4 comments

• Stephen Richter

  December 8, 2022 at 11:24 pm

  “… test the autogenous pressurization system. …”

  This is an advancement, correct? Meaning the booster and starship will not have to consume scarce helium? ( But then, is helium scarce in the world? I do worry every time I see helium balloons in my local supermarket. )
• Stephen Richter

  December 8, 2022 at 11:29 pm

  The problems with the concrete of the launch pad shattering into pieces … is that occurring because the booster is held in place during the static fire? Normally the booster clears the launch pad before doing this level of damage to the concrete?
• Stephen Richter

  December 8, 2022 at 11:50 pm

  Is SpaceX being ultra cautious out of concern that a launch explosion will result in the FAA locking them down for an extended period of time? Would an actual super heavy launch with a subset of its raptor engines meet the same testing requirements of these static fire tests, with the added advantage of SpaceX being able to also test how they can get super heavy to land safely back on Earth.
• Edward

  December 9, 2022 at 6:37 pm

  Stephen Richter asked: “[the autogenous pressurization system] is an advancement, correct? Meaning the booster and starship will not have to consume scarce helium? ( But then, is helium scarce in the world? I do worry every time I see helium balloons in my local supermarket. )”

  From the linked article:

  Autogenous pressurization is a method that uses a gaseous propellant to pressurize the vehicle’s propellant tanks. Using the same propellants already present in the tank allows the removal of a separate pressurization system that would use an inert gas — such as helium — to keep the tanks at flight pressure. This gas would need to be stored onboard the vehicle throughout the flight, so the removal of such a system removes mass and complexity from the booster.

  Although there is some scarcity of helium on Earth, there is no known supply on the Moon or on Mars, two targets for Starship. If the Starship design can avoid using helium, then it has a much better capability of using onsite resources (in-situ resource utilization) without the need to bring supplies from home. Since Starship can — or will — use the propellants as pressurants, then why not do the same for Super Heavy? It should also make the ground support hardware less complicated.

  There are problems to overcome, however, because this has not really been done before, so Stephen is correct, it is an advancement. Helium can be stored onboard at high pressure and released into the propellant tanks without fear that it will condense, but the same is not so true when using the propellants themselves. I suspect that SpaceX had that problem with one of the Starship landing tests, last year. When a gas (e.g. helium, oxygen, methane) goes from a high-pressure tank into a lower-pressure tank the reduction in pressure cools the gas, and there is a risk that the gas condenses into liquid form and does not increase the pressure in the target tank as it is supposed to do.

  Another concern that I have is that the propellants may be chilled to near the freezing point, so any gaseous propellant could be chilled by the liquid propellant and condense, decreasing rather than increasing the tank pressure.

  SpaceX has probably been spending the past two to six years trying to figure out how to do this successfully. I would not be surprised if they keep this as a proprietary trade secret.