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Comment by wolf550e | Hacker News Reader

Yes, Zubrin has been advocating for this since 1990.

https://www.youtube.com/watch?v=3UChuIqIKF4&t=1722

His explanation about the real situation with NASA and why the human spaceflight program has not accomplished anything is extremely disheartening.

https://www.youtube.com/watch?v=3UChuIqIKF4&t=417

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The real problem is you need to deliver so much material to orbit to create artificial gravity (a rotating space station) it's very expensive.

We could create a simple rotating system with two pods connected by a long cable, but then it's not easy to dock to it, and there are balancing issues.

> you need to deliver so much material to orbit

Not that much. You'll need an inflatable module (so the wide part can still fit in the cargo fairing of an SLS) and a carousel that can be assembled inside it to rotate and give the crew enough gravity to counteract the effects of the zero-g environment. You'll need power to keep it rotating and radiators to get rid of the heat.

The unfortunate thing is that this cannot be tested attached to the ISS as the vibration would ruin the micro-gravity environment crucial for many experiments there.

I agree that artificial gravity, plus radiation protection, are must haves for long duration deep space flights.

With inflatable structures, artificial G is possible to do with much less mass than you think. Using Bigelow Aerospace's BA330 as a proxy (60kg/cubic meter of habitable space), you would need between 5,000 to 20,000kg to build a 100m long passageway between 1 to 2m across on the interior. Inflatable structures are made from materials that handle tensile loads well (the hoop stress from pressurization in particular).

As an added bonus, the inflatable passageway, besides functioning as a tether, creates usable habitable space, so if one is clever, it is not strictly speaking deadweight mass.

Alex Tolley and I looked at this in detail while working on papers related to our "spacecoach" design pattern, you can find a good intro at https://medium.com/@brianmsf/traveling-to-mars-just-add-wate...

> Inflatable structures are made from materials that handle tensile loads well (the hoop stress from pressurization in particular).

And conveniently, hoop stress due to pressure in a cylinder is twice the axial stress due to pressure, so you're free to add quite a bit of axial stress due to the mass of all the items in your artificial gravity environment!

That should get much cheaper once spacex gets things right.

Even if SpaceX made the launch costs a hundred times cheaper than the shuttle, it would still cost over $500 million and that would only launch a tiny fraction of the mass needed for a full artifical gravity space station. The estimated cost of the International Space Station so far is over $100 billion not including launch costs so even if another company cut costs there by a factor of ten, thats $10 billion, again a small fraction of what you would need. You can cut out bureaucracy and save money with a private company instead of government agencies but this would be a one off design made for space habitation so there really isn't much room to drastically reduce costs. If you want this thing to also travel around the solar system, you'd need to complicate the design even more because the ISS is solar based and has only orbital correction propulsion which is much cheaper.

It's possible but I don't think it will be economical or practical for a long time.

10 billion is about the same order of magnitude as an aircraft carrier. The US has ten.

Yes, but the US Navy builds them one at a time, every 5 years, so $2B/year and they are used to guarantee the cooperation of an important ally/partner with the USA instead of with Russia or China. There is a big cost, but there is a monetary benefit from the deals made by promising to always keep a carrier strike group near someone's shores, ready to defend from foreign aggression.

NASA's budget in 2015 was about $18 billion while the defense budget was just shy of $600 billion. If we lived in a fantasy world where NASA was considered as important as defense, we'd be an interplanetary species by now. Alas, we don't, and when we consider the feasibility of an idea we have to take that into account.

> It's possible but I don't think it will be economical or practical for a long time.

So is there an actual technical path to make things cheaper in the very long run ?

That is entirely unclear due to how the geopolitical landscape has been evolving. SpaceX's major innovations amount to cutting out corporate bureaucracy, cutting operating costs, and taking advantage of economies of scale not available to the last generation of aerospace manufacturers. SpaceX hasn't invested in science, they've invested in engineering and logistics that make them competitive with the current state of the art, up to and including their first stage recovery technology. For example, they use kerosene instead of liquid hydrogen, cutting out the huge manufacturing and storage cost, and because they're not subject to Congressional pork barreling, they don't have to split manufacturing across many states and districts. Whether they can make the leap from basic chemical propulsion to something that can really drop costs by an order of magnitude or two remains to be seen.

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