications. This idea I had was just one way. One I think could be used and improved on - that's all. (To SpaceX: if you use it or a variant of it give a donation to some charity)
It might sound like a complicated method, but really is not, and the benefits of removing the need to glue half the glued tiles is not negligible either.

BTW, if the robots used today welded the studs after stacking the ship they would avoid glueing all those tiles at the section junctions. Anyone who has watched the tiling knows using glue takes at least 10 times longer and is pure hell to remove. (I would hate to see an astronaut try using solvents in space to remove the glue behind a tile)

[OTV Booster]

Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.

I know that those welding wires are thick (I have done some DIY welding), that is why I am asking those who might know more than me. But don't forget that the gaps between tiles are a few mm (I can only compare the size of the gaps on photos to those of a tile).
My alternative is to use holes in the tiles that connect directly to the studs. Their small size would be of the same order as the gaps and could easily be tested in a lab to show if they would add to the risks.

You mention replacing tiles in space. I would counter that with the cases when workers have had to use crowbars and chisels to remove tiles. Doing that in space will be a challenge to say the least.

I know that the installation of tiles has improved a great deal and am pretty sure they will do fine. But what I was looking at was how to automate and simplify the process (and reduce the number of tiles cracked during installation). SpaceX's tile experts could I am sure find better modifications. This idea I had was just one way. One I think could be used and improved on - that's all. (To SpaceX: if you use it or a variant of it give a donation to some charity)
It might sound like a complicated method, but really is not, and the benefits of removing the need to glue half the glued tiles is not negligible either.

BTW, if the robots used today welded the studs after stacking the ship they would avoid glueing all those tiles at the section junctions. Anyone who has watched the tiling knows using glue takes at least 10 times longer and is pure hell to remove. (I would hate to see an astronaut try using solvents in space to remove the glue behind a tile)

Absolutely agree that the pin welding would best be done on the stacked ship. Conjecture: the current method is a SpaceX 'good enough' for current testing needs. I haven't been following closely but it appears that barrel fabrication easily outstrips stacking so they weld the pins while the barrels are waiting to stack. That'll change as the fabrication process matures.


They really need at least one launch and EDL attempt before they can have a clue on refinement or pivot to something different. Once they have a better idea of where they're going they'll refine the mounting process. We'll need to keep our eyes open for tile fabrication and installation changes following first launch. Unfortunately, the new factory will hide much (but not all) of what they do.


Your idea on welding cable holes in the tiles kicked off a thought. There has been talk of small holes to allow injection of hydrophobic chemicals. There are latches that are very robust that release easily when pressed by a thin stiff wire. This might be two birds with one stone.


Your idea for welding the pins pre installed on the tiles, is IMO, a non starter for so many reasons. Ignoring the difficulties of the cable size, think of the Y bracket and the three pins as one mostly conductive circuit. If current is applied directly to one pin there is a ground path through the pin to the hull. There is also a ground path from the pin to the Y bracket and on to the other two pins. The powered pin would weld to the hull and the Y bracket and the Y bracket would weld to the other two pins, and those pins would weld to the hull.


If the power is applied directly to the Y bracket it's essentially the same problem with the small advantage that all three pins might do a more even but still shitty weld at both ends. With so many paths and semi gaps it would be impossible to replicate conditions from one weld to the next. No replication, no consistency.


To make the problem worse, all the work is hidden and no visual inspection is possible. And because the Y bracket would be welded to the pins, tile removal would be more difficult than it is now. 


Then there is that thermal blanket underlayment. It would have to be preinstalled and the pins (bayonet clips really) designed to pierce through it with a highly reduced footprint at the contact point. That's bad for weld integrity. The blanket could have holes prepunched to allow passage of the pins with full sized bases. Making that floppy squirmy blanket line up consistently would be another can of worms. Not impossible but definitely a new set of problems.


In the end your pin concept would most likely create more problems than it fixes. It has all the hallmarks of an idea you're in love with and not to be discarded lightly. That happens here. Please, please, think about divorce. It'll be better for the children.


IANARS or a master welder. The opinions expressed above are those of the author and not NSF...

[RamsesBic]

  Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.

[john smith 19]

They really need at least one launch and EDL attempt before they can have a clue on refinement or pivot to something different. Once they have a better idea of where they're going they'll refine the mounting process.

A full flight to orbit would shake out a lot of issues.

Your idea on welding cable holes in the tiles kicked off a thought. There has been talk of small holes to allow injection of hydrophobic chemicals. There are latches that are very robust that release easily when pressed by a thin stiff wire. This might be two birds with one stone.

At the back end of the X33 programme the metal tiles were being mounted by (IIRC) 4 screws, 1 at each corner, with a superalloy cap backed by high temperature insulation. However at the very end of one of the reports there were notes about a better proposal. An adaptation of some kind of commercial tool. Very thin head that could slide between the tiles and squeeze some kind of spring that would allow the tile to come off very easily while being very light as well.

Unfortunately that's all I can remember about it.  .  IIRC the actual TPS contractor was Rohr, who are (or were) quite big in building parts of ships.

[OTV Booster]

Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.

A misconception. The holes will not close on heating. They will enlarge. This is any material. The mean space between molecules becomes greater over the entire object. All dimensions increase.


The current Y bracket, or at least the last one I remember seeing, has three slots for the clips, not holes. The tile can expand over the clips without binding and cracking. If not the Y bracket, some other mechanism is needed to allow for the expansion differences of tile and hull. Three clips without this would lead to failure, most probably of all the tiles.


I was also wondering about how they test clip welds. It may be that they did extensive testing to find the exact setting needed for a good weld and measure current draw during the weld process to point out anomalies. I'm old school enough that I always want to see my work product. Even dogs and cats do it.    This, and every other test I can think of other than imaging of some sort becomes murky through two interfaces (pin to hull and pin to Y bracket).


The thermal blanket is a, well, thermal blanket. It is a backup. TBH, I don't know if there is anything solid on this or if it's NSF lore. AIUI, it also reduces scuffing from vibration as you point out, and it is (speculated? known?) that it puts a bit of springiness behind the tile to keep the pins mechanically loaded, which sorta overlaps on the vibration thing.


Think through the idea of a patchwork thermal blanket a bit larger than a tile. Lay down tile number 1. Assume the intended gap is 5mm. Assume the extra fringe of blanket is 10mm. Lay down tile number 2. Hmm. It overlaps the fringe of tile 1 but it's fringe can only lap on top of tile 1. Ah ha! We can modify the blanket to stay flush on three faces and extend out 10mm on three faces. We now have a tile that can only go on with only one specific orientation. Bummer. It just got more complicated.


Next, picture loosing one tile. Hmmm. The blanket is pinched under three tiles and being held in place but is flapping in the breeze around half its circumference. And why exactly is this a good thing?


To my knowledge, however imperfect, I know if no time a stud was bent while pushing the blanket over them. It looks to be roughly the texture of a dense fiberglass insulation batt.


Really, honest to mergatroid,  cross my heart and pinky promise, welding the pins as you suggest would make it harder, more expensive, and more prone to breakage. Did I mention it wouldn't work?


Are you sure you aren't in love with this idea? I know a good counselor...


In a more serious vein, you're new here. I strongly suggest starting at the beginning of this thread and at least skimming through to see what the discussion has covered. It's a lot to digest but if you're here because you're curious about the topic, you will come away from your reading with a reasonable education on the general issues and the specifics of what SX has has done to address these issues. And you would be doing the rest of us a curtesy by not hammering on something that has already been hammered to death. You haven't done that last. You've hit on something new. Bravo!

[Nomadd]

 Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

[InterestedEngineer]

Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

Butane torch goes to something like 1400degC.

I don't think a mineral wool like Superwool is ablative.  That makes this stuff better than Superwool.

A super high temperature version of something like Nomex?  It can't be organic, the molecular bonds can't be made strong enough.

[RamsesBic]

Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.

A misconception. The holes will not close on heating. They will enlarge. This is any material. The mean space between molecules becomes greater over the entire object. All dimensions increase.


The current Y bracket, or at least the last one I remember seeing, has three slots for the clips, not holes. The tile can expand over the clips without binding and cracking. If not the Y bracket, some other mechanism is needed to allow for the expansion differences of tile and hull. Three clips without this would lead to failure, most probably of all the tiles.


I was also wondering about how they test clip welds. It may be that they did extensive testing to find the exact setting needed for a good weld and measure current draw during the weld process to point out anomalies. I'm old school enough that I always want to see my work product. Even dogs and cats do it.    This, and every other test I can think of other than imaging of some sort becomes murky through two interfaces (pin to hull and pin to Y bracket).


The thermal blanket is a, well, thermal blanket. It is a backup. TBH, I don't know if there is anything solid on this or if it's NSF lore. AIUI, it also reduces scuffing from vibration as you point out, and it is (speculated? known?) that it puts a bit of springiness behind the tile to keep the pins mechanically loaded, which sorta overlaps on the vibration thing.


Think through the idea of a patchwork thermal blanket a bit larger than a tile. Lay down tile number 1. Assume the intended gap is 5mm. Assume the extra fringe of blanket is 10mm. Lay down tile number 2. Hmm. It overlaps the fringe of tile 1 but it's fringe can only lap on top of tile 1. Ah ha! We can modify the blanket to stay flush on three faces and extend out 10mm on three faces. We now have a tile that can only go on with only one specific orientation. Bummer. It just got more complicated.


Next, picture loosing one tile. Hmmm. The blanket is pinched under three tiles and being held in place but is flapping in the breeze around half its circumference. And why exactly is this a good thing?


To my knowledge, however imperfect, I know if no time a stud was bent while pushing the blanket over them. It looks to be roughly the texture of a dense fiberglass insulation batt.


Really, honest to mergatroid,  cross my heart and pinky promise, welding the pins as you suggest would make it harder, more expensive, and more prone to breakage. Did I mention it wouldn't work?


Are you sure you aren't in love with this idea? I know a good counselor...


In a more serious vein, you're new here. I strongly suggest starting at the beginning of this thread and at least skimming through to see what the discussion has covered. It's a lot to digest but if you're here because you're curious about the topic, you will come away from your reading with a reasonable education on the general issues and the specifics of what SX has has done to address these issues. And you would be doing the rest of us a curtesy by not hammering on something that has already been hammered to death. You haven't done that last. You've hit on something new. Bravo!

I have been following for over 2 years. I just don't jump in that often.