19 thoughts on “Starship Progress”

  2. It seems Elon is going the Mig-25 Foxbat route. Too bad that they will use methane and not pure ethanol for the active cooling. I understand that ground crews in remote Soviet airbases used to love having to service visiting Foxbats. That meant that they would have to dispose of (i.e., consume) the old, worthless coolant.

      1. The physics is interesting. At Mars return entry speeds, radiative heating becomes more important than with lunar (or LEO) entry. So the shininess could help suppress heating. Additionally, the coolant can be sourced from space, just like propellant.

        I do wonder if the surface will degrade with use. Time to swab the stainless, mates.

        1. When the Sun’s reflection off the Starship on Mars is painful through your helmut visor, you’ve probably swabbed enough….

        2. One other thing stainless tanks would do: allow the use of hot pressurizing gas. This would reduce the mass penalty from said gas during launch.

      2. I suspect that what tipped the scales in favor of stainless steel was its ability to be dynamically cooled for TPS purposes with very little extra mass beyond that needed to meet structural margin minimums. Using propellant as TPS requires only some additional pumps of modest mass. Coolant channels can be corrugated stainless welded to the interior surfaces of the vehicle and can contribute to structural strength.

        Carbon fiber composites are very strong and light, but can’t take sustained exposure to lunar or Mars-class re-entry speeds. Huge swaths of PICA-X would be needed. That seems to have been the original plan, but I suspect even SpaceX couldn’t find a way to make the necessary TPS mass low enough to beat dynamically cooled stainless.

  4. Elon also made some mention of a new Raptor variant using a new process metal. I think he referred to it as SX550? Is this stainless or Inconel?

    1. Technically neither, but per Elon it’s closer to an Inconel (e.g. nickel alloy):

      “SX 300 & soon SX 500. Kind of a modern version of Inconel superalloys. High strength at temperature, extreme oxidation resistance. Needed for ~800 atmosphere, hot, oxygen-rich turbopump on Raptor rocket engine”

      1. These alloys typically contain rhenium, an extremely rare metal (second least common stable element in the Earth’s crust). I wonder how common it is in asteroids.

          1. Rhenium is used in alloys for modern jet engine turbine hot sections. So I would not be surprised if it was good for rocket engines as well.

            But knowing the Russians they probably just used loads of Chromium when they had the same issues.

  6. I wonder why they applied to the Federal Communications Commission, rather than the Federal Aviation Administration, for an experimental permit…since the FCC doesn’t issue anything like that. And the FAA’s experimental permit is nothing like a “streamlined” version of a license. If anything, it’s more horrific.

    1. Rockets in flight that transmit any RF signals – and they all do – are required to have FCC licenses to do said transmissions.

    1. Looking at that picture it certainly does not seem like it to me. They look more like sea level optimized nozzles. I think Elon stated some time ago that they decided against having differently optimized nozzles in the second stage because it made little difference in performance. I’ve heard similar things in the past. That as you increase the engine pressure the bell nozzle shape becomes less and less of a factor.

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