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Well, obliviously they do have a comprehensive model since they are able to: 1. start the most advanced rocket engines (full-flow staged combustion cycle engin

by nuccy 6y ago

Well, obliviously they do have a comprehensive model since they are able to: 1. start the most advanced rocket engines (full-flow staged combustion cycle engines [1]) 2. ascend to 10km gradually shutting down (and throttling) engines to keep relatively constant speed while methane and oxygen are depleting 3. switch from vertical ascent to horizontal descent flight profile, and from 10km "fall" (or rather fall/glide) into the 30 meters target of the landing pad 4. reach soft landing (almost accomplished by the SN10) BTW Roughly only the first two of those items are in the "normal" checklist of any other rocket company for an orbital rocket. SpaceX is following somewhat Soviet rocket development approach with many testing, which is not a bad thing by itself. It is just different to what we are used with NASA/ULA/et al. SpaceX is also very open with their testing, you can literally see the rocket from 50 meters away, and its launch (from 8km) freely. We obviously have an observational bias here, while not knowing how many failures others have. [1] https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-f...

HarryHirsch 6y ago
start the most advanced rocket engines (full-flow staged combustion cycle engines [1]) Well, not. During SN9 flight, one engine could not be re-lit, so SN9 crash-landed. During SN10 flight, the two engines that were needed for landing were lit, but there was an imbalance in the fuel mixture, one engine burned noticeable more yellow than the other, and now this. You'd think they'd analyze telemetry data from flights and on-ground testing and improve their design, but visibly they don't. And they are on notice already from the FAA for routinely blowing stuff up near a populated area.
- vardump 6y ago
  Wasn't SN11 already completed when SN10 failed? SpaceX has a production pipeline, they're working on multiple rockets in the same time. The lessons from SN9 and SN10 are probably incorporated SN20 or even later version. (Or corresponding versions of Raptor engines.)
- PeterisP 6y ago
  The key parts of SN11 were manufactured before SN9 was launched, obviously it can't incorporate design feedback from that. SN15 (the next launch) has a tweaked design of engines, but once again they are going to have multiple launches with these specific engines even if data from the first launch suggests some improvements. In fact, they had originally planned to do even more testing with this design (SN12,SN13,SN14 which had a bunch of work already done).
  - avmich 6y ago
    F-1 development included creating a particular debugging technique for rocket engines - bombs were put into chamber and exploded to create instabilities, so engine dampening capabilities were tested. I wonder if while making Raptors some interesting techniques were created. For F-1 the result was so good the production engines routinely dampened instabilities, so Saturn-V didn't have this kind of problem in flight. Raptors seem to be less developed - of course, they have much higher chamber pressure and efficiency...
- DennisP 6y ago
  They're having no trouble starting the engines on the ground, for launch, like any normal rocket company. They're having some trouble restarting them on landing, because getting the fuel to flow properly with that dramatic flip in the air is a bit of a challenge, which nobody else has ever attempted.
  - HarryHirsch 6y ago
    Engine relighting in zero gravity is routinely done these days. All current upper stages do this.
    - Gwypaas 6y ago
      They also generate their own gravity using ullage motors. This gives us very different profiles regarding the time constraints.
    - DennisP 6y ago
      If the landing maneuver put the engines and fuel tanks in zero-g, that might be relevant.
- greedo 6y ago
  Yeah, I'm sure they're ignoring telemetry data. They probably just go outside with a few polaroid cameras and capture pics. I can't tell if you're trolling, or if you're serious? SpaceX does an incredible job of instrumenting their rockets. They do plenty of "on ground testing" of Raptor, but some things can only be tested during flight.
- ctdonath 6y ago
  How often does software run perfectly on the 1st-4th try? FAA gives launch approval knowing full well what can, and does, go wrong. It’s FAA’s job to deny on the slightest justification of risk notice.

by nuccy 6y ago

HarryHirsch 6y ago

start the most advanced rocket engines (full-flow staged combustion cycle engines [1]) Well, not. During SN9 flight, one engine could not be re-lit, so SN9 crash-landed. During SN10 flight, the two engines that were needed for landing were lit, but there was an imbalance in the fuel mixture, one engine burned noticeable more yellow than the other, and now this. You'd think they'd analyze telemetry data from flights and on-ground testing and improve their design, but visibly they don't. And they are on notice already from the FAA for routinely blowing stuff up near a populated area.

vardump 6y ago
Wasn't SN11 already completed when SN10 failed? SpaceX has a production pipeline, they're working on multiple rockets in the same time. The lessons from SN9 and SN10 are probably incorporated SN20 or even later version. (Or corresponding versions of Raptor engines.)
PeterisP 6y ago
The key parts of SN11 were manufactured before SN9 was launched, obviously it can't incorporate design feedback from that. SN15 (the next launch) has a tweaked design of engines, but once again they are going to have multiple launches with these specific engines even if data from the first launch suggests some improvements. In fact, they had originally planned to do even more testing with this design (SN12,SN13,SN14 which had a bunch of work already done).
- avmich 6y ago
  F-1 development included creating a particular debugging technique for rocket engines - bombs were put into chamber and exploded to create instabilities, so engine dampening capabilities were tested. I wonder if while making Raptors some interesting techniques were created. For F-1 the result was so good the production engines routinely dampened instabilities, so Saturn-V didn't have this kind of problem in flight. Raptors seem to be less developed - of course, they have much higher chamber pressure and efficiency...
DennisP 6y ago
They're having no trouble starting the engines on the ground, for launch, like any normal rocket company. They're having some trouble restarting them on landing, because getting the fuel to flow properly with that dramatic flip in the air is a bit of a challenge, which nobody else has ever attempted.
- HarryHirsch 6y ago
  Engine relighting in zero gravity is routinely done these days. All current upper stages do this.
  - Gwypaas 6y ago
    They also generate their own gravity using ullage motors. This gives us very different profiles regarding the time constraints.
  - DennisP 6y ago
    If the landing maneuver put the engines and fuel tanks in zero-g, that might be relevant.
greedo 6y ago
Yeah, I'm sure they're ignoring telemetry data. They probably just go outside with a few polaroid cameras and capture pics. I can't tell if you're trolling, or if you're serious? SpaceX does an incredible job of instrumenting their rockets. They do plenty of "on ground testing" of Raptor, but some things can only be tested during flight.
ctdonath 6y ago
How often does software run perfectly on the 1st-4th try? FAA gives launch approval knowing full well what can, and does, go wrong. It’s FAA’s job to deny on the slightest justification of risk notice.