Idea for an Ablative heat Shield System on Starship

[Kassander]

Addressing the Limitations of Thermal Protection Systems in Reusable Spacecraft: A Concept for an Ablative Shield with Integrated Air Pockets and Automated Repair

The thermal protection system (TPS) has long been a critical factor in the design and operation of reusable spacecraft. The Space Shuttle, despite its pioneering role in reusable spaceflight, suffered significant challenges due to the complexity and maintenance demands of its heat shield tiles. These tiles, which protected the Shuttle from the intense heat of atmospheric reentry, were individually fragile, required precise positioning, and were highly susceptible to damage. Over time, the cost and labor-intensive process of inspecting and replacing these tiles after each flight became a major contributor to the Shuttle's unsustainable operational expenses. This limitation, among other factors, contributed to the Shuttle’s eventual retirement.

SpaceX’s Starship, which is intended to be fully reusable, faces a similar challenge. Currently, it employs a heat shield based on ceramic tiles, but this system shares some of the same vulnerabilities as the Shuttle. While the technology has advanced, the core issue remains: to ensure reliable thermal protection while reducing the need for costly and time-consuming manual maintenance.

In light of these challenges, I propose an alternative: an ablative heat shield system featuring air pockets formed within a hexagonal honeycomb structure and an automated maintenance process utilizing robotic arms equipped with 3D printing technology. The following graphic was created by ChatGPT and is probably more suitable for entertainment than a serious graphic representation 😁. But it should be enough to get an idea of what the whole thing should look like:

The Concept

1. Use of Air Pockets for Material and Weight Efficiency: The key innovation in this design is the incorporation of a raised hexagonal honeycomb structure on the surface of the spacecraft, where the hexagonal walls stand perpendicular to the surface, forming air pockets inside each cell. These air pockets act as thermal insulation during reentry, reducing the amount of heat that reaches the underlying spacecraft structure. By leveraging the insulating properties of trapped air, it may be possible to reduce the amount of ablative material needed, thereby saving weight while maintaining effective thermal protection. The hexagonal walls themselves would slowly ablate during reentry, gradually wearing away while protecting the spacecraft, and would be replaced as needed after each mission.

2. Automated Maintenance with Robotic Arms and 3D Printing: Another crucial aspect of this concept is the potential use of robotic arms equipped with 3D printing capabilities to automate the repair process. In this system, robotic arms would scan the surface of the spacecraft post-mission, detecting areas where the honeycomb structure has worn down or where air pockets have been compromised. The idea is that these robotic systems could then use 3D printing to deposit new layers of aluminum or other materials to restore the honeycomb structure. However, it is important to note that while robotic arms with 3D printing capabilities are becoming increasingly sophisticated, the feasibility of this concept in the context of high-precision repairs for spacecraft TPS systems is still speculative. Currently, 3D printing with metals in terrestrial environments is possible, but adapting this technology to meet the specific demands of spacecraft reusability, precision, and thermal stress would require further development. Therefore, this concept is more of a proposal for further investigation rather than a proven solution.

Seeking Feedback from the Scientific Community

While this concept offers clear potential advantages, particularly in terms of weight reduction and automated maintenance, it remains speculative at this stage. I am presenting this idea to initiate a discussion and to invite the expertise of this community. I would greatly appreciate feedback on the following aspects:

• Thermal effectiveness: How effective would air pockets within the honeycomb structure be in insulating the spacecraft compared to traditional materials? Could this provide sufficient protection in the extreme conditions of atmospheric reentry?
• Structural integrity: The honeycomb walls must withstand both aerodynamic forces and extreme heat. Would a system like this remain structurally sound under such conditions, or are there potential failure points?
• Ablative material selection: Is aluminum a viable material for this purpose, or would another material be better suited for a system that needs to balance ablation with heat insulation?
• Robotic repair feasibility: Is it technically feasible to develop robotic arms with the precision needed to detect and repair damaged sections of the heat shield on Earth using 3D printing? What challenges could arise in implementing such a system in terms of material deposition, accuracy, or durability?

 

Thank you for your time and input!

[exchemist]

17 minutes ago, Kassander said:

Addressing the Limitations of Thermal Protection Systems in Reusable Spacecraft: A Concept for an Ablative Shield with Integrated Air Pockets and Automated Repair

The thermal protection system (TPS) has long been a critical factor in the design and operation of reusable spacecraft. The Space Shuttle, despite its pioneering role in reusable spaceflight, suffered significant challenges due to the complexity and maintenance demands of its heat shield tiles. These tiles, which protected the Shuttle from the intense heat of atmospheric reentry, were individually fragile, required precise positioning, and were highly susceptible to damage. Over time, the cost and labor-intensive process of inspecting and replacing these tiles after each flight became a major contributor to the Shuttle's unsustainable operational expenses. This limitation, among other factors, contributed to the Shuttle’s eventual retirement.

SpaceX’s Starship, which is intended to be fully reusable, faces a similar challenge. Currently, it employs a heat shield based on ceramic tiles, but this system shares some of the same vulnerabilities as the Shuttle. While the technology has advanced, the core issue remains: to ensure reliable thermal protection while reducing the need for costly and time-consuming manual maintenance.

In light of these challenges, I propose an alternative: an ablative heat shield system featuring air pockets formed within a hexagonal honeycomb structure and an automated maintenance process utilizing robotic arms equipped with 3D printing technology. The following graphic was created by ChatGPT and is probably more suitable for entertainment than a serious graphic representation 😁. But it should be enough to get an idea of what the whole thing should look like:

The Concept

1. Use of Air Pockets for Material and Weight Efficiency: The key innovation in this design is the incorporation of a raised hexagonal honeycomb structure on the surface of the spacecraft, where the hexagonal walls stand perpendicular to the surface, forming air pockets inside each cell. These air pockets act as thermal insulation during reentry, reducing the amount of heat that reaches the underlying spacecraft structure. By leveraging the insulating properties of trapped air, it may be possible to reduce the amount of ablative material needed, thereby saving weight while maintaining effective thermal protection. The hexagonal walls themselves would slowly ablate during reentry, gradually wearing away while protecting the spacecraft, and would be replaced as needed after each mission.

2. Automated Maintenance with Robotic Arms and 3D Printing: Another crucial aspect of this concept is the potential use of robotic arms equipped with 3D printing capabilities to automate the repair process. In this system, robotic arms would scan the surface of the spacecraft post-mission, detecting areas where the honeycomb structure has worn down or where air pockets have been compromised. The idea is that these robotic systems could then use 3D printing to deposit new layers of aluminum or other materials to restore the honeycomb structure. However, it is important to note that while robotic arms with 3D printing capabilities are becoming increasingly sophisticated, the feasibility of this concept in the context of high-precision repairs for spacecraft TPS systems is still speculative. Currently, 3D printing with metals in terrestrial environments is possible, but adapting this technology to meet the specific demands of spacecraft reusability, precision, and thermal stress would require further development. Therefore, this concept is more of a proposal for further investigation rather than a proven solution.

Seeking Feedback from the Scientific Community

While this concept offers clear potential advantages, particularly in terms of weight reduction and automated maintenance, it remains speculative at this stage. I am presenting this idea to initiate a discussion and to invite the expertise of this community. I would greatly appreciate feedback on the following aspects:

• Thermal effectiveness: How effective would air pockets within the honeycomb structure be in insulating the spacecraft compared to traditional materials? Could this provide sufficient protection in the extreme conditions of atmospheric reentry?
• Structural integrity: The honeycomb walls must withstand both aerodynamic forces and extreme heat. Would a system like this remain structurally sound under such conditions, or are there potential failure points?
• Ablative material selection: Is aluminum a viable material for this purpose, or would another material be better suited for a system that needs to balance ablation with heat insulation?
• Robotic repair feasibility: Is it technically feasible to develop robotic arms with the precision needed to detect and repair damaged sections of the heat shield on Earth using 3D printing? What challenges could arise in implementing such a system in terms of material deposition, accuracy, or durability?

 

Thank you for your time and input!

Why would it be less laborious to replace this proposed ablative surface than to replace thermal tiles?

[Kassander]

6 minutes ago, exchemist said:

Why would it be less laborious to replace this proposed ablative surface than to replace thermal tiles?

It would take less work to replace this system if it could be done with 3D printing. Alternatively, it could probably be manufactured and anchored in individual parts. This should still be more efficient than the heat protection tiles. Spacex itself is currently looking for an ablative system for heat protection. As mentioned at the beginning, the Space Shuttle failed because of these tiles. Each individual tile has an individual shape adapted to the hull. Furthermore, they are very sensitive and expensive.

[exchemist]

5 minutes ago, Kassander said:

It would take less work to replace this system if it could be done with 3D printing. Alternatively, it could probably be manufactured and anchored in individual parts. This should still be more efficient than the heat protection tiles. Spacex itself is currently looking for an ablative system for heat protection. As mentioned at the beginning, the Space Shuttle failed because of these tiles. Each individual tile has an individual shape adapted to the hull. Furthermore, they are very sensitive and expensive.

So 3D printing is the key feature. I see.

What material would it be made of then, that can be 3D printed (I assume ceramic tiles cannot be)? 

[Kassander]

5 minutes ago, exchemist said:

So 3D printing is the key feature. I see.

What material would it be made of then, that can be 3D printed (I assume ceramic tiles cannot be)? 

The material is still an open question. Aluminium would be a possibility. It is light, relatively durable and heat-resistant. It is also suitable for 3D printing. But there might be better materials. Therefore, the question of a more suitable material is one of the 4 questions that I formulated at the end.

[exchemist]

2 hours ago, Kassander said:

The material is still an open question. Aluminium would be a possibility. It is light, relatively durable and heat-resistant. It is also suitable for 3D printing. But there might be better materials. Therefore, the question of a more suitable material is one of the 4 questions that I formulated at the end.

Al will be a hopeless choice: it melts at 660C. Also, being a metal it conducts heat!

You will need something far more refractory that is also a good insulator (e.g. even tungsten won't do).  I know nothing about 3D printing but I fear your idea may come to grief on this point, if you can't find a high melting point insulator that can be worked by your 3D printer. 

[Kassander]

3 minutes ago, exchemist said:

Al will be a hopeless choice: it melts at 660C. Also, being a metal it conducts heat!

You will need something far more refractory that is also a good insulator (e.g. even tungsten won't do).  I know nothing about 3D printing but I fear your idea may come to grief on this point, if you can't find a high melting point insulator that can be worked by your 3D printer. 

Thanks, I remembered that completely wrong. I thought the melting point was over 2000°. But you are right it is at 660.3°. However, since it dissipates heat again through ablation, it could still be suitable. It is supposed to partially evaporate to dissipate heat. The additional layer of insulation is an important point. I forgot to mention this in the description of my concept, but of course it would be necessary to apply an insulating layer in between.

[exchemist]

3 minutes ago, Kassander said:

Thanks, I remembered that completely wrong. I thought the melting point was over 2000°. But you are right it is at 660.3°. However, since it dissipates heat again through ablation, it could still be suitable. It is supposed to partially evaporate to dissipate heat. The additional layer of insulation is an important point. I forgot to mention this in the description of my concept, but of course it would be necessary to apply an insulating layer in between.

Graphite is often used, as it conducts heat well only along the plane of the structure and has a very high sublimation point (it doesn't melt), over 3,000C. Something that melts at 660C will lose mechanical strength well before then and will just disappear. I really think you need to work harder on this aspect. 

[Kassander]

6 minutes ago, exchemist said:

Graphite is often used, as it conducts heat well only along the plane of the structure and has a very high sublimation point (it doesn't melt), over 3,000C. Something that melts at 660C will lose mechanical strength well before then and will just disappear. I really think you need to work harder on this aspect. 

True, but steel could work. The melting point of steel is around 1500°. It is heavier but also more stable. So less material would be needed. In the end one have to calculate it. The heat should remain below 1500° when re-entering. Since heat is dissipated through melting it could be enough, but without the ability to calculate this it remains an estimate.

Here is a somewhat more realistic picture of what such a structure can look like. It probably shouldn't be a honeycomb structure due to the aerodynamics at take-off. This shape is also better suited to forming air pockets upon re-entry. The grey lines on the bottom are intended to symbolize the printed metal lines. Of course, the size of the lines and air pockets is not realistic and would have to be calculated precisely. This graphic is only intended to give a better idea.

[TheVat]

5 hours ago, Kassander said:

Ablative material selection: Is aluminum a viable material for this purpose, or would another material be better suited for a system that needs to balance ablation with heat insulation?

Aluminum melts at 660 C.  Would melt faster than a kid's ice cream cone at the Arizona state fair.

 

PLEASE DELETE ACCIDENTALLY DUPLICATED POST ALREADY ANSWERED THIS

Edited October 14 by TheVat

[exchemist]

3 hours ago, Kassander said:

True, but steel could work. The melting point of steel is around 1500°. It is heavier but also more stable. So less material would be needed. In the end one have to calculate it. The heat should remain below 1500° when re-entering. Since heat is dissipated through melting it could be enough, but without the ability to calculate this it remains an estimate.

Here is a somewhat more realistic picture of what such a structure can look like. It probably shouldn't be a honeycomb structure due to the aerodynamics at take-off. This shape is also better suited to forming air pockets upon re-entry. The grey lines on the bottom are intended to symbolize the printed metal lines. Of course, the size of the lines and air pockets is not realistic and would have to be calculated precisely. This graphic is only intended to give a better idea.

 

According to the attached NASA slideshow, temperatures reach 1700C for slower, "flying" type re-entry, but hotter for capsules that make a "ballistic" re-entry.  

It's quite interesting for you to read. They have, not surprisingly, given quite a bit of thought to this topic.

daryabeigi-NMS talk-2c.pdf

Edited October 14 by exchemist

[Kassander]

48 minutes ago, exchemist said:

According to the attached NASA slideshow, temperatures reach 1700C for slower, "flying" type re-entry, but hotter for capsules that make a "ballistic" re-entry.  

It's quite interesting for you to read. They have, not surprisingly, given quite a bit of thought to this topic.

daryabeigi-NMS talk-2c.pdf 1.92 MB · 2 downloads

This is extremely helpful. Thank you! I'll definitely go through this carefully. However, the Starship appears to have a maximum temperature of 2600 degrees Fahrenheit or 1430 degrees Celsius during re-entry. At least that's what it says in the following link:

https://www.ndtv.com/world-news/watch-spacex-starship-stunning-return-to-earth-moments-before-it-was-lost-5242748

[exchemist]

22 minutes ago, Kassander said:

This is extremely helpful. Thank you! I'll definitely go through this carefully. However, the Starship appears to have a maximum temperature of 2600 degrees Fahrenheit or 1430 degrees Celsius during re-entry. At least that's what it says in the following link:

https://www.ndtv.com/world-news/watch-spacex-starship-stunning-return-to-earth-moments-before-it-was-lost-5242748

You don’t want to use a material that is within 100C deg of its melting point. It will have lost all its strength. And steel,  being a metal, is a conductor of heat, which would be catastrophic. Anyway, have a read. There’s quite some discussion of the options for various materials and the challenges involved.

[Kassander]

20 minutes ago, exchemist said:

You don’t want to use a material that is within 100C deg of its melting point. It will have lost all its strength. And steel,  being a metal, is a conductor of heat, which would be catastrophic. Anyway, have a read. There’s quite some discussion of the options for various materials and the challenges involved.

The forces acting on this structure are not as great as many seem to think. It only serves to form the Air Pockets. The previous heat protection tiles are also very sensitive and are usually not destroyed when they are re-entered. It was already clear during the test joints that the Starshipt's fins had been unprotected for a long time and although they were particularly exposed to heat and pressure, they did not break off. This means that the Air Pockets walls would hardly break off even if they were heated to well over 1000°. In addition, the aplation dissipates heat, i.e. the structure is cooled.

There is another effect that should provide cooling that I haven't mentioned yet. The Air Pockets will slowly but consistently release relatively cool air. This has 2 reasons.

Firstly, the walls of the running Pockets are slowly worn away. This means that less air can bind there and thus the Air Pockets themselves are removed along with the walls of the air cushions. This results in a constant flow of relatively cold air around the Starship's hull. A positive side effect is that the walls of the Air Pockets are removed so evenly. If the erosion were stronger in one place, most of the cool air would flow out of the air cushion there. This would mean that very little would be removed there until the level equalizes again. Conversely, a lot is removed where previously little was removed because this area protrudes and is particularly exposed. The removal is therefore self-regulating and occurs evenly.

The second reason why relatively cool air is constantly released from the Air Pockets is that this air also warms up slowly. This increases their volume, which leads to the Air Pockets “overflowing”. It's like slowly heating a glass of water that's filled to the brim and it then overflows. This overflow also leads to a thin but constant flow of cold air around the Starship, which should also keep the temperature down.