Sadly, the asteroid belt isn't the place to showoff your ace pilot skills. It is so sparse you wouldn't even see an asteroid most of the time if you flew through it.

But Saturn's rings! The rings cast shadows on the planet, indicating that that most photons passing through them hit something. The tidal forces of Saturn are thought to prevent the particles from condensing into moons despite the high density.

We assume contemporary technology (except with better ecosystems/life support for the colonies themselves) and we want to design a fighter to attack and defend ring colonies. I believe that the relative velocities of the boulders are low enough that collisions are harmless if you are co-moving with them, as large kinetic energies would have long ago dissipated. However, if you are maneuvering fast enough that would change.

Here are some considerations:

Delta V Delta V is a problem, unless you use ring material as reaction mass. With a nuclear reactor there is almost unlimited energy to mechanically push against the ring objects, so almost infinite delta V.

Hiding Stealth in space is hard due to heat emissions. But this isn't empty space. Would hiding behind ring material stealth be (at least short term) feasible? Or even looking like ring material to enemy radars.

Weapons If an enemy is behind a large object, it may be possible to attack them by creating shrapnel in nearby objects to the side of them. Would launching ring material at them save on ammo?

Tactics Space is 3D, but the rings are only 10m thick! This makes the arena very 2 dimensional. Attacks from above and below may have a good vantage point but you lose the reaction mass (maybe you could carry a boulder with you and push off against it, but doing so slows you down). Throwing an enemy spaceship away from the ring plane will cause them to have to expend precious fuel or wait ~5 hours (1/2 an orbit) for the tidal forces to pull them back.

Windows Unlike deep space the morale boost from the view (artists impression) combined with the visceral sense of being there rather than looking through sensors can't be ignored. How bad would the windows be for ionizing radiation?

Given these and other considerations, can we make a rough sketch of what a dogfight could look like?

  • $\begingroup$ Other considerations - need to think about the level of radiation near the rings $\endgroup$
    – Slarty
    Oct 12, 2019 at 15:23

2 Answers 2


With a nuclear reactor there is almost unlimited energy to mechanically push against the ring objects, so infinite delta V.

Weeeeell... yes and no. Your reactor fuel isn't infinite, for one thing. More importantly though, your ability to accelerate is likely to be heavily influenced by your choice of reaction mass. You'll want to be throwing it away from you at a few km/s, and you want to be throwing it straight so you can't trivially just punt out any old chunk of ice. Haul it inboard, melt it via your coolant loop and then blow the water out through your engine, which will probably be some sort of solid core nuclear thermal rocket, resistojet or microwave electrothermal rocket, given the sort of tech-level you're considering and given the need to be able to use water as reaction mass (which rules out other things like arcjets or ion drives).

Both kinds of engine have limited lifespans for various reasons that I shan't go into here, but do consider than infinite delta-V is basically impractical.

Would hiding behind ring material stealth be (at least short term) feasible?

Given the thickness of the ring, there's milage in dropping off some little automonous sensor drones to look above and below and report back, so you'd have to hide in the ring, and that's a mildly hazardous place to be, what with all the rocks. At low speeds (relative to the material of the ring around you), this seems like it might be practical, and certainly an interesting setting for a fight. If you see a drone, even after they've seen you, you can pop it with some suitable weapon and your opponent only knows where you were and still needs to procede either cautiously, or with force majeure (if they have it).

Or even looking like ring material to enemy radars.

Unless you had the same heat signature and same average velocity as the other bits of the ring, you'll stand out like a nuclear rocket strapped to a chunk of ice. You might manage a very sloooow, long duration sneak attack if you were lucky and clever, though.

If an enemy is behind a large object, it may be possible to attack them by creating shrapnel in nearby objects to the side of them.


Moreover, other weapons that don't necessarily work well in space, like nukes, suddenly become a little more interesting. All those spare x-rays they emit will be absorbed by nearby ring material, which will probably go bang. It still won't be as dangerous as a nuke in an atmosphere, but it will present a considerable hazard.

Would launching ring material at them save on ammo?

This is a related problem to the infinite delta-V thing... you'll need to refine the lumps of ice in order to make practical projectiles. The means you use to propel them might have some other limitation, like carrying a finite number of sabots for railguns or coilguns.

Also... how would you launch the material? Docking with it, then pushing it with your main engines is obviously workable, but any point defences directed at the rock are going to hit you once the rock has broken up. Disengaging and slowing back down or redirecting yourself costs delta-V. Drones sent out to do the job will have limited delta-V. Laser ablation is deeply unsubtle and power hungry (which means lots of heat to dissipate) and can be countered in the same way. And so on.

On the flipside, if you can harvest and process ice rapidly, you can very quickly refill coolant tanks and that lets you fire your weapons harder and for longer, and heat is the number one enemy of most space weapons.

Throwing an enemy spaceship away from the ring plane will cause them to have to expend precious fuel

Most weapons you'll be using are of the "massive overkill" kind. There's a very narrow window between "no good as a space weapon" and "target reduced to partially ionised grit". Odds are good that if you can hit them, they'll be in big trouble. Falling away from the ring makes them a clear target, and it'll be much easier to finish them off.

How bad would the windows be for ionizing radiation?

It is hard to find good figures on the radiation environment around the rings. Here's a render from some recent work on radiation belts:

Saturn radiation belts

You may find that the rings themselves are actually fairly benign, as far as space radiation goes.

To be honest though, worrying about your windows is like worrying about your choice of sunglasses when wearing shorts and a t-shirt in the middle of the sahara. There's not much you can usefully take with you to protect yourself from most high energy cosmic radiation. Means of protecting against radiation are a bit outside the scope of this answer though!

What you might need to be more cautious about is nuke flash and laser beams, and you want something opaque between them and your eyes. Even indirect reflections and the flash of an object being zapped can blind.

  • $\begingroup$ Maybe this will be a low speed battle? A 100m/s boulder at close range will be hard to dodge and is doable with mechanical catapults and without "refining" it. Yes, a higher speed projectile would be better but it's hard to beat "unlimited" ammo and delta V even if it means warfare in the 100m/s range (nuclear subs run out of life support before they run out of fuel). $\endgroup$ Oct 12, 2019 at 17:59
  • $\begingroup$ @KevinKostlan a 100m/s boulder will be quickly dispatched by a point defence projectile weapon; that's straightfoward even with modern day technology. A boulder big enough not to be easily dispatched will be much harder to accelerate without the target seeing you. $\endgroup$ Oct 12, 2019 at 18:15
  • $\begingroup$ @KevinKostlan also remember, as the good book says, space is big. Really big. The rings are no exception. You need to fly fast to get anywhere, and you'll have to do that well clear of the rings themselves... you'll be able to see people coming, and even dodging back and forth between the sides of the ring will still give some good long lines of sight and opportunities for pop-up attacks. $\endgroup$ Oct 12, 2019 at 18:17
  • 1
    $\begingroup$ Probably worth noting that the existence of the radiation belts in a colonised saturian system is a bit questionable. If the the terran belts are any measure to go by, clearing out the saturian radiation belts will be trivial. Using low frequency radio waves or electrical tethers are quite simple measures to clean up such a big nuceance. $\endgroup$ Oct 12, 2019 at 21:38

First, two points need clarification:

DeltaV is mostly determined by exhaust velocity. Since the description of the ships suggests they are powered by a mass driver acting as a rocket engine (which also doubles as a weapon), you are ultimately limited by the velocity the mass driver can project objects.

What you are probably thinking of is ISP, the figure of merit for how efficient the engine is. High ISP's are generally associated with high temperature or velocity exhausts, and a low molecular weight exhaust. Since you can scoop reaction mass from the rings themselves, you have effectively unlimited ISP. However, before you celebrate, there are some considerations to think of.

This site has most of the calculations you will need to determine things like the size and actual performance of your mass driver. One example in the site descrbes the performance of a mass driver that can accelerate reaction mass at 15 Km/sec:

The reaction mass or payload is loaded into a lightweight bucket banded by a pair of superconducting loops acting as armatures of a linear-electric guideway. The thruster illustrated accelerates the bucket at 75,000 gee's, utilizing 7 GJ of electromagnetic energy stored inductively in superconducting coils. The trackway length is 390 meters. One 36kg of reaction mass is ejected each minute at 15 km/sec. The bucket is decelerated and recovered. Cryogenic 77 K radiators cool the superconductors.

Even with the modest performance described, you will have a ship over 400 m long, a bit difficult to hide or disguise as a hunk of rock or ice. Another example with a 30 km/sec performance has correspondingly larger power requirements, and a very high performance spacecraft with a 90 km/sec exhaust velocity will be larger still by a factor of about 10 (10 X longer, ten times greater power consumption, 10 X more mass).

enter image description here

What a medium performance mass driver would look like under construction

Another issue is refueling. The ice has to be taken aboard, melted (it may be full of rocks and gasses which also need to be dealt with) and frozen in shapes that fit the sabots for the mass driver. In order to ensure the ship reacts the way you expect, every single "shot" needs to be the same size, shape and mass, otherwise your thrust will not be uniform, and it will be more difficult to manoeuvre the ship. Gathering ice will require you to be moving almost at rest with respect to the ice in the rings, which will be a moment of vulnerability. You will not be refueling in the manner of a bomber drawing from a tanker plane, although it will be much easier than condensing the drinking water out of the air of a jumbo jet in flight to supply the passengers. In many respects, you would be better off ignoring the ice and using drop tanks or a supply ship from Titan or other moon.

enter image description here

Ring Interior. Your 400 m long spaceship might get in a bit of difficulty

Finally, staying in the plane of the rings makes you very predictable and easy to find and strike. A ship coming in from a highly elliptical orbit or a polar orbit will be moving much faster and at a different aspect and angle to your ship in the rings, potentially placing you at a huge disadvantage as you are showered with ice pellets moving at between 15 and 90 km/sec. An object moving at 3 km/sec already has kinetic energy equal to its weight in TNT, and the kinetic energy increases with the square of the velocity, so even one hit will be crippling. While a captain might choose to lurk in the rings for a short while as a tactical solution to a limited problem, the overall performance of spacecraft means they will want to use the entirety of the Saturn System, from skimming the edge of the atmosphere to the most distant moons.

enter image description here

Innermost part of the Saturn Theater of Operations. The enemy ship in the rings is about to get pummeled with some kinetic impactors moving at 90 Km/Sec


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