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"It's optimising for the hardest part of the trip: re-entry." Is it really the hardest part? I would say that for fully reusable rockets, the hardest part is

"It's optimising for the hardest part of the trip: re-entry." Is it really the hardest part? I would say that for fully reusable rockets, the hardest part is quick turnaround. For future space activities, it will be a huge economic difference if you can send the ship back in, say, 12 hours vs. 120 hours.

everyone 2y ago
I agree with this, I may have said the same thing.. But I was thinking that the tech used for re-entry is what tends to increase the turnaround time (Eg. ablative heat shields, tiles). Making something that's rapidly re-usable which can also withstand re-entry from orbital speeds is probably the greatest challenge in this domain. The shuttle was originally envisaged to be cheap and rapidly re-usable for the time. As built it didnt turn out that way, it would have been overall cheaper and probably faster to launch a fully un-reusable rocket than a shuttle.
- inglor_cz 2y ago
  Yeah, my guess is that quick turnaround is a function of mainly two variables: a good protection of the ship during re-entry and very reliable engines that require little to none manual checking and can withstand lower thousands of cycles before needing refurbishment. Of those two, I am fairly sure that SpaceX can produce great engines. The Raptors are not quite there yet, but their 4th or 5th iteration will likely be extremely good. Not so sure about the heat shields. Much less aggregated corporate experience there.
  - cubefox 2y ago
    It was quickly taken down, but there was a video on YouTube from someone who got hold both of a Space Shuttle and a Starship heat shield tile. He analyzed it with a microscope. He found that the material was nearly identical. I do wonder why SpaceX thinks they can make a ceramic heat shield work when it needed lots of checks and refurbishment for the Space Shuttle. Recently Musk even said they will add an ablative heat shield in certain areas. On the other hand, the at least the reusability of the lower stage shouldn't be a problem.
    - HPsquared 2y ago
      There are quite a large number of parameters other than the material, surely. The whole design is different.
      - cubefox 2y ago
        Not at all. The tiles just consists of two layers. The main body and the dark layer on top. According to the electron microscope analysis, the two tiles were mostly the same.
        HPsquared 2y ago
        I mean more, the size and shape of the ship, the size/shape/thickness of the tiles, the attachment method, the substrate material, the flight profile...
        cubefox 2y ago
        I'm not seeing where SpaceX could have achieved a major innovation here that solves the problems the Space Shuttle had with the heat shield. I think the latter used glue rather than pins, but probably not because the Space Shuttle people couldn't make pins. If it was that easy...
        HPsquared 2y ago
        Those details could affect the heat flux and temperatures the material is exposed to. The two spacecraft have very different designs.
        cubefox 2y ago
        I guess one advantage of SpaceX compared to NASA is that the former are very trial and error based in their design, so they can iterate much more. NASA tends to design and plan everything in advance and only build it at the end. So when the Space Shuttle reusability didn't quite pan out, they couldn't easily change things up.

everyone 2y ago

I agree with this, I may have said the same thing.. But I was thinking that the tech used for re-entry is what tends to increase the turnaround time (Eg. ablative heat shields, tiles). Making something that's rapidly re-usable which can also withstand re-entry from orbital speeds is probably the greatest challenge in this domain. The shuttle was originally envisaged to be cheap and rapidly re-usable for the time. As built it didnt turn out that way, it would have been overall cheaper and probably faster to launch a fully un-reusable rocket than a shuttle.

inglor_cz 2y ago
Yeah, my guess is that quick turnaround is a function of mainly two variables: a good protection of the ship during re-entry and very reliable engines that require little to none manual checking and can withstand lower thousands of cycles before needing refurbishment. Of those two, I am fairly sure that SpaceX can produce great engines. The Raptors are not quite there yet, but their 4th or 5th iteration will likely be extremely good. Not so sure about the heat shields. Much less aggregated corporate experience there.
- cubefox 2y ago
  It was quickly taken down, but there was a video on YouTube from someone who got hold both of a Space Shuttle and a Starship heat shield tile. He analyzed it with a microscope. He found that the material was nearly identical. I do wonder why SpaceX thinks they can make a ceramic heat shield work when it needed lots of checks and refurbishment for the Space Shuttle. Recently Musk even said they will add an ablative heat shield in certain areas. On the other hand, the at least the reusability of the lower stage shouldn't be a problem.
  - HPsquared 2y ago
    There are quite a large number of parameters other than the material, surely. The whole design is different.
    - cubefox 2y ago
      Not at all. The tiles just consists of two layers. The main body and the dark layer on top. According to the electron microscope analysis, the two tiles were mostly the same.
      - HPsquared 2y ago
        I mean more, the size and shape of the ship, the size/shape/thickness of the tiles, the attachment method, the substrate material, the flight profile...
        cubefox 2y ago
        I'm not seeing where SpaceX could have achieved a major innovation here that solves the problems the Space Shuttle had with the heat shield. I think the latter used glue rather than pins, but probably not because the Space Shuttle people couldn't make pins. If it was that easy...
        HPsquared 2y ago
        Those details could affect the heat flux and temperatures the material is exposed to. The two spacecraft have very different designs.
        cubefox 2y ago
        I guess one advantage of SpaceX compared to NASA is that the former are very trial and error based in their design, so they can iterate much more. NASA tends to design and plan everything in advance and only build it at the end. So when the Space Shuttle reusability didn't quite pan out, they couldn't easily change things up.