SpaceX Will Install Two More Raptor Engines and Start StarHopper Tests

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The SpaceX Starhopper is on a cement launch pad. Elon Musk has indicated the Raptor engine delivery and installation will start next week. SpaceX will one or three engines and begin hop tests. It is clear that SpaceX will start tests before adding a new nose cone is placed onto the Starhopper.

SpaceX is talking about very low tethered hops as a start.

SOURCES- Elon Musk, Twitter, Cowboy Dan Twitter

Written By Brian Wang

20 thoughts on “SpaceX Will Install Two More Raptor Engines and Start StarHopper Tests”

  1. If an engine goes kablooey, odds are the tanks will be going off shortly thereafter. Starhopper doesn’t look exactly armored. Also, it’s a hopper: hopping over a wall with a mushy start would be pretty easy.

  2. Seems now its getting easier to see the versatility of the design and design challenges they were facing. For a while i had thought there was no end to the design changes. I complained some. Now i appreciate it.

  6. A raised dirt platform, yes, but it doesn’t really protect the storage tanks from, say an engine going kablooie, because the Starhopper legs raise them up level with the top of the dirt.

  7. Good point on the legs.

    The Akin stuff is based on a statistical regression of previous tank designs, so I suspect that it does account for bipropellant tanks with a bulkhead.

    I have to say that when I came up with almost exactly 1000 m^3 of tank volume, it kinda felt like the right answer. Given that my base scale for this whole exercise was comparing the height of the wheels on the crawler with a nominally 6-ish ft worker, followed by judicious use of a ruler held up against stills from the video, the finer points of endcap geometry seemed like overkill.

    On the other hand, less dry mass makes the hoverslam problem even worse. Maybe they’re really, really confident in the avionics and algorithmic work they’ve done for F9 and its application to Starhopper, but that doesn’t seem very conservative to me. It seems more likely that dry mass is more than I’ve computed.

    Of course, it’s also possible that they view the hoverslam as so much lower risk than everything else that they’re not expecting to get that far in the first tests…

  10. The cement launch pad will not stand up to the engine blast. It should have been built with concrete. s/

  11. Minor: 3 legs, so 6T rather than 8T ?

    Does Atkins take into account tanks with 2 chambers – i.e. with an internal wall separating fuel from oxidizer? Plus some internal tanks if I correctly recall some diagrams showing.

    From other pictures, the dome portion seems to have two parts with different curvature, total of which looks about 3m tall. (I’d guess the lower curvature matches that of the nose cone.)

    The top and bottom 3m of an 11m sphere would be about 1/2 the volume, not 2/3rds. https://en.wikipedia.org/wiki/Spherical_cap

  12. Tank farm looks pretty small at present. A small fuel load (e.g. tethered tests) wouldn’t be much threat, and a big fuel load (hops/flights) would probably leave the tank farm mostly empty?

  13. The launch pad is concrete, not cement. Cement is the powder used in the manufacture of concrete. More concrete is manufactured worldwide than any other material. Despite concrete being a very common material it is unfortunately frequently misnamed as cement.

  14. If we assume that Starhopper has a 9 m diameter, then from the previous pictures of moving day, the cylindrical portion is 10.8 m high, and the dome is 2.4 m high. As a SWAG, the dome looks to be about 1/3 of an 11ish m sphere, and we should assume that the other end cap is the same. So the volume should be (2/3)*(4/3)*pi*5.5^3 + (10.8-2.4)*pi*4.5^2 = 999 m^3. Sounds suspiciously like 1000 m^3 to me. Surface area will be (2/3)*4*pi*5.5^2 + (10.8-2.4)*pi*9 = 491 m^2.

    Raptor has O:F = 3.58, so the average density of the methalox should be 884 kg/m^3, so total prop mass is 884 tonnes.

    If we use Akins’s mass estimating relationships ( https://spacecraft.ssl.umd.edu/academics/791S16/791S16L08.MERsx.pdf ), that should be 12.16*1000=12.2 t of tank mass.
    Insulation should weigh 1.123*491 = 0.55 t.

    SWAG Raptor mass = 0.9 t, so 3 of them should be 2.7 t.

    Thrust structure should be 2.55E-4*(1700E3*3) = 0.43 t.

    Total mass before wiring and avionics: 900 t.

    Avionics = 10 * 900E3^0.361 = 1.4 t.
    Wiring = 1.058 * 900E3^0.5 * (10.8+2.4)^0.25 = 1.9 t.

    Landing legs? 2 tonnes apiece? So 8 t?

    Grand total mass: 911 t = 8928 kN weight.
    Dry mass: 27 t = 265 kN weight

    T/GLOW with 3 Raptors: 0.57.
    T/Dry weight @ 1 Raptor throttled to 20% = 1.28.

    Hmmm.

    So:

    1) They’re not going to fill it all the way, and use it later for 7 engine tests,
    2) It lands with a hoverslam, which sounds pretty weird for a test article, or
    3) Somebody should check my arithmetic.

  16. Thanks for the update. So a tethered (vs bolted down) test might not melt the test pad? While the grasshopper did not need one I expect this optimized MOX monster engine that is the raptor will toss some incredible heat.

  17. I hope they put up a blast wall between the Hopper and the tank farm. Otherwise an accident could be spectacular.

  18. His headline suggests that three will be installed before testing begins, for which there is no evidence. In fact it’s already been proven false, as they’ve started tank testing before even the first install. Check out twitter account @SPadre.

  19. “SpaceX will one or three engines and begin hop tests.”

    Brian isn’t disagreeing with you, he just forgot the “install”.

  20. And by next week, you mean this week. Raptor number 1 is already on site.

    Also, there’s been no indication there will be more than one Raptor installed before the nosecone gets replaced. Hopper can get plenty of altitude with just the one.

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