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If refueling was already a highly questionable proposition given 5 or 10 years of fuel, having ~20 years of fuel certainly doesn't increase the reward in risk-v

If refueling was already a highly questionable proposition given 5 or 10 years of fuel, having ~20 years of fuel certainly doesn't increase the reward in risk-vs-reward analysis.[0] In what hypothetical scenario does fuel deplete at a greater than expected rate, in a way that wouldn't also call into question the reliability and expected lifespan of the remaining limiting factors? Accidental commanded release? A leak? Station-keeping being more demanding than expected? Those would all move risk-v-reward in the wrong direction. And it doesn't substantially decrease the cost or risks, other than what might be gained by an extended development period, which would need to be weighed against simultaneous advances better applied to and spent on a successor. So maybe not an absolutism, but an already highly-unlikely proposition who's chances of implementation just decreased dramatically due to the new information at hand. [0] By ending up with an older/ closer to failure but refueled satellite, and a decreased relative value of remaining potential science/observations, presuming highest value science is done first.

dredmorbius 5y ago
These are good points. They are not the elements of your initial nor follow-up comments with which I've had issue. And you continue to not address those. As for what might lead to low-fuel-but-serviceable observatory: reaction-wheel degreadation shy of failure (there are multiple redundant wheels for each axis of rotation), possibly some kind of solar-storm or solar-wind interaction which increases station-keeping requirements. It's difficult to foresee what previously anticipated scenarios might emerge, for all the obvious reasons. But if I had a $10 billion low-on-fuel observatory on my hands, it was still turning in good science, and my capabilities to provide it with fuel had improved markedly, and there was nothing else obviously imminantly limiting lifetime ... I might opt for the top-up. Even at a cost of a few sheckles. Keep in mind that the opportunity cost isn't the amortised value of the observatory, but its projected future life and the cost of replacing that functionality. I don't know what the associated values here are. I could envision a reality in which those turned favourable for a refueling mission. Which, again, contradicts your original, and several-times-sustained, "completely unneeded" assertion. The horse seems quiet well flogged, and in the interests of a peaceful death, I'm begging off further beating of it.
- beerandt 5y ago
  I think we'd be pretty much in agreement if only 5 years of fuel were left.

dredmorbius 5y ago

These are good points. They are not the elements of your initial nor follow-up comments with which I've had issue. And you continue to not address those. As for what might lead to low-fuel-but-serviceable observatory: reaction-wheel degreadation shy of failure (there are multiple redundant wheels for each axis of rotation), possibly some kind of solar-storm or solar-wind interaction which increases station-keeping requirements. It's difficult to foresee what previously anticipated scenarios might emerge, for all the obvious reasons. But if I had a $10 billion low-on-fuel observatory on my hands, it was still turning in good science, and my capabilities to provide it with fuel had improved markedly, and there was nothing else obviously imminantly limiting lifetime ... I might opt for the top-up. Even at a cost of a few sheckles. Keep in mind that the opportunity cost isn't the amortised value of the observatory, but its projected future life and the cost of replacing that functionality. I don't know what the associated values here are. I could envision a reality in which those turned favourable for a refueling mission. Which, again, contradicts your original, and several-times-sustained, "completely unneeded" assertion. The horse seems quiet well flogged, and in the interests of a peaceful death, I'm begging off further beating of it.

beerandt 5y ago
I think we'd be pretty much in agreement if only 5 years of fuel were left.