So I'm writing a story that takes place in Saturn's atmosphere, and I've run into a bit of a problem. You see, I wanted it to be possible to have some pretty badass scenes with sci-fi fighter jets taking place. (Yes, I know that real life fighter plane combat is a lot of hoping the targeting computer is right about how to hit that speck miles away, if the speck is visible at all. I've got plot devices to fix that.) The problem is that planes need oxygen to run, and rockets are too inefficient for long distance travel. Unless you do suborbital jumps, I guess, but I want planes dammit. My question is, what sort of propulsion system could work in the atmosphere of Saturn? I know electrically driven propellers might do the job, but that feels kind of slow.

Note: Planes need not be SSTO capable, they can land and refuel at large stations in the atmosphere at "surface" level (1 atm pressure)

  • $\begingroup$ A engine designed for Saturn's mostly hydrogen atmosphere (!75% H2, 25% He, with some trace gasses) could simply use oxygen as its fuel. $\endgroup$ – jamesqf Nov 2 '16 at 4:47
  • $\begingroup$ That should be a full answer $\endgroup$ – Innovine Nov 2 '16 at 7:20
  • $\begingroup$ Ironic since you've chosen the windiest place in the solar sys to dogfight... $\endgroup$ – user6760 Nov 2 '16 at 7:49
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    $\begingroup$ Obligatory xkcd reference. $\endgroup$ – kingledion Nov 2 '16 at 11:15

You do not actually need combustion for a jet engine.

The integrated turbine is a heat engine: its energy comes from increasing the thermal energy by fuel combustion. But any method of increasing the energy between the compressor and turbine works. A heat exchanger from nuclear power plant or even an electric heater will work without really changing anything fundamental.

The only real issue is that burning fuel within the the engine is very efficient method of transferring the heat into the medium. So if fuel combustion is an option that is probably what will be used. Not sure if anything other than those nuclear jet prototypes has even been ever built. Unless you need those days of flight time or operational range that exceeds the Earth circumference burning fuel has always been just better.

There are actually other options such as simply supplying oxidizers (or some other form of two component fuel) or rotating the fans and the entire compression side with electric engines without having the integrated turbine.The turbine is not actually needed for jet engine. It is simply the most efficient method of powering the engine per mass we have, so it is the only one we really use. (Aircraft being very sensitive to excess mass.)

My guess would be that is you need extreme range you use nuclear engines with electric engines powered by whatnot used for short range. This because most current or projected nuclear power plants have fairly large minimum mass. Although this is largely shielding. The proposed supersonic nuclear missile that was specifically designed to contaminate whatever it flies over was fairly efficient. It really all comes down what kinds of power tech your people have available.

  • $\begingroup$ Nuclear thermal propulsion for Saturnian atmosphere fighters is nice concept. They would have better range than oxidizer using aircraft. A thought provoking answer. $\endgroup$ – a4android Nov 3 '16 at 8:31
  • $\begingroup$ These were all really good answers, it was hard to choose, but I'd say this one is best for allowing my characters a "cheap" solution to flying in an oxygen poor environment. $\endgroup$ – Desolationgame Nov 3 '16 at 12:07

The fighter aircraft could be a wingless electromagnetic air vehicle (WEAV) which gets its lift and propulsion by ionizing the surrounding air and gaining lift. Details here for this type of vehicle which resembles a flying saucer. The source is the Scientific American.

The saucer will hover and propel itself using electrodes that cover its surface to ionize the surrounding air into plasma. Gases (such as air, which has an equal number of positive and negative charges) become plasma when energy (such as heat or electricity) causes some of the gas's atoms to lose their negatively charged electrons, creating atoms with a positive charge, or positive ions, surrounded by the newly detached electrons. Using an onboard source of energy (such as a battery, ultracapacitor, solar panel or any combination thereof), the electrodes will send an electrical current into the plasma, causing the plasma to push against the neutral (noncharged) air surrounding the craft, theoretically generating enough force for liftoff and movement in different directions (depending on where on the craft's surface you direct the electrical current).

The fighters can solve their energy problems by using an matter-antimatter power system. Assuming that the practical problems of using antimatter as a power source have been solved.

A similar magnetohydrodynamic (MHD) vehicle was described in an article "How To Design A Flying Saucer" by Dr Richard J Rosa published in Analog and reprinted in The Analog Science Fact Reader (1974) edited by Ben Bova. That suggested that this type of craft could produce large volumes of low-speed ionized air for travelling slowly and hovering, but narrow its air intake to generate smaller volumes of high-speed ionized air to accelerate to high velocities. Rosa's proposed MHD vehicle could land and take-off VTOL style, so it wouldn't need extensive infrastructure.

The fighters could accelerate through the Saturnian atmosphere and once it reached the upper atmosphere use an matter-antimatter power system to ionize reaction mass such as water stored in propellant tanks to attain orbital velocities to rendezvous with the space-station bases or spaceships orbiting the planet Saturn.

Whichever type of fuel is for reaction mass, the procedure is the same. using the power output from its matter-antimatter system the reaction mass is totally ionized and accelerated via powerful magnetohydrodynamic accelerators. Instead of an exhaust velocity of 4 km/s from chemical rocket propulsion MHD accelerated ionized reaction mass could have an exhaust of 100 km/s. This means the vehicle will consume far less reaction mass than a chemical rocket system.

  • $\begingroup$ Probably more efficient simply to react antimatter with a small portion of the gas flow through the engine, and the heat produced would expel the gas at high velocity. In effect, it's a jet engine which "burns" antimatter as a fuel. $\endgroup$ – WhatRoughBeast Nov 2 '16 at 5:26
  • $\begingroup$ This answer was going so well: novel ideas, established scientific principles, reference to an interesting article, and then... BAM! ... antimatter! +1 anyways. $\endgroup$ – kingledion Nov 2 '16 at 11:13
  • $\begingroup$ Antimatter makes the rest of the ideas moot. Given sufficient power, anything can fly in an atmosphere. $\endgroup$ – JDługosz Nov 2 '16 at 23:26
  • $\begingroup$ @JDługosz Of course! Why fly in an atmosphere with insufficient power? The OP wants fighter jets, this model will give fighter jets with bells on. $\endgroup$ – a4android Nov 3 '16 at 8:17
  • $\begingroup$ @kingledion I understand your reservations about antimatter. I had qualms myself. Saturn's atmosphere is big and deep, anything that was underpowered would struggle. I though of fusion reactors, but their power-to-mass ratio might be difficult to manage. I may have overdone it allowing the fighters to travel to and from orbit as well. Plasma aircraft will need lots of power. Antimatter may be overkill. As I said above, the OP wanted fighters in Saturn's atmosphere, this will do it, perhaps it overdoes it, but it should be workable (in theory). $\endgroup$ – a4android Nov 3 '16 at 8:23

The simplest way to build a jet engine (or any other combustion engine) designed for Saturn's mostly hydrogen atmosphere (~75% H2, 25% He, with some trace gasses) is simply to use oxygen as its fuel.

Wouldn't surprise me if all you had to do was change the fuel flow metering on a standard jet engine, and install insulated liquid oxygen tanks.

PS: Which brings up another question that my knowledge of chemistry is insufficient to answer. We use hydrocarbons for fuel in our oxygen-rich atmosphere because (in part) they're conveniently liquid at ambient temperature. Are there equivalent oxygen-rich liquids that we could burn in a hydrogen atmosphere?

  • $\begingroup$ I really like this one. It's so elegant! $\endgroup$ – Werrf Nov 2 '16 at 20:25

While a realistic scenario would be the WEAV designs referenced by a4android, the OP is clearly hoping for some sort of aerodynamic vehicles.

The problem is actually multifold. The atmosphere has no free oxygen to allow the use of conventional jet engines, the distances to cover are orders of magnitude longer than that of Earth (imagine flying from an air base in Minnesota to a spot over the Indian Ocean before you even encounter the first enemy craft, then having to dogfight, then flying back. Without air to air refuelling your "fighter" would be the size of an A-380

enter image description here

A-380 in flight

Finally, the atmosphere of Saturn itself is very violent, with some of the fastest winds recorded in the Solar System. Planes caught in a downdraft might have a real possibility of being sucked into a layer of the atmosphere where the pressure exceeds the aircraft's "crush depth", so instead of air war we are looking at a weird hybrid of air and submarine warfare.....

However, there may be some ways to handwave this. If you can get to Saturn in the first place, there is probably some compact energy source like fusion, so a suitably large airframe coupled to a suitably small fusion reactor would make a sort of rocket or ramjet powered craft (the fusion reactor can be heating atmospheric gases, for example). This is similar to the proposed nuclear powered aircraft designs of the 1950's.

enter image description here

Nuclear jet engine

I would expect the aircraft to be at least the size of an F-15 "Strike Eagle" to house the fusion plant and any associated equipment.

Because you are working in a very complex fluid dynamic environment, the airframe would need to be able to "morph" appropriately. If you are in the lower, denser layers of the atmosphere, you need less lifting surface, while in the upper layers, you will need far more lifting surfaces. As well, you will need a strong shape to resist "crush depths" should you be forced down for whatever reason. A large "blended wing" lifting body design is probably a good starting point:

enter image description here

Boeing X-48 Blended wing design

Because of the added complications of atmospheric pressure and turbulence, regular weapons like air to air missiles or SFnal weapons like lasers would have limited utility (they would not have sufficient range, for example). This might be worked around by arming the craft with a powerful rail or coilgun. The projectile could have limited ability to be guided onto target, but as the range increases the effects of atmospheric drag and turbulence would eventually break the target lock and the round would fall into the depths of Saturn. Explosive warheads would not really be necessary.

One issue which you have not brought up is where these craft are going to be based, or why they need to fly and fight in the atmosphere anyway? The design I hand waved could serve as an SSTO and fly to and from space to carriers orbiting Saturn, but the "why" is pretty open.

  • $\begingroup$ I'll edit the question to mention that there are inhabited aerostats in the atmosphere, thanks for reminding me! $\endgroup$ – Desolationgame Nov 2 '16 at 21:48
  • $\begingroup$ The absolute wind speed shouldn't matter much. If it's a uniform wind, everything is carried along with it. The question is turbulence. $\endgroup$ – jamesqf Nov 3 '16 at 4:18
  • $\begingroup$ Like the combination of aerodynamics and fusion power, even Airbus sized fighters has appeal. Enjoyed your answer. Plus one from me. $\endgroup$ – a4android Nov 3 '16 at 8:28

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