Starship heat shield

[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. 

[Skyway]

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up...

Not true.

You cited these vehicles as an example before anyone else. I just answered it.

https://forum.nasaspaceflight.com/index.php?topic=50748.3140

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.

[Action]

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up...

Not true.

You cited these vehicles as an example before anyone else. I just answered it.

https://forum.nasaspaceflight.com/index.php?topic=50748.3140

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.

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.

[Skyway]

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.

Fair enough. That's ok.

[chopsticks]

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.

Huh?

 Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

[john smith 19]

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.

Which begs the question how fragile are these tiles to begin with.

The patent on which they are based suggests a 2 component design with a thickish "top hat" around a rigid ceramic foam core. This is a physically seperate part, although it's not clear if the core is formed in-situ or they are mechanically fitted together.

The Shuttle tiles also used a ceramic foam core but their skin was a very thin, fragile glass for thermal emissitivty. This could be cracked quite easily. It was also mostly on the top only. On later flights in high damage areas NASA eveloped a graded tile coating that ran more deeply into the tile itself but added weight.

My instinct is that SS tiles are substantially tougher than Shuttle era tiles. Their all-over outside coating should also make them basically waterproof. However that still leaves moisture absorption (Shuttle foam was open cell, although at least one contract bidder proposed closed cell, like a form of Autoclaved Aerated Concrete).

Wheather this water vapor is an actual threat, or evaporate harmlessly at some stage in the flight, depends on the relative sizes of several different phenomena that occure during ascent and descent.

It's not clear what their areal weight is relative to shuttle tiles. With the closing of the Shuttle TPS database you can't look the numbers up any more either. 

[edzieba]

You're thinking of TUFROC, which is not what SpaceX are using.
SpaceX's tiles (seen thus far) are the same construction as the STS tiles: silica fibres are sintered into a brick, the brick is cut down to size, a thin Borosilicate glass coating is applies to some (front and part of each side) surfaces, and the finished tile is impregnated in its initial waterproofing agent (that burns off on first exposure to high temperature).
They are not multi-part, and they do not have an all-over RCG coating.

[john smith 19]

You're thinking of TUFROC, which is not what SpaceX are using.
SpaceX's tiles (seen thus far) are the same construction as the STS tiles: silica fibres are sintered into a brick, the brick is cut down to size, a thin Borosilicate glass coating is applies to some (front and part of each side) surfaces, and the finished tile is impregnated in its initial waterproofing agent (that burns off on first exposure to high temperature).
They are not multi-part, and they do not have an all-over RCG coating.

In that case they will have the fragility of Shuttle tiles, being about 95% air and hydroscopic.

What's likely going kill turnaround time with this technology is the waterproofing, or rather the re-waterproofing, as the original stuff burnt off after one application. It was also pretty toxic and every single tile needed to be individually injected.  Great for employing lots of staff. Not so great for cost control. 

 I believe SX have found something better and TBH it should be a stage in the production process for new tiles, but something is going to have to be done about doing it after X number of landings (I'm hoping the new stuff lasts more than one landing, but I don't think anyone knows).

Ames had developed a hydrophobic transition metal coating designed to make the tiles permanently waterproof, but it was never flight tested. Operationally that would be the Holy Grail for this stuff. Waterproof-for-life.  The Applied Physics group at NASA also developed faster ways to dry the tiles and ways to form the tiles without machining  and at a larger size than the standard 6"x6" size were developed.

BTW IIRC basic Shuttle tile density was 12lb/CuFt. That's 192.63Kg M^-3. IE an SG of 0.19263 relative to water.

[AnalogMan]

From earlier in this thread:

A Density comparison between chalk and Shuttle Orbiter tiles.

Chalk 156 lb/ft³ typically (varies from ~ 112 to 168 lb/ft³)

Shuttle Orbiter tiles:

LI-900 (black tiles on underside) 9 lb/ft³
LI-2200 (black higher strength around windows & landing gear doors) 22 lb/ft³

FRCI-12 (improved tiles to replace some LI tiles) 12 lb/ft³

LRSI-9  (white tiles on upper surfaces) 9 lb/ft³
LRSI-12 (white tiles on upper surfaces) 12 lb/ft³

BRI-18 (strongest & toughest tile produced, replacement for critical areas)  18 lb/ft³

Water 62.4 lb/ft³
Styrofoam packaging and insulation typically 1 to 2 lb/ft³

Conversion to metric:

1 lb/ft³ is equivalent to 0.016 g/cm³ or 16.0 kg/m³

[Action]

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.

Fair enough. That's ok.

Thank you.

[Action]

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.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

[livingjw]

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.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

[Action]

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.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

A capsule shape on top of a regular super heavy seems like the obvious alternative.  I believe Stoke Space Technologies is proposing something vaguely like it.

It would not have the same cross-range and it would have moderately higher-g reentry, if you feel those things are very important.  The trade would be that you get better structural mass fraction, easier reentry more amenable to tougher heatshield solutions, and no mode switch on landing.

[schuttle89]

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.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

A capsule shape on top of a regular super heavy seems like the obvious alternative.  I believe Stoke Space Technologies is proposing something vaguely like it.

It would not have the same cross-range and it would have moderately higher-g reentry, if you feel those things are very important.  The trade would be that you get better structural mass fraction, easier reentry more amenable to tougher heatshield solutions, and no mode switch on landing.

The goal is landing on Mars and Earth with the same second stage. I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)

[edzieba]

Very early ('Big Falcon Rocket' era) Starship designs were essentially scaled up Dragons utilising supersonic retropropulsion to expand the bow shock (works with canted-out engines, direct firing ones disrupt the shock) as Red Dragon was intended to demonstrate. Part of what killed Red Dragon was that the Starship design changed to sideways entry with aerodynamic lifting, so that demo mission became internally redundant.

[john smith 19]

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

Well lifting capsule designs IE with offset Cg, like Apollo managed 0.3. I think up to 0.5 is viable, but it gets tough about that.

I think people's intuition about entry is quite badly skewed by seeing the final stages of the Shuttle landings. Most of Shuttle's decelleration took place (IIRC) around 46deg to the airflow. This is very high AoA compared to normal aircraft's level flight (IIRC standard commercial airline climb out is about 7deg) and SS is going to come in at about 70deg?

These are the sort of attitudes you see combat aircraft do at air shows when they want to show off their vectoring engine nozzles.    People see these displays and ask "How can an aircraft stay in the air like that?"

[Action]

I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)

In addition to the Dragon-based proposals, I think Gary Hudson proposed a system based on Phoenix to do that.

[livingjw]

I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)

In addition to the Dragon-based proposals, I think Gary Hudson proposed a system based on Phoenix to do that.

Phoenix? What is that? Do you have a reference?

John

[Action]

Phoenix? What is that? Do you have a reference?

John

Phoenix was Hudson's name for a family of SSTO proposals, all of which were Bono-style big-capsule shapes, though they were small by the standards of SSTO proposals.

I can't find a free copy of the paper about using it for Mars, but the citation is: HUDSON, GARY. "Employing a chemical rocket VTOVL SSTO for high velocity Mars round trip travel." 24th Joint Propulsion Conference. 1988.

[livingjw]

Phoenix? What is that? Do you have a reference?

John

Phoenix was Hudson's name for a family of SSTO proposals, all of which were Bono-style big-capsule shapes, though they were small by the standards of SSTO proposals.

I can't find a free copy of the paper about using it for Mars, but the citation is: HUDSON, GARY. "Employing a chemical rocket VTOVL SSTO for high velocity Mars round trip travel." 24th Joint Propulsion Conference. 1988.

- Found the Phoenix papers. Gumdrop/capsule approach doesn't scale well for large, heavy, low ballistic coefficient vehicles. In order to handle the heating with known TPS you will need Shuttle, or lower, ballistic coefficient. To manage g's and atmospheric variations you will need the ability to generate an L/D of 0.5-1.0. A capsule shaped Starship design would need a diameter of ~26m to match Starship's sideways approach. Not very good for ascent aerodynamics.

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John