Where is my von Braun wheel?

Here's a summary of the themes expressed in the Hacker News discussion, presented in markdown format with direct quotes:

The Potential of Starship and its Impact on Space Infrastructure

The discussion frequently centers on the transformative potential of SpaceX's Starship, particularly its capacity for launching large masses to Low Earth Orbit (LEO) and its implications for future space endeavors. Starship is viewed as a significant engineering gamble, but one with a high potential reward.

• PaulHoule believes that "Assuming Starship makes it to orbit, it enables a range of structures larger than the ISS but smaller than the O'Neill colonies." He also notes, "A mission to Luna or Mars involves 12-20 launches of fuel tankers, for the same cost you can put up a lot of mass to LEO."
• TMEHpodcast describes Starship as "the ultimate engineering gamble, so many moving parts (literally) that getting it right might be as hard as building the habitats it’s meant to launch."
• bryanlarsen sees it as a "no-lose gamble though. If they fail we still end up with SuperHeavy as a massive, cheaper Falcon like architecture. If it succeeds, finally our space dreams can start to be realized."
• PaulHoule also states, "Starship to LEO is technologically conservative -- it's hard for me to believe that something like that couldn't be made to work. The uncertainty is that there's not a big market right now for launching things that size but the hope is that the low cost creates the market and maybe Starlink bootstraps it."
• dylan604 counters this by saying, "Is that true? It seems like there have been the want of lifting large payloads that must be shrunk to fit the actual launch capabilities. This usually means sacrificing so the thing that is launched is not what was really wanted originally. I think the market is there and just waiting for the thing to work."

The Challenge of In-Situ Resource Utilization (ISRU) and Atmospheric Composition

A significant portion of the conversation revolves around the practicalities of establishing self-sufficient space habitats, with a particular focus on the availability and utilization of resources like water and nitrogen.

• PaulHoule raises concerns about O'Neill colonies, stating, "O'Neill colonies with large airspaces seem impractical because you'd need large amounts of nitrogen or some other inert gas: you can find oxide rocks everywhere in space but pure oxygen environments aren't safe."
• TMEHpodcast wonders, "On nitrogen, I keep wondering: if in-space manufacturing matured, couldn’t we generate atmosphere by cracking water for oxygen and synthesizing nitrogen analogues through hydrogen-based pathways? Or is Earth’s air mix so specific that importing nitrogen stays unavoidable?"
• Response from jitl to TMEHpodcast’s questioning regarding atmospheric generation: "This is like saying “once we solve the problem, the problem will be solved”."
• Regarding water availability, dylan604 mentions, "There have been lots of new releases of frozen water discoveries on various bodies. Typically in craters that pretty much stay in shadow. Water doesn't seem to be that scarce. It's just not as abundant as on Earth."
• jitl questions the economics of lunar water, stating, "Going to the moon to get water and bring it back to earth orbit is going to be much more expensive than sending water from earth for a long time."
• PaulHoule argues the opposite regarding water transport efficiency: "Nitrogen needs a high-pressure bottle which is wasted mass, whereas water you can send to orbit in thin plastic and fabric bags like they do on ISS. Often on ISS they're actually shipping oxygen as water, but still the wasted mass of water being 11% hydrogen plus the wasted mass of the bag is more efficient than a high pressure gas cylinder."
• PaulHoule specifies for his proposed Bernal sphere: "For my baby Bernal sphere it is shipped either as LN2 or NH4. The large airspace needs a lot of it compared to the water inventory."
• Regarding Ceres as a resource, PaulHoule states, "Colonization of Ceres dominates all other space colonization opportunities in the solar system because there is no shortage of water and no shortage of nitrogen."
• Addressing the source of nitrogen and alternatives, PaulHoule lists: "(1) producing it by nuclear processes which looks tough and (2) various other alternative breathing gases such as Argon, Helium, SF6, etc."
• wildzzz offers a practical solution for transporting nitrogen: "We already built LOX tanks into rockets. Just send up a tank of LN2. It doesn't need the strength of a bottle, you just need thermally insulating materials which can be very light."

The Need for Space-Based Manufacturing and Economic Viability

The discussion touches upon the economic justification for manufacturing in space, differentiating between products that can only be made off-world and those that compete with terrestrial production.

• PaulHoule suggests that "The later work of O'Neill's students focused a lot on manufacturing. The proposal to build large structures by vapor deposition of metals onto a balloon still looks feasible. The solar power satellites shrank considerably in mass and it seemed that they could be built more practically from terrestrial materials."
• Later, PaulHoule elaborates on the economic aspect of space manufacturing: "I don’t think space manufacturing can ever be competitive for the terrestrial market but it can be competitive for things that can only be made in space."
• He also mentions a potential application: "A radiation shield for a deep space station or a simulated asteroid to test mining and manufacturing technology might compete with terrestrial materials."
• Another user, abe94, posed a fundamental question about priorities: "One question i've had is if its given that we care about making humans space faring, why focus on getting to new planets and colonisation and not instead on building the massive megastructures mentioned in the article as an end in itself?"

The Role of Advanced Propulsion and Construction Techniques

The evolution of propulsion and construction methods is discussed, moving beyond older concepts towards more modern and potentially viable solutions.

• PaulHoule critiques older ideas: "The image of the really big mass driver that looks like a train you get from O’Neill or Heinlein is obsolete. The US Navy built a 2.5km/s railgun you could fit on a ship."
• Regarding lunar resources, PaulHoule states, "The moon has at best a large glacier on it and my guess is Lunarians, if they could vote, would not want to export a gram of it but rather incorporate it into a circular economy."
• PaulHoule also expresses skepticism about asteroid capture mechanisms: "O’Neill’s students never came up with believable catcher and I’ve yet to see one I like."
• He further discusses the challenge of aerobraking: "I guess you could get to LEO if you could aerobrake but it looks tough because the outer atmosphere is always changing and a wild shot could trash your target, talk about a space junk problem."
• The feasibility of Lunar refueling is also brought into question: "Refueling on the Moon looks tough: water on the moon looks like a good bet, if we're lucky we find frozen carbon sources at the poles or in asteroid residues on the surface [1], but a hydrogen-oxygen rocket looks like a surer thing."

The Importance and Debate Around Artificial Gravity

The necessity and current understanding of artificial gravity versus zero-gravity environments for long-term space habitation are debated.

• bryanlarsen, reflecting on the ISS, states, "Long term zero gravity experience and experiments were very important information for future space flight. Now we know a lot more about the muscle atrophy, bone loss, and vision problems that the author complains of. Having the first space station be zero-g was probably the right move. But for the second one, more information on artificial gravity through centripetal force makes a lot of sense."
• In contrast, lupusreal argues, "The problem is the ISS wasn't the first station and we already knew zero-g fucks people up long before the ISS was built. Building the ISS anyway so we can waste more time studying the minutia of exactly how badly and quickly it fucks people up was a mistake. In truth the ISS exists for political reasons, not because it was a sound investment from a science and research perspective."
• bryanlarsen defends the ISS's contribution: "Because of the ISS we know that stays of greater than 12 months in zero gravity have real but minor impacts on the human body. So 3-4 month trips to Mars in zero-g are feasible."
• On the topic of gravity gradients in rotating habitats, schiffern notes, "If you can tolerate +/- 5% gravity level (which should be doable), instead of a stick for the habitable area you can rearrange the modules into a more compact blob, which should reduce radiation shielding. In LEO it doesn't really matter but it's more important in deep space."

The Role of Humans vs. Automation in Space Exploration

A point of contention is the extent to which human presence is necessary for space exploration and development, versus relying on robotic and automated systems.

• Animats makes a strong statement: "All the things worth doing in space turned out to be do-able without humans. Telescopes, radio relays, etc. The ISS doesn't really have much of a mission. Here's the list of current ISS experiments.[1] Many are aimed at the problems of keeping humans alive long term without gravity."

The Practicalities of Habitat Design and Repair

The discussion also touches on the physical challenges of building and maintaining habitats in space, including structural integrity and repair.

• rich_sasha expresses a common concern: "Made from soft materials, like rubber and nylon, there were concerns that collisions with micrometeorites could puncture the station with fatal outcomes. I fixed many an inner tube punctures, but I'd rather not be blowing at glue while my precious oxygen is hissing out towards outer space!"
• dylan604 humorously suggests a solution: "Just send up a case of Flex Seal. Maybe the spreadable version instead of a spray on version. Not sure what zero-G would do to an aerosol can like that."
• tokai offers a more technically oriented suggestion: "I bet something like tubeless sealant could be utilized for automatic sealing."