Idobox

For insulation: Wood looks cool, but is very heavy. If you want insulation inside the pressurized capsule, plant fibers or even wool might be a better solution. Astronauts wearing furs! But really, having a second layer outside with a vacuum in between (easy in space), is technically the best option, and completely possible with Victorian technology and science. I assumed you were talking of orbit, and thus didn't talk about life support (if the flight is short enough, you don't need it). We already talked about temperature. Food and water are not particularly difficult to store for a week or two, it leaves us mostly with atmosphere. CO2 is known since the XVII century, and had already been liquefied and frozen by the early 1800s. I'm not sure how well its chemistry was known in the era, but activated charcoal or concentrated caustic soda solutions can be use as scrubbers. I'm sure there are plenty of other simple reactions that could be used. That leaves us with oxygen. Commercial production of liquid oxygen started in 1895 in the real world, so a simple vat is an acceptable option. Peroxyde has already been proposed, but it is unstable and liquid, and also likely expensive with steampunk technology. Modern oxygen generators often use sodium chlorate, which turns into salt and oxygen when heated above 300°C, and was industrially produced in 1892, although I'm not sure they were aware of the oxygen production properties by then.

You can use RF two ways to do that. The cheap way is to use measure power: Put an emitter on the person, for example a phone with bluetooth, put a receptor on the drone, measure power, which is proportional to 1/r², get distance. With off the shelf components, the signal might too powerful at this kind of range to be measured accurately, and require an attenuator (can be done with resistors). With two or more receptors, you'll know in what direction to move, with one, you will to "wiggle" to find out. A variant is to use a RFID reader and passive tags, and measure RSSI (return signal strength intensity). You would have to use UHF, 2.4GHz or higher, because lower frequencies use magnetic coupling, which for a number of reasons, would be a nightmare to use on a drone (think contactless cards or NFC phones). The advantage over the previous is that passive tags are pretty much just stickers, which might be handier than a active radio source. The issue is that it would be more expensive, and not all RFID readers have RSSI. The second option, which is a bit more complex, is to measure phase, ie time of flight. To do that, the easiest way is to put an emitter on the drone (let's say 13.56MHz, free frequency) and a frequency doubler on the target (can be as simple as a diode with an antenna). You then measure the phase difference (can be done with a XOR gate) between the 27.12MHz signal that rebounds from the target to one you generate on board of the drone (using a diode again). At 27.12MHz, the wavelength is about 10m, so if you get a phase difference of 2*pi/10, it means the signal traveled 10m/10 = 1m, and since the signal traveled form the drone to the target and then back, the distance is 0.5m. The first solution is simpler, but a lot less accurate. Antennas don't transmit with the same strength in all directions, so if you tilt the drone or the beacon, the system will detect a change in distance even if it doesn't happen. Also, as the components heat up, the calibration will change a little bit, and cause a small error. The second solution is a lot more accurate, but a little bit more technical. Calibration isn't much of an issue: you are comparing two signals coming from the same source, so you only need a stable frequency source, which costs a few $.

Nitrocellulose was invented in 1862, so definitely fits the steampunk theme, and is an actual rocket propellant. The sprint antimissiles are fueled by nitrocellulose with zirconium layers (that one isn't very steampunk) and gellified nitroglycerine, and accelerates at 100g. SRB is the steampunk way of doing rockets. Guns, despite what Verne wrote, can't work with that technology. Ram accelerators and multi-charge guns are an actual option today, but the technology is more dieselpunk/atompunk. Hybrid or liquid fuel rockets without turbopumps are a decent option for circularisation and other orbital maneuvers, with their good isp and low TWR. Cold gas RCS and gyroscopes are also available technologies. A story about a space race between Great Britain and France in Victorian times (I can't think of any other power willing to invest the absurd sums required at the time, but if you feel like adding USA, Russia or Austria, it's your choice) would be amazingly enjoyable. Fighting in the colonies to get suitable launch sites, oversized steam boats carrying giant SRBs, engineers devising mechanical "flight computers" to keep the rocket pointing the right way, discovering hypersonic aerodynamics, reentry heat, cosmic rays, that natural rubber is crap in a vacuum, that copper and glass don't like 400°c thermal cycles, etc... I imagine it could start with single stage suborbital rockets with simple aerodynamic stabilization could be used in the beginning, with mechanical scientific tools on board, like pressure and temperature loggers. Steel would be the material of choice for most of the rocket. Explosive bolts and electric systems might be possible, but coolness requires hydraulic or wire systems for the control surfaces and stage separation. In particular, for the stages, I imagine two concentric rings, with a number of cylinders in the radial direction, a bit like the big bank safe doors. Once shock heating is discovered, transpiration cooling using water would probably be one of the first proposed ideas. Ablative heatshields could also be made of a variety of low tech materials, including cork or leather. Thermal amplitude and airtightness would be trickier. Dewars were invented in 1892, and are a very good option for insulation. They would just require one airtight capsule surrounded by a thin metallic shell and a few spacers between the two. The lower tech option is to increase thermal inertia, IE bring a big chunk of ice. The best material for the capsule would be metal, since they knew how to make boilers. Riveted steel sheet would be a material of choice, but copper or brass might be viable options. For joints, I would have them use resin or asphalt first, before discovering they're crap for space, and moving to soft metals like lead or tin, and designing the capsule so that internal pressure keeps the joints tight. And also, I'd expect a few catastrophic failures before they give up on glass windows, and even doors.

Although proper stealth would be almost impossible, decoys and blinding could be rather easy. The whole argument is that hiding your IR signature is almost impossible, unless you're actually a rock, and even then, you might be detected. But launching a few hundred very hot but small decoys would be a viable strategy. The enemy would know you're up to something, but they would have a lot of trouble identifying the actual target. Of course, unless you're very close, they will also have lot of time to find out which one is the relevant target, and also send a counter-attack weeks, months or even years before you reach them. The other option is to blind their detectors. A focused beam of strong IRs targeted at your enemy's bases would blind its telescopes while you do your burn. If you can emit it continuously, or at least quite frequently, they couldn't know when you did your burn, or even if one happened. The weaponized version of that uses a stronger IR beam, possibly pulsed, to deplete the coolant used on their telescopes, rendering them unusable. The blinding solution of course works only for burns close to your emitter, logically close to your planet/base or main fleet. You will still need to find a way to hide your waste heat during the actual transfer. The only type of mission it would make sense for would be spying/infiltration. For actual warfare, shooting first from far away would be a safer option, especially if you have access to lasers, particle beams or relativistic projectiles (basically weapons that give only seconds or minutes between the moment firing is detected by the target, and the moment the target is rendered unable to detect anything ever again, even less retaliate).

Let me develop on that. The limit on how much energy you can store in a capacitor is the breakdown voltage, where the insulator stops insulating, and you get a nice spark usually accompanied by smoke. This breakdown voltage is a function of insulator material and thickness. If you use a thicker insulator, you get a higher breakdown voltage, but also a lower capacitance. in the end, the quantity of energy you can store is proportional to the volume of insulator used. As said, superinsulators will leak less, but keeping a capacitor charged for hours is already possible. What you want for better capacitors are materials with very high breakdown voltages.

I don't think so. Friction of the projectile with the rails is probably more significant than air resistance at those speeds. Given the time scales, an ion engine would be much better. You could also imagine putting solar sails. They might have terrible TWR, but you could use mass from phobos to build them, and over thousands of years, they'll provide a significant deltaV.

A nuclear ramjet/NERVA wouldn't be ideal on Earth, for the same reason air-augmented rockets are not used: the air breathing part of the flight would be quite short, and wouldn't justify the extra-weight. Plus all the issues with nukes. Now, for a Venus or Titan probe, it's a completely different story. You could use the NERVA for the transfer and different orbital manoeuvres, then aerobrake, use the jet mode in the atmosphere to go around, land and take off again. Because the atmosphere on Venus is so thick, you get to use the jet mode a lot longer than on Earth.

I'm pretty sure AAR and solid fuel ramjets (not that different) are used on air to air missiles. That's because they stay in places where the atmosphere is thick, and don't try to go anywhere near orbital speed. I can see them being used on SRB. Of course, TWR is very important for a SRB, more than ISP, but it could make sense to use it for the first minute or so.

If you use a flat enough reentry angle, and have enough drag, the impact velocity will be the same you would get from dropping it by plane. For a skydiver, terminal velocity is about 200km/h, a cake delivery package could easily be around 100km/h or less. If we assume the max deceleration a cake can survive is about 10g (imagine putting 15kg on top of it), and terminal velocity is 30m/s, it would take about 5m to brake. That's far too much to use bubble wrap or equivalent, but some kind of long air piston could probably do it.

I don't think you can call urine an object, or say it's been manufactured. But there have been instances of astronauts building stuff out of other stuff, like commander Chris Hadfield showing space darts. I'm not sure when the first one happened, probably very early.

CO2 capture makes sense where there is a lot of it, in the exhaust of some factories or power plants. So, we agree on that point. Now, buying cement or steel from other countries is going to be very expensive. Also, if your politicians play that game, they won't either try capturing CO2, which would increase tax and energy costs, when they could just hope other countries will be greener.

You still need to pump hundreds or thousands of tons of air through your system to extract tons of CO2. And that's expensive, both in term of energy and money. Even if fossil fuel power plants are closed, you could still have biomass power plants and use the CO2 for algae farms. Also, cement and steel production are two of the largest CO2 emission sources, and will keep existing for a long time. But the first step we have to do is to cut our energy consumption. Stop driving cars, use good insulation, live in dense cities and you have solved 70% of the problem. Plant trees every where you can, and you have a massive and cheap carbon sink. Stop eating meat, especially beef, and you're almost there. Then, you can start thinking of how to produce the electricity you need. Trying large scale capture of CO2 before you have done all that is waste of resources, because you would have a larger impact for less cost with any of those.

On the contrary. Solid Oxide Fuel Cells have typical operating temperatures between 800-1000°C, molten carbonate fuel cells work at 650°C, so the 470°C superfluid CO2 would be an excellent cold sink for one. Actually, you could even slap a Peltier elements around the fuel cell to get a few more percent of efficiency. By the way, while looking for fuel cell operating temperatures, I found a bit (but not much) on carbon fuel cells. Apparently, you can use carbon or carbon rich materials in either SOFC and MCFC, which makes fuel storage much easier. I haven't checked, but it might be possible to use with other oxidizers than O2. And then, there's wind.

The temperature is less than 500°C. Sure it's hot, but not crazy hot, most parts of a well built probe can perfectly deal with that. Old dumb steel and copper can, many plastics can, glass can, ceramics won't even notice the difference. Transistors can be made to work at those temperatures, but it would be very difficult to dump heat, which is why I suggest thermionic devices for power applications. The only parts that really need cooling are microelectronics, and maybe some sensors. Keeping them cool with a heat pump is totally feasible. Lajoswinkler, are you suggesting a heat machine as the power source? RTGs, which are the only such power source used for probes, won't have a good efficiency, which is why I spent some time proposing other power sources that won't mind the temperature.

And that's the right approach for many problems, but there is very little CO2 in air, and lots of air, so you need a massive collecting area to do anything meaningful, and a cheap way to concentrate the CO2. And right now, harvesting biomass is the best option. Capturing CO2 straight out of the exhaust of power plants and other big emitters is also an option, and here, big centralized works. But of course, the first thing we have to do is to stop releasing so much CO2 in the atmosphere in the first place.