Sci-fi Weapons, Vehicles and Equipment

Cool. Thanks.

Worth noting that any sufficiently powerful gun inevitably ends up having to deal with indirect fire.

But yes the overwhelming practical application is that your gun will certainly be power-limited so weaker shots allow you to fire faster.

So a DMR/SMG hybrid? Adjust power-per-shot depending on the distance?

Historically, even machine guns have been used in the indirect-fire role from time to time. The Brits would incorporate machine gun batteries into their artillery barrages in WWI.

Edited by AFP on Apr 24th 2024 at 9:12:26 AM

^ Still can be used for that role. Just isn’t commonly even thought to be used for that because there are simply better weapons for that.

Like mortars or Mk 19’s or an A-10 on station.

Are there any concepts for space propulsion techniques that don't require propellant, but require a sufficiently strong (say 1-100 gauss) space magnetic field to operate?

Isn’t that a plasma torch essentially? A true Reactionless Drive may or may not be a scientific impossibility.

But drive systems that aren’t conventional chemical burners or powered by literally riding the blast wave of nuclear warheads do exist.

Also the Ion Drive. Which not only exists but the fastest ever man made object is powered by one. Kinda sucks at acceleration though, best fuel economy ever however.

Nay, ion drives and the plasma torch use propellant - the eponymous ions and plasma - and hence aren't what I am asking about.

While I lack the detailed scientific knowledge to understand how a magnetic drive would work in detail, I can observe that all propulsion systems (indeed, all machines in general) operate using enthalpy: that is, by taking advantage of a gradient in energy.

I don't know that the magnetic gradient in deep space would be enough to "grip" onto to provide motive force. Seems like you'd need to be close to a neutron star for that to be even remotely feasible.

Magnetism is a terrible propulsion option at long ranges because it falls off as the fourth root of distance.

^^ That clarifies it a bit. Both plasma torches and ion drives utilize magnetic fields but they are not the core propulsion component, the ejected ions/plasma are.

You’re talking strictly magnetic field manipulation I suppose.

Edited by MajorTom on Apr 25th 2024 at 10:45:00 AM

Aye, but I don't need it to work in deep space - close to a planet, a star, or (pertinently) a neutron star works as well. You don't need delta-v to coast through deep space, after all, and the idea is to cut propellant needs, not necessarily to abrogate them entirely.

Might be a crazy question, but do we know if air-to-air missiles from tactical aircraft travel faster/slower at different altitudes?

I know that modern A 2 A missiles tend to climb sharply to glide down on targets. The thinner air at high altitude produces less air resistance letting a missile travel faster for longer.

Is this what you mean?

Yes. I was wondering if you fired a missile at an aircraft ceiling could you reach your target faster.

Sorta. With less air resistance a missile will accelerate and reach a faster top speed.

The difference however is insignificant in terms of performance.

That said many missiles perform better in terms of range at high altitude not because they’re faster but because there’s less drag.

Some forms of air to air and surface to air missiles depend upon this to function effectively at all. For example the AIM-54 Phoenix missile used by the F-14 performs absolutely terribly at low altitude and at short range. If launched from high altitude it can intercept almost anything from 100 km away.

Very useful at killing tactical bombers armed with ship killing missiles like the Tu-22M Backfire. Not so much at stopping say an A-10 in the middle of a gun run on ground forces at low altitude.

Hmmmm, Probably! Most A 2 A missiles are rocket propelled so the only issue is making sure the missile has enough air for the control surfaces. Even then, some missiles have vectored thrust so even in the thinnest air the missile will have some guidance.

The only exception is if the missile uses an air breathing engine, like an A 2 A version of the JASSM. At that point the missile might stall out and crash if it's above the missile's operating ceiling.

In the absence of atmosphere, the most efficient path between any two locations on the surface is a parabola.

Any vehicle traveling at higher altitude will encounter less air resistance and thus be capable of reaching higher sustained speeds. All other things being equal, this should translate into longer range. Of course, you have to expend fuel to get to that altitude, but this is why commercial aircraft travel as high as possible.

The main limits on how high most aircraft can fly are (a) atmospheric pressure to support lift, (b) oxygen to feed the engines. A missile cares about neither of those, although its steering method can be affected by air density. Gimbaled engines are effective at any altitude but aerodynamic surfaces have limits to their performance.

Edited by Fighteer on Apr 27th 2024 at 8:10:45 AM

Lots of missiles use jet engines (like Stormshadow or Tomahawk) so they still need oxygen to fly.

It also seems to me you basically have two operational ranges: fins and such can give a lot of stability and maneuverability in air but not high-altitude, whereas thrust vectoring can give a lot of maneuverability at high altitudes but not low ones.

Thrust vectoring gives you control at any altitude but requires that the vehicle be actively propelling itself. If you're already using a jet engine, you might as well go with control surfaces because they're simpler and you need wings for lift anyway. Ballistic weapons are usually only under thrust for a portion of the flight, making thrust vectoring useless after that point.

This is one of the key distinctions between rockets meant for orbit and rockets meant for suborbital trajectories. The latter employ steering fins since more of their flight is in atmosphere, whereas they're only effective for a very small portion of the flight regime of an orbital rocket. (There are a ton of ways to steer a rocket, which I won't exhaustively list here.)

As a minor addition, it is more technically challenging to steer solid-fuel rockets with gimbaling. Not impossible, but an engineering challenge that may not be rewarding enough to justify the added complexity.

Edited by Fighteer on Apr 28th 2024 at 7:26:12 AM

Was about to mention that a fair number of missiles and even bombs do in fact use wings to produce lift for the simple reason that it extends their range. Late in WWII, the Navy used to have a setup where a bomber would drop a glider that would travel a fair distance before it was low enough to drop a torpedo into the water, allowing the bomber to stay clear of most anti-air defenses that a ship might be able to employ short of fighter aircraft.

Also, on the topic of the Phoenix missile, it's one of my favorite bits of irony that the Memetic Badass missile in question is derived in part from the AIM-4 Falcon, which has a reputation as one of the worst air-to-air missiles to ever see combat use in the history of the US military. To be fair to the Falcon, it was, much like the Phoenix, designed with Soviet strategic bombers in mind, so single-engine fighters over Southeast Asia may have been a bit outside of the intended scope of use. But then, the US Air Force had a lot of fundamental doctrinal problems going into Vietnam.

On that topic, you could get some good storytelling potential in pretty much any genre out of a military force prepared for the "wrong war" as it were. Wrong equipment, wrong tactics, etc. and the associated learning curve once "metal hits the meat."

Something else to consider for steering a ballistic weapon is that aerodynamic control within hypersonic, transonic, and subsonic flight regimes is very different.

The most successful orbital rocket in use today is Falcon 9, whose first-stage booster typically reenters and touches down on a drone ship or landing pad. To steer itself within the atmosphere, it employs grid fins, which don't provide aerodynamic lift but instead alter the vehicle's center of pressure to allow for steering authority at hypersonic velocity. Effectively, the entire rocket acts as a lifting body.

Of course, Falcon 9 isn't designed as a weapon. A ballistic impactor might use a different steering mechanism during its terminal phase, since it's not trying to slow down for landing but rather to go as fast as possible.

Space capsules that reenter from orbital velocity or higher instead employ blunt-body aerodynamics, with heat shields designed to spread out the forces over as wide an area as possible. They steer by being slightly asymmetrical, so by rotating themselves they can generate differential forces (aka lift).

Edited by Fighteer on Apr 29th 2024 at 10:22:26 AM

As the saying goes, you go to war with the army you have, not the one you want.

It brings me to a bit i've been thinking about: military technology and doctrine is heavily path-dependent,so how your setting develops military space technology depends heavily on how you get there. I would expect the first space warships will be little more than civilian ships carrying a missile or two, but it would be interesting how that spins around.

Stretching the definition of sci-fi, but I remember reading that World War Z had that problem happen in-universe. Modern militaries were trained and equipped to fight against combined arms forces, not human wave attacks by foes that cannot feel fear or pain, thus cannot be demoralized into routing and cannot be incapacitated by injury. Pretty much all modern tech ended up being abandoned in favor of artillery, large-caliber anti-personnel rounds and melee weapons (to ensure incapacitated but still alive zeds are down for the count before someone inattentive steps next to the "corpse" and gets bitten in the ankle).

Edited by amitakartok on Apr 29th 2024 at 12:09:50 PM

I would say with total honesty that zombie stories are sci fi.

More like science fantasy. There's no such thing as a "zombie" (duh). What I mean by that is that if it is a biological entity it can be killed by depriving it of whatever makes it run. It must consume energy and turn that into motive force somehow. Scientists would figure that mechanism out and target it. Sooner or later there'd be a toxin that neutralizes the zombies and/or kills whatever biological agent is responsible. Then we'd gas the infected areas and be done with it.

If it literally is The Undead, such that it is powered by Hell or something, we are now in fantasy land and we might as well start consulting the witches and warlocks.

Zombie Apocalypse stories annoy me for their effort to have their brains and eat them too. They don't seem to obey thermodynamic laws.

Edited by Fighteer on Apr 29th 2024 at 10:20:46 AM