Using beamforming to help a ship maintain stealth while transmitting radio signals.

[PTNLemay]

EDIT: To clarify, the discussion is in regards to NAVAL ships, not space ships. I know that stealth in space is notoriously difficult regardless of how much beamforming you use.

I've heard that a bunch of modern routers have the ability to "direct" the wifi beams in specific directions, so you can help strengthen a signal in an otherwise weak zone. That or help extend the range or the signal strength. What I'm wondering is just how much of the energy gets focused, and how much is still transmitted omnidirectionally and gets ignored as losses?

Could a warship use beamforming technology to help transmit signals straight at it's target, and have enough of the signal get focused so that the residual "losses" would be too weak for eavesdroppers to pick up.

Also, how many watts typically go into one of these long-range radio-communication setups? And how many watts would be enough for an enemy ship to pick up the transmitted signal, or at least to go "AHA! We don't know what it is they're saying, but we know their location!"

In case anyone's wondering, this line of thinking came to me while watching The Last Ship, with the Russian battlecruiser hunting the little American destroyer. The former is tracking the later through it's radio transmissions.

Edited August 6, 2014 by PTNLemay

[Nuke]

you can do that, but thing is in space, stealth doesn't work.

[LaytheAerospace]

you can do that, but thing is in space, stealth doesn't work.

Not in the traditional sense, no. But it's not unreasonable to conjecture about the future of something like metamaterial cloaking, or something similar. You'd still have to figure out what to do with all the heat from your ship, or deal with pathetically short duration effective cloaking before being forced to dump your waste heat.

Maybe you don't need to cloak the whole ship, though. I'm not familiar enough with metamaterial cloaking, but it seems like it may be possible to cover only part of the ship with the material, leaving an exhaust port uncloaked to vent heat (yeah, lots of hand waving here). Just keep that exhaust port pointed away from the bad guys, and you could theoretically use it for something like laser communication, which wouldn't be detectable by anyone not in the path of the beam. For sending messages to the ship, you could use standard radio, and rely on the radio waves finding their way through that window on their own. Huge logistical problem to hit something like that with a laser consistently, anyway.

Bonus, your cloaking metamaterial may also be an effective defense against lasers, provided it can withstand the power density and they can't get a shot at your exhaust port.

Disclaimer: Most of what I said is probably nonsense.

Edited August 5, 2014 by LaytheAerospace

[Seret]

you can do that, but thing is in space, stealth doesn't work.

"Stealth" works fine in space, especially when you're talking about aspects of stealth like emissions control. To the OP, highly directional RF signals aren't new, and indeed are inherently harder to intercept and/or degrade. Generally keeping an eye on the enemy's emissions is a good passive way to detect them. It's called Electronic Surveillance Measures (ESM) and you'll find that the military strictly control what they transmit to avoid giving the game away. It's not like in the movies where everybody is using their radar all the time, in reality folks will often keep their transmitters shut down a lot of the time. Even for a powerful active sensor like a radar the enemy can detect you via ESM from a lot further away than you can detect them directly with your radar. Pretty much all aircraft and warships have a reasonable ESM ability, although there are examples of both that specialise in it and pack all sorts of sneaky gear.

[Seret]

it seems like it may be possible to cover only part of the ship with the material, leaving an exhaust port uncloaked to vent heat (yeah, lots of hand waving here). Just keep that exhaust port pointed away from the bad guys

Not really handwaving, that's a legit idea. Anything in GEO could stick the radiators on top and have a very much reduced IR signature to anything at the same or lower altitude (ie: pretty much everything).

[Nuke]

then you bring up your thermograph and find out that the target is a different shade of black from the background of space. then you might control your emissions to match. thin these things called stars start blinking when an object moves in front of them, you can detect targets by their silhouette. so you might increase the resolution of your active camo, and fake the starts. this might fool the human eye but chances are if point your mass spectrometer at those dots and find out the spectra is all wrong for those stars. there was a whole thing on atomic rockets about stealth in space being a bogus concept.

[Mazon Del]

Designing a system to detect a ship occluding a star succesfully with any amount of reliability is a VERY difficult problem. It is far easier to create a system to locate something by the light coming off of it. Additionally, space within a solay system isn't exactly just a perfect area for light to travel straight ahead. When we make those IR maps of the sky, there is a minimum bound they can be set to before the heat coming off of solar wind and such begins to show up. Pointing a focused IR telescope at a spot you are pretty certain has a ship will very likely let you see it, but creating an omni-directional system that detects ships is going to be very fraught with false positives. Once you have found a ship, keeping tabs on it is not very difficult. But finding one that is trying to hide WILL be very hard. All you need to do as the defender is to make sure that your heat/EM emissions towards an enemy position are low enough to be lost in the 'foreground scatter' of generic solar winds while not standing out too much from the 'background' of space.

Now, when you are firing your engines, depending on the type of exhaust, stealth could be a quite laughable concept. Firing off a NERVA for a big boost is likely something that we can detect 'fairly easily' from the exhaust plume. So if you are trying to hide from a specific detector (say you were at Mars and you wanted to hide the fact that you were launching somewhere from the Earth based detectors) you would do your boosting behind an object (such as Mars in this example) and then coast the rest of the way.

However if the EMdrive/Q-Drive/Q-Thruster ends up scaling well, you won't even have engine emissions to search for.

[Seret]

there was a whole thing on atomic rockets about stealth in space being a bogus concept.

If you read it carefully their main objection is that a manned spacecraft can't have a thermal signature low enough. Fine, that's probably true, but why in the heck would a combat spacecraft be manned? It does make you wonder if they're deliberately ignoring the point, or if they just haven't really thought about it. The author seems to have their head stuck in sci-fi land, not the real world if you ask me.

Apart from that your point seems to be that a spacecraft couldn't be made perfectly undetectable. If so, that's completely true. Nothing is completely undetectable. Stealth technology doesn't attempt to make something undetectable, it just degrades the effectiveness of the sensors trying to find the target. Even the fanciest stealth fighter can in fact still be detected.

[Sirrobert]

then you bring up your thermograph and find out that the target is a different shade of black from the background of space. then you might control your emissions to match. thin these things called stars start blinking when an object moves in front of them, you can detect targets by their silhouette. so you might increase the resolution of your active camo, and fake the starts. this might fool the human eye but chances are if point your mass spectrometer at those dots and find out the spectra is all wrong for those stars. there was a whole thing on atomic rockets about stealth in space being a bogus concept.

Now you're just throwing around technobable to look smart.

Mass Spectrometers have NOTHING to do with emissions, in space or otherwise. They break up samples into single molecules/atoms and measure the mass of those particles(a hint to this fact is in the name).

I know Hollywood likes to call everything that does some fancy science thing 'Mass spectrometers', but I'd expect better from the people on this forum

If you read it carefully their main objection is that a manned spacecraft can't have a thermal signature low enough. Fine, that's probably true, but why in the heck would a combat spacecraft be manned? It does make you wonder if they're deliberately ignoring the point, or if they just haven't really thought about it. The author seems to have their head stuck in sci-fi land, not the real world if you ask me.

Thing is, scenarios like stealth in space won't come up for a very long time. By the time they do, the level of technology will probably resemble current sci-fi more than it'd resemble current technology. We don't know how things like that would evolve right now

[linkxsc]

Apart from that your point seems to be that a spacecraft couldn't be made perfectly undetectable. If so, that's completely true. Nothing is completely undetectable. Stealth technology doesn't attempt to make something undetectable, it just degrades the effectiveness of the sensors trying to find the target. Even the fanciest stealth fighter can in fact still be detected.

I remember watching a documentary a while ago talking about how the f-22 and f-35 only had particularly small radar cross-sections from the front and sides by other aircraft at about the same alt, and were easily detectable from the rear top or bottom. Well then in a head to head fight, or maneuvering around they have an advantage over other fighters but in a dogfight theyd rely on speed and thrust vectoring.

The f-117 was made for ground attack and hence was built to be less detectable to radars on the ground physically below it (however we later found it had issues with getting tracked by radars operating at frequencies above spec). This is why for example the exhaust from the engines was run over the top of the wing so it would have some time to cool and be less receptive to thermal sams.

[linkxsc]

Now yoiu're just throwing around technobable to look smart.

Mass Spectrometers have NOTHING to do with emissions, in space or otherwise. They break up samples into single molecules/atoms and measure the mass of those particles(a hint to this fact is in the name).

I know Hollywood likes to call everything that does some fancy science thing 'Mass spectrometers', but I'd expect better from the people on this forum

I think youre overreacting a bit, i fairly well understood his statement as a light spectrometer, similar to the ones we use now to guesstimate the chemical makeup of stars.

[Ralathon]

If you read it carefully their main objection is that a manned spacecraft can't have a thermal signature low enough. Fine, that's probably true, but why in the heck would a combat spacecraft be manned? It does make you wonder if they're deliberately ignoring the point, or if they just haven't really thought about it. The author seems to have their head stuck in sci-fi land, not the real world if you ask me.

Apart from that your point seems to be that a spacecraft couldn't be made perfectly undetectable. If so, that's completely true. Nothing is completely undetectable. Stealth technology doesn't attempt to make something undetectable, it just degrades the effectiveness of the sensors trying to find the target. Even the fanciest stealth fighter can in fact still be detected.

Lets do some napkin maths.

Say you have a tiny warhead in orbit around L4 in the earth-moon system. Say it only had 1m^2 of surface area facing earth because our tech is that compact. First of all you'd have to paint it perfectly black to ensure earth doesn't see the reflection of sunlight on the hull. With current detection tech (Where we don't have to worry about warheads in high orbits) you'd have to cool the hull to 163K to avoid thermal detection (see equations on Atomic Rockets). You receive around 1.3kW per square meter from the sunlight at 1AU and at some point during our orbit that light will directly hit our cloaking plate. So we'd have to pump 1.3kW of heat from 163K to our radiators. Say we have a generous 10m^2 of radiators hidden behind our cloaking plate. Assuming the temperature of the CMB is negligible and your radiators are perfect black bodies Stefan-Boltzman tells us our radiators need a temperature of about 220K. So you're lifting those 1.3kW over a 60 degree temperature difference. Assuming a perfect Carnot efficiency you can do this with 385% efficiency. So you need an energy source producing 338W just for cooling. This would require at least another 2.5m^2 of radiator to get rid of that output. 338W is a lot of juice in spaceflight, that's almost as much as the Voyager probes at launch. Producing that energy is going to induce more waste heat to worry about, requiring more radiators or higher temperatures. You see where this is going:

You can't keep adding more radiators to keep your system cool though. At some point they'll stick out behind the spacecraft simply by the parallax caused by the rotation of the earth. And all this is for current passive detection. Imagine what kind of hoops you'd have to jump through to avoid detection when people are actively looking for you and a few more decades of technological progression.

It is undoubtedly possible to hide something in space if you really really want to, but it is ridiculously difficult as I hope this example shows.

[Mazon Del]

but why in the heck would a combat spacecraft be manned?

Depends on the location of use honestly. If in near Earth orbits (I'm calling out to the Moon as being here for this purpose) you can likely get away with using radios and such to instill remote control (which you would want to some extent! You do NOT want a weapon that you launch and have no ability to recall. Almost no major weapon (even fire and forgets) cannot be at least remotely destroyed via radio command. For something with the bang of a warship, you are going to want humans in the loop for all kinds of reasons. Out somewhere like Mars, you cannot wait the hour for comms to work for you.

[undercoveryankee]

I'm familiar with what Atomic Rockets has on stealth. It's written mostly to rebut claims that stealth will ever be good enough to guarantee total surprise up to the moment of firing weapons.

There are probably still tactically useful tricks that are possible, especially if you have an idea of where the sensors are located and what their capabilities are. You can probably arrange that if a known sensor picks you out of the background it will have no way to tell that you're not an inert asteroid until it's too late. Planning the times and paths of any necessary radio communication and using the least detectable beam shape at your disposal are part of that.

[linkxsc]

-snip-

It is undoubtedly possible to hide something in space if you really really want to, but it is ridiculously difficult as I hope this example shows.

Math works out with my napkin. However there are a couple things that have come to my thoughts.

1 It itsn't clear which L4 we are talking about, Sun-Earth, or Earth-Moon, so lets do some figuring with both situations

Sun-Earth. Your 1m^2 warhead would be sitting ~1AU from earth itself (merhaps moer perhaps less, unless my figuring is wrong, but I believe it should be roughly the distance from earth to sun

At that range, before considering temps or anything your target from earth or a near earth satellite would be roughly, 2 sin-1[c/(2r)]

c being the length of a chord, or in this case the diameter of our object. And r being the radius of a circle, or basically our range to the target.

2 sin-1[1m across /(2*149,597,870,700m from earth)] = ~5.62*10^-12 radians... or something on the order of 10^-10 degrees

Now if you already know you're supposed to be looking at L4 to track this thing, yeah you might be able to pick it up with an expensive accurate thermal telescope. But thats with it being in there amongst all the other debris that may be filling up L4 in the future. And thats a pretty dang narrow beam of detection, just sweeping across the whole of the angles that teh L4 region takes up would take days or weeks, maybe even years to pick up something that small. And if theres other debris around, good luck. Would be better off trying to pick up targets within 1million km from earth before working on the 150million range. Although, you could always just have a scanning array built in L4, sicne in this space future you might need sats there to keep in communications with bases on mars and such (unless those got destroyed, and now there's more debris absorbing heat to try and sift through.

More realistic would be the craft sitting in Earth-Moon L4. This is only ~384,400km and our 1m^2 target would be 2.18*10^-6 wide from our perspective. I think we could do a pretty good job of picking that up, its over a million times larger in a scope compared to before, and we already have a few satellites out there, or if we don't already, they would be great aides to communicating with bases on the far side of the moon (being relays for sats sitting at E/M L2) This however also could have a chance to hide because thered probably be more stuff floating around there. maybe some space colonies, maybe a station or 2, ofcourse those stations and colonies could pick it up, but well, who are we at war with, they may be the ones holding those colonies or stations.

But again, assuming your craft is the 1 above with several meters of radiator/solar panel to keep itself powered and cool, you'd be easily spottable from the lunar surface, sats/stations in L1,2,3,4, and 5.

With some angling, and redesign though you might hide yourself from earth, moon L1,2,4,5 but still be noticeable from L3. Therefore if you want to be stealthy your best hiding spots would actually be L3, farthest from all the other points, and all the points are within ~60degrees infront of you, so the craft could be designed... maybe with a cone shaped "cloaking" array, to have a better chance of hiding. Although, thats still assuming there aren't a bunch of sats/stations/colonies sitting out around L3 which could easily be hidden around becuase they would be vastly higher thermal sources.

Stealth as I see it in space is much less not being detected through technology, its not being detectible relative to the other junk floating around.

Also a ship could always carry its own thermal/radar decoys to draw attention of scanners away, they could be launched by hydraulic piston away from the ship, after drifting a few hundred KM, they fire up and do their job (make burns different to what you're making your burn and such) heck could get all tactical with ships in 1 area launching decoys to draw the attention of scanners to a different part of the sky, so that ships elsewhere can have their time to make a burn.

Makes me wish I had a team of developers where we could go make a sim game that you have to deal with and work with all the problems of range and detection and such. It'd be like "Silent Hunter" only ~30x as hardcore

Edited August 5, 2014 by linkxsc

[PTNLemay]

lol, actually I meant for regular ocean-travelling ships...

Too late now, the Stealth-in-Space debate has it's claws firmly sunk into this thread.

[linkxsc]

lol, actually I meant for regular ocean-travelling ships...

Too late now, the Stealth-in-Space debate has it's claws firmly sunk into this thread.

Oh well in that case... isn't this basically what we're doign with phased scanning arrays? They electrically steer the sending beam for their radars, also they can similarly do it to send things like communications signals, VOR beacons work like this to an extent too. However this isn't even really a new technology. We've had highly directional, tight beam antennas for years.

As a matter of fact in the early stages of WW2, the Germans used this to their advantage when directing bombers to targets in England.

Initially there were 2 tight beams, 1 that the bombers would travel along, and a second that when met, they would drop their bombs. This worked pretty well for a while actually, just set up the 2 beams so that they cross over the factory or w/e you want to bomb and go. Later though the English started picking up those signals with their own systems and would have fighters waiting at areas they thought the bombers would hit, or they'd evacuate. So the Germans instead added a 3rd beam. Like before they would fly along beam 1, but when they hit beam 2 it would start a timer counting up, when they hit the 3rd beam the timer would stop and start counting back down to 0, and when it hit 0 that would be their target and they'd drop. After that some stuff started where a radio station in England figured out the frequency they were using and would start/stop the timers prematurely so that their drops would be far off course. And that was in the 40's

[Nuke]

Now you're just throwing around technobable to look smart.

Mass Spectrometers have NOTHING to do with emissions, in space or otherwise. They break up samples into single molecules/atoms and measure the mass of those particles(a hint to this fact is in the name).

I know Hollywood likes to call everything that does some fancy science thing 'Mass spectrometers', but I'd expect better from the people on this forum

i think i got my scientific instruments mixed up. i think i may have meant spectrograph, but idk, im not a scientist, but i know they have a machine they can point at something and look at its spectra lines. also by thermograph, i mean ir cameras. with sensor technology currently booming id expect to have cameras that can detect and measure wide swaths of the em spectrum. its not technobabble, this stuff exists, even if i dont know what its called.

[Seret]

lol, actually I meant for regular ocean-travelling ships

Highly directional RF is nothing new. We've used it for things like navigation, comms and search for decades just by designing the antenna a particular way. Not all comms is broadcast via non-directional antennas, if you want to go point-to-point for whatever reason (such as being harder to detect) then you can use a tight beam. Doing so requires a lot less power than going non-directional.

If you want to see a nice low-tech example check out the "cantennas"people hack together to improve point-to-point Wi-Fi.

Edited August 6, 2014 by Seret

[linkxsc]

If you want to see a nice low-tech example check out the "cantennas"people hack together to improve point-to-point Wi-Fi.

Cantennas are nice and easy to make, just punch a hole in a pringles can (although coffee cans seemed to work better in my testing), put a wifi dongle sticking though, and run a wire down to your computer. We were able to pick up known routers from ~1/4th - 1/2 mi with that.

But my friend and I managed an 8mi wifi link using a pair of "WokFi" antennas and attaching them to the roofs of our houses. Getting the angle right was annoying though, using a wok and an omni router we've also pulled of a 2mi uplink with only needing to direct 1 antenna.

Actually with a goofy network of antennas we've built, most of my local friends can all connect to the same wifi even though we're all spread across a 6-7 mi area. Early on, we didn't have good cable internet up in our area (and still kinda don't, but dialup wasn't gonna do it for lanning starcraft/warcraft) so when we wanted to LAN, we had to get creative.