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It's fantastic that the Super Heavy booster fully completed it's mission! Much bigger deal than the ship itself failing. Before that last flight it seemed like

It's fantastic that the Super Heavy booster fully completed it's mission! Much bigger deal than the ship itself failing. Before that last flight it seemed like engine reliability wouldn't get solved. But now they have a clear path to orbit. I doubt the heat shields will hold up on the first several re-entry attempts but there's been recent sightings of a new heat shield that has tiles about half the size. Maybe smaller tiles will have less lever action and will have 4x the fasteners.

ramesh31 3y ago
>Maybe smaller tiles will have less lever action and will have 4x the fasteners. This is still the number one problem with Starship. There were all these wild claims of an exotic new liquid cooled reentry system at the beginning. But because physics they ended up going right back to using ablative. They'll suffer the same fate as the shuttle for it. Nothing has fundamentally changed in ceramic or adhesive technology since then, and the lack of aerodynamic control means they will have to survive even steeper descents with greater thermal load. I imagine the idea of Starship as an earth return vehicle in general will probably be abandoned, so they can optimize it for interplanetary transport and lunar operations.
- tekla 3y ago
  Of course the problem with this post is that the Starship heat shield isn't ablative, nor does it share the problems with the Orbiter heat shield (Needing glue to attach every single unique tile to the body of the ship.) > the lack of aerodynamic control There are literally wings on the ship.
  - ta1243 3y ago
    I had to read it twice as I saw "lack of aerodynamic control" and assumed they meant the Shuttle, which was about as aerodynamic as a squirrel
    - lstodd 3y ago
      Well in fact at about 4:1 glide ratio subsonic it was much better than Siberian Flying Squirrels which are usually about 1.5. https://en.wikipedia.org/wiki/Siberian_flying_squirrel https://en.wikipedia.org/wiki/Siberian_flying_squirrel
  - ramesh31 3y ago
    >Starship heat shield isn't ablative Yes, it is. There is no such thing as a non-ablative reentry vehicle. The tiles are effectively no different than what was used on the shuttle. >There are literally wings on the ship. Starship has no meaningful aerodynamic control beyond what is required to perform the flip. It has no ailerons or elevators. It falls to the earth in a completely ballistic trajectory.
    - danbruc 3y ago
      Insulating tiles are not an ablative heat shield, they are a thermal soak heat shield. Ablative heat shields are non-reusable as they work by slowly burning off material which creates a cooler boundary layer between the plasma and the heat shield. [1] [1] https://en.wikipedia.org/wiki/Heat_shield#Spacecraft https://en.wikipedia.org/wiki/Heat_shield#Spacecraft
      - rpmisms 3y ago
        Ablation will still happen, but the tiles aren't designed to ablate as the primary method of heat dissipation.
        danbruc 3y ago
        Sure, everything going through the atmosphere at supersonic speeds will lose at the very least a couple of atoms here and there, but that was not the point and that does not make thermal protection tiles an ablative heat shield.
        avmich 3y ago
        Let's remember definitions. Thermal soak heat protection: the protective material absorbs - soaks - the heat, becomes really hot, and after the process need to dissipate the heat. Also - which is important - the heat capacity of the material should be enough to absorb the whole heat flux going into it. Also - thermal conductivity of this protection should be such that the protected material behind it won't get too much heat. For this kind of protection to work you want small temperature differentials - less heat flux - and small time of heating - otherwise the material will become too hot. However - as materials have varying thermal conductivity - the thermal soak is always present to some degree. Radiative protection: the protective material heats up so much it stops accepting more heat, because it radiates heat back with the same speed. After the process the surface of this material is really hot. Important requirement - low thermal conductivity, as the high temperature on the surface shouldn't get behind the protective layer. Also known as refractory protection. Space Shuttle thermal protection is an example. Ablative protection: the surface of the protective material releases its material in the form of gases, and this gasification process cools down the material. The material gets consumed, that's the main problem with this cooling approach - neither big thermal capacity nor small thermal conductivity are needed. Early Merlin engines used ablative cooling. According to Wikipedia, SpaceX uses ablative protection for Crew Dragon - https://en.wikipedia.org/wiki/Atmospheric_entry#Thermal_protection_systems https://en.wikipedia.org/wiki/Atmospheric_entry#Thermal_prot... - "A second enhanced version of PICA—called PICA-3—was developed by SpaceX during the mid-2010s. It was first flight tested on the Crew Dragon spacecraft in 2019 during the flight demonstration mission, in April 2019, and put into regular service on that spacecraft in 2020." . Also from Wikipedia, tiles of Starship are made of silica - https://en.wikipedia.org/wiki/Starship_rocket#Starship_spacecraft https://en.wikipedia.org/wiki/Starship_rocket#Starship_space... - "Starship's heat shield, composed of eighteen thousand[131][132] hexagonal black tiles that can withstand temperatures of 1,400 °C (2,600 °F),[133][134] is designed to protect the vehicle during atmospheric entry and be used multiple times with minimal maintenance between flights.[135] The tiles are made of silica[136] and are attached with pins rather than glued,[134] with small gaps in between to allow for heat expansion.[2]" which makes them a kind of radiative or refractory protection.
- deleted 3y ago
  [deleted]
- idontwantthis 3y ago
  Neither the space shuttle nor Starship use ablative heat shield tiles.
  - ramesh31 3y ago
    >Neither the space shuttle nor Starship use ablative heat shield tiles. They are effectively ablative in the sense that neither vehicle has (or will) be able to complete successive missions without massive replacement of damaged and missing tiles. The fundamental approach is not suitable to reusability, as we learned with the shuttle.
    - idontwantthis 3y ago
      You might end up right but that’s still not what ablative means.
    - timschmidt 3y ago
      Shuttle tiles were unique, and glued in place. Starship tiles are mostly identical, and secured with steel spring pins.
    - tekla 3y ago
      The heat shield is not ablative. You are simply wrong.
    - 0xfae 3y ago
      What you are doing is effectively mental gymnastics to avoid admitting you used the incorrect word.
      - plorg 3y ago
        That could be because there are a dozen replies fixated on the use of the wrong word and maybe one that responds to the substance of the comment.
    - panick21_ 3y ago
      First of all, that's not what ablative means. Tiles potentially falling of does not make the heat shield ablative. Because tiles falling off is not a the heat transfer mechanism, rather a mechanical failure. The Dragon Capsule for example has an Ablative Heat-Shield. But that doesn't necessarily mean it can't do multiple missions in a row. It just depends on how the shield is designed. The Dragon could potentially do many earth missions without replacing the heat shield. Second, you are wrong in that there is anything fundamental about Starship or Shuttle heat shield not being able to fly multiple missions. If the tiles are still attached and not damaged, then all that has to happen is for the tiles to cool down. After that they are ready for another flight, meaning the tiles are not ablative. Now experience on Shuttle has shown that if you are not careful tiles could fall of or be damaged. Damage can be reduced in various was and Starship without an external tank is already much better by design. Additionally Shuttle had to glue tiles to a fragile aluminum frame making the installation very hard and the tiles very fragile. Starship on the other hand uses welded studs on a steel frame. So even if a tile is lots, the steel should still hold up pretty well. In on case Shuttle was saved because there just so happened to be steel under a damaged tile. So you are right, heat shield is one of the biggest issue that could cause problems with rapid reputability. You are wrong, the tiles are not ablative cooled. But Starship tiles are totally different then Shuttles, they have made many improvements in the heat shield and its construction and in the heat shield tiles themselves. Starship can likely survive even with a number of missing tiles if required. In some position tile lose can certainty be fatal.
- p1mrx 3y ago
  > I imagine the idea of Starship as an earth return vehicle in general will probably be abandoned, so they can optimize it for interplanetary transport and lunar operations. Starship will need several launches of methane+oxygen to travel beyond LEO. That model requires a reusable orbital tanker to make sense economically.
  - imtringued 3y ago
    Most of the engines are on the booster. The upper stage is the cheapest part of the entire rocket. At a worst case of 2 million per engine you're talking about 66 million dollars for the booster. I honestly don't understand this whole post chain. The booster needs to survive because it is the most valuable part of the rocket and yet we are supposed to praise it for exploding? The hot staging concept isn't viable over the long term because it goes counter to the goals of reusability. I don't need people to rewrite history by claiming that if the booster of the SLS exploded, it would be considered a success since nobody intends to reuse it. Yeah, that is how you get a two billion dollar launch tag. You can't convince congress to drop the SLS if you keep losing boosters.
    - p1mrx 3y ago
      They attempted a novel hot staging sequence where the booster grid fins interact with the second stage exhaust to rotate the booster. The booster rotated too violently, and shook up the tanks like a can of beer before exploding. They need to improve the control systems so the rotation happens more smoothly. I wouldn't praise the booster for exploding, but I would praise the engineers for getting it all the way to staging without engine failures. That's all most boosters are expected to do. SLS isn't expected to explode because it's based on space shuttle parts that stopped exploding decades ago.
- panick21_ 3y ago
  > There were all these wild claims of an exotic new liquid cooled reentry system at the beginning. Its not that wild. That technology is likely used on certain military equipment. I was certainty something not tested at that scale but it wasn't a crazy thing to think about. > But because physics they ended up going right back to using ablative. They are not ablative. > Nothing has fundamentally changed in ceramic or What's your evidence? Have you done lots of study on Space Heat shield? Please share your findings. > adhesive technology since then That just wrong. Starship uses mostly welded studs steel frame. Totally different from Shuttle. > and the lack of aerodynamic control They have sufficient aerodynamic control. What evidence do you have that they don't? They have shown simulation of this before. I'm gone go with SpaceX on this unless you show me some simulation that shows insufficient control.
idlewords 3y ago
That 'clear path to orbit' depends on what the performance of the raptor engines is, as flown. Getting the first stage to work on all engines was a big achievement, but how effectively those engines are working is another big part of the puzzle.

ramesh31 3y ago

>Maybe smaller tiles will have less lever action and will have 4x the fasteners. This is still the number one problem with Starship. There were all these wild claims of an exotic new liquid cooled reentry system at the beginning. But because physics they ended up going right back to using ablative. They'll suffer the same fate as the shuttle for it. Nothing has fundamentally changed in ceramic or adhesive technology since then, and the lack of aerodynamic control means they will have to survive even steeper descents with greater thermal load. I imagine the idea of Starship as an earth return vehicle in general will probably be abandoned, so they can optimize it for interplanetary transport and lunar operations.

tekla 3y ago
Of course the problem with this post is that the Starship heat shield isn't ablative, nor does it share the problems with the Orbiter heat shield (Needing glue to attach every single unique tile to the body of the ship.) > the lack of aerodynamic control There are literally wings on the ship.
- ta1243 3y ago
  I had to read it twice as I saw "lack of aerodynamic control" and assumed they meant the Shuttle, which was about as aerodynamic as a squirrel
  - lstodd 3y ago
    Well in fact at about 4:1 glide ratio subsonic it was much better than Siberian Flying Squirrels which are usually about 1.5. https://en.wikipedia.org/wiki/Siberian_flying_squirrel https://en.wikipedia.org/wiki/Siberian_flying_squirrel
- ramesh31 3y ago
  >Starship heat shield isn't ablative Yes, it is. There is no such thing as a non-ablative reentry vehicle. The tiles are effectively no different than what was used on the shuttle. >There are literally wings on the ship. Starship has no meaningful aerodynamic control beyond what is required to perform the flip. It has no ailerons or elevators. It falls to the earth in a completely ballistic trajectory.
  - danbruc 3y ago
    Insulating tiles are not an ablative heat shield, they are a thermal soak heat shield. Ablative heat shields are non-reusable as they work by slowly burning off material which creates a cooler boundary layer between the plasma and the heat shield. [1] [1] https://en.wikipedia.org/wiki/Heat_shield#Spacecraft https://en.wikipedia.org/wiki/Heat_shield#Spacecraft
    - rpmisms 3y ago
      Ablation will still happen, but the tiles aren't designed to ablate as the primary method of heat dissipation.
      - danbruc 3y ago
        Sure, everything going through the atmosphere at supersonic speeds will lose at the very least a couple of atoms here and there, but that was not the point and that does not make thermal protection tiles an ablative heat shield.
        avmich 3y ago
        Let's remember definitions. Thermal soak heat protection: the protective material absorbs - soaks - the heat, becomes really hot, and after the process need to dissipate the heat. Also - which is important - the heat capacity of the material should be enough to absorb the whole heat flux going into it. Also - thermal conductivity of this protection should be such that the protected material behind it won't get too much heat. For this kind of protection to work you want small temperature differentials - less heat flux - and small time of heating - otherwise the material will become too hot. However - as materials have varying thermal conductivity - the thermal soak is always present to some degree. Radiative protection: the protective material heats up so much it stops accepting more heat, because it radiates heat back with the same speed. After the process the surface of this material is really hot. Important requirement - low thermal conductivity, as the high temperature on the surface shouldn't get behind the protective layer. Also known as refractory protection. Space Shuttle thermal protection is an example. Ablative protection: the surface of the protective material releases its material in the form of gases, and this gasification process cools down the material. The material gets consumed, that's the main problem with this cooling approach - neither big thermal capacity nor small thermal conductivity are needed. Early Merlin engines used ablative cooling. According to Wikipedia, SpaceX uses ablative protection for Crew Dragon - https://en.wikipedia.org/wiki/Atmospheric_entry#Thermal_protection_systems https://en.wikipedia.org/wiki/Atmospheric_entry#Thermal_prot... - "A second enhanced version of PICA—called PICA-3—was developed by SpaceX during the mid-2010s. It was first flight tested on the Crew Dragon spacecraft in 2019 during the flight demonstration mission, in April 2019, and put into regular service on that spacecraft in 2020." . Also from Wikipedia, tiles of Starship are made of silica - https://en.wikipedia.org/wiki/Starship_rocket#Starship_spacecraft https://en.wikipedia.org/wiki/Starship_rocket#Starship_space... - "Starship's heat shield, composed of eighteen thousand[131][132] hexagonal black tiles that can withstand temperatures of 1,400 °C (2,600 °F),[133][134] is designed to protect the vehicle during atmospheric entry and be used multiple times with minimal maintenance between flights.[135] The tiles are made of silica[136] and are attached with pins rather than glued,[134] with small gaps in between to allow for heat expansion.[2]" which makes them a kind of radiative or refractory protection.
deleted 3y ago
[deleted]
idontwantthis 3y ago
Neither the space shuttle nor Starship use ablative heat shield tiles.
- ramesh31 3y ago
  >Neither the space shuttle nor Starship use ablative heat shield tiles. They are effectively ablative in the sense that neither vehicle has (or will) be able to complete successive missions without massive replacement of damaged and missing tiles. The fundamental approach is not suitable to reusability, as we learned with the shuttle.
  - idontwantthis 3y ago
    You might end up right but that’s still not what ablative means.
  - timschmidt 3y ago
    Shuttle tiles were unique, and glued in place. Starship tiles are mostly identical, and secured with steel spring pins.
  - tekla 3y ago
    The heat shield is not ablative. You are simply wrong.
  - 0xfae 3y ago
    What you are doing is effectively mental gymnastics to avoid admitting you used the incorrect word.
    - plorg 3y ago
      That could be because there are a dozen replies fixated on the use of the wrong word and maybe one that responds to the substance of the comment.
  - panick21_ 3y ago
    First of all, that's not what ablative means. Tiles potentially falling of does not make the heat shield ablative. Because tiles falling off is not a the heat transfer mechanism, rather a mechanical failure. The Dragon Capsule for example has an Ablative Heat-Shield. But that doesn't necessarily mean it can't do multiple missions in a row. It just depends on how the shield is designed. The Dragon could potentially do many earth missions without replacing the heat shield. Second, you are wrong in that there is anything fundamental about Starship or Shuttle heat shield not being able to fly multiple missions. If the tiles are still attached and not damaged, then all that has to happen is for the tiles to cool down. After that they are ready for another flight, meaning the tiles are not ablative. Now experience on Shuttle has shown that if you are not careful tiles could fall of or be damaged. Damage can be reduced in various was and Starship without an external tank is already much better by design. Additionally Shuttle had to glue tiles to a fragile aluminum frame making the installation very hard and the tiles very fragile. Starship on the other hand uses welded studs on a steel frame. So even if a tile is lots, the steel should still hold up pretty well. In on case Shuttle was saved because there just so happened to be steel under a damaged tile. So you are right, heat shield is one of the biggest issue that could cause problems with rapid reputability. You are wrong, the tiles are not ablative cooled. But Starship tiles are totally different then Shuttles, they have made many improvements in the heat shield and its construction and in the heat shield tiles themselves. Starship can likely survive even with a number of missing tiles if required. In some position tile lose can certainty be fatal.
p1mrx 3y ago
> I imagine the idea of Starship as an earth return vehicle in general will probably be abandoned, so they can optimize it for interplanetary transport and lunar operations. Starship will need several launches of methane+oxygen to travel beyond LEO. That model requires a reusable orbital tanker to make sense economically.
- imtringued 3y ago
  Most of the engines are on the booster. The upper stage is the cheapest part of the entire rocket. At a worst case of 2 million per engine you're talking about 66 million dollars for the booster. I honestly don't understand this whole post chain. The booster needs to survive because it is the most valuable part of the rocket and yet we are supposed to praise it for exploding? The hot staging concept isn't viable over the long term because it goes counter to the goals of reusability. I don't need people to rewrite history by claiming that if the booster of the SLS exploded, it would be considered a success since nobody intends to reuse it. Yeah, that is how you get a two billion dollar launch tag. You can't convince congress to drop the SLS if you keep losing boosters.
  - p1mrx 3y ago
    They attempted a novel hot staging sequence where the booster grid fins interact with the second stage exhaust to rotate the booster. The booster rotated too violently, and shook up the tanks like a can of beer before exploding. They need to improve the control systems so the rotation happens more smoothly. I wouldn't praise the booster for exploding, but I would praise the engineers for getting it all the way to staging without engine failures. That's all most boosters are expected to do. SLS isn't expected to explode because it's based on space shuttle parts that stopped exploding decades ago.
panick21_ 3y ago
> There were all these wild claims of an exotic new liquid cooled reentry system at the beginning. Its not that wild. That technology is likely used on certain military equipment. I was certainty something not tested at that scale but it wasn't a crazy thing to think about. > But because physics they ended up going right back to using ablative. They are not ablative. > Nothing has fundamentally changed in ceramic or What's your evidence? Have you done lots of study on Space Heat shield? Please share your findings. > adhesive technology since then That just wrong. Starship uses mostly welded studs steel frame. Totally different from Shuttle. > and the lack of aerodynamic control They have sufficient aerodynamic control. What evidence do you have that they don't? They have shown simulation of this before. I'm gone go with SpaceX on this unless you show me some simulation that shows insufficient control.

idlewords 3y ago

That 'clear path to orbit' depends on what the performance of the raptor engines is, as flown. Getting the first stage to work on all engines was a big achievement, but how effectively those engines are working is another big part of the puzzle.