Primary energy use per capita is a good discussion to have about our footprints on earth, but they include significant inefficiencies that simply wouldn’t be present on a spacecraft.

First, on Earth, we consume a lot of energy on transportation. There’s not really an analogue in the spaceship side of things, except maybe the spaceship’s own propulsion. Even then, though, most propulsion technology wouldn’t generate all that heat in the spacecraft itself, so there’s no need to cool an equivalent amount of energy used.

Second, we use a lot of energy making our living spaces habitable, with heating and cooling. Using proper reflection and radiation and shielding and all that can help keep a spaceship a comfortable temperature without spending as much energy as would be required to heat or cool a residence on the Earth’s surface.

Third, with Earth statistics, we talk of primary energy usage, which includes a lot of wasted energy. Thermal power plants tend to have less than 50% thermal efficiency, and fuel-burning heat engines tend to have less than 30%. That waste heat is part of the global energy consumption stats in a way that wouldn’t need to be factored in for a solar panel powered spaceship, because there’s not an equivalent source of excess waste heat.

So I think when you look at individual energy usage, you’ll see there are literally multiple orders of magnitude difference between different individuals with different lifestyles, even within the same developed economy. A population who never leaves the confines of the ship doesn’t have to budget energy for transportation (28% of the world’s energy usage), heating and cooling buildings (25% of the world’s energy use), or anything like most of the industrial sector.

For things like cooking or heating water, there may need to be major qualitative differences in order to support a living arrangement in a ship (more enclosed cooking appliances like pressure coolers or microwaves, fewer stoves that emit waste heat all around).

And agriculture is of course the big problem. But we wouldn’t be able to naively assume that the energy use per food calorie produced would be within an order of magnitude. Photosynthesis is really inefficient. So is the whole growing of an entire plant to focus on the parts of the plant that we eat. There may need to be some form of synthetic food, or partially synthetic food, that creates edible macronutrients without a biological feedstock.

But that’s a separate problem. I still don’t think that solving habitable spaceship cooling requirements will necessarily overlap with solving space data center cooling requirements.

Figuring out data centers in space is pretty much a prerequisite for any sort of significant transorbital flight

I don’t think that’s true. They seem like two separate problems.

AI datacenters use power at such magnitudes that trying to solve the cooling problem for that kind of satellite or ship might not be all that applicable to a ship occupied by living humans.

A data center satellite might be able to run hot to improve cooling characteristics. The Stefan-Boltzmann law makes radiators much more effective at higher temperatures. So maybe the solution there would involve building out chips and server components that can run hot, like above 90°C, with cooling systems designed to operate at those higher temperatures.

Meanwhile, it might be that the human occupied space stations will need to have temperatures that support human life, closer to 18°C. At the same time, why would a human occupied space station need megawatts of power, and the accompanying need to reject megawatts of waste heat?

However, there’s probably a reason traditional power plants never use jet engines for power production.

They don’t use used jet engines, no. But a gas turbine for a gas power plant shares many engineering principles with jet engines, and often many shared parts.

And generally, for stationary plants, the heat of the exhaust can be used to boil steam and get another cycle’s worth of work out of the heat, for even greater efficiency.

Please describe how sunshine alone will sustain this unchanged.

Because you’re ignoring the hugely inefficient baseline of how much sunlight we have historically been able to harvest.

From this page, sunlight-to-biomass efficiency of wild plants is less than 1%. For crops specifically bred over thousands of years to grow as much useful biomass as quickly as possible in each season, the number ticks up to 2%. But even that number also fails to account for the periods in which fields lay fallow between seasons, or for crop rotation.

Then, once you have that biomass, converting it into a useful form of fuel for burning, or food for biomechanical energy, has huge efficiency losses along the way.

Meanwhile, solar panels achieve approximately 25% solar efficiency.

That’s how we can collect far more energy from the sun today than at any point in the past. Biology is inefficient compared to photovoltaics.

Nuclear plants that are already running are very cheap to continue running.

That’s mostly beside the point, though, because, as you explain, they’re very expensive to construct, and that’s before even getting to the ones that never get completed because the cost overruns get the project canceled.

So I’m always in favor of running existing nuclear plants as long as possible, but am pretty skeptical of building any new nuclear plants.

Most usable energy on Earth comes from fusion of hydrogen into helium in the Sun, creating radiation that hits the Earth. That’s solar energy, of course, either thermal or photovoltaics, but also the wind caused by uneven warming, the evaporation and condensation of water that flows downhill for hydro power, the chemical bonds formed by photosynthesis making renewable biofuels or older fossil fuels.

Some portion of energy on Earth is gravitational potential energy and the kinetic energy of stuff moving around settling into a lower energy state: the moon dragging the oceans around, the heat of the Earth’s core spinning and tectonic plates moving from the momentum of all the dust that got pulled into what is now a planet. Geothermal and tidal energy mostly come from these planet scale phenomena.

Some portion of energy is the release of energy stored in nuclei formed from some past supernova, of less stable isotopes of atoms heavier than iron. Some portion of geothermal is traceable to this kind of nuclear decay, and obviously we can isolate and enrich those nuclear elements into fission fuel for nuclear power, as well.

Hard to categorize the second and third categories into solar power, though. Yeah, it comes from astronomical phenomena tracing back to how our solar system and planets were formed, from the materials they’re made out of, and found their way into their current shapes and orbits, but is that solar power?

New nuclear plants take like 10 years to build, and need to plan out a 50+ year useful life in order to be worth the up-front construction costs.

I wonder what the state of energy production in 2075 will be, where a nuclear power plant designed in 2025 and completed in 2035 will still have 10 years in order to break even on cost, competing with whatever the state of the art is on generation in 2075. Fusion? Widespread solar+wind+geothermal+batteries? Something we haven’t even dreamed of?

That’s why I’m skeptical of nuclear fission these days. It locks us in too long.

since there are many jurisdictions that won’t build nuclear capacity for political and societal-preference reasons, rather than technical ones

Most jurisdictions aren’t allowed to build nuclear, for nonproliferation reasons. That’s because nuclear technology can be used for nefarious purposes, and requires a highly functioning security apparatus in order to enforce safety requirements. So as a society we’ve tried to keep it out of the hands of those that the great powers have decided can’t be trusted with the tech.

Which then raises the uncomfortable question of whether we should trust ourselves, the current great powers, with this technology? If we plan out a 50-year useful life for a power plant, do we trust that the governments and companies operating that plant (and its supply chains and its waste management) will still be doing things safely in 50 years?

These days, I’m less sure.

You’re all over the place. Are you talking about performance or price? Porsche has created a track monster in the Taycan Turbo GT, setting impressive times in established tracks (Laguna Seca, Nurburgring), much faster than most ICE supercars. Plus I guess it holds the bizarre title of fastest production 4-door around those tracks (despite having no rear seat), EV or ICE.

But if we’re talking about actual track performance, which you brought up first, there are EVs at the top that can hang with ICE supercars. Yes, they can also drag race. The other stuff you’re saying about “fun” is different (it’s more fun to drive a manual transmission, but at this point manuals are slower), and talk of resale value is entirely different.

EVs weight too much for anything other than drag racing.

Most production EVs perform pretty well compared to similarly priced vehicles. Nurburgring records, for example, have plenty of electric cars getting sub-8:00 times, including some that cost less than $50k. Not a lot of street legal ICE vehicles you can say that about.

The Hyundai EVs are ugly, but so are Hyundai ICE vehicles. Their whole brand’s design language is very ugly to me.

Kia, on essentially very similar (if not basically the same) platforms, looks way better, but generally costs more.

I’ve done a few cross country moves where I would only try to time out a stop for all three reasons at a time: restroom, refuel, meal. I was doing pretty great with only one stop every 4-5 hours or so, 14 hours of driving per day.

As an EV owner (and a parent who now usually has kids in the car), I go at a much more leisurely pace and don’t need to do that kind of road trip anymore. But I totally get why it’s the default for a lot of people trying to get from one place to another

For major highway corridors, we need to have chargers that are less than a 5 minute detour from the highway, at least one every 50 miles.

Otherwise someone with 250 miles of range, who prefers 50 miles of buffer (in case a charger has a long line or is broken) might need to stop every 150 miles. That’s a break a little bit too frequently.

Isn’t the stereotype that in Europe, 100 miles is a long distance, but in the United States, 100 years is a long time?

Yeah, I’m not an aerospace guy, but I’m wondering whether the maturity of the commerical passenger air travel industry has lessons to adopt for the 60 years since the Concorde was designed. The cabin and fuselage were so small that there’s not a lot of room for different seating configurations, the over-land speed restrictions limited its feasible routes.

I’m middle of the road when it comes to optimism about whether commercial supersonic flight will approach business class prices within the next 2 or 3 decades, and whether such a service could one day be environmentally equivalent to the 2026 impact of 2026 commerical air travel.

Yeah, the Concorde was interesting in that its design was optimized for cruising, so that taxiing, takeoff, and reaching cruise altitude/speed took a gargantuan amount of fuel compared to other aircraft and even to its own cruising efficiency.

I can see why someone could look at that and assume that they could do better with modern design principles, including the knowledge that planes need way more passenger seats to improve the per passenger efficiency.

Then again, the company that took the most concrete steps towards developing a supersonic engine pivoted to creating gas turbines for AI data centers (but was just dropped by its major customer on that, so who knows what they do next).

Based on their work on the X-59, I wonder if they just want to collect sensor data on its sonic boom characteristics, and feed that into a model for sonic booms.

They don’t need to be able to build something in order to be able to learn something from that thing in operation.

What’s interesting about supersonic flight is that there’s been some developments on making supersonic flight more fuel efficient.

The F-22’s big strategic advantage is that it can supercruise at Mach 1.5, without afterburners, and although the details are not publicly known, the publicly known facts suggest that it’s about 3x as fuel efficient as the other fighters in the US arsenal.

If they can get supersonic flight to be more fuel efficient, and avoid sonic booms (an active area of research for NASA’s X-59 project), and we develop manufacturing capacity for huge amounts of synthetic sustainable aviation fuel from CO2 and water and green energy, then maybe we’ll be at a place where supersonic commercial flights can be both economically feasible AND environmentally responsible. Probably not in my lifetime, but still something I expect to happen in the next century or so.

that 20000-30000 premium over ICEs

What currency are you using for this comparison? Definitely not USD.

A Tesla Model 3 runs for about $40k. A Camry runs for about $35k. Or if we want to go down market a Nissan Leaf is about $30k and probably comparable to a $25k Sentra.

Similar trim levels of vehicles offered as both EV and gasoline powered show minimal difference. Compare the Ford F-150 Lariat in both the gasoline ($75k) and the EV versions ($79k). Or the new Lexus ES, where the EV ($49k) is actually cheaper than the hybrid ($51k).

And if you go into the used market, EVs are starting to hit that market in real numbers, too. Plenty of options for under $20,000, and a handful of options for under $10,000.

Cars are expensive. EVs generally are close to that already expensive price.

I think you have to look at the actual orders of magnitude difference in raising the temperature of water versus air. The Arizona story you linked is about a study that found up to +4°F (+2.2°C) temperatures in air.

The same amount of heat, spread across the same volume of water moving at the same speeds, would only raise that water by 1/830 as much, for a +0.0048°F (+0.0027°C) 1/3300 as much, for a +0.0012°F/+0.00067°C temperature change across the same area/volume.

(I got to 830 by taking the specific heat of dry air of approx 1 J/g K at room temperature and regular atmospheric pressure and 1.22 kg/m^3, versus water’s 4.184 J/g K and 1000 kg/m^3).

(Edit: I fucked my math. Water has approximately 3300 times the heat capacity as air, per unit volume, and I just looked it up directly).

The higher conductivity of water might be offset by the higher convection potential of air (because air responds to temperature changes with differences in density/pressure, which creates wind in itself), so that the heat will spread through either medium relatively quickly and therefore dissipate very quickly with distance to the source.

I just don’t see a world where a data center raises the water by even 1°C, even locally.