5 ms·

But the primary cost of lifting fuel (if you have a reusable rocket) is fuel. Leaving us back at cheap. But we're essentially arguing whether max payload per l

• saagarjha 7y ago
  With exponential compounding, I wouldn’t be so sure that it’s still cheap…
  • CydeWeys 7y ago
    Yeah, and with much higher required dv and more required stages this would be a huge problem. But we only need two stages to orbit when launching from Earth, so it's really not that big of a deal, and it turns out that optimizing for reusability ends up being a lot cheaper than optimizing for minimum fuel use. For example, it only costs $200k for a fuel load of Falcon 9 fuel. If you got rid of reusability you'd need less fuel and could save tens of thousands of dollars ... but at the cost of needing to build a new $54M spacecraft with each launch. Clearly that trade-off isn't worth it. So yes, fuel is cheap.
    • Retric 7y ago
      Fuel becomes more expensive on reusable spacecraft. Granted, the first pound of fuel is cheap, but the costs keep rising. With one and done you have a larger mass fraction to work with. Reusable spacecraft operate on much tighter constraints. Every single wasted pound in Space X’s design likely costs them 100’s of thousands of dollars in lost profit over time.
      • Retric 7y ago
        Not sure what’s to disagree with about that: “The reusable Falcon 9’s performance to GTO is listed at 5,500 kilograms. The same rocket in fully expendable version can lift 50 percent more payload — 8,300 kilograms. For the Falcon Heavy, the performance to GEO is about 2.8x that of the reusable version” https://spacenews.com/spacexs-new-price-chart-illustrates-performance-cost-of-reusability/ https://spacenews.com/spacexs-new-price-chart-illustrates-pe... Reusable means cost savings, but it has a dramatic reduction in cargo capacity. This means more trips to get the same mass into orbit, which means mire fuel directly used and every extra lb in the design is then carried up multiple times while further requiring more trips.
        • ncmncm 7y ago
          Which trips each cost much less because you don't have to build another rocket to do each with. Or, equivalently, in one trip with a bigger rocket you have left over from another launch, because you didn't ditch it.
          • Retric 7y ago
            That’s great if you’re transporting large numbers of the same thing like star link satellites. However, many payloads are worth sacrificing the first stage. Just look through the “No attempt“ missions in 2018 for some of the reasons why: https://en.m.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_Heavy_launches https://en.m.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_... Which again demonstrates reusability is really expensive, though clearly not always as expensive as a new rocket.
            • JshWright 7y ago
              Many of the "no attempt" 2018 missions were because they were reflights of older models of cores (pre-Block 5) that weren't worth keeping around. Expendable launches for Block 5 boosters are far less common.
              • ncmncm 7y ago
                Right, if you can throw away an obsolete rocket stage as part of profitably launching a much bigger load than you would have done with a re-usable one, it's hard to justify not doing it, and just selling it for scrap instead.
                • Retric 7y ago
                  They are also removing new rockets. SpaceX is simply going to prioritize older ones for destruction assuming they can handle the payload. Remember while the first stage is significantly more valuable, it's not just a question of fuel the upper stage is destroyed with both approaches. So, combined with significantly lower payloads the cost per kg does not drop as much as you might think.