Newtonian Stealth

[Steve Walmsley]

I know stealth in space is probably difficult to achieve. However, a large part of the fun in Aurora (for me anyway) is that most of the time you don't know what you are up against and enemies can appear in unexpected and unwelcome locations. Detection is a very important part of the game and this is one those areas where I think fun should take precedence over realism.

Steve

[Steve Walmsley]

The solution to that is twofold:
1. There's only a very limited amount of handwavium in a given system.  This forces the exploration, while removing the "I have to move how many tons between systems?" issue.  A 10,000 ton ship takes 9,950 tons of metals and plastic and 50 tons of handwavium, but an average system only contains 500 tons of handwavium total.
2. Give planets a carrying capacity, and make it so that you have to explore and spread to thrive. 

There are two issues. One is that with eleven different mineral types, you face different shortages in each game that affect different parts of shipbuilding or your economy, which may have a significant effect on strategy. The second is that if the amount of handwavium is only small, there is no significant logistical effort required to move it and logistics are both a huge part of the game and one of the reasons for creating new production hubs. Those wouldn't be necessary if you could create a few small, fast ships that brought everything back to Sol.

Steve

[bean (OP)]

I will admit that in an FTL setting like this, stealth is a lot easier.  You can burn your engines well out of sight of the enemy.  However, because of the much longer tactical lag (you also can't just turn around and run) some increase in detection range is probably a good thing at the very least.

I suppose you're right on the minerals thing, too. (You are by definition, but your logic makes sense too.)  I'm not a fan of handwavium in general (if you didn't notice).

[UnLimiTeD]

While I can't really disagree with you that much, it is interesting how we came from entirely different standpoints.
I actually expected logistics to increase.

Why?

A) Every godforsaken rock in space, of a reasonable size, would be a source for one of those potential base resources. This means that even a system that otherwise comes out empty, is now worth at least something.

B) Let's be generous and assume 8 kinds of handwavium; each of them is also needed in smaller quantities, maybe about 75% of now, while the rest is done by stock materials; and is available half as often.

Now you might be in a situation where you have a large Asteroid field with tons of those stuff, but no large planet or gas giant near, so even if there was a small planetoid available and you got 7 of 8 handwavium at hand, you would need to get that stuff home somehow.

C) Stock materials would be required for the civilian industry as well, and harvesting them from inhabited planets could result in pollution, just simulated by unrest. This would mean to feed the voracious appetite of a 100 year old spacefaring Industry, one would have to place mines on a good dozen planets, and not every single one might contain rare minerals or fossil fuels in large and accessible enough quantities that it would be worth simulating in Aurora.

D) Single Example: Sorium being a bit more rare, mostly on Gas Giants, would allow players to set the mix for their standard fuel.
For a massive peacetime economy, small rations might be enough, maybe 20%; but a Warship would have 50% Sorium fuel to allow for a bit faster acceleration and higher fuel storage while retaining small size.
One could even devise Sorium Boosters that burn the valuable stuff to try and get out of the way of an incoming projectile quickly.

Additionally, you have to keep in mind that Logistics will be somewhat simplified by now having jump routes anymore.
You could complicate matters by making FTL drives cost a certain amount of special fuel, and commercial engines being not as much more effective as the ships are larger, possibly resulting in systems that are a great staging ground for attacks, but too far off to make it economical at the current tech level to ship that fuel home.

Also a possibility
You could even go as far as change the demand for various materials as times change.
EXAMPLE: Player UnLimiTeD recently finished research of Reactive Electric Armor, with a durability 20% higher than Ceramic. However, this new type of armor requires microcapacitors as part of it's structure, which require a different type of handwavium. UnLimiTeD currently does not have enough of that, and doesn't want to buy it from Steve. So he decides to keep using the old armor and order additional amounts of resources for the next Transport convoy to his mining system, hoping that by the time the stuff arrives, he'll still need it.

Theoretically, you could go as far as having those armors be more efficient against various attacks, like an extremely heat resistant ablative armor protecting against Lasers (-25% dmg) but having an overall lower strength.^^Aww, I know you won't.

As for stealth, I suppose as a compromise, you could give Living space a thermal signature, even if it's low.

Suggestion #2 (or was it 3?): Could you theoretically change the range calculation a bit? Instead of linear, it could be ^1.5, somewhere on the way to reality, with a higher base range, and factor in things like where the sensor is based.

A military Thermal Sensor Array on a battleship patrol would be able to find you rather easily unless you employ extensive handwavium technology, but a thermal on a Civilian ship that is not constantly monitored, while theoretically having nearly the same range against blatantly obvious threats, would be nearly bling to a small flare now and then, sneaking into position.
On Planets, Active sensors could be hindered by the gravitational field of the planet, and Passive listening posts are more efficient outside Atmosphere.
While this in total might mike stealth harder, it offers interesting decisions, where an ambush on a civilian fleet is possible when a Military fleet would possibly detect one, and covering a system in sensors will be a bit more logistically demanding. It might offer a nice amount of hide&seek where one party raids the other and disappears before the military forces come to hunt them down. As far as that is available in space.

Would a Shield generator be able to hide a thermal signature, but in turn provide an EM signature that is not scanned for on Civs, but might give Military ships a valid target ID on longer than normal ranges?^^

[jseah]

Detection is a very important part of the game and this is one those areas where I think fun should take precedence over realism.

I know I go out of my way to ensure nothing escapes my sight. 

I remember building a huge PDC on my homeworld that was nothing but three max-size Active Sensors (Size 1, 20, 100).  At TL5, that could see basically everything in the system (the size 100 covers all jump points any time of the year)

[Yonder]

When people say things like "using current technology we have the ability to spot a 0^o C ship from 50m kilometers away what sort of field of view are you talking about? Is this a sensor looking out over an entire hemisphere, or a 1 degree cone of sky?

Also something to keep in mind about engine efficiency is that while the more efficient the engine the less energy is released as heat, the higher the temp of the plume that is released. This may not be that important of a point though, since I am guessing that Steve will have the Thermal Sensors purely based on the power of the heat produced, and not the actual wavelengths of lights produced. (Although designing sensors that were the most sensitive at different wavelengths would be a pretty cool design metric if it wasn't overly complicated, especially since this may allow ways to pick up fighter engines. If fighter engines are less efficient that would mean that the plume was cooler (makes sense, as the plume would be smaller, so the center of the plume would be closer to the nozzle wall, meaning it would have to be cooler), meaning that if your sensor was more sensitive to the lower wavelengths you would see cooler engines (fighters) earlier than their larger ships. Another important point about that is that (As done in The Mote in God's Eye) you can guess from the temperature of the drive how efficient the engine technology is).

I also think that everyone may be a little hung up on one form of propulsion, the enormous cone of plasma thermal radiation in every direction (even in front of the ship since the plume will be bigger than the ship). Other forms of propulsion may not have the same lack of subtlety. So far the only example of an alternative drive in that of a mass driver, which could work, although it is admittedly low in acceleration. (Although I would add that in addition to the actual projectiles a Railgun would certainly emit some sort of muzzle flash, a Coil Gun may be able to avoid that). Another alternative would be a laser engine, this would take up a huge amount of power, but would only be visible in a small cone along the thrust vector (ignoring reflections off of asteroids, other ships, and even dust. In a Nebula this would be a very visible form of travel), an Ion engine is another example.

For another fairly invisible form of propulsion look no further than alpha radiation. A lower thrust fusion engine may just be able to fuse those Hydrogen atoms and toss the helium atoms out the back at relativistic speeds without the signature plasma tail, if it was being slower and more careful with it's reaction to avoid all the plasma.

Now obviously all of these methods require that the heat from your reactor be expelled in a very targeted way, because if they can see your ship then seeing your exhaust doesn't matter. However, if that can be attained you can also get stealthy movement, albeit much more slowly than a large, high-thrust rocket. I don't know exactly how Steve would model all of this stuff, would it be very hard to model ship emissions as cones (/ triangles in 2d)? The engine emission cones would always be in the direction of thrust, and maybe the thermal radiation would always be aft as well, or maybe you could optionally reorient it. (Or maybe it could just be handwaved as an engine with a smaller thermal signature)

[bean (OP)]

When people say things like "using current technology we have the ability to spot a 0^o C ship from 50m kilometers away what sort of field of view are you talking about? Is this a sensor looking out over an entire hemisphere, or a 1 degree cone of sky?

Whole sky scan over a couple of days, which is plenty of time at that range.

Also something to keep in mind about engine efficiency is that while the more efficient the engine the less energy is released as heat, the higher the temp of the plume that is released. This may not be that important of a point though, since I am guessing that Steve will have the Thermal Sensors purely based on the power of the heat produced, and not the actual wavelengths of lights produced. (Although designing sensors that were the most sensitive at different wavelengths would be a pretty cool design metric if it wasn't overly complicated, especially since this may allow ways to pick up fighter engines. If fighter engines are less efficient that would mean that the plume was cooler (makes sense, as the plume would be smaller, so the center of the plume would be closer to the nozzle wall, meaning it would have to be cooler), meaning that if your sensor was more sensitive to the lower wavelengths you would see cooler engines (fighters) earlier than their larger ships. Another important point about that is that (As done in The Mote in God's Eye) you can guess from the temperature of the drive how efficient the engine technology is).

The temperature of the exhaust is inherently related to the exhaust velocity in gas/plasma engines, which is the rocket equivalent of fuel efficiency.  As to actual efficiency, thermal engines (which includes most types explicitly described in Aurora) convert the heat of the gas into motion.  That is going to leave a lot of heat anyway.  You can't cool it enough to hide the exhaust.

I also think that everyone may be a little hung up on one form of propulsion, the enormous cone of plasma thermal radiation in every direction (even in front of the ship since the plume will be bigger than the ship). Other forms of propulsion may not have the same lack of subtlety. So far the only example of an alternative drive in that of a mass driver, which could work, although it is admittedly low in acceleration. (Although I would add that in addition to the actual projectiles a Railgun would certainly emit some sort of muzzle flash, a Coil Gun may be able to avoid that). Another alternative would be a laser engine, this would take up a huge amount of power, but would only be visible in a small cone along the thrust vector (ignoring reflections off of asteroids, other ships, and even dust. In a Nebula this would be a very visible form of travel), an Ion engine is another example.

Engines that produce plasma are pretty much the only option on the table for practical space travel.  I find mass drives very iffy for any sort of reasonable propulsion, not to mention venting the waste heat.  Lasers are completely impractical for onboard use.  300 MW/N is never going to be adopted by anyone in the forseeable future.  And ion engines do produce plasma, if slightly colder then, say, fusion.
Edit: The ion engine exhaust should be very difficult to detect, but they have the same heat problem as mass drivers.  So do lasers, for that matter.

For another fairly invisible form of propulsion look no further than alpha radiation. A lower thrust fusion engine may just be able to fuse those Hydrogen atoms and toss the helium atoms out the back at relativistic speeds without the signature plasma tail, if it was being slower and more careful with it's reaction to avoid all the plasma.

That's just impossible.  You cannot have a fusion reaction without very hot plasma.

Now obviously all of these methods require that the heat from your reactor be expelled in a very targeted way, because if they can see your ship then seeing your exhaust doesn't matter. However, if that can be attained you can also get stealthy movement, albeit much more slowly than a large, high-thrust rocket. I don't know exactly how Steve would model all of this stuff, would it be very hard to model ship emissions as cones (/ triangles in 2d)? The engine emission cones would always be in the direction of thrust, and maybe the thermal radiation would always be aft as well, or maybe you could optionally reorient it. (Or maybe it could just be handwaved as an engine with a smaller thermal signature)

This requires perfect stealth and perfect detection to coexist.  I dealt with this earlier in the thread, but, fundamentally, directional radiation is impractical because you have to know where all of the enemy's pickets are.  And the picket can be the size of Voyager, with a decent IR camera.

[nafaho7]

You fellows do realize that Mr.  Walmsley is calling this project "Newtonian" Aurora, and not, say, "Maxwellian" Aurora.   Right?  His goal is to introduce some (not all!) of the basic elements of Newtonian physics with regards to movement in what is otherwise a very non-realistic setting.   I have seen, over the course of this discussion of stealth, a great deal of careful thought about the present understanding of Thermodynamics as applied to what are supposed to be science fiction engines.   Are we, perhaps, focusing on the wrong thing?
I have also noticed a very great deal of displeasure with the concepts of "Handwavium" and "Narrativium. "  This seems very strange, as such elements are the bread and butter of any science fiction story or game.   After all, if there was no fiction involved, then this would be a test engine, not a game.

If we are to discuss stealth, then let us discuss stealth as it applies to Aurora.   The present system for active sensors, as I understand it, uses certain variables to adjust the effective size of a ship for the purposes of detection.   Opposing this, one is allowed to adjust certain variables to adjust a given sensor platform's range to detect ships which are above a certain size.   Added to this, passive sensors, with significantly greater range than active sensors, are available, with the important trade-off that they can not be used for the purpose of target acquisition.   Additionally, passive sensors do not make a ship, or other platform using them, more visible to potential hostiles.   Finally, all sensor information is available to all allied ships in, and out of, system in real time, at all times.   Is there anything in particular that we would like to see changed, that would not massively complicate the coding of the game beyond a practical level to ask of Mr.  Walmsley?

As far as I know, making sensor data Slower Than Light(STL) is generally considered to be far more trouble than Mr.  Walmsley is willing to code.   Making the transfer of information STL would also massively complicate administering a Multi-System Polity.   So, STL information is, for the foreseeable future, off the table.

For the purpose of hiding from active sensors, at present, one can

• Install a Cloaking Device to reduce a ship's apparent size for the purpose of detection.
• Actually make a ship smaller. (Insufficiently Fun. )

For the purpose of hiding from passive sensors, at present, one can

• Reduce a vessel's EM signature by deactivating shields and active sensors.
• Reduce a vessel's Thermal signature by operating at less than full power.
• Reduce a vessel's Thermal signature by investing in stealthier, more expensive engines
• Reduce a vessel's Thermal signature by using fewer actual engines, capable of lower output. (Insufficiently Fun)

Do any of these options seem particularly broken or useless, given the theme of Newtonian Aurora?

For the purpose of discovering ships that do not wish to be found, one can

• Increase the efficiency of sensor platforms, through research.
• Increase the size of a given sensor installation.
• Alter the size for which a particular sensor platform is optimized to search.

Are there any other methods that should be included on this list for Newtonian Aurora?

Given the new acceleration and velocity rules, and how they affect reaction times, should detection ranges be pushed upwards for active sensors?  Should passive sensors get a boost?  If there is a boost, should it be in the form of a linear shift to the power of sensors, either upwards or downwards?  Should sensor technology improvements become exponential in nature?  Or should we do something else completely, that is only now possible because of the new movement rules?

[voknaar]

I have a few Bad Ideas™ I'd like to throw at people regarding cloaking and detection. Has nothing to do with actual science or maths. So if you like either in your games go to your happy place. Are you there yet? No? Now? Excellent.

Bad Idea 1):  Perhaps adding a time lag to detect signatures based on 1% chance per sensor per minute + Crew Experience(s) if within passive sensor strength at the target ships signature output. If the ship is outside that range then this same check is made every hour instead. Ships that are designed for/use less emissions than passives are optimised for looking for the check is make every hour again. (except for Ground Based Sensor stations in this case.)

 If a ship remains both low emissions and out of range then a check is made every 4 hours.

Any ship currently successfully evading detection that changes its current emissions output (changing speed, direction, shields etc...) while in a system with ships or deep space tracking stations and not sharing sensor data through a treaty agreement has to make a new check again to see if the change gets detected. A 1% chance is small but it is based on all sensors within a solar system working together wirelessly.


Bad Idea 2):  In systems with a heavy presence it is still almost impossible to get away undetected without stealth systems. Cloaking could be made to make a flat negative roll on the chance to be detected. Or better yet could cost power to produce a field that when the detection rolls say you should have been detected could cost power to make it remain negative. As well as a flat operation power cost.

This could make cloaking tech useful in short bursts such as showing up to a enemy colony. You'll be detected ages out, but you could launch a salvo gather Intel or Grav Survey a specific point. Then when hostiles are expected to get in range for a pot shot activate the cloak and make a break for it hoping it will last long enough to evade missiles or beam/munitions fire.

Bad Idea 3):  Hyperspace exists in aurora. What it is or where it is, is undefined as far as I know. Therefore it could be the "handwavium" people are looking for. It already exists in the game now lets see how it could be expanded. So my brilliant bad idea is that ships with a hyperdrive could have a component added into the engines to generate a place to vent thermal radiation and unwanted materials. Heatsinks can become thermal batteries that need to be drained by venting directly into hyperspace. The downside to this could be that dedicated search sensors such as Deep Space Tracking can detect hyperspace signatures. A Hyperdump™ can be detected but the presence in system can remain unknown. Allowing ships designed from the ground up for power capacity, fuel effency and reduced emissions to perform good stealth missions but not much else since size will need to be kept to a absolute minimum.


This will allow a good sensor net a good chance to detect these cloaked pests. The down side is a lot of sensors need to be in system to catch the cloaked ships quickly. I like these ideas in general but they all still need tweaking and math values to get a good balance of stealth vs detection.

I'm going to regret this, but thoughts and opinions on the above are welcome.

[ardem]

I'm going to regret this, but thoughts and opinions on the above are welcome.

You shouldn't do, if the forums keep to their same friendly aspect and people respect other rights to differing opinions

Foolish question on IR (thermal imaging) As I understand it IR cannot be used through object. Example as if your inside a dumpster then the IR signal that will be picked up is a dumpster, not the person in it, unless you are up against the side of the dumpster transferring the heat, then you would see a hot spot.

What if a spaceship had a large non conductive heat web in front of the vessel that does not conduct heat or is very minimal, with a reflective membrane on the inside to reflect the heat back. then it would hide the main heat of the ship, depend on the web you would get a aurora around the web of IR. Or would you? IR detection relies of IR waves heading towards the sensor. If those waves are not heading towards the sensor then you not pick up the IR or thermal image. It would be no different to say hiding behind an asteroid.

You may not be able to get 360 degree stealth, but you may be able to achieve 180 degree stealth.

Also with all the stars in the night sky producing IR, if you are in front of one would it blind the receiver of an object.

[UnLimiTeD]

A thermal shield has been discussed, but you would need to be very far out to deploy it. You must not actually have contact to it.
However, as directional stealth is hard to code with FTL Sensors, all this is impractical.

@nafaho7:

You may express contempt for the discussion, but this entire thread is about how to make stealth more realistic;
Sure, theres been a bit of discussion on how to make logistics more challenging and other stuff, a matter of believability, but I feel we have a good reason to discuss this in a potential system where a 2 ton nuke can annihilate a capital ship.

Leaving alone the economy+logistics discussion, to which I'd like, but don't expect an official response (see wall of text above), the whole discussion comes down to the following points:

A) Stealth for manned Ships is extremely hard in real space. So much for the basis.
B) Stealth in Aurora is too easy to achieve, and excruciatingly boring in that way; Emisions can not only be reduced, but eliminated.
C) The only way to reliably defend against stealth in current Aurora is absolutely humongous Active sensors, as passives become completely useless as soon as an enemy turns of his shields and stops moving.

This implies that the following changes could be useful:

A) A revamp of the range collection, lying somewhere between the current linear and the realistic sqrt range falloff. Maybe half sig=1/3 detection range or something.
A1) Possibly increase range of passives sightly, maybe only for military ships, allowing hide and seek if one raids civies.
B) Giving Crew Quarters, weapon systems, and reactors their own heat signature. While it may be small, and with the current sensor system would still allow to evade detection, it will make passives more useful as theres always a small bit of radiation. Maybe not enough for someone not actively searching, but certainly enough for an Asteroid-Based DTS.
Shields might be able to mask it, but emit stronger EM
C) Allow passives, within a fraction of their range, say, 50%, to give a target id, at a steep hit penalty, for non-homing projectiles.

[Yonder]

Engines that produce plasma are pretty much the only option on the table for practical space travel.

That depends on your definition of practical. A craft with .1g acceleration may not seem practical when their opponents have 3g acceleration, but for some missions it may be worthwhile. Sending a team on a three-month trajectory to destroy a poorly defended Sorium harvesting fleet can be better than sending a team on a two-day trajectory to destroy a heavily defended Sorium harvesting fleet.

That's just impossible.  You cannot have a fusion reaction without very hot plasma.

The plasma has to be at the site of the fusion, it doesn't have to be anywhere else. Hydrogen is fusing right before your engine nozzle, then sure, you are spitting out a huge plume of helium spray and plasma. However if you are fusing the hydrogen in an internal reactor and using a magnetic screen to divert the flow of plasma so it remains in the reactor while the neutral helium molecules are shot out as thrust then that's completely different. You now have a stealthy engine, albeit a more complicated, lower thrust engine that has huge thermal issues since it's not expelling most of the heat that its reactions produce.

This requires perfect stealth and perfect detection to coexist.  I dealt with this earlier in the thread, but, fundamentally, directional radiation is impractical because you have to know where all of the enemy's pickets are.  And the picket can be the size of Voyager, with a decent IR camera.

You have to know where every single picket is to guarantee stealth. You don't need to know where any pickets are to have a better (aka non-zero) chance at stealth. Make sure that your emissions aren't pointing near any planets/moons, comets and pray. Remember that the theoretical goal of stealth is to be perfectly invisible to your enemy, but the practical goal of stealth is to buy you as much time before detection as possible.

If two months into your three month trip your emission sweeps across a picket you don't know that, but if at that point the enemy fleet around their home planets fires up their engines and heads straight at you or your target then you know that somehow you were detected, and it's time to switch to your "practical" engines. You weren't able to get all the way to your target without being detected, but your stealth systems got you a lot closer than you otherwise would have.

[Napoleon XIX]

You shouldn't do, if the forums keep to their same friendly aspect and people respect other rights to differing opinions

Foolish question on IR (thermal imaging) As I understand it IR cannot be used through object. Example as if your inside a dumpster then the IR signal that will be picked up is a dumpster, not the person in it, unless you are up against the side of the dumpster transferring the heat, then you would see a hot spot.

What if a spaceship had a large non conductive heat web in front of the vessel that does not conduct heat or is very minimal, with a reflective membrane on the inside to reflect the heat back. then it would hide the main heat of the ship, depend on the web you would get a aurora around the web of IR. Or would you? IR detection relies of IR waves heading towards the sensor. If those waves are not heading towards the sensor then you not pick up the IR or thermal image. It would be no different to say hiding behind an asteroid.

You may not be able to get 360 degree stealth, but you may be able to achieve 180 degree stealth.

Also with all the stars in the night sky producing IR, if you are in front of one would it blind the receiver of an object.

Some major problems with that idea:
1 - The shield will reflect some of the heat back to the spacecraft, exacerbating its original problem.
2 - 180 degree stealth is useless - the enemy only needs to have a minimum of two pickets out there in order to be able to see you.
3 - How do you make the shield accelerate at the same rate as the ship, so the two don't either collide or part company.
4 - No matter how good an insulator it is, it will still conduct some heat. Thus, it will be significantly above the cosmic background (3K).

Personally, I don't mind stealth in space if this is done for game play reasons. Though, there exist no ways of doing it in reality, which necessitates a certain quantity of hand waving.

[bean (OP)]

Foolish question on IR (thermal imaging) As I understand it IR cannot be used through object. Example as if your inside a dumpster then the IR signal that will be picked up is a dumpster, not the person in it, unless you are up against the side of the dumpster transferring the heat, then you would see a hot spot.

Over the short term, you are correct.  Over the long term, you would heat up the dumpster.  We just don't notice due to the enviroment being relatively close to your body's temperature already.

What if a spaceship had a large non conductive heat web in front of the vessel that does not conduct heat or is very minimal, with a reflective membrane on the inside to reflect the heat back. then it would hide the main heat of the ship, depend on the web you would get a aurora around the web of IR. Or would you? IR detection relies of IR waves heading towards the sensor. If those waves are not heading towards the sensor then you not pick up the IR or thermal image. It would be no different to say hiding behind an asteroid.

You may not be able to get 360 degree stealth, but you may be able to achieve 180 degree stealth.

That wouldn't really work.  Some heat would be absorbed, which would heat up the shield.  And as mentioned above, the reflected heat would compound your problems.  It might help some, but also as mentioned above, 180 degree stealth isn't terribly useful.

Also with all the stars in the night sky producing IR, if you are in front of one would it blind the receiver of an object.

Actually, that's backwards.  If you're in front of the star, the observer would be more likely to notice a star missing, and conclude that something was there.  A star is going to have an angular size much smaller then your vessel.

That depends on your definition of practical. A craft with .1g acceleration may not seem practical when their opponents have 3g acceleration, but for some missions it may be worthwhile. Sending a team on a three-month trajectory to destroy a poorly defended Sorium harvesting fleet can be better than sending a team on a two-day trajectory to destroy a heavily defended Sorium harvesting fleet.

Reasonable thrust and specific impulse.  A thermal engine can have much, much higher specific power then a non-thermal drive.  And why would the two-day trajectory fleet be more defended?  If you set up the vectors right, then they can't intercept you in the available time.

The plasma has to be at the site of the fusion, it doesn't have to be anywhere else. Hydrogen is fusing right before your engine nozzle, then sure, you are spitting out a huge plume of helium spray and plasma. However if you are fusing the hydrogen in an internal reactor and using a magnetic screen to divert the flow of plasma so it remains in the reactor while the neutral helium molecules are shot out as thrust then that's completely different. You now have a stealthy engine, albeit a more complicated, lower thrust engine that has huge thermal issues since it's not expelling most of the heat that its reactions produce.

Nope.  The fact that it is plasma is a function of its temperature.  The helium in question will also be plasma, and you will have to use several kinds of magic to neutralize it before you can spit it out.  Not to mention keeping it that way.

You have to know where every single picket is to guarantee stealth. You don't need to know where any pickets are to have a better (aka non-zero) chance at stealth. Make sure that your emissions aren't pointing near any planets/moons, comets and pray. Remember that the theoretical goal of stealth is to be perfectly invisible to your enemy, but the practical goal of stealth is to buy you as much time before detection as possible.

If two months into your three month trip your emission sweeps across a picket you don't know that, but if at that point the enemy fleet around their home planets fires up their engines and heads straight at you or your target then you know that somehow you were detected, and it's time to switch to your "practical" engines. You weren't able to get all the way to your target without being detected, but your stealth systems got you a lot closer than you otherwise would have.

This assumes that lack of time before detection can enhance the performance of the mission.  That is only true for extremely short timescales.
Everyone has agreed that, by nature, a stealth ship is going to suffer severe performance penalties compared to a conventional ship.  I believe that detection timescales will be such that a stealth ship offers no advantages over a conventional ship.  If it takes the SS three months, and the CS a month, then if the SS is detected a month out, it's no more effective, and more expensive for its combat power.
If you can avoid detection until lack of time hampers the enemy's ability to respond, then it becomes a viable method.  However, I just don't see that as happening.

[Yonder]

Reasonable thrust and specific impulse.  A thermal engine can have much, much higher specific power then a non-thermal drive.  And why would the two-day trajectory fleet be more defended?  If you set up the vectors right, then they can't intercept you in the available time.

The two-day trajectory is more defended because on your two-day trajectory everyone in the solar system sees you and where you are going, so the defensive fleet is waiting for you, or intercepts you. The idea that there exists a solution to "set up your vectors right" so that interception is impossible doesn't really seem to be a valid assumption.

Nope.  The fact that it is plasma is a function of its temperature.  The helium in question will also be plasma, and you will have to use several kinds of magic to neutralize it before you can spit it out.  Not to mention keeping it that way.

I agree that there is a little bit of hand waving, but if you filter out the existing plasma and only let out the helium that have already emitted their photons to leave their excited state then they aren't going to randomly reignite into plasma once they leave the reactor.

Everyone has agreed that, by nature, a stealth ship is going to suffer severe performance penalties compared to a conventional ship.  I believe that detection timescales will be such that a stealth ship offers no advantages over a conventional ship.  If it takes the SS three months, and the CS a month, then if the SS is detected a month out, it's no more effective, and more expensive for its combat power.

That's not true. If the stealth ship is detected two months into it's journey then it is two thirds of the way there. It fires up its normal engine and gets there in ten days, the stealth system gave it 20 extra days to play with the Sorium harvesters and begin their escape trajectory. Sure the fact that it has a normal engine and a stealth engine may mean that its shields are halfsize, or it doesn't have as many weapons. But how many weapons do you need to destroy undefended Sorium Harvesters in twenty days?