AckSed

It's what was predicted way back when: once nuclear fusion happened and the price of energy plummeted, no need to drill for hydrocarbons when you can take it out of the air and the sea. It's just that this is happening with wind power. Another small company, Terraform Industries, is proposing to use cheap solar power to make methane to be sold as a further chemical feedstock. When I look at how many processes a crude oil refinery employs to clean the salt and sulphur out of crude & make lighter compounds, this backwards, inefficient pathway that produces light hydrocarbons from the start seems elegant in comparison. The heavier hydrocarbons used in asphalt and diesel may be a problem, but polymerisation and desaturation are already an established business.

There is another option for lifting gas: carbon monoxide. About the same lifting power as nitrogen, a product of multiple industrial processes including the extraction of oxygen from CO2, and an intermediary in extraction of carbon for all the graphene you'll need... and quite toxic, but you can't have everything. It can also be burned with O2 as a mediocre rocket fuel. (Or in a turboprop, for the control needed to travel between habitats and factory complexes.)

If I don't miss my guess, Helion's fusion reactor is using a magnetohydrodynamic generator to gather energy, which makes sense. You already have the magnetic coils to compress the fusion plasma, so once the fuel fuses, they allow it to expand, pushing against the magnetic field & generating electricity directly. It's not like the concept's unknown or unused, as the lack of moving parts is highly appealing, and Wikipedia says that it's been trialed on several coal or gas power plants around the world. (I have also seen it proposed in a kooky 70s design document plugged into a Saturn V 1st stage as a one-time megawatt power source.) But it lost out to fission, the Brayton cycle and boiling water. Its key advantage is compact size.

I can think of a survival sense, if not an economic sense, for there to be mining of the Venusian surface. Say an aerostat colony has been cut off from resupply missions. They typically sustain themselves by airmining noble gases, making advanced plastics, carbon nanotube composites and fusing deuterium into He3, but they do not have the resources to transmute certain trace elements like phosphorous for enriching their soil. In that case, they could make a pressure vessel and mine the peak of Maxwell Montes. At a 'chilly' 380 deg. C and 41 atmospheres it's... within sight of sanity. It makes me wonder how much cooling could be had with a kite-lofted radiator or similar, though,

Sled-assisted launcher concepts. "So what," they ask, "if the first stage was not thrown away but stuck to the ground?" It's fairly attractive: what's oft-quoted is that the Space Shuttle used a third to 40% of its fuel just to get up to 1000MPH. Cutting out that mass either leads to a lighter, cheaper vehicle that can lift the same payload or lift an increased payload. It makes a SSTO much less massy. Rocket-sleds are a classic, proposed for Bono's Hyperion among many, many others: Maglifter (magnetic levitation) was seriously studied by NASA before the turn of the 21st century: http://www.projectrho.com/public_html/rocket/images/surfaceorbit/rocketSled11.jpg They are usually struck down by the massive infrastructure costs and/or the challenges of finding a suitable slope. But I think the study that was low-tech enough to actually work today was the Closed End Launch Tube. Spurred by the proposed development time of 25 years for the Maglifter, it was essentially a sled stuck to a pneumatic train. It wasn't as beefy, but it would have been much simpler, requiring little more than low-pressure steel vessels, concrete, valves and compressed air. The chamber wouldn't be evacuated much either. Acceleration for a combined 700 metric ton sled and craft was calculated at a modest 20 m/s per second (or 2 G), release velocity around 260 m/s or 936 km/h and along a 6km track. It was meant to supplement a ramjet vehicle.