Comment by blkhawk | Hacker News Reader

Comment by blkhawk | Hacker News Reader

I find most interesting about Seveneves is how the technological assumptions have changed since the book predates the first landing of a falcon 9 booster stage. Getting the tin cans into orbit is described as using traditional use-once rockets. Assuming that you can reuse the first stage 20 times alone would enormously scale up the avaible cargo and m³ you can get into orbit since the upper stages would need not nearly as many rocket engines (and those would be the limiting factor in onstruction really).

if you could get a starship booster to work with similar reliability you could put up about 2-3 times the m³ of the ISS with each launch (assuming a wet-workshop design for he upper stage where the empty fuel tanks are prepared to be made habitable).

assuming an "ISS" can host 10 people that means for 20k people in orbit you need 50 boosters launch 20 times each for a total of 1k launches. This is a very small amount for a larger country like the US on a war economy considering that the upper stages would be the somewhat easier to construct parts.

I would assume that basically every industralized country on earth put up at least as many.

I think the biggest technological assumption, and the one I simply couldn't get past, was that the technology from pre-zero time would last long enough for very small groups of people with very limited resources could keep functioning for long enough for the society to develop its own capacity for fabricating new parts. The stuff they have would wear out long before that could happen.

- the spacers would run out of enough water as there would always be a small loses that accumulate, but a growing population would mean less available for propulsion needed to get at new comets. The cleft had lots of metal, but little else. The also had a set energy budget, there was no new nuclear power devices to be had, and they couldn't manufacture new solar cells - these would degrade over time.

- the diggers would be toast from heat. If the earth heated up as much and for as long as stated, they'd fry. If they dug deeper the earth gets hotter, if they are too close to the surface its gets hotter. Over time the surface heat would penetrate further and further in. There would be no place from them vent waste heat.

- the pingers would go first. The deep ocean environment allows no mistakes. Even minor failures would cascade into major ones.

there is a source of volatiles "close" by - earth. with all that water in the atmosphere you can build satellites that orbit low and siphon it and other valuable gases like nitrogen off. The Satellites would use aerodynamic effects and the siphoned atmosphere for propulsion.

As for Solar cells there are factors to consider - they would degrade differently than cells in low earth orbit since factors like atomic oxygen and thermal cycling are less of an issue while I imagine micrometeorites are just terrible. Modern cells degrade at at 0.5% per year in LEO. At 1%/year degradation that means you have 85% capacity after 15 years. So we are talking decades for cells once they have been manufactured here. Cells not in the sun would last forever so they do not degrade in storage.

In the case of the diggers I have not done the math on thermal propagation through bedrock but It would all depend on when the people in orbit start building a sunshade at L1.

the pingers are not in the deep ocean. They are whatever depth the water is below 30°. Some considerations of diving change if you cannot or not plan to surface - ever. We are talking open diving bell environments here and heh - topmarines or ü-boats :) They have a very easy source of energy in the gradient between the very hot atmosphere and the cooler ocean water. no need for nukes for power. you distill oxygen as a byproduct of that snorkeling process. main issue would be metals.

> there is a source of volatiles "close" by - earth

The spacers weren't near earth, they were out at the (former) moon's orbit. Getting to and from Earth or anywhere not near moon's orbit would require considerable propellent. This is even assuming that the thrusters continue to work - they only have so many parts.

The book makes reference to hundreds if not a 1000 years before the spacers really started to develop things again - well past the base case for solar cells.

For the diggers, the sunshade would have been way after and even if in place would have provided no help as all the energy of consequence was coming from the bolides burning up in atmosphere and hitting ground. This worst of the hard rain lasted for at least a few hundred years in the book, although the OP analysis suggests maybe the peak hard rain may have been shorter.

For the pingers, another big issue would be corrosion. I imagine the ocean would eat away at most of their stuff long before they could develop the capacity to make more.

I could get past their survival (if they didn't there would be no more story!) but the level of technological development really strained my imagination. I mean, are we supposed to witness a space-faring civilization that can hoist a fucking city block on carbon fibers (or whatever) and move it up to space and then back down on Earth, while simultaneously:

- It has no Cold War era level technology to build a dozen spy satellites to survey every square meter of the earth, with which most of the Part 3 plot would simply not happen;

- It cannot build a simple propeller plane, so the pilot has to instead strip naked (I think - it's been a while since I read it) and wear some kind of scifi haptic feedback suit that will tell you how the wind is blowing so that you can steer your unpowered glider in the correct direction.

Honestly the second point reads like the author's sexual fantasy leaking into the story.

In the Acknowledgements, Neal thanks the Blue Origin team for the time he spent with them in the 2000s. Maybe he didn't want to hurt their feelings.

They only had a chance in space because they happened to have that iron asteroid in orbit to hide behind. I don’t think they could have fit a huge number of crafts or many bigger ones behind it.

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