Short post about plasma thrusters
Short post about plasma thrusters
After considering a few technologies for flight, I settled on plasma thrusters, because their ear-æsthetics and eye-æsthetics are both
– take a look.Any time you see a flying car in fiction humming and shooting glowing stuff out the bottom, that's plasma.
Ion drives have received a lot of attention for spacecraft propulsion, but here I am talking about in-atmosphere air-breathing ones, like the one in this 2020 paper from Wuhan University. (There's video of their thruster firing in the link.)
The study demonstrated a plasma drive that would be sufficient for an all-electric flying car or jetpack. Let's see what that would look like...
Thrust density –
- Thrust density (the amount of thrust per square-meter of exhaust) is low in other kinds of ion-drive, but the air-breathing one in the paper gets "2.4 × 10⁴ N/m²"
- This means a square meter of exhausts could lift 2400kg
- A flying car would need to lift less than 1600kg, so need thrusters ⅔ of a square meter spread across the bottom of the car.
- A thruster the size of an A4 sheet of printer paper could lift 136kg, sufficient for the jetpack in the top picture. These thrusters are spread across boots, gloves, and backpack for extra stability and ccontrol.
Energy
- The thruster in the paper "can generate approximately 10 N of thrust at 400 W", so 400W to lift 1kg. (It takes 10N to lift 1kg in Earth's gravity.)
- The flying car is an all-electric vehicle, electricity-to-flight. Hydrogen liquid has an energy density over 30,000 watt-hours per kilogram, way over even advanced batteries. So the vehicles will compress or liquify hydrogen and use them to power the flight. This is wasteful on energy (because compressing it takes energy) but we don't care about being efficient here.
- The jetpack will use about 36 kilowatts (call the person plus their clothes plus the device plus their stuff 100kg). If you store 1kg of hydrogen you get one hour flight-time
- Call the flying car 1500kg, and it'll use 535kW to go straight up, but going vertically up or down "requires about three times more power than forward flight". When the engines are pushing forward (not up) and wings are lifting, it'll use more like 200kW