Space carrier/reaction engines question

[Batman]

So how dangerous would it be for space fighters approaching a reaction driven carrier from behind while the carriers engines are operating? How tightly focused would the engine exhaust be? I realize the most obvious answers are a) depends on the drive type and performance, and b) whatever I want it to, it's my universe afterall.
I'm not asking for a drive that works, I'm asking assuming I have a drive that works, how big would the drive plume be, and how far away from it would landing fighters need to be to be safe.
If the answer is 'insufficient data', as I very much suspect it's going to be, by all means tell me what data you need to attempt to answer the question.

[Destructionator XV]

I tend to think the danger of exhaust plumes is really overestimated.

Yes, it's probably hot. Yes, it might be focused.

But, it is going to be expanding rapidly and there may or may not be a lot of of it - the quantity of stuff sent out depends on the type of engine, how fast it is operating etc.


Anyway though the rapid expansion is pretty much guaranteed and that is going to limit the danger of it. Probably won't want to fly straight into the stream, but other angles should be diffuse enough to handle.

[Stofsk]

Wouldn't answering this question require details on what drive you're employing? Even so, if it's anything but a nuclear drive or fusion torch, or something that employs anti-matter, would it even be a problem? Of course, you probably won't put tiny thrust ion drives on a huge space carrier.

Another factor you might want to consider is how space combat ranges affect things. Do fighters need to get that close to be a threat to space carriers? Are they a threat from a couple hundred ks away?

[Batman]

Nevermind fighters getting close enough to shoot at it. This is about the carrier's own fighters safely approaching from the rear so they can land.

As for drive type we're theoretically talking fusion torch (albeit not a particularly hard scifi one-think Battletech drop/warship drives).

[Hotfoot]

A lot of questions need to be answered. One is if the carrier is even under active thrust. In space, motion is relative and unlike modern airplanes and naval vessels, which require constant thrust to maintain constant movement, space vessels do not. The only time such a ship would be burning is if it were actively under maneuvers. Doing so would actively make it harder for fighters to land because they would have to burn more reaction mass just to keep up, never mind overtake, their parent craft.

Another question is what sort of thrust is being applied? Do the ships in question use magical mass reduction technologies to achieve higher delta-v, or just incredibly efficient drive systems that require very little fuel for a thrust system that is both very efficient and very powerful (no mean feat). This will determine how hot, how much, and how fast the materials coming out of the engine will be. Note that they may well retain their heat for some time in space, since there is very little to transmit the heat to, and so all heat loss will be from radiation. Granted, the particulate is likely small, but how fast it's thrown out will increase the drive tail.

Next, what sort of protection do these ships have from attack? Energy shields? Armor of some kind? If it's shielding, then there's probably some protection from the drive tail, at least up to a certain point. If it's armor, depending on the kind there could be similar protection, but it would still cause possible damage and material fatigue if you do it continually.

Additionally, how much of the rear (or front, even) of the ship is made up of exhaust ports? Once you close to a certain distance, there should be blind spots in the exhaust of most ships that you can maneuver in without trouble.

Last, why would the fighters have to approach from the rear of the ship? Even if the landing bays are in the back end (which is...special), under Newtonian Mechanics, they should be able to slide in from any direction and make a few last minute course adjustments to end up in the hangar bay. Unlike modern aircraft, fighters designed for space combat wouldn't need a landing strip per se. Depending on the level of technology, you could have tractor beams, magnetic docking arms, or even webbing to catch the darn things. Since motion is relative in space, unless the ship is still under maneuvers, there's no need to put the launch and landing ports anywhere in particular, since once the fighter matches relative velocity, they can come in on any vector they need to.

Granted, most games tend to go for the WW2 Fighter/Carrier model, which is admittedly fun, but they don't bother making many of the sensible considerations of space and technology to begin with, much less any for drive system damage.

As an addendum, if you're doing a damn Battletech versus debate, may twelve generations of your family scorn your name, may your pets disown you, and may your suitors dispose expensive drinks upon your visage.

[Batman]

A lot of questions need to be answered. One is if the carrier is even under active thrust.

Um-yes? That's sort of the point? Asking if it's dangerous to approach from the rear while the engines are operating is moderately pointless if they aren't.

In space, motion is relative and unlike modern airplanes and naval vessels, which require constant thrust to maintain constant movement, space vessels do not.

I'm marginally aware of that, thank you.

The only time such a ship would be burning is if it were actively under maneuvers.

Assuming you consider straight-line acceleration 'maneuvering' I guess. I absolutely know spaceships don't need engines to be live to just keep going.

Doing so would actively make it harder for fighters to land because they would have to burn more reaction mass just to keep up, never mind overtake, their parent craft.

Not a problem in this scenario as fighters have considerably more acceleration and easily sufficient powered endurance (at one g, fighters tend to have enough fuel for 12-24 hours of constant burn with even bombers having a peak accel of 4.5g vs a maximum of 1.5g for the carrier, and if you think this is unrealistic, it is. Guess what-I don't care. I never said this was a particularly hard SciFi setup).

Another question is what sort of thrust is being applied? Do the ships in question use magical mass reduction technologies to achieve higher delta-v, or just incredibly efficient drive systems that require very little fuel for a thrust system that is both very efficient and very powerful (no mean feat). This will determine how hot, how much, and how fast the materials coming out of the engine will be. Note that they may well retain their heat for some time in space, since there is very little to transmit the heat to, and so all heat loss will be from radiation. Granted, the particulate is likely small, but how fast it's thrown out will increase the drive tail.

Is there any way to determine how this would work out for Battletech fusion drives? Alternatively, if I have only the mass of the ship and the intended acceleration, is there any way to work this out?

Next, what sort of protection do these ships have from attack? Energy shields?

Nope.

Armor of some kind?

Yep.

Additionally, how much of the rear (or front, even) of the ship is made up of exhaust ports?

3 60m circular exhaust ports on a 380x140m rear facing.

Once you close to a certain distance, there should be blind spots in the exhaust of most ships that you can maneuver in without trouble.

In case it makes a difference, the landing bays are NOT between the engines, they're slightly above them (and about 280m forward of them, but the general landing area starts 20m immediately above them).

Last, why would the fighters have to approach from the rear of the ship? Even if the landing bays are in the back end (which is...special)

No room for more landing bays in the front of the ship? Besides, a) redundancy and b) aesthetics. While landing bays along the flanks probably make more sense I happen to like the traditional carrier layout.

, under Newtonian Mechanics, they should be able to slide in from any direction and make a few last minute course adjustments to end up in the hangar bay Unlike modern aircraft, fighters designed for space combat wouldn't need a landing strip per se.

Known and ignored because I like the traditional (as in 'behaves like a modern day aircraft carrier') approach.

Depending on the level of technology, you could have tractor beams, magnetic docking arms, or even webbing to catch the darn things.
Since motion is relative in space, unless the ship is still under maneuvers, there's no need to put the launch and landing ports anywhere in particular, since once the fighter matches relative velocity, they can come in on any vector they need to.
Granted, most games tend to go for the WW2 Fighter/Carrier model, which is admittedly fun, but they don't bother making many of the sensible considerations of space and technology to begin with, much less any for drive system damage.

How about you assume I'm going for the same model because I happen to like it only I want to know how if at all drive system damage figures into it.

As an addendum, if you're doing a damn Battletech versus debate, may twelve generations of your family scorn your name, may your pets disown you, and may your suitors dispose expensive drinks upon your visage.

Why in Valen's name would this be about a Vs debate?

[frigidmagi]

In case it makes a difference, the landing bays are NOT between the engines, they're slightly above them (and about 280m forward of them, but the general landing area starts 20m immediately above them).

Hmmm... Why? This makes launching and maintenance more difficult then it needs to be. Keep in mind a carrier has to carry fuel for the fighters, spare parts, pilots and mechs, living quarters and supplies for the same. Packing in every launch bay and fighter you can at all cost actually degrades the combat effectiveness of the carrier.

[Batman]

I'm afraid you'll need to elaborate on that.

[Batman]

In case it makes a difference, the landing bays are NOT between the engines, they're slightly above them (and about 280m forward of them, but the general landing area starts 20m immediately above them).

Hmmm... Why?

Because I like that layout.

This makes launching and maintenance more difficult then it needs to be

As none of the launching nor maintenance happens at the rear of the ship (the launch bays are at the front of the ship, and maintenance happens on the hangar decks, not in the recovery bays) I'm not sure what you're getting at.

Keep in mind a carrier has to carry fuel for the fighters, spare parts, pilots and mechs, living quarters and supplies for the same. Packing in every launch bay and fighter you can at all cost actually degrades the combat effectiveness of the carrier.

I do. I also know the dimensions of the carrier. 1100 by 380 by 140m with a planned aerospace wing of 360 or so birds roughly the same size as modern day carrier planes. Given I'm thinking 6 20x60 metre launch bays in front and 6 20x60metre recovery bays (3 front, 3 rear) I think I'm being conservative.

[frigidmagi]

As none of the launching nor maintenance happens at the rear of the ship (the launch bays are at the front of the ship, and maintenance happens on the hangar decks, not in the recovery bays) I'm not sure what you're getting at.

Wait you have separate bays for launching and landing?

[Batman]

As none of the launching nor maintenance happens at the rear of the ship (the launch bays are at the front of the ship, and maintenance happens on the hangar decks, not in the recovery bays) I'm not sure what you're getting at.

Wait you have separate bays for launching and landing?

Yes?

[Hotfoot]

Fuck me, I know I do the bullet point thing from time to time, but would it kill you not to go sentence by sentence? Especially when the response to several sentences in the same blood soaked paragraph is repeating yourself? Never mind that repetition of a sentence does not equate to any manner of actual fact. Were I to say that I have in my hands a real, functional lightsaber thirty thousand times, that would not make it true.

Yes, by definition, if a starship is undergoing active thrust, it is maneuvering. It may be a simple maneuver, it may not be, the matter is irrelevant. What purpose does a carrier have of altering its velocity in a non-battle situation? Yes, that includes increasing thrust. Even in soft sci-fi, there should be a reason for why the ship is burning reaction mass. There may be a reason, I'll freely grant, but it should not be standard operating procedure to land a craft while the parent craft is under active thrust. It's a waste of resources, and again, while this waste is possible to be justified, it would not be reasonable to assume that would be the case for a given military ship.

The reasoning of why should be clear, but in case it's not, it wastes not only fuel on the part of the parent and parasite craft, but it has the engines of each working longer and harder than they need to be under the situation. While military craft are generally capable of high end maneuvers and such, that is under limited use and good maintenance. Push the limits of the craft, and more man-hours are needed to get it back into proper shape in addition to needing to resupply sooner than normal. As a general rule, while you might have 12-24 hours of constant burn at 1g for the fighters, the higher you go above that thrust, the less efficient the fuel is going to be, and the more of it you'll burn at once. At 4.5 times that expenditure, you're looking at 2.6-5.3 hours of thrust if the efficiency manages to remain the same, and potentially far less if it's not.


As far as the drive trails, that depends entirely on the mass of the ship moving, what the acceleration rate is, what the reaction mass is and how much is used per hour/minute/second, and potentially, how much distance the reaction mass travels before it is ejected from the thruster.

If the landing bays are 280m ahead of the engines, there shouldn't be a huge problem. Hell, if they were designed properly (i.e. pointed outward), there wouldn't be any problem at all. Why fly in the way of the drive tails? You have over a quarter of a kilometer to adjust course? A simple five degree descent should steer you away from the tails anyway, even keeping with the old "like WW2 fighters" style, which I'll point out I'm a fan of myself, I just like to see more cool tech involved with it. I mean come on, we've got lasers and FTL, but we can't figure out a better way to land a plane?

As far as assumptions, look man, you come in with a vague question, you only clarify with very vague things, I'll make whatever damn assumptions I will, and I gave several possibilities, so don't whine about it, either take the ones the work for you and move on, or don't. Either way, roll with it. As far as this being about a versus debate, it's a reasonable assumption, because this is the sort of topic that could come up as a point of discussion in a versus debate, and it's not like you've never involved yourself in those before. It's like if I came in with a question like this, there's only one of three possibilities why I'm asking it, I'm using it for a game, I'm using it for a story, or I'm using it for a versus debate.

Remember Bats, nobody here is psychic. We work off of what you post, same as anyone else. If you're not happy with that, maybe you should work on expressing yourself more completely.

[frigidmagi]

Yes?

That is a terrible idea. It means you have to move the entire fighter through the whole ship before you can relaunch it. Recovery bays should either be one with the launch bay or as close as possible.

[Batman]

Yes?

That is a terrible idea. It means you have to move the entire fighter through the whole ship before you can relaunch it. Recovery bays should either be one with the launch bay or as close as possible.

So? Being refueled/rearmed the fighter is going to be out of commission for anything from 30 minutes to an hour if modern turnaround times are any indicator (and that's ignoring possible battle damage that needs to be fixed), who cares if it takes another 3 minutes or so to taxi to the launch bays?
Plus, I like the distance between them. If the launch bays (or the forward landing bays) get rendered inoperable, the rear landing bays remain functional and vice versa.

[Batman]

Yes, by definition, if a starship is undergoing active thrust, it is maneuvering.

I wouldn't call straight line acceleration maneuvering, but if you say so.

It may be a simple maneuver, it may not be, the matter is irrelevant. What purpose does a carrier have of altering its velocity in a non-battle situation?

Who cares? I think by now you lot are putting a lot more thought into this project than I ever did.'

If the landing bays are 280m ahead of the engines, there shouldn't be a huge problem. Hell, if they were designed properly (i.e. pointed outward), there wouldn't be any problem at all.

Well they're not.

Why fly in the way of the drive tails? You have over a quarter of a kilometer to adjust course? A simple five degree descent should steer you away from the tails anyway, even keeping with the old "like WW2 fighters" style, which I'll point out I'm a fan of myself, I just like to see more cool tech involved with it. I mean come on, we've got lasers and FTL, but we can't figure out a better way to land a plane?

Sure there's a better way-approach from the sides or straight above, it's not like they'd have to worry about stalling. But as I said, I like the traditional approach.

As far as assumptions, look man, you come in with a vague question, you only clarify with very vague things, I'll make whatever damn assumptions I will, and I gave several possibilities, so don't whine about it, either take the ones the work for you and move on, or don't. Either way, roll with it.

You're working on the assumption that I have more concrete information. I don't. Not only is this a work in progress, but some of us don't work out every nuts and bolts detail when doing something like this. I didn't arrive at the 1g acceleration figure by analyzing engine efficiency, fuel consumption etc, I blithely decided this was how fast it could go, well, faster. The drives are fusion-ish because this is kinda sorta parked in Battletech and that's what they use. If that information would have been helpful earlier I apologize, I just didn't consider it relevant to the question.

As far as this being about a versus debate, it's a reasonable assumption, because this is the sort of topic that could come up as a point of discussion in a versus debate, and it's not like you've never involved yourself in those before. It's like if I came in with a question like this, there's only one of three possibilities why I'm asking it, I'm using it for a game, I'm using it for a story, or I'm using it for a versus debate.

There's a 4th possibility, actually. I design ships simply because I like designing ships. This carrier is being designed for no other purpose than my personal amusement.

Oh, and thank you for your input, everyone.

[frigidmagi]

So? Being refueled/rearmed the fighter is going to be out of commission for anything from 30 minutes to an hour if modern turnaround times are any indicator (and that's ignoring possible battle damage that needs to be fixed), who cares if it takes another 3 minutes or so to taxi to the launch bays?
Plus, I like the distance between them. If the launch bays (or the forward landing bays) get rendered inoperable, the rear landing bays remain functional and vice versa.

You're not thinking about this are you? Unless you got a massive powered system, it'll take more then 3 minutes, also you're adding in another failure point to your design. What if the railway (I'll call it a railway for now) has a power failure, then you have to push your fighters through the whole bloody ship, which as is the nature of carriers, will be bloody huge. What if a fighter flips over or gets stuck or any number of things that stops it from moving, you now have a traffic jam, in the middle of a shooting match that renders your carrier less effective. Not to mention you now have to route everything around this fighter highway running through the middle of your ship!

As for your who cares about 3 minutes? It's a glaring reminder of how little experience you actually have in combat, which is to say none. 1 minute is a fucking eternity in combat, 30 seconds is enough to get everyone you know killed and 5 seconds is to long. You want the fastest turnaround for your fighters possible given that they are your carriers main offensive weapons, in some designs your only offensive weapon! It's like declaring you see nothing wrong with having the shell storage for your main guns on the other side of the ship and who cares if it adds another 3 minutes to the firing time.

Keep in mind while your recovering and rearming/refueling the fighter, odds are that people are trying to kill you! Every minute might has well be dripping gold and oil for it's value. I mean check the battle of midway where the Japanese carriers were destroyed... Because their planes were caught on the deck refueling and rearming. That led to the Japanese losing 40% of their carrier strength.

[Derek Thunder]

Question - would it be possible to forego the WW2-style carrier model and think bigger and wilder? A diffuse cloud of Von Neumann machines could make pretty short work of any enemy fleet, at a very low cost. I mean, given the vast distances of space even a slow-acting swarm could consume a ship in the time it takes to travel between star systems.

[Lys]

Von Neumann swarm is very unspecific as to the actual capabilities of the weapon in question. From context I assume it's supposed to be very small deconstructor robots? They are unlikely to be very effective. Just for starters because the machines are small they would have limited power supplies, and they'll go inert before doing any damage worth mentioning. Also due to their small size they would be vulnerable to the harsh conditions of outer space, and subjected to cosmic rays and various sorts of radiation. Their circuitry may not survive, again rendering the machines inert. Then there are counter measures that could be put into the place by the defenders. A number of drones sufficient to actually cause damage is liable to also be detectable, and if they can detect it then they can also shoot it until it dies. There is also the possibility of the enemy employing friendly swarms to function as a sort of ship immune system, which would benefit tremendously from ready access to the ship's resources, and thus put the attacking swarm at a disadvantage.

[frigidmagi]

Derek is actually talking about these only weaponized. It's an interesting idea and I can see advantages and disadvantages to using them as such as well as a number of counters. Given that we already assume fighter craft work, I have no problem assuming unmanned probes can be shielded enough to work in space, after all we've already put up a number of small machines into the void.

[rhoenix]

Maybe - but ship-eating nanobots (your Von Neumann machines) would be at best a defensive weapon in practical terms, or a terror weapon if used offensively on emplacements, no?

The little robots can only go as fast as the container that takes them, as I imagine that strapping proper space maneuvering thrusters to them would make them significantly larger - a Von Neuman robot that could move properly in space would necessarily be large enough to render its function nearly moot without some form of trickery.

This means that the swarm won't be moving very fast, and that's setting aside all the little issues Lys pointed out about how space isn't very friendly to unshielded electronics.

I can say this discussion is fascinating, and not just because of Frigid's prior practical experience as a U.S. Marine.

[Cynical Cat]

Nanoweapons suck in space. The problem with being tiny is no shielding against radiation, no temperature regulation ability (a serious, serious issue), and tiny energy storage capacity. Fuel and propulsion issues also abound.

Now true Von Neumann style machines are dangerous in a different way, turning asteroids into robot battlefleets.

As for Batman's carrier question, it's stupid. He's worrying about realism issues with thruster placement while openly admitting that he's ignoring realism for every other aspect of his design. Any half way serious design wouldn't include giant corridors to haul planes from one side of the carrier to the other and exist only to use up that space.

[frigidmagi]

I don't think Derek means for the Von Neumann machines to be nanobots, which frankly would make the whole thing harder to do then it needs to be. Nanobots are very weak against radiation and the other hazards of the void.

[Cynical Cat]

This is what he wrote:

A diffuse cloud of Von Neumann machines could make pretty short work of any enemy fleet, at a very low cost. I mean, given the vast distances of space even a slow-acting swarm could consume a ship in the time it takes to travel between star systems.

That isn't a warfleet, that's a swarm.

[frigidmagi]

Does a swarm have to be made of nanomachines?

[rhoenix]

Does a swarm have to be made of nanomachines?

Not necessarily - the Zerg approach works too.

However, that approach isn't very practical for a carrier.