Thoughts about Sensors in Ship Combat

[Golan2072]

This web page, which is concerned with debunking some of the handwaves of "soft" sci-fi, says the following about sensors (which it calls "scanners"):

The fact is that Space, though big, is a lousy place to try and hide in. At any temperature above absolute zero (far too cold for crew comfort), all objects in Space - including all Combat Spacecraft - radiate energy, easily detected by Scan gear from zillions of kilometers away. Moreover, DRIVE engines and weapons such as BEAMS put out scads of energy, in forms that are not only easily detected but pretty readily identified for what they are.

I think that the main limits to a ship's detection ability would be sensor resolution (remember, we're talking about tiny IR sources in a HUGE volume of space) as well as finding a needle in a haystack (i.e. figuring out which IR source is a ship and which isn't).

What do you think about that subject? How easily detectable should starships be? From which range?

 

[Daneel Olivaw]

The website you quote says that detection of any powered object's electromagnetic emissions in space, at virtually any distance within a star system, is inevitable.

This is substantiated by this site. This suggests that all space sensors may end up being passive sensors except for proximity radar detectors for docking maneuvers, etc.

I imagine that the only way to avoid detection would be to put an asteroid, planet, moon or star between your ship and the searching vessel. Unfortunately, the searching vessel would be hidden from your sensors as well, unless you employed sensor drones at different locations, but they would also be detectable.

As for range... The reliability of a target's position and vector is inversely proportional to the range at which it is detected. There may be a distance beyond which sensor data takes too long to receive to be of any tactical use. In other words, the target may have altered its vector significantly, been destroyed or engaged its jump drive long before your sensors will have registered these events. Sensor data could take hours to travel across a star system.

And yes, it's a big area to search, but our modern-day, early 21st century radars are capable of scanning huge areas in a matter of seconds. In the future, sensor arrays will only get better, and space itself provides the most noise-free, highest-contrasting background to any electromagnetic source.

Maybe massive stellar flare activity could make EM detection difficult?

 

[flykiller]

At any temperature above absolute zero (far too cold for crew comfort), all objects in Space - including all Combat Spacecraft - radiate energy, easily detected by Scan gear from zillions of kilometers away.

when the cassini probe arrived at saturn it promptly discovered several new moons orbiting that planet. these things are hundreds of miles across, some of them are bright white, they weren't trying to hide, and people have been studying saturn intently for hundreds of years - yet they were missed until a probe arrived locally. claims of omniscient sensors just don't seem to be reflected in reality.

 

[Anthony]

The truth is, a non-maneuvering craft can hide pretty easily at interplanetary ranges. Extant sky surveys are unlikely to spot stuff dimmer than about magnitude 12, and a full sky survey much below magnitude 20 (about a 200m object at 1 AU) starts being an unmanageable effort, so at a distance of 1 AU most spaceships, if not using a lot of power for something, will probably not be seen.

The big problems are thrust (reaction drives are Amazingly Bright) and combat ranges. 5 light-seconds is only 0.01 AU.

 

[sinbadsam]

Some note on Radars that apply to non atmospheric environments.

Range/resolution is Dependant on wavelength. Most high definition radars of very high(Megahertz range or higher) in the frequencies used, but high frequency radars do not have the range that low frequency radars have. But low frequency radars lack resolution.

Also giving a high freq radar just more power there is a point where it does not help.

A typical set up would be a low frequency radar just to detect something is out there. Once detected a high definition sensor is brought to bear upon the "bogey" like Ladar or High Frequency beam oriented radar ie Maser.

As for RL radars detecting things over a large area quickly....only if things are absolutely perfect conditions etc, otherwise NO.

Passive detection takes alot longer before you can gain a "target lock".

Former USN Surface Fire Controlman here, MK 23 Tas, MK 91 GMFCS "Sea Sparrow", WLY-1 EWS, SLQ-32 EWS, CWIS (Phalanx) and MK 86 GFCS. Had to something on those West Pacs.

 

[Daneel Olivaw]

But we're talking about the far future. In centuries to come, sensor technology will no doubt have improved on a revolutionary scale, not just evolutionary.

A note about the newly-detected moons of Saturn - these are cold bodies, emitting no energy other than that which they reflect from the sun. In a century or two, we may well be detecting such objects in other star systems, dozens if not hundreds of light years away.

So far we've been discussing EM detection only. What if we learned how to detect gravity as a force - not just movement and acceleration as a function of gravity?

 

[atpollard]

The basics of optics remains virtually unchanged from the time of Galileo to the present (400 years). The only real difference between the first telescope and Hubbell is size and moving beyond atmospheric distortion.

While we have learned to 'see' farther across the EM spectrum, the basics of focal length and seconds of arc remain unchanged. The spectacular results in astronomy are due to very clever tricks to increase the size of the lens. Multiple stations working together can increase the 'lens' to the diameter of the earth. Using a distant star as a gravity lens can create a truly giant lens.

While we will probably be able to detect the moons of a gas giant in another star system some day, it will probably require an array of stations orbiting near the ort cloud and working together. Even in the 25th century, such capabilities are not likely to fit on a starship hardpoint to detect enemy ships across thousands of AU.

 

[far-trader]

Originally posted by atpollard:
...Even in the 25th century, such capabilities are not likely to fit on a starship hardpoint to detect enemy ships across thousands of AU.

The only thing I'd add in here is that if we allow that artificially gravitically lensed lasers* can be mounted (three) to a single hardpoint then it's not too far a stretch to allow the same performance leap for passive sensors. And if (as many do) you take the computer tonnage to be in large part sensors then you have at a minimum a part of 1ton and as much as part of 9tons for sensors.

* about the only way to achieve the type of performance seen

Do I think you can use a starship's sensors to "see" another starship across parsecs? No. And more to the point how useful is such information? Not terribly when it's years old.

Do I think you can always, immediately, and with full data, detect a starship in a starsystem? No. Mainly because I like the idea of a chance for running silent and sneaking around. You won't be sneaking around in a Class A system, there's just too many eyes. And you will be spotted before long in a Class B system, again due to the number of eyes. But a Class C system might miss you if you're careful and don't linger over long in areas of interest. And you could get away with some sloppiness in a Class D system and still not be found.

Likewise any single ship trying to find another single ship is going to have to work for it in my opinion. Again if for no other reason than to make a game of the game.

 

[Daneel Olivaw]

Originally posted by atpollard:
The basics of optics remains virtually unchanged from the time of Galileo to the present (400 years). The only real difference between the first telescope and Hubbell is size and moving beyond atmospheric distortion.

I don't believe that Galileo's contemporaries would have imagined that we would be able to see as far as we do now.

The site I mentioned and other sources which appear to be well-researched indicate that detection of functioning spacecraft across interplanetary distances is more than feasible with today's technology.

I know that the idea of stealthy, submarine-like engagements in our SFRPGs is appealing, but I just don't think that reality will be that way. On the other hand, Traveller's lack of FTL communication lends a lot of stealth and intrigue on a strategic (i.e., interstellar) scale. And within a star system there would still be some opportunity to hide behind asteroids, etc.

 

[Golan2072]

Hmmm... Also, in well-travelled and/or well-settled systems, as long as you blend in the traffic (i.e. travel in the vicinity of oter ships, a lightsecond or two away from most of them) while this could be you'll be hard to pick out - the signature of, say a PowerPlant-D is the signature of a Powerplant-D after all, right?

This makes Q-ships very useful

 

[sgbrown]

Originally posted by Daneel Olivaw:
-clip- I don't believe that Galileo's contemporaries would have imagined that we would be able to see as far as we do now.

No doubt capabilities will increase - otherwise it wouldn't be a higher TL - so at TL F we may be able to find things most folks can't imagine now (of course most folks can't imagine now what we can find now . )

The site I mentioned and other sources which appear to be well-researched indicate that detection of functioning spacecraft across interplanetary distances is more than feasible with today's technology.
-clip-

The ability to detect is not the same as automatic detection. Nor is having the data and having it in usable form the same thing. Inside our own system we are still discovering near earth asteroids, and just recently an amatuer astronomer (from Austrailia I believe?) discovered a comet that wasn't picked up by the professionals - who certainly have better detection capability. The shear number of objects moving on various orbits would make separating a ship from the background clutter at distances over an AU pretty difficult at least part of the time.

 

[sgbrown]

Originally posted by Daneel Olivaw:
-clip-
The site I mentioned and other sources which appear to be well-researched indicate that detection of functioning spacecraft across interplanetary distances is more than feasible with today's technology.
[/QB]

Interesting site!

Another point - the projectrho site postulates ships using nuclear rockets - i.e drives that would qualify as at least bay sized beam weapons in destructive power (according to the link to John's Law on the site as WMDs, but I think that's hyperbole).

If the ship has the traveller thruster plate technology, it would be considerably less visible than the site predicts (note the site assumes current physics - thruster plates aren't possible within the current understanding of physics.)

However, if it's using HEPLAR, I can readily see the point that it would stand out from random space junk if its manuevering. As would a ship firing a plasma gun or other high signature weapon. (Personal opinion - lasers would only qualify as high signature if you're on the recieving end or if the laser is dispersed by something - such as sand or the hull plating of a target vessel.)

 

[Anthony]

Oh yes, any ship using a reaction drive would be highly visible. HEPlaR has an apparent exhaust velocity of about 20,000 km/sec, and thus has a power output of 10 MW/N, or 200TW for a scout ship (thrust 20 million newtons), which pretty well qualifies as WMD (it's 50 kT/sec). Yes, HEPlaR is not much better as a handwave than grav plates.

 

[Daneel Olivaw]

The ability to detect is not the same as automatic detection. Nor is having the data and having it in usable form the same thing. Inside our own system we are still discovering near earth asteroids, and just recently an amatuer astronomer (from Austrailia I believe?) discovered a comet that wasn't picked up by the professionals - who certainly have better detection capability. The shear number of objects moving on various orbits would make separating a ship from the background clutter at distances over an AU pretty difficult at least part of the time.

I'm sorry - I'm talking about the detection of spacecraft, whose life support power alone would emit enough radiation to be seen across interplanetary distances:

From Atomic Rockets:
"The maximum range a ship running silent with engines shut down can be detected with current technology is:

Rd = 13.4 * sqrt(A) * T2
where:
Rd = detection range (km)
A = spacecraft projected area (m2 )
T = surface temperature (Kelvin, room temperature is about 285-290 K)

If the ship is a convex shape, its projected area will be roughly one quarter of its surface area.

Example: A Russian Oscar submarine is a cylinder 154 meters long and has a beam of 18 meters, which would be a good ballpark estimate of the size of an interplanetary warship. If it was nose on to you the surface area would be 250 square meters. If it was broadside the surface area would be approximately 2770. So on average the projected area would be 1510 square meters ([250 + 2770] / 2).

If the Oscar's crew was shivering at the freezing point, the maximum detection range of the frigid submarine would be 13.4 * sqrt(1510) * 2732 = 38,800,000 kilometers, about one hundred times the distance between the Earth and the Moon, or about 129 light-seconds. If the crew had a more comfortable room temperature, the Oscar could be seen from even farther away.

To keep the lifesystem in the spacecraft at levels where the crew can live, you probably want it above 273 K (where water freezes), and preferably at 285-290 K (room temperature). Glancing at the above equation it is evident that the lower the spacecraft's temperature, the harder it is to detect. "Aha!" you say, "why not refrigerate the ship and radiate the heat from the side facing away from the enemy?"

Ken Burnside explains why not. To actively refrigerate, you need power. So you have to fire up the nuclear reactor. Suddenly you have a hot spot on your ship that is about 800 K, minimum, so you now have even more waste heat to dump.

This means a larger radiator surface to dump all the heat, which means more mass. Much more mass. It will be either a whopping two to three times the mass of your reactor or it will be so flimsy it will snap the moment you engage the thrusters. It is a bigger target, and now you have to start worrying about a hostile ship noticing that you occluded a star."

And receiving and processing the data? Again from Atomic Rockets (one of my favourite sites, if you hadn't already guessed)...

"Ken Burnside said:

A full spherical sky search is 41,000 square degrees. A wide angle lens will cover about 100 square degrees (a typical SLR personal camera is about 1 square degree); you'll want overlap, so call it 480 exposures for a full sky search, with each exposure taking about 350 megapixels.

Estimated exposure time is about 30 seconds per 100 square degrees of sky looking for a magnitude 12 object (which is roughly what the drive I spec'd out earlier would be). So, 480 / 2 is 240 minutes, or about 4 HOURS for a complete sky survey. This will require signal processing of about 150 gigapizels per two hours, and take a terabyte of storage per sweep.

That sounds like a lot, but...

Assuming 1280x1024 resolution, playing an MMO at 60 frames per second...78,643,200 = 78 megapixels per second. Multiply by 14400 seconds for 4 hours, and you're in the realm of 1 terapixel per sky sweep Now, digital image comparison is in some ways harder, some ways easier than a 3-D gaming environment. We'll say it's about 8x as difficult - that means playing World of Warcraft on a gaming system for four hours is about comparable to 75 gigapixels of full sky search. So not quite current hardware, but probably a computer generation (2 years) away. Making it radiation hardened to work in space, and built to government procurement specs, maybe 8-10 years away.

I can buy terabyte hard drive arrays now.

I can reduce scan time by adding more sensors, but my choke point becomes data processing. On the other hand, it's not unreasonable to assume that the data processing equipment will get significantly better at about the same rate that gaming PCs get significantly better.

Now, this system has limits - it'll have trouble picking up a target within about 2 degrees of the sun without an occlusion filter, and even with one, it'll take extra time for those exposures.

It won't positively identify a target - it'll just give brightness and temperature and the fact that it's something radiating like a star that moves relative to the background.

On the other hand, at the thrusts given above, it'll take somewhere around 2 days of thrust to generate the delta v to move from Earth to Mars, and the ship will be in transit for about 1-4 months depending on planetary positions."

 

[sinbadsam]

hmm well I guess the US Governments IR Sats are defective in picking up that Russian Oscar submarine, cruising underneath the ocean. They have a hard enough time picking up surface ships thru cloud cover.

I guess they need to put "Ken Burnside" to work for them.

Interesting "theoretical poppycock" from the majority what I have skimmed.

SGB - Steve B has some very good points that he has made.

But to each his/her own.

 

[Anthony]

Originally posted by Sinbad Sam:
hmm well I guess the US Governments IR Sats are defective in picking up that Russian Oscar submarine, cruising underneath the ocean. They have a hard enough time picking up surface ships thru cloud cover.

Spotting stuff on the ground is vastly harder than spotting stuff in space. The numbers given are comparable to modern-day astronomical instruments.

 

[shadowdragon]

hmmm.... try a simple test
find a big flat field- say a freshly mowed hayfield.
have a friend take a large marble and place it on a 5" stand and place it in a random location in a random field. take a pair of binoculars and find it.
then get an accurate range and bearing.
tell us how long it takes.

thanks

 

[Anthony]

Now, go to a large field on a moonless night in an area with little urban glow. Put a lighted candle on a 5' stand. How long does it take to find? Ships are easy to find in space because space is really dark.

(For accurate range and bearing, don't be silly. Computers don't think like humans. It's trivial for any computer to generate an accurate bearing on an object that moves slowly and that the computer can reliably identify -- such as a pointlike light source).

 

[Daneel Olivaw]

Originally posted by Sinbad Sam:
hmm well I guess the US Governments IR Sats are defective in picking up that Russian Oscar submarine, cruising underneath the ocean. They have a hard enough time picking up surface ships thru cloud cover.

I guess they need to put "Ken Burnside" to work for them.

Interesting "theoretical poppycock" from the majority what I have skimmed.

SGB - Steve B has some very good points that he has made.

But to each his/her own.

Ken Burnside is president of Ad Astra Games. If you look at the games they publish and their forum discussions, particularly the AV:T Related Science Topics forum, you'll find that Ken and his colleagues have put a lot of thought and effort into the scientifically-based portrayal of space combat.

Also, the Atomic Rockets site has an extensive bibliography of material supporting the assertions from which I'm drawing for this dicussion.

Again, I can appreciate the appeal of softer-science, "hide-and-seek" space combat in Traveller. However, I don't think it's necessary to dismiss these sources as "theoretical poppycock".

 

[Supplement Four]

Originally posted by Anthony:
Now, go to a large field on a moonless night in an area with little urban glow. Put a lighted candle on a 5' stand. How long does it take to find? Ships are easy to find in space because space is really dark.

It's not always that dark in space. Space combat will take place inside a solar system 99.99% of the time, near a star or two.

So, go out into that same field. Place a lighted candle on a 5' stand. Then travel west a distance from that candle. Wait until the sun rises in the east.

Can you see the candle? The 5' stand? Or, just the big bright splotch?

Depends. It depends on how close you are to the candle. The farther you are away from it, the more likely it is the sun will blot out everything when looking in its direction.

So, there are times, in space when radiation interfers with sensors.

And this interference doesn't have to be just from the system's star. Strong electro-magnetic interference when close to a gas giant or solar winds might interfere as well.

One more thought: Space is large and for the most part dark. Sensor range is probably incredible. But, it's one thing to "see" a target. It's a totally different thing to "hit" a target in combat.

A 200 ton vessel at 50,000 km can't even be seen with the naked eye. Sensor will have to locate it.

But, even if we assume that detecting the other vessel is automatic (that sensors are *that* good in Traveller-science...which I don't think is a stretch at all), hitting that ship with your beam laser turret is a whole different matter. That takes much more precise "tuning" of the sensors.

-S4

PS: GREAT topic, by the way. Enjoying both sides of this.