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I was saying that the processes used to be more brittle, at least from a outsider's point of view. I always found the shuttle "single attempt" landing as not c

by joss82 10y ago

I was saying that the processes used to be more brittle, at least from a outsider's point of view. I always found the shuttle "single attempt" landing as not cautious at all. What if anything go wrong? Do you just crash and kill all crew on board? Well, I'm comparing apples to oranges actually. See Spacex booster landing is quite hit and miss also, actually. Sorry, forget what I was saying, it's just the wrong things to compare :)

mikeash 10y ago
I don't think the Shuttle landing was particularly problematic. They had a lot of control over the glideslope and lots and lots of runway to work with. I'm sure it's a lot more challenging than the sailplanes I fly, but I wouldn't have any major safety concerns flying on the Shuttle during landing. It's true that SpaceX's booster landings are fairly unreliable, but they don't have to be reliable. They make a bit of a mess when they go kerplooie, but it's no big deal. Lives aren't at risk, and the equipment is cheap enough to lose. The launch was a much better example of brittleness in the Shuttle system. The solid rocket boosters couldn't be shut off or ejected once they lit, so that was about two minutes where there were no options if anything went wrong. Even after booster separation, the abort modes were so difficult that NASA refused to ever test them. The first Shuttle commander said that a return to launch site abort would require "six miracles followed by an act of God" to pull off. Every other manned spacecraft has the capability of aborting a launch at least semi-reliably, and proves it with testing.
- samcat116 10y ago
  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.
- ben_bai 10y ago
  > I don't think the Shuttle landing was particularly problematic. They had a lot of control over the glideslope and lots and lots of runway to work with. I'm sure it's a lot more challenging than the sailplanes I fly, but I wouldn't have any major safety concerns flying on the Shuttle during landing. Well the shuttle is a big heavy glider with little wings. One try, and down from 30,000 feet to ground in 3 minutes. Not problematic, but very special. https://www.youtube.com/watch?v=Jb4prVsXkZU https://www.youtube.com/watch?v=Jb4prVsXkZU
bisby 10y ago
The booster landings are all lumped together, but they all have very different parameters. They've never failed a landing on land. and since they succeeded at sea, they've only failed once since then, and that was coming in from GTO, which is borderline not possible by their own admission, they only tried just to get more data points. The upcoming Echostar 23 mission is flying in expendable mode (no landing attempt) because the mission parameters simply don't allow for a landing. They could try and fail, but they don't really need more data points - especially when people don't realize that these experimental landings are just experimental, and it winds up with bad press. spacex does walk a fine line between "rapid development causing potential issues" (see AMOS-6) and "abundance of caution" (see CRS-10 delay on saturday)

by joss82 10y ago

mikeash 10y ago

I don't think the Shuttle landing was particularly problematic. They had a lot of control over the glideslope and lots and lots of runway to work with. I'm sure it's a lot more challenging than the sailplanes I fly, but I wouldn't have any major safety concerns flying on the Shuttle during landing. It's true that SpaceX's booster landings are fairly unreliable, but they don't have to be reliable. They make a bit of a mess when they go kerplooie, but it's no big deal. Lives aren't at risk, and the equipment is cheap enough to lose. The launch was a much better example of brittleness in the Shuttle system. The solid rocket boosters couldn't be shut off or ejected once they lit, so that was about two minutes where there were no options if anything went wrong. Even after booster separation, the abort modes were so difficult that NASA refused to ever test them. The first Shuttle commander said that a return to launch site abort would require "six miracles followed by an act of God" to pull off. Every other manned spacecraft has the capability of aborting a launch at least semi-reliably, and proves it with testing.

samcat116 10y ago
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.
ben_bai 10y ago
> I don't think the Shuttle landing was particularly problematic. They had a lot of control over the glideslope and lots and lots of runway to work with. I'm sure it's a lot more challenging than the sailplanes I fly, but I wouldn't have any major safety concerns flying on the Shuttle during landing. Well the shuttle is a big heavy glider with little wings. One try, and down from 30,000 feet to ground in 3 minutes. Not problematic, but very special. https://www.youtube.com/watch?v=Jb4prVsXkZU https://www.youtube.com/watch?v=Jb4prVsXkZU

bisby 10y ago

The booster landings are all lumped together, but they all have very different parameters. They've never failed a landing on land. and since they succeeded at sea, they've only failed once since then, and that was coming in from GTO, which is borderline not possible by their own admission, they only tried just to get more data points. The upcoming Echostar 23 mission is flying in expendable mode (no landing attempt) because the mission parameters simply don't allow for a landing. They could try and fail, but they don't really need more data points - especially when people don't realize that these experimental landings are just experimental, and it winds up with bad press. spacex does walk a fine line between "rapid development causing potential issues" (see AMOS-6) and "abundance of caution" (see CRS-10 delay on saturday)