It is time once again for our regular Open Thread. Talk about whatever you want, so long as it isn't Culture War.
The USNI Christmas Sale is on, and it's a great option for anyone who wants to bulk up their naval library. Most everything is half off, and shipping is free. Particularly tempting among recent releases are the Revised Edition of Friedman's US Aircraft Carriers, the 2023 Seaforth World Naval Review, What Happened to the Battleship?, Friedman's new US Navy Attack Aircraft (although it's somewhat less substantial than his usual works) and reprints of Atlantic Escorts and The Battleship Builders. Other good options include Friedman's other Illustrated Design Histories, the 14-volume Morison set, the excellent Russian and Soviet Battleships, and most of the stuff on Drachinifel's reading list. I don't have half a dozen, and a few more aren't great (Learning War and The Battleship Holiday are the most prominent here) but it's a pretty good place to start. Other good choices are Freidman's World Naval Weapon Systems and Network-Centric Warfare, DK Brown's Before the Ironclad, Warship Builders, about the USN's construction program in WWII, and Brian Lavery's superb Nelson's Navy.
As the archive has grown, the work of doing overhauls has expanded, and I'm going to end the practice of doing a full read on all older posts. I'm doing a lot less revision than I did in the first few years, because my writing style has gotten more consistent and I'm writing less, particularly on topics related to those I did 4-5 years ago. I'll check any that look likely to need link updates, and note any where actual updates take place, as well as doing normal checks on the year-old posts. If there's interest, I might continue to list all of the older posts in the relevant time period.
Minor updates were made to Early Guided Weapons Parts one and two and Coastal Defenses Part 6. 2021 overhauls are A Visit to NSWC Carderock and my review of the US Navy Museum and Navy Memorial.
Comments
I'm not sure if this is actually unclear, or if it's just early-ish on a Saturday morning, but... Are "Learning War" and "The Battleship Holiday" prominent on the reading list, or prominent among the not-so-great entries on that list?
Prominent among the not great. I have both, and wouldn't really recommend either. Learning War is basically pure pentagonese, and Battleship Holiday doesn't really have a niche that isn't filled by better books.
Visited Intrepid and Growler today and was surprised to see there wasn't a Naval Gazing review of them. I'm not knowledgeable enough to judge them fully but here are my observations:
Dark Tech over on YouTube has an interesting video about the British/Swedish NLAW anti-tank missile, the cheaper but less capable complement to the Javelin.
In the US, you need a college degree to become a military officer. The military doesn't seem to care what you studied during that degree, though, so I suspect this degree is mostly used as a screen for general ability rather than any specific skills.
But let's suppose an aspiring officer is determined to do better than that. What can you study at a typical college that won't just show examiners that you is capable, but might actually be useful for a military leader?
Just for starters, it would be a good idea to understand the likely enemy. For the coming generation, that's likely to be China, with side orders of Russia, Iran, and North Korea. So, spending some portion of your four years studying Russian history, politics, and language, say, would be time well spent.
What else?
Johan Larson:
The officer/enlisted distinction used to be a nobility/commoners distinction so it could just be an attempt to replicate it in a society that doesn't really have a nobility.
As for general ability, why not just use ASVAB?
Johan Larson:
A degree that actually requires you to be smart to pass.
Also something necessary that most others don't think of.
Johan Larson:
Agreed, OTOH the enemy may change.
Seems like the ideal degree would be Supply Chain Management (aka logistics).
I could see a case for also taking classes in history, linguistics, nuclear engineering, aerospace engineering, mechanical engineering, medicine, and a variety of others. And of course you should fill out your time with extracurriculars in something athletic and/or something you can demonstrate leadership.
Some specialized staff functions have useful corresponding civilian degrees. If the officer responsible for building military roads and trenches and temporary bridges has a civil engineering degree, that seems like a reasonable fit. Some of that knowledge would transfer. Similarly, the guy responsible for the nuclear powerplant of a sub could reasonably have a degree in nuclear engineering. The harder questions revolve around more general command positions. What courses or degrees have something to offer the commander of a tank company, or the skipper of a frigate?
Directly? Probably taking as many military history classes as you can find. Not so much because of what it will teach you for your immediate job, but there's a lot of value in that stuff in getting the broader picture.
Understanding the physical domain you fight in would be useful. So, physical geography for land commanders, oceanography for sailors, and atmospheric science (if that's the term) is for aviation commanders. A bit of meteorology for everyone, actually, since weather always matters.
Are languages only a pay boost for enlisted, non-coms, and contractors? That seems like something that's very useful, but potentially not given much weight for career purposes.
@Bernd
I am pretty sure that if you go to one of the academies, they make you study an enemy language. (Your choice of which)
@ike: But the Army, the Navy, and the Air Force already all speak the same language. Even the Marines, when they do more than grunt.
@Bernd
The Foreign Language Proficiency Bonus is open to all US military members. You get paid based on level of proficiency and how important the language is to the military. It's good for enlisted and officer. If you look up 'FLPB pay tables' you can see what it's worth on DFAS.mil.
@ike
They do that in Australia but none of the academies require anything more than a normal college does (ie 2 semesters of language study). USAFA offers Arabic, Chinese, French, German, Japanese, Portuguese, Russian or Spanish.
James:
The omissions are also interesting.
Where's Korean and Persian?
Monterrey. If the military wants someone to have specialized language expertise, they send them to the Defense Language Institute, which exists entirely to teach language skills the military needs. This isn't the same as civilian language classes, or as a book I read once put it, "how do you order a bombing run"? Looking at the catalog at USNA, their basic language courses don't seem that different from those you might see in a normal college, particularly in languages that aren't Arabic and Chinese (the only two languages you can major in there).
When my cousin was at West Point, you needed to choose one of Arabic, Chinese, or Russian. Russian was the popular slacker-choice.
We have an assignment. The Department of the Army has asked us, the Internet Reserve Corps of Influencers to devise a new stereotype about the US Navy. The old one was that everyone in the Navy was gay. Unfortunately that's just not that pejorative anymore; only the butchest have a problem with sharp fashion choices and fabulous taste in interior decorating. So, the Army needs some other nasty rumor they can spread about the folks in blue. The budget for a whispering campaign has already been approved, but it needs a topic. What do we have in mind?
The navy will have to pry my gay jokes from my cold dead hands the same way they separate the men from the boys.
BTW, is there any interest in an SSC-style 2023 naval events prediction thingy? It was fun to see Bean's guess confirmed on the 500 ship navy plan, and I'm curious what else you all think is going to happen in the future.
Unfortunately I'm already batting zero after Secretary Espurr inexplicably failed to use Psybeam or even evolve into Meowstic during a press conference.
Are the problems with defence procurement limited to the big-ticket items or does it trickle backwards throughout the supply chain?
@Lambert The government often produces bizarrely long specifications for the even simple items. This article discusses a 15-page specification for a cookie.
In principle, this is supposed to let the government avoid subjective determinations about which vendor's goods are preferable. Instead, they publish detailed specs, and accept the lowest bidder whose product meets the spec.
In practice, this behavior means that only very specialized organization that have learned to work within the system bother to deal with the military procurement system at all. There aren't a lot of companies like that in any given domain, so bidding isn't very competitive. And some of the most advanced practitioners have learned how to influence the procurement system, to tailor the specs to their own strengths, so they are more likely to win bids.
If you don't have the full fifteen-page specification for a cookie, someone will just figure out that they can make cookies extra cheap if they e.g. don't bother cooking them completely (or take care not to overcook them), then insist that since they delivered unappetizing lumps that are technically "cookies" for half the price of those primadonnas at Nabisco or Mrs. Fields, therefore give us the contract and all the money or we'll sue!
A hundred years ago, the Navy would just show up with one of the alleged cookies in court and that would be the end of it. But we now have almost four times as many lawyers per capita than we did a hundred years ago, and they've all got to find work.
I know the Navalgazing preference in space battleships leans more towards "freshly raised from the East China Sea," but I thought this short video was very cool for anyone who appreciates gimballed engines, glowing radiators, and invisible lasers.
There's also a french ship that would fit right in to Bean's latest Aurora playthrough.
I think you misspelled "Space Battleship Iowa."
More seriously (but not, you know, a LOT more seriously), it's funny how the US adaptation of SBY dispensed with the whole "IJN battleship sunk during WW2" thing. And more broadly, it's funny how much military-themed anime there is, and how much of it amounts to "What if WW2... but this time we win somehow?"
Weirdly, no. Before I got into battleships seriously, realistic space warfare was the subject of my greatest geekitude.
Space warfare would make a really interesting post series, if you felt it fit the blog. Could always frame it as "ways space warfare is not analogous to naval warfare"
Cool how each geopolitical adversary also has its own alphabet/writing system.
Also, do gimballed main engines make sense in deep space? You're going to have attitude control thrusters anyway, and gimballing those big boys seems non-trivial.
According to the Children of A Dead Earth guy, they often do.
For one thing if you have 5 engines and one goes down to a catastrophic pebble-through-the-nozzle, a gimballed setup gives you 80% thrust minus some losses for thrusting off-center, while a non-gimballed setup has 60% thrust after shutting down the opposite engine for balance.
They're also good for the kind of turn-and-burn the ship was doing in that video, to maneuver away from one part of a missile salvo while engaging the other part. You're also going to be doing a lot of random-walking because projectile accuracy depends on cross-section times the volume of your potential maneuver cone; a ship with no engines can die to a railgun trick-shot from across the solar system.
Sure, maneuvering is great. The question was, is it worth it to gimbal the main engines instead of beefing up the RCS?
Re CoaDE, I alt-f4-uninstalled when I saw my ship was shooting ballistics at a target under constant thrust, and missing because the aiming logic didn't take into account the target's acceleration. It's either realistic space war or it ain't.
Yes, it's worth it to gimbal the main engines rather than beef up the RCS. In order to "beef up" the RCS in able to compensate for an off-centerline main engine failure, your RCS thruster would have to be very nearly a main engine in its own right. And even if you've only got one main engine on the centerline, it's not going to be exactly on (or aligned with) the centerline. You can compensate for that with an RCS thruster, maybe, but RCS thrusters are going to be less efficient than main engines so you'll be burning more fuel than you need to.
The Apollo Service Module and the Lunar Module's descent stage both used a single gimballed main engine. The Space Shuttle OMS engines, used only for orbital maneuvers where the RCS thrusters are also available, are gimballed. The main engine on a Soyuz, and I assume also Shenzou, is gimballed. That's not always the case for satellites, but when you get to something the size and complexity of a manned spacecraft, it's usually worth it to put the main engine(s) on gimbals.
@Lambert
Yes, it very much is. Governments are bad at proportionality, and the rules they cook up for the F-35 often get applied to buying stationary.
@Bernd
I've thought about doing that, but that particular framing definitely won't be the one I pick unless I get really desperate. Yes, obviously space maneuvers and naval maneuvers are different. Understanding this is table stakes, and if anyone wants the explanation, there's always Atomic Rockets. (And I'm generally fine with their version, in part because bits of it are mine.)
@John Schilling Thank you, that makes sense now.
@bean Speaking of which, is Atomic Rockets abandoned now? Haven't seen new content there since the author's health took a turn for the worse, and if it goes out some day the world will be poorer for it.
Based on the Patreon updates, there's at least some plan to hand the site over to someone else at some point, so I hope that we're safe on that front.
@John Schilling, I'm sure the gimbal or not gimbal question relies a huge amount on the relative size of the engine.
All our space craft to date have had engines that were small relative to the fuel tanks (or just plain small with the lunar landers).
With a Space Battleship Yamoto style layout where you've got some giant engine the size of the rest of the ship... no gimbal would probably be the choice.
@berd. This is where we mention the early Honor Harrington books, where a careful selection of speeds, accelerations, weapons range and sensor range meant that the space battles were exactly isomorphic to Napoleonic naval battles. Only scaled up a million times. Arbitrary decisions about spaceship design even made everyone use broadsides.
The author could then use existing orbital velocities to replicate the effect of wind and tide and lift entire battle plans and descriptions from O'Brien and Marryat.
Sadly, the usual SF temptation of making every thing grow in power and ability with each new story meant that the scaling broke down.
See also "War in 2080" by David Langford, a non fiction speculative book published in 1980 about the future of weapons tech, based on fundamental physics and tech and then projecting where it could go. I read it in the early 1980s, and I remember the claim that the early 21st century would become dominated by small, cheap, unmanned but semi-autonomous flying weapons like smart cruise missiles.
Also, trying markdown in this comment to see how it goes.
It seems to me that, if you're just random-walking out of the way of incoming fire rather than trying to go in any particular direction, you'd better have your main engine pointing sideways relative to the long axis of your craft (rather than along the axis, as in CoaDE). That allows you to change your acceleration vector by spinning, as quickly as possible, and by a larger angle than the gimbal limit of a nozzle.
VICE has an interesting report of the Netherlands fielding THeMIS ground remotely-operated vehicles. This is in a "semi-operational environment." The article incldes a lot of pointers to other recent trials of ground combat drones, including a 2018 experiment by the Russians in Syria and one by the Estonians in Mali in 2019.
Semi-operational, that means you're doing real work but don't expect hostilities, is that right? So, something like guard duty at bases or border patrol.
Let me add this excerpt:
@DampOctopus
Intuitively it seems easier to build a structure that takes thrust length-wise than crosswise in the middle, am I wrong on this?
Also, if you do gimbal the main engine, isn't it more effective at rotating the ship if it's at one end, rather than in the middle?
I mean, even fast juking wouldn't be primarily by gimballing, but by rotating the ship (by RCS and/or gimballed mains and/or gyro) and thrusting "for reals" on a new axis, right?
If you're constantly jinking in a spaceship how long are you going to even have propellant left?
Maybe the best way for your enemy to defeat you isn't to blow you up but to run you out of remass.
@hnau's account of Intrepid inspired me to add some impressions of my recent visit to the pre-WW1 armoured cruiser Giorgios Averof in Athens.
My son, who had been before, said he found it underwhelming compared to HMS Belfast. And I can see his point but I still found it worthwhile - it is after all one of (afaik) only two remaining major warships of the pre-dreadnought era, and I'm unlikely ever to make it to Japan.
Price: two euros iirc. Practically free, so basically a no-brainer despite my son's opinion.
Accessibility: not as easy to get to from central Athens as it should be. The radial metro rail line is poorly integrated with the shoreline tram service, and even once you've disembarked at the right tram stop it's not well signposted. But still only around forty minutes from our Monastiraki hotel. We arrived around 10:30 and appeared to be the first visitors of the day, although it got a lot busier later.
Overall impression: the areas open to the public are indeed, as my son said, far more restricted than on Belfast (or Warrior), but still well worth it for the extremely low price and the uniqueness of the ship. Some other impressions:
Officer's Quarters. I've read several accounts of ships built for foreign governments, then taken into RN service, having very plush officers' accommodations versus very basic facilities for the enlisted crew. See for example HMS Agincourt aka "The Gin Palace". The stereotype certainly seems to be confirmed here: I thought the wardroom was pretty plush, until I saw the admiral's staterooms.
Little or no subdivision of interior spaces. Huge open deck spaces in which fragments from anything that gets through the belt are going to kill everybody present. But hopefully not many people in these spaces when at action stations?
No tertiary armament. The 9.2" and 7.5" turrets are still present (although not open to visitors) but nothing else. So you can't see anything of either the original anti torpedo boat or the later AA armament.
Superstructure? Barely. There's a small bridge (not open to the public) and an even smaller armoured conning tower - which made it pretty clear to me why armoured conning towers weren't much used and were often quickly removed/abandoned. And of course the multiple floors of sensor & communications gear and personnel that were present on a WW2 cruiser like Belfast didn't exist yet two generations earlier, which makes it pretty clear how much and how quickly things changed in those thirty years.
Engine rooms: not open to the public
Museum exhibits about Greek naval history: of no use to me as I can't read Greek.
Also, two piers over: trireme!
@AlexT
You're not wrong about the potential structural issues, although how much that matters is very dependent on the details of your scenario.
@AlanL
Thanks for that. I will link it from the Museum Ships index post.
@AlexT:
I hadn't considered the structural implications of a structure balanced on thrust at its midpoint, but it seems to me that it's easy to overcome. Just space your engines along the length of the structure, so the thrust is applied more evenly. As a bonus, with a combination of gimballing and selective throttling, you can rotate on either long or short axes faster than you can with a cluster of gimballed engines at the endpoint, for plausible gimbal limits.
On your second point: yes, to evade you need to thrust in a specific direction, rather than just rotating your ship. But, if you're slow to rotate, your enemy knows roughly which direction you're thrusting, and can predict your future location within a limited cone. Fast rotation is required to keep your acceleration vector unpredictable.
Another point I should have added: in order to present a minimum profile along the threat axis, you'd generally like to be end-on to your enemy. To evade, then, you need to accelerate orthogonal to this.
@Anonymous:
A few minutes, I guess, assuming chemical fuels? But, as you implied, if your enemy runs out of reaction mass first, you've won: they can't dodge your shots any more, and they can't go anywhere either.
Note that if you assume a nuclear engine, the need to shield the crew from radiation pushes you towards putting it at the far end of a long (to maximise distance from the crew) and thin (so the radiation shield can be smaller and lighter) rocket.
Speed of rotation is also going to be limited by what the crew can handle (while unmanned missiles have no such limitation).
Realistically space warfare probably won't involve much maneuvering, i.e. there won't be any dogfights.
@Anonymous: crew gee limitations also support my contention, I think. If you want to rotate a cylinder without squishing the people living in it, you can do that much faster by rotating around the long axis.
Also, what we're talking about here isn't much like a dogfight. Think of engagements as in Children of a Dead Earth, with the combatants making a single pass by one another as their orbits intersect - but with a bit of jinking on the approach.
@Alexander: I take your point about the placement of the reactor for a nuclear rocket. You could perhaps put the reactor at the endpoint and pipe the exhaust to nozzles elsewhere, though I imagine this ranges from difficult (waste heat will get everywhere) to impossible (exhaust from a gas-core reactor will melt any conceivable piping). With nuclear-powered ion propulsion it works, of course - you can distribute electric power wherever you need it - but that's a bit low-thrust for this application.
I think a lot of the "dogfighting" comes down to assumptions about how small you can make nuclear-engined missiles. If burning away from low delta-v chemical missiles is on the table, I'd expect main engines thrusting all over the place. It's like how ship speed is important vs torpedos but useless vs ASMs.
If all you can do is random-walk to dodge unguided projectiles, maybe chemical RCS is the way to go; the fuel won't need to last more than a few minutes either way.
Then again that's making even more assumptions, since all space bullets are probably guided due to the costs of being-in-space dominating hardware costs.
Thanks for the review Alan! At this rate maybe Navalgazing will someday have a wiki database of all the world's naval museums.
Bernd:
LOL. That won't work if your enemy can fire from longer range or even use lasers.
Bernd:
Maybe not, being-in-space has high costs today, but the future is not the present and by the time serious fighting takes place in space our space technology is likely to be very highly developed and probably pretty cheap.
Also space is so vast that we'll be in the phase where there's enough to go around, no need to fight over resources for some time so civilian space technology will advance nicely while military tech will be largely neglected until someone finds something to fight about.
Not if the control section is near the center of mass, and that's where the crew would likely be in combat, watching screens and pushing buttons, not manning the forward guns (or tweaking the nuke drive at full power).
Going slightly more meta, dodging in space at plausible ranges seems one of two things: utterly trivial against anything unguided, and impossible against anything guided and/or lasers. So you'd want the trivial case covered, by giving your warship the ability to apply bursts of high thrust, while being aware that any missile will be able to out-thrust you, so you'll have to shoot it down and eat the debris.
Which is where ship layout comes in, where I propose lining up the ship sideways on the threat axis and putting the guns on the side towards the threat. This gives max surface to put sensors and weaponry, and high-velocity debris pokes holes across a long cylinder rather than along it.
Like the sea, space is a transit medium. Nobody'll own a particular volume of deep space, but control of who/what passes through that volume will be worth fighting over. And specific valuable points of interest (resources, infrastructure, industry, population) will definitely be worth fighting over too.
I strongly suspect that guided projectiles will be universal. The mass leverage you get even with very weak guidance is enormous, and if you have to transport it anywhere, that's going to be decisive.
AlexT:
You don't need to be all that far from the CoM to get serious centrifugal forces from rapid rotation.
AlexT:
They may not even necessarily be doing it on the ship doing the fighting, a command ship holding back a bit is a much safer place to be and you might not need much AI on the fighting ship to be able to tolerate a few seconds lag.
AlexT:
But if it turns out everything is guided or a beam weapon you'll be designing in a capability that is never going to be useful and probably making sacrifices elsewhere to get it.
AlexT:
Why fight a battle that would destroy lots of infrastructure when there are thousands of other rocks you can have instead?
bean:
The one niche for unguided projectiles might be defending fixed installations, probably using coilguns to launch. In that case you have a ready source of raw materials but may not have the ability to create a lot of guidance systems.
It'd probably be viewed as a last ditch defense but it could be quite an effective one.
Also in science fiction stories in which space travel is routine but computers with kiloFLOP performance take up whole buildings.
I assumed that by default we were talking about dodging lasers here, rather than unguided projectiles. This isn't impossible: at a range of X light-seconds you have 2*X seconds to get out of the way, including the sensor lag. Even if you can't dodge it entirely, you can minimise the time it spends focused on a single spot on your hull.
Regarding unguided projectiles, though, another niche for them is a cloud of particles too small, individually, to be practically engaged by point defenses. Maybe grains of sand, depending how good targeting technology is. They wouldn't destroy a target, but they could erode exposed sensors etc. I wouldn't imagine this as being fired directly, though: more likely to be a payload for a missile, to get as close as it can without being shot down, then deploy.
@DampOctopus
My problem when lasers have ranges >=c*s is that I think most technology bets are off at that point. To my mind, current tech is chem rockets and fission nuke thermals, plausible is fusion thermal propulsion, PD lasers, coilguns and nuke-pumped laser warheads, and grasers belong with metastable metallic hydrogen and antimatter drives.
Agree re unguided submunitions - get a missile on a high-speed collision course and release a cloud of nasties as late as possible. Dodging the shrapnel would depend on particulars, but it doesn't feel likely if the missile and the ship use comparable technology.
Unguided might also be really good as PD. Worse accuracy than lasers, but you're shooting incoming - your target does its best to reduce deflection and range diminishes rapidly. Whereas it's probably safe to say that 1 slug hit = 1 dead missile, and you can even use chemical propellants, so dirt cheap and no power drain; even cooling might not be required with the right gun design.
@anonymous
You have to keep the other guy honest, is why. You make sure you don't die from stupid stuff, so the competition doesn't get a free lunch.
Yes, but let's talk numbers. 5g at 2m from the CoM means the ship rotates at about 5 radians per second, if I haven't screwed up my math, which seems unlikely in a manned combat ship. Also, anything 100m from the CoM would experience 250g - better hope those engines, weapons and sensors are bolted down real tight.
To secure the best ones and leave your competitors with the dregs, the same it's always been.
A thousand times this. Lasers are very much range-limited weapons, and getting them to the point where they can do damage at ranges where you can even theoretically dodge requires technology that just looks nuts.
Re sand clouds, has someone been reading my old space warfare stuff?
And yes, there is some room for unguided projectiles in cases where the target basically can't dodge. But if dodging is on the table, then I stand by the statement that guidance is all but certain because you have to fire orders of magnitude fewer projectiles.
Okay, putting in some actual numbers...
With current technology, we can definitely phase up a D=6.5m composite mirror at lambda=600nm (the JWST at the short end of its band). That gives you a diffraction-limited beam size of theta = lambda/D = 9e-8 rad.
A practical upper limit to effective range is when the spot size on the target is the same as the mirror diameter: at this point, the intensity on the target is the same as the intensity on your mirror, so if your mirror's not being ablated, they can use the same surface/cooling/etc. to armour themselves. This gives us a range of r = D/theta = 7e7m = 0.23 light-seconds (approximating over the near-vs-far-field distinction).
To get a significant benefit from evasion, you need to be able to move the spot on your hull to a new position - i.e. move it by its diameter - within a round-trip time of t = 0.46s. This means you have to accelerate at a = 2D/t^2 = 59 m/s^2 = 6 gees.
That's high - high enough that I'll agree it's impractical with current technology. (Targeting technology, anyway. Integrating an actual laser with the mirror is left as an exercise to the reader.) But it's close enough to be worth considering.
DampOctopus:
Until you run out of propellant.
Lasers also mean that you don't get to know that the beam is on its way until it hits, the best way to use lasers in space war is to start shooting early on even if it'll take a long time to do damage simply to make your enemy waste propellant dodging (and if they sit there and take it, so much the better). Unless you've got a torchship anyone who can shoot a damaging laser beam over light second range can kill you slowly or run you out of propellant before you're in kinetic range.
AlexT:
Just an extrapolation based on well known principles of optics.
AlexT:
WTF would you use fusion thermal? Much more efficient to just send the reaction products straight out the back.
Discussions of space warfare do have the issue that the technology level of the fight can be highly variable, it'd be like discussing the possibility of air combat and having to simultaneously deal with biplanes and supersonic jet fighter and even that difference may be small compared to variation in space war tech levels (even if we stick to the laws of physics that we know of).
AlexT:
I would expect people to be further from the CoM, unless we're talking single seat fighters.
AlexT:
A beefy structure like that is not going to be good for your mass ratio.
AlexT:
Except that your competitors will be destroying your infrastructure, if not at first then after you start blowing their stuff up.
DampOctopus:
Doing better is unlikely to be much of an issue, the JWST mirror is limited in size by the fact that it has to fit inside of a payload shroud, a warship built in space is not likely to have that constraint, it also is in pieces since to fit in a shroud smaller than itself it had to be folded up.
DampOctopus:
Also to be able to target it you need to know where the target is and the resolution limit happens to be the minimum laser spot size (and realistically you'll want the spot size to be much smaller than the mirror size).
DampOctopus:
I'm pretty sure that's far-field.
That seems an odd choice to me. If spot size equals mirror diameter, that means guaranteed zero damage on target, assuming hull plating is more durable, more reflective and better cooled than the primary mirrors. Shouldn't it rather be spot size = D/10 or some such?
Although personally, I can't see laser weapons in space using mirrors. Gamma ray or bust.
@anonymous
My point was that if you're fighting someone who can hurt you with his laser from 1cs away, you'd better have at least a torchship, if not the starship Enterprise.
Also, there's no such thing as "kinetic range" in space.
If you expect to spin a lot, the CoM is exactly where you'll put the control room. The point being that centrifugal force from maneuvering isn't likely to be a problem for the crew until the ship itself breaks apart.
Which sounds like the vast majority of wars ever fought by people.
For high thrust when you need it. The rocket equation holds for torchships too, you can have high isp or high thrust; sometimes you want the one, sometimes the other, or some combination. The point was that it's not electrical - it would use the reactor's output directly, without turning it into electricity first.
This may not be a good assumption. In particular, lasers can use dielectric mirrors, which are incredibly reflective, but also require quite specific wavelength and geometry. At the same time, I don't really expect mirrors to be sized by the need to avoid melting themselves.
It strikes me as highly unlikely that a random patch of hull plating will be more durable, more reflective, and better cooled than the primary mirror of a laser beam director. The mirror is in a protected location, less likely to be e.g. pitted by micrometeoroids. It can afford to be much more expensive than a similarly-sized patch of hull, and the focus of more dedicated support like active cooling loops. And it's got one job - to reflect light of a particular frequency without overheating.
It's almost certainly going to do that job better than whatever you are making spaceship hulls or even armor plate out of.
Interesting. I suggested, as a rough figure for the maximum effective range of a laser, the distance at which the focused spot is the same size as the focusing mirror ... and people have been advancing reasons both why this is too long and why this is too short.
@JohnSchilling: I can think of a couple of reasons why armour could be more durable than a mirror. One is that it still works when it's warped from thermal stress, which a focusing mirror does not. Another is that you can make it semitransparent, so pulsed lasers are absorbed down to a depth of (say) a few mm rather than ablating the surface. But the points you and Bean raised - dielectric mirrors, more dedicated active cooling, etc. - apply in the other direction, too.
@Anonymous:
I think this is an excellent analogy.
AlexT:
More durable is possible but more reflective is unlikely (though it may have higher emissivity if you coat your ships with second surface reflectors) and is also unlikely to be better cooled (the mirror will have its entire backside as a radiator, probably in the form of a second surface reflector).
AlexT:
Yes, but for other reasons.
AlexT:
Sufficiently large mirrors can give lasers quite good range and they'll work up into the UV (which also gives an inherently tighter beam).
Also warning shots would need to use visible light (or even IR) as sending ionizing radiation is an attack, not a threat.
AlexT:
Your own laser that can also hurt them might be the best you can get.
AlexT:
Not completely, but if you fire from too far out they'll be able to take potshots at your projectiles knocking out any guidance system and the optics needed to see them with enough precision to point unguided projectiles is also the optics needed in an effective laser weapon.
AlexT:
Yes, but 2 m from the CoM means the room can't be much bigger than a bedroom. You're just not going to fit many people in it.
AlexT:
Not really, before industrialization it was possible to gain from starting a war, now the best you can hope for is the prevention of evil at significant cost. Doesn't completely stop war as Putin is demonstrating but it does reduce the amount of wars quite a lot.
AlexT:
Rare enough that the fusion rocket will mostly operate directly, not in an afterburning mode.
AlexT:
The point of a torchship is to have both high thrust and high exhaust velocity at the same time.
AlexT:
A fusion rocket would not generate much electricity (or even any if you're doing a Longshot style configuration) instead the charged reaction products would just be directed out the back.
bean:
Even just Al is pretty reflective and likely to be available in large quantities extremely cheaply and would give you frequency agility if you need it, say to use UV for hurting, visible light for warning shots and the ability to pick a frequency the atmosphere of a target planet won't block too much of for orbital fire support.
bean:
Probably not, they'll be sized based on spot size at range though a larger mirror would also be able to handle focusing a more powerful laser and if the laser and its electricity generating equipment is cheap enough maybe running the mirror to its limit is the best thing to do.
John Schilling:
I doubt that, the mirror is going to be by far the largest part of the ship, there's really no way you're going to be able to armor it.
Coming in late, but David Drake's take on "Aubrey and Maturin IN SPACE!" (Lt. Leary Commanding, et al. often known as the RCN series) has some interesting variations on the usual tropes of starshipping. The starships (and spaceships as well) are all (barring extremely specialized exceptions) cigar-shaped vessels with the main motors mounted (on gimbals!) along the dorsal side. This is (in universe) because all the ships we see are trans-atmospheric single-stage-to-orbit, and this means that thrust gravity and landed gravity are always aligned the same, simplifying the internal layout of the ships. Despite being reaction driven, the ships are almost always thrusting at 1G in flight for crew comfort reasons; the FTL system of the setting permits entry and exit (nearly) without regard to local gravitational conditions (and while in FTL flight the interior of the ship experiences 1G gravity along the same axis as when in powered flight or on the surface, while the space outside the hull is in microgravity for reasons that are never explained), so the time spend expending reaction mass is a relatively small part of the voyage time. Mr. Drake never bothers to do the sort of infodumping Mr. Weber is fond of, so fine details are up to the reader to provide for themselves