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While this remains a paper rocket for now, its engine (which looks to be a pretty big deal in its own right) was test-fired for the first time yesterday: h

by dasmoth 10y ago

While this remains a paper rocket for now, its engine (which looks to be a pretty big deal in its own right) was test-fired for the first time yesterday: https://twitter.com/elonmusk/status/780275236922994688

ygra 10y ago
A scale model of the engine. It's not full-size yet.
- dasmoth 10y ago
  Are you certain of that? It's mentioned in a few places (including Wikipedia), but I've not seen any SpaceX sources saying this was a sub-scale test article. On the contrary, we've heard Elon say that because of the very high chamber pressure, you can get the thrust they're looking for out of an engine about the size of a Merlin. And while it's hard to be 100% sure, from the pictures I've seen the unit tested at the weekend looks kind-of Merlin sized. Not conclusive, of course, but likewise I've not yet seen any hard evidence to support the idea that it is sub-scale.
  - ygra 10y ago
    Admittedly, I was going by Wikipedia and r/SpaceX. The latter tended to imply that the source was conversations with employees, but I don't know of a quotable source either. So might in fact be wrong. Elon tweeting something that might imply the same size of the engine, albeit with a qualifier (»Chamber pressure is almost 3X Merlin, so engine is about the same size for a given area ratio«). Naïvely dividing booster diameter by the number of engines across the diameter yields 1.2 m for Merlin 1D and 1.7 m for Raptor (although the ITS seems to have a bit of space around the center cluster since only those gimbal).
- tux1968 10y ago
  It's full size they just use 27+ of them on the heavy lift version of their rocket, and 40+ on the proposed rocket for lifting the Mars ships off of Earth.
  - peeters 10y ago
    Falcon Heavy will use 27 Merlin engines, not Raptors. The Merlin is already being flown in Falcon 9, and they're producing dozens per year. The Heavy is basically a Falcon 9 with two more Falcon 9 first stage cores strapped on the side as boosters. Though I think there is talk of moving all Falcon to the Raptors eventually.
    - tux1968 10y ago
      You're right. Although Musk did make the point that the Raptor and the Merlin are essentially the same size. The scale is the same.
    - mentando 10y ago
      With the ~3 times of thrust from the Raptor engines, do you think they will move to a "Falcon-3" design with 3 Raptor engines? Because that would decrease the redundancy, right? With Falcon-9 you would lose 2/9 of thrust if you turn off the mirrored engine in the best case. In a Falcon-3 scenario, you would lose at least 1/3 for middle engine failure or 2/3 for a side engine failure.
      - peeters 10y ago
        Interesting question. I really don't know what their plan would be, but it's worth noting that even with the Merlins, they land with only one of nine Merlins at its lowest thrust. And even then, it delivers more thrust than its weight, meaning it can't hover. That's why landings are so difficult for them. They have to fire the engine at the exact right time, or else they'll just blast off again (or land too hard). The numbers I could find said minimum thrust of Merlin is 360 kN. The stat sheet for Raptor showed minimum thrust of 20%, which works out to 610 kN. So with a single engine at minimum thrust, they'd need to either come in even harder than the Falcon 9 currently does, or find a new method of propulsive landing. More relevant to your question, a 3 engine configuration doesn't allow firing a single engine because there'd be no middle engine like the Falcon 9 has. You'd need at least 4 to have symmetry and a centre engine.
    - 10y ago

by dasmoth 10y ago

ygra 10y ago

A scale model of the engine. It's not full-size yet.

dasmoth 10y ago
Are you certain of that? It's mentioned in a few places (including Wikipedia), but I've not seen any SpaceX sources saying this was a sub-scale test article. On the contrary, we've heard Elon say that because of the very high chamber pressure, you can get the thrust they're looking for out of an engine about the size of a Merlin. And while it's hard to be 100% sure, from the pictures I've seen the unit tested at the weekend looks kind-of Merlin sized. Not conclusive, of course, but likewise I've not yet seen any hard evidence to support the idea that it is sub-scale.
- ygra 10y ago
  Admittedly, I was going by Wikipedia and r/SpaceX. The latter tended to imply that the source was conversations with employees, but I don't know of a quotable source either. So might in fact be wrong. Elon tweeting something that might imply the same size of the engine, albeit with a qualifier (»Chamber pressure is almost 3X Merlin, so engine is about the same size for a given area ratio«). Naïvely dividing booster diameter by the number of engines across the diameter yields 1.2 m for Merlin 1D and 1.7 m for Raptor (although the ITS seems to have a bit of space around the center cluster since only those gimbal).
tux1968 10y ago
It's full size they just use 27+ of them on the heavy lift version of their rocket, and 40+ on the proposed rocket for lifting the Mars ships off of Earth.
- peeters 10y ago
  Falcon Heavy will use 27 Merlin engines, not Raptors. The Merlin is already being flown in Falcon 9, and they're producing dozens per year. The Heavy is basically a Falcon 9 with two more Falcon 9 first stage cores strapped on the side as boosters. Though I think there is talk of moving all Falcon to the Raptors eventually.
  - tux1968 10y ago
    You're right. Although Musk did make the point that the Raptor and the Merlin are essentially the same size. The scale is the same.
  - mentando 10y ago
    With the ~3 times of thrust from the Raptor engines, do you think they will move to a "Falcon-3" design with 3 Raptor engines? Because that would decrease the redundancy, right? With Falcon-9 you would lose 2/9 of thrust if you turn off the mirrored engine in the best case. In a Falcon-3 scenario, you would lose at least 1/3 for middle engine failure or 2/3 for a side engine failure.
    - peeters 10y ago
      Interesting question. I really don't know what their plan would be, but it's worth noting that even with the Merlins, they land with only one of nine Merlins at its lowest thrust. And even then, it delivers more thrust than its weight, meaning it can't hover. That's why landings are so difficult for them. They have to fire the engine at the exact right time, or else they'll just blast off again (or land too hard). The numbers I could find said minimum thrust of Merlin is 360 kN. The stat sheet for Raptor showed minimum thrust of 20%, which works out to 610 kN. So with a single engine at minimum thrust, they'd need to either come in even harder than the Falcon 9 currently does, or find a new method of propulsive landing. More relevant to your question, a 3 engine configuration doesn't allow firing a single engine because there'd be no middle engine like the Falcon 9 has. You'd need at least 4 to have symmetry and a centre engine.
  - 10y ago