Starship heat shield

[Action]

and not a fatal problem with careful engineering.

That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.

[Hog]

and not a fatal problem with careful engineering.

That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.

Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.

[chopsticks]

and not a fatal problem with careful engineering.

That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.

Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.

He's not wrong.

[john smith 19]

Ya, a chunk the " heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.

Always you must watch the assumptions. 

Had that foam hit the RCC at the RCC's design operating temperature a) the foam would be a squidgy fluid lump b) The RCC would not have been brittle. One of RCC's much launded properties is how it gets stronger as it gets hotter (provided of course there's no O2 about, or the oxidation resistant skin is intact)

Instead the fairly brittle RCC (at near room temperature) got hit by a lump of rigid foam at about (IIRC) M2. The old story about the wood splinters found buried in the side of an armoured car after a hurricane comes to mind.

WRT to this thread that event chain cannot happen.

The question becomes what could damage the SS TPS, and what standards does it need to be made to reduce turbulence issues?

[Action]

and not a fatal problem with careful engineering.

That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.

Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.

I didn't mean to be cheering for the Shuttle solution.  There were several large problems with their approach.  I just meant to say it wasn't fragile tiles or turbulent flow that got them, it was having a large TPS acreage exposed on the way up where stuff could fall on it.

Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.

[john smith 19]

I didn't mean to be cheering for the Shuttle solution.  There were several large problems with their approach.  I just meant to say it wasn't fragile tiles or turbulent flow that got them, it was having a large TPS acreage exposed on the way up where stuff could fall on it.

Actually it was fragile tile and turbulent flow. RCC panels were only on the wing leading edge and nose. Everything else were either various kinds of blanket topside, or tiles bottom side. But all of them were backed by the skin, which would have given them some "bounce." The wing leading edge had nothing behind it. . If it had it (arguably) would have survived the impact. That cavity acted as a trap for very high speed airflow. The rest is history.

Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.

Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

Of course on orbit it's a different story...
 This is where having a standard shaped tile (or at least a very restricted number of different types) makes on-orbit repair possible.

[Action]

Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.

Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]

[john smith 19]

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]

Practically that only works if the heatshield is underneath the vehicle, like a Bono plug nozzle design. Wrapping the whole S2 in a shroud strong enough to avoid damage is going to add a lot of mass to S2 and probably make slying off a failed S1 impossible. 

IRL in the 3rd decade of the 21st century SS will have Vehicle Health Monitoring sensors to continuously monitor tank pressure and temperature (puncture shows as falling pressure. Tile damage should show as hot spot boiling off too much propellant), probably as part of a suite of skin monitors, or some kind of deployable boom.

The Shuttle programme developed a bunch of concepts for this, most of which were never used, but they do exist and have been discussed.

I'd like to remind people of Mary Shafer's words. Mary was a Flight Engineer at NASA Dryden during a lot of test flying programmes. Every one was flown by a top class pilot after extensive preparation but there was casualty rate of about one pilot death a year throughout the 1950's. Her comment was "Insisting on perfect safety is for people who don't have the balls to live in the real world."

Everything has a level of risk. Normally this is a subject only actuaries concern themselves with. Some of those risks can be reduced, some cannot. Going to orbit, for a long time to come is going to be substantially more risky than taking a commercial airline flight or similar scheduled transport.

[Skyway]

I'd like to remind people of Mary Shafer's words. Mary was a Flight Engineer at NASA Dryden during a lot of test flying programmes. Every one was flown by a top class pilot after extensive preparation but there was casualty rate of about one pilot death a year throughout the 1950's. Her comment was "Insisting on perfect safety is for people who don't have the balls to live in the real world."

Everything has a level of risk. Normally this is a subject only actuaries concern themselves with. Some of those risks can be reduced, some cannot. Going to orbit, for a long time to come is going to be substantially more risky than taking a commercial airline flight or similar scheduled transport.

Thanks for the collaboration and just to try to clarify the matter, I must say that Safety is not the same today as it was in the 50s. Today such a sentence sounds like complete nonsense, due to the current stage of maturity of the concept.

There is a balance point, and it is not constant. And precisely because it is not constant, the search for Safety is uninterrupted, always leading to endless changes in systems, procedures, and training throughout the operation.

I agree with the meaning of what you said. The tendency of many people to want to "manage" a risk using the most radical and guaranteeing measure possible is utopian and therefore does not exist in reality.

Risks exist, but they are managed. I only disagree with the way in which the statement that some risks cannot be reduced was made. It makes it appear that risks that cannot be reduced are simply accepted, which is not the case if the score for the probability X severity ratio for that risk is high.

If a risk scores high in this ratio and it cannot be reduced, then the operation does not continue. And this is true as far as SpaceX and especially NASA are concerned.

As for mitigating the risk of tile loss during take-off, it doesn't have to be radical. A vehicle airworthiness reliability study in the event of such a system failure to a greater extent than is regularly experienced on flights would already manage this risk. A system such as the aforementioned vehicle health monitoring system that would abort takeoff when detecting this type of occurrence would be suitable as well. In-orbit repair measures... various possibilities that do not involve adding weight to the vehicle.

[Skyway]

Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.

Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]

The thermal protection of the Dragon capsule is at the bottom for the sake of aerodynamic design.

The capsule was designed in that way, taking into account its use as the "nose" of the rocket on the way up, but mainly to have better balance (control) and less exposure of the capsule body during re-entry. Therefore, the thermal protection is in the "fit" with the trunk.

It doesn't stay there to be protected along the way up. This is a good consequence of other requirements. And it is also a fact that the edge of the thermal protection is exposed, and damage there would potentially cause many controllability problems during re-entry.

Wanting to protect the thermal protection during ascent is the same as putting grilles on the air intake of commercial aircraft engines. It's a very exaggerated measure compared to the probability of significant damage, and it ends up adding other failure modules that were previously non-existent.

In addition to being an immense effort focused on just one of the vehicle's operational risks, in an ocean of so many others as or more severe and/or probable.

Risk is managed surgically, not with a sledgehammer.

EDIT: Just to add that I'm talking about Dragon's heat shield. The Capsule has thermal protection on its body as well.

[Action]

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]

Practically that only works if the heatshield is underneath the vehicle, like a Bono plug nozzle design. Wrapping the whole S2 in a shroud strong enough to avoid damage is going to add a lot of mass to S2 and probably make slying off a failed S1 impossible. 

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.

[john smith 19]

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

This is the dictionary use of "stage," not the common one, IE a stage that is required to deliver substantial velocity to get to orbit. Neither of your examples does so. They are basically passive payloads during ascent. You might like to consider how they would work if they carry crew and there is an emergancy. What happens then?

For an actual example in this context you would be looking at versions of the Centaur, that used an extended payload fairing to protect the boiloff insulation on the LH2 tank during ascent.

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.

Then that would not be the design SX is going with. It would be a totally different vehicle.

[Skyway]

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

The Soyuz is also a spacecraft that is launched inside a fairing, but it is not for the protection of any heat shield. It's simply because it was also thought of as payload, even with humans inside.

Is it possible to cover a stage with a fairing? Yes, it is possible. But is it beneficial? In the case of Starship, no.

Simply because there isn't a problem in Starship that requires this kind of solution.

[Action]

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.

Then that would not be the design SX is going with. It would be a totally different vehicle.

Yes, of course.  Well, not totally different - the same engines and the same basic structure in a different shape. 

I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

I mostly agree that shrouding the second stage somehow is probably not the best idea.

[Action]

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

That makes no difference to the argument.  They're sideways reentering vehicles with fragile heat shield technology, just like Starship.  So they go up protected.

[Skyway]

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

That makes no difference to the argument.  They're sideways reentering vehicles with fragile heat shield technology, just like Starship.  So they go up protected.

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

A risk is created of something colliding with the thermal shield where there was no such risk before, to protect that thermal shield from collisions.

OK.

[Action]

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]

[eriblo]

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]

How is enclosing an almost optimally bullet shaped spacecraft (that has to withstand atmospheric reentry) with a larger fairing going be an improvement?

[Skyway]

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]

The point is that you are claiming these vehicles are launch inside fairings also to protect their thermal protection systems. This statement is not consistent with reality.

What if I told you that the fairing has nothing to do with the thermal protection systems of these vehicles?

What if I told you that the vehicle you use as a basis for comparison (X-20) was a 5-ton, 6-meter-wide vehicle and that it didn't have a fairing big enough in the 60's to take it inside?

It's all about aerodynamic load. The relation between lift, drag, laminar flow, turbulent flow, and attachment points. Also, the impact of those things on the rocket's performance is huge.

[Action]

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]

How is enclosing an almost optimally bullet shaped spacecraft (that has to withstand atmospheric reentry) with a larger fairing going be an improvement?

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up.  That's not a relevant benefit for Starship, or at least it's a pretty minor benefit.

I've also been clear in stating I think this is an inferior option.  It is though, for completeness, another way of protecting a fragile side-mount heat shield.