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The 4th Starship test flight was absolutely great test, which really pushed the state of the art - both in general (after all, Starship 2nd stage is 1.5-2 times

by avmich 2y ago

The 4th Starship test flight was absolutely great test, which really pushed the state of the art - both in general (after all, Starship 2nd stage is 1.5-2 times heavier - when empty - than a Space Shuttle returning from orbit) and specifically for developing the Starship as a robust launch system. Regarding return from orbital (and above) velocities - there was a flight ( https://space.skyrocket.de/doc_sdat/irdt-fregat.htm https://space.skyrocket.de/doc_sdat/irdt-fregat.htm ) in 2000 when the payload was returning from orbit using inflatable heat shield, which would tolerate much less of heat flow than Starship. The approach was to dissipate a lot of energy in high enough atmosphere, so that while temperature (measure of gas molecules kinetic energy) is high, the heat flow (amount of gas molecules with that kind of high energy to the ship) is low and so heat effects on the ship are also low. Another approach was used e.g. in Zond-6 flight ( https://en.wikipedia.org/wiki/Zond_6 https://en.wikipedia.org/wiki/Zond_6 ) when the spacecraft entered the atmosphere, shed some speed and got heated, then ballistically exited the dense atmosphere layers, cooled down a bit, then got into atmosphere again with less speed and so less heat load. The point is we still have some tricks up our sleeve to fight the problems of atmospheric reentry.

computerdork 2y ago
The Orion capsule (in 2022) used atmospheric bounce during reentry to cool off the craft: https://www.livescience.com/orion-capsule-lands-in-ocean https://www.livescience.com/orion-capsule-lands-in-ocean
gabesullice 2y ago
Something like this is what I've been thinking about post flight. In the heat of the moment ;), I was thinking about what SpaceX was learning about the ship's hot spots. After more reflection, I realized that the bigger picture is learning about how quickly it decelerates and how quickly it heats up. With that data, they can design a different reentry profile. E.g. maybe it's better to "plunge" to lower altitudes and experience higher peak pressure for a shorter duration or maybe it's better to have a very gentle but slow reentry to minimize peak pressure. After seeing how robust the ship is (and knowing SpaceX :P), I wouldn't be surprised if they decide to go for a higher peak pressure/temp. A better reentry profile is like massless heat shielding! Maybe more challenging than the profile or optimizing the heat shield though: how are they going to reject heat from the flap joint? Maybe relocating the flaps leeward, like Elon's been saying for a while, will do the trick

by avmich 2y ago

computerdork 2y ago

The Orion capsule (in 2022) used atmospheric bounce during reentry to cool off the craft: https://www.livescience.com/orion-capsule-lands-in-ocean https://www.livescience.com/orion-capsule-lands-in-ocean

gabesullice 2y ago

Something like this is what I've been thinking about post flight. In the heat of the moment ;), I was thinking about what SpaceX was learning about the ship's hot spots. After more reflection, I realized that the bigger picture is learning about how quickly it decelerates and how quickly it heats up. With that data, they can design a different reentry profile. E.g. maybe it's better to "plunge" to lower altitudes and experience higher peak pressure for a shorter duration or maybe it's better to have a very gentle but slow reentry to minimize peak pressure. After seeing how robust the ship is (and knowing SpaceX :P), I wouldn't be surprised if they decide to go for a higher peak pressure/temp. A better reentry profile is like massless heat shielding! Maybe more challenging than the profile or optimizing the heat shield though: how are they going to reject heat from the flap joint? Maybe relocating the flaps leeward, like Elon's been saying for a while, will do the trick