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I wouldn't say that the booster landings are fairly unreliable. Technically they are still in the experimental stage. They're also 8 for 14 at this point, with

I wouldn't say that the booster landings are fairly unreliable. Technically they are still in the experimental stage. They're also 8 for 14 at this point, with the last landing failure being at least 4 launches ago I believe. Plus it is a big deal when they go kerplooie. On each coast, they only have 1 ASDS for landings, and if a core explodes on one of those then it's out for like a month of repairs. Failures on land are probably easier to deal with, but we haven't even seen one of those yet. Plus within the next year they are basically going to stop producing new cores, so loosing one won't be "cheap"

mikeash 10y ago
Losing 6 out of 14 is more than enough for me to call it "fairly unreliable." Imagine if NASA had destroyed six Space Shuttles during development. The genius of SpaceX's approach is that they built a landing system where it's OK to be unreliable for a while. Instead of being a billion-dollar item like the Space Shuttles were, the Falcon 9 boosters are a few tens of millions of dollars apiece, and the launches are priced to cover the entire cost of them plus more. ASDS repair depends on the nature of the failure. When a low-margin GTO mission miscalculates and craters, that does indeed take some fixing. A JASON-style tip over and kaboom seems to basically involve picking up the pieces and repainting the lines. I think your last sentence reverses cause and effect. If they substantially cut down on core construction, that will be because the landings became reliable enough for that to happen. That doesn't make failures costly now. I will also note that their landing approach is inherently unreliable to a degree, because there's little redundancy. If Falcon 9 loses an engine on the way up, it's fine. If it loses an engine during the landing burn, it's going to kerplode. If it loses an engine on the way up, then that will likely wreck the fuel margin needed for landing. I'd be shocked if Falcon 9 can ever achieve anything like the Shuttle's perfect 133 out of 133 landing record. (I'm not counting Columbia since it was ultimately a launch accident that manifested on reentry, and never got anywhere near the actual landing.) But that's fine, they don't need to.
- gozur88 10y ago
  >The genius of SpaceX's approach is that they built a landing system where it's OK to be unreliable for a while. For booster landings it's probably okay to be unreliable forever as long as the failure rate is estimated properly and the value of recovered boosters exceeds the cost of developing and maintaining recovery capability. Since there are no people or cargo involved it's a straight exercise in accounting.
- samcat116 10y ago
  I believe I read somewhere that the 3 engine landing burn could loose one engine for LEO missions and such, but don't quote me on that.
  - JshWright 10y ago
    The landing burn is generally a single engine. The only time they have done three engine landing burns is for very tight margin GTO launches (and even then, it's not three engines all the way to the ground, the two outboard engines shut down about halfway through the landing burn). In cases where they are using three engines during the landing burn, losing one would be catastrophic. You'd lose a third of the thrust you were counting on, and the remaining thrust would be highly asymmetric. The other outboard engine can't gimbal far enough to keep the thrust vector through the center of mass of the rocket.

mikeash 10y ago

Losing 6 out of 14 is more than enough for me to call it "fairly unreliable." Imagine if NASA had destroyed six Space Shuttles during development. The genius of SpaceX's approach is that they built a landing system where it's OK to be unreliable for a while. Instead of being a billion-dollar item like the Space Shuttles were, the Falcon 9 boosters are a few tens of millions of dollars apiece, and the launches are priced to cover the entire cost of them plus more. ASDS repair depends on the nature of the failure. When a low-margin GTO mission miscalculates and craters, that does indeed take some fixing. A JASON-style tip over and kaboom seems to basically involve picking up the pieces and repainting the lines. I think your last sentence reverses cause and effect. If they substantially cut down on core construction, that will be because the landings became reliable enough for that to happen. That doesn't make failures costly now. I will also note that their landing approach is inherently unreliable to a degree, because there's little redundancy. If Falcon 9 loses an engine on the way up, it's fine. If it loses an engine during the landing burn, it's going to kerplode. If it loses an engine on the way up, then that will likely wreck the fuel margin needed for landing. I'd be shocked if Falcon 9 can ever achieve anything like the Shuttle's perfect 133 out of 133 landing record. (I'm not counting Columbia since it was ultimately a launch accident that manifested on reentry, and never got anywhere near the actual landing.) But that's fine, they don't need to.

gozur88 10y ago
>The genius of SpaceX's approach is that they built a landing system where it's OK to be unreliable for a while. For booster landings it's probably okay to be unreliable forever as long as the failure rate is estimated properly and the value of recovered boosters exceeds the cost of developing and maintaining recovery capability. Since there are no people or cargo involved it's a straight exercise in accounting.
samcat116 10y ago
I believe I read somewhere that the 3 engine landing burn could loose one engine for LEO missions and such, but don't quote me on that.
- JshWright 10y ago
  The landing burn is generally a single engine. The only time they have done three engine landing burns is for very tight margin GTO launches (and even then, it's not three engines all the way to the ground, the two outboard engines shut down about halfway through the landing burn). In cases where they are using three engines during the landing burn, losing one would be catastrophic. You'd lose a third of the thrust you were counting on, and the remaining thrust would be highly asymmetric. The other outboard engine can't gimbal far enough to keep the thrust vector through the center of mass of the rocket.