15 thoughts on “Falcon 9”

  1. While not ideal from a manufacturing perspective, having a basic core that can be used for a regular Falcon 9 or as a Falcon Heavy strap-on with a strengthened FH center core makes sense. The center core is going to carry heavier payloads and be subject to significantly higher stresses than the outer cores. If they make all the cores strong enough to be FH centers, they’ll be unnecessarily heavy and inefficient.

    1. Yes, but I don’t understand why the outer cores would be the same as the single core. I’d think that the inner core would be. Both the inner and single core have to take the compression from the upper stage, while the outer cores don’t.

      1. I think the central core has extra plumbing for the propellant cross-feed. That is the problem.

      2. From a weight perspective, the optimum solution would be to have different first stages for the F9, FH center, and FH outer cores. The FH outer cores don’t have anything on top so they could be built lighter. The FH center core needs to be able to handle the stresses from the outer cores plus the much greater payloads than the F9 (F9: 13,150 kg to LEO, FH: 53,000 kg to LEO). The F9 needs to be stronger than the FH outer cores but not as strong as the FH center core.

        From a manufacturing perspective, the optimum solution is for all the cores to be the same. However, that would mean the F9 and FH outer cores would be heavier than needed, decreasing payload. It seems SpaceX has decided that the F9 and FH outer cores are more in common than the FH center core. If they aren’t going to make three kinds of core, then their decision makes sense to me. The extra weight of making the F9 and FH center cores identical would cut into the F9’s payload, especially when you factor in reusability.

  2. Well, a couple of obvious things, though i’m sure there’s more:

    — the core has to have the thrust structure to carry the force from both side boosters;
    — the core has to have four cross-feed connections – two from each side booster – while the latter only need two each.

    So the core is the “oddball” unit in the FH first stage. The above also fits with her comment that they will use side booster types for the regular, single stick F9.

  3. So presumably all of the standalone/outer cores come with legs and the inner FH cores don’t. I wonder if they’re going to put the crossfeed hardware on the outer cores. Presumably, you’d engineer both the legs and the crossfeed hardware to be removable when you didn’t need them.

    Don’t know if anybody watched the hearing yesterday, but there seemed to be two takeaways:

    1) Everybody (well, maybe not Gwynne) agreed that the 1608 language had to change or the Air Force was in deep prune yoghurt on the RD-180 inventory.

    2) Substantial freak-out over ULA’s intention to mothball the Delta IV-H line ASAP, because nobody (except for SpaceX) thinks that SpaceX can get FH EELV qualified much before 2020. Bruno pretty much said that he’d keep the line and pad ops going as long as NRO needed them, but there was a pretty broad hint that it was gonna cost extra to do so.

    Interesting comment by Bruno on SpaceX’s lack of a high-energy upper stage for FH. I wonder if SpaceX will build a Raptor upper stage for FH? That would be yet another reason to let the designs for center and outer cores drift away from each other.

    Best Shotwell slam of the afternoon, in response to a question about why SpaceX costs were so much lower: “I don’t even know how you’d build a $400 million launcher.”

    1. nobody (except for SpaceX) thinks that SpaceX can get FH EELV qualified much before 2020
      They’re wrong though. I also expect that by 2020 SpaceX will have tested a 2nd generation rocket with improved engines to replace the F9H.

      Interesting comment by Bruno on SpaceX’s lack of a high-energy upper stage for FH. I wonder if SpaceX will build a Raptor upper stage for FH? That would be yet another reason to let the designs for center and outer cores drift away from each other.
      Doesn’t matter at all. F9H has a lot more payload to LEO than Delta IV Heavy to begin with. AFAIK Delta IV Heavy is mostly used to launch big birds for the NRO to SSO so it probably doesn’t even need multiple restarts. If SpaceX needed to, for whatever reason, they could just add a 3rd stage like the Russians do.

      Yes Raptor will improve the ISP a bit but it is never going to have as much ISP as LOX/LH2. Then again it is so much cheaper so who cares.

      1. AFAIK Delta IV Heavy is mostly used to launch big birds for the NRO to SSO so it probably doesn’t even need multiple restarts.

        For those from Vandenberg, you’re right. For those Delta IV Heavy launches from the Cape, their missions most likely go to GEO. Whether the upper stage puts the payload into GTO or all the way to GEO is unknown.

        Looking at the Delta IV launch log, they’ve launched only 8 of the Heavies. The first was a demo mission and the last carried the Orion. Of the remaining 6 DH launches, 4 were from the Cape and two from Vandenberg.

    2. “Best Shotwell slam of the afternoon, in response to a question about why SpaceX costs were so much lower: “I don’t even know how you’d build a $400 million launcher.””

      Wasn’t this some conflation between price and cost?

      1. Yeah, and Bruno screeched about it. But nobody ever did get around to following up on what part of the development costs got amortized by the military. Of course, you could make a similar argument about F9 dev costs and COTS. Let’s just say that accountants have been involved for all parties.

        Still, for a hearing smackdown, it was at least the equivalent of a good Chair Shot.

        1. NASA studied SpaceX’s number in depth and determined that it cost about $350 million to develop the F9. NASA admitted that it would’ve cost them ten times as much to do the job themselves. The Air Force provided $500 million each to Boeing and Lockheed to develop the Delta IV and Atlas V. They continue to pay ULA a billion dollars every year for “launch assuredness.”

  4. Summarizing the differences:
    1. The central core needs cross feeds from both sides to the outer cores’ one-side each,
    2. The central core needs to distribute three cores worth of thrust and support the payload.
    3. The one-core launch separates its upper stage at a lower altitude than the central core separates from the upper stage in a three-core launch.
    4. The dry mass of the outer cores is only carried until outer core separation, while the inner core is carried further.
    5. The inner core needs to kill more delta V to get to the drone ship.

    Implications: Similarly to a second stage, the central core can use lighter, more expensive materials and more labor for fine tuning. The central core can also have a nozzle that emphasizes performance at higher altitudes.

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