Space Combat in The Expanse

I break down the three major tiers of space combat in James S.A. Corey's The Expanse.

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[Spacedock]

So who's excited for a Season Three trailer? Gotta be soon right? :)

[TheStRyder]

"Combat in The Expanse generally takes place over extremely long range"

Alex: Hold my beer.

[xensan]

What really impressed me was the speed of that nuke in the beginning, covering thousands of kilometers in just a few seconds. This type of space combat is something we rarely see in visual media. I get it, it's hard to make battles exciting when you can't see two combatants on the screen simultaneously. But stuff like The Expanse has its own brand of tense and captivating combat.

[miketacos]

I love that there are no energy shields. You get hit, you done for.

[dreadnought-ai]

The range of a projectile weapon in space decided by reaction time.... Finally

[dreadnought-ai]

missile/torpedoes long-range (guided tracking weapons)
Rail guns medium-range (high-speed projectile weapons)
And point defence (pretty much CIWS)

All over ranges measured in hundreds of kilometres.

Goddamnit I wish more sci-fi did it this way.

[TheVargr]

In the book it is stated that the Donnager engagement was the first time CQB actually ever happened outside of simulations

[benjaminodonnell]

I agree The Expanse is the most realistic space combat yet depicted on screen, but I can think of a few things they could have added for even greater realism.

*Countermissiles:* As someone else said, relying on PDCs alone to destroy incoming torpedoes is silly - it means you just sit there letting the torps approach until they reach close range and then pray your PDC algorithms are good enough to destroy them before they hit you. At long range, countermissiles would be practical, especially ones with shrapnel warheads, which create a large debris field that would be hard for incoming torpedoes to evade.

*Shrapnel warheads:* Speaking of shrapnel warheads, why limit them to countermissiles? A torpedo with a shrapnel warhead would only need to explode nearby to the target, preferably somewhere in its future flightpath.

*Drones:* Unmanned craft will always be faster & more maneuverable, because there are no squishy humans to crush with g-forces and no life support systems to take up mass. Basically, these would be larger torpedoes with their own weapon systems attached. They could also act as anti-torpedo countermeasures, by flying towards the torps and using their PDCs to create multiple zones of fire before the torps reach the target's own PDC zone. Drones would also be essential as reconnaissance devices, extending the radar/lidar vision of the mother ship by relaying reports back.

It's possible that torpedoes could be "modular", with the same missile being usable as a torpedo, countermissile or drone depending on its software package & payload. But I suspect drones, at least, would be a separate unit.

[speestechsupport]

This why I love this show (realist combat, utilization of inertia, realistic design and science)

[theboard]

The MCRN Donnager is one of the most beautiful ships ever designed.

[lord_kinbote]

Plasma torpedoes are probably essentially nuclear shaped charges: directing a nuclear explosion using a reflector to convert a tamper such as a slab of tungsten into a concentrated jet of plasma. Basically a HEAT warhead on steroids.

[lincolnnoronha]

The rail guns actually fire at a non negletible fraction of the speed of light. I think their effective range is a bit higher (something like 10.000 kms or 100.000 kms). Also, there is one instance in the books where PDCs are used effectively at rail gun range. But its a trick. The Rocinante fires its PDCs at a position where the enemy has been consistently evading rail gun shots to (being an algorithm doing the evading, it becomes predictible), than a few moments ladder, it fires the rail gun, making the enemy evade (as predicted) to the position where the PDC bullets are flying towards (being vaccum, they just keep going), and that makes the enemy ship get hit. ;)

[Mjr]

You should do a "What would a real space battle look like" with you're space battle animation that could be really cool.

[pschroeter]

I like how the torpedoes will drop off and launch facing the wrong way than maneuver and point themselves towards the target.

[cptnoname]

Very late to the party, but...

TL/DR: effective range is arbitrary and it's going to vary by target

It's stated in the books (when the Roci is forced to for its railgun in [to avoid spoilers] a "different mode") that the projectile fires at 5 km/s, which is pretty realistic given the length of any rail that the Roci could reasonably accommodate.

At 5 km/s the kinetic warhead would pass the 1000 km range band in 200 seconds.

That's one minute and forty seconds, by the way.

At even one gee of acceleration, a target ship at that range would be able to put a ∆V of about 2 km/s toward evading that shot, and it could change its actual position vs any trigger-time projected trajectory by up to 200 kilometers, easily side stepping the projectile. At 10 gees a ship could displace itself 2000 km in the same amount of time.

None of that takes into account the amount of time the enemy pilot needs to react to the incoming fire, nor the response time of the drive. Allowing a few seconds for a drunken pilot and a commercial drive would be negligible compared to a 1:40 flight time. Even the Canterbury could evade a railgun round at 1000 km.

It would come down to how quickly the target can evade the shot, which would be a function of it's reaction and response time, acceleration capability and the physical size of the ship along whatever profile it's presenting to the attacker. Its lateral thruster capabilities would come into play as well, especially if it's presenting its forward face to the gun, in an attempt to minimize its profile. Roci would need to rotate slightly to avoid a shot at close range even at full thrust, since she has no real thrust laterally (with exception, maybe, for the books, where she lands horizontally instead of vertically, but those thrusters would presumably be only along the landing side of the ship).

Let's assume the best possible scenario, where the Roci is trying to evade a shot fired against her from 90 degrees to port (or any other side, really). Even if they aimed at where her nose was projected to be at the time the shot arrived, she would have to displace herself as little as 45 meters to avoid the shot. At one gee, ~10 m/s², she could do that in 3 seconds. So the range would have to be less than 20 km if it took Alex and the Roci one second combined to respond.

Of course, Roci can accelerate at 15 gees. Assuming the same response time and orientation, Roci could dodge a shot fired from more than 8873 *meters* away.

The attackers' gunner will be trying to predict how the Roci might respond, and that will increase the size of the danger zone, but one would have to have near Jedi-like predictive powers to extend that very far. Unless Alex is drunk. But even if he's so drunk that he needed 5 full seconds to get the ship to fire it's thrusters, the attacker would have to be within 28.9 km.

The MCRN's Donnager class has much bigger railguns, and with longer rails you get higher speeds, so the danger zone against one of these capital ships will also be greater, increasing proportionally with the muzzle velocity of the projectile.

The only way to hit a ship in CQB with a railgun is to be really close or to produce such a volume of fire with other weapons that you can limit its options for evasion. Putting lateral rocket motors on the projectile to fine tune its path could increase the chances of a hit as well, but with 2kg slugs as per the books and the show that would be of pretty limited utility.

Hitting anything with a railgun in The Expanse's world of high thrust ships would be next to impossible.

[GI.Jared]

the funny thing is this isn't too dissimilar to actual modern naval combat

[ItzmeFlez]

Very good explanation! I only recently startet watching the Expanse and am only halfway through season one, but so far I love it! The universe really does feel alive and so far every character seems really interesting. Defenitily one of my favorite Sci-Fi series so far

[Daimon-X]

'Big guns never tire.' In space, no one can hear when you shoot...

[PuissantPeacock]

I'm sitting drinking a margarita on a distant planet about 60 light years from the events of The Expanse. Suddenly, my house and most of my property instantaneously explodes in a massive detonation. "Where the hell did that come from?" My AI droid standing next to me says, "Calculating... Sir, it was a rail gun round from Earth's solar system that missed it's target in the battle over Mars...it has been traveling here for over 300 years." "You have got to be kidding me!"

Yeah, what happens to all of the rounds that miss? Without something to stop them, they just keep moving through the vacuum of space at the same velocity until they hit "something" like my house 60 light years away! 😂

[simonegeezer]

Love the show. Feels like space engineers physics. Flak weapons, like a battlestar, would've been a good idea