Thoughts about Sensors in Ship Combat

[Anthony]

Originally posted by Supplement Four:
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.

True to a point. However, the background is that dark, and if you're willing to put a hood over your camera so no sunlight falls on it, you can generally treat space as being completely black.

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

Does it matter? As long as you can see the splotch, you know there's a candle there.

The numbers on those sites are based upon the methods used by real astronomers. In particular, it's a very close match to real-world near-earth-asteroid automated searches.

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.

True, but combat range is usually pretty short, and if you're using beam weapons the pointing accuracy of the beam will be on the same scale as the beam focus, which means if you can hurt it you can hit it.

Now, at ranges beyond a few tenths of a light-second, against Traveller starships, you may miss because of speed of light delays. At a range of 1 light-second, you know your target's position one second before you fire, and it takes your fire another second to arrive, giving the target two seconds to no longer be where you shot at.

 

[Supplement Four]

Originally posted by far-trader:
And more to the point how useful is such information? Not terribly when it's years old.

This is an exceptional point that is easy to forget. It takes time for a signal (Radar) to be sent out and returned. And, it takes time for light to travel, even with Passive sensors.

The longer the range, the more this lag is. Weapons have to compensate. Correlation has to be made. Predicitions.

Again, just because you see a target doesn't mean you can hit it.

 

[Supplement Four]

Originally posted by Daneel Olivaw:
But we're talking about the far future.

We are talking about the far future. But, Far Future does not always equal High Tech.

For typical Traveller spacecraft, we're typically talking TL 13-15. Which is high tech. But, a TL 13 craft is a much lower tech vessel than a TL 15 ship.

And, I bet there might be some TL 11 or TL 12 ships out there.

 

[Supplement Four]

Originally posted by Anthony:
However, the background is that dark, and if you're willing to put a hood over your camera so no sunlight falls on it, you can generally treat space as being completely black.

I wouldn't agree with that at all. If you're looking outsystem, then, yes, you could generally treat space as completely black.

If you look towards the system's star (and there are a lot of angles where this would be a factor), the brightness of the star will many times be stronger than any sensor signal you get from a ship's drive, effectively cloaking the target.

 

[Anthony]

Originally posted by Supplement Four:
[QB]I wouldn't agree with that at all. If you're looking outsystem, then, yes, you could generally treat space as completely black.

If you look towards the system's star (and there are a lot of angles where this would be a factor)/QB]

If you're looking directly at the star, you're limited to the angular resolution of your sensors and you detect by occultation. The range at which this is possible is fairly short, but is in fact the same as targeting range (you cannot accurately target at ranges exceeding the angular resolution of your sensor).

If you're looking near the star, you have to mask it out somehow. This is trivial at 90 degrees or more from the star, fairly easy at 60 degrees, and becomes increasingly annoying as you aim closer to the star. It is plausible to assume spaceship sensors will have significant problems within about 6 degrees of the primary (separation <= distance/10).

This is not a terribly common situation, and can easily be dealt with by having two sensor platforms at a reasonable separation, meaning at least one of them is not looking right at the primary. There are several other reasons multiple sensor platforms are desirable.

 

[Ptah]

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.

...

Space is also really, really big. It is all about how "hot" your ship, or more accurately how many photons you are putting out. Spread them over a big enough sphere and they may be hard to distinguish from background and the noise on your sensors from you own ships heat, shot noise, gama rays and other things zinging through your electronics.

I'm assuming that there are no confounding signals, ship traffic, space based industires, et.c that might create "light pollution" etc. An system with active interstellar commerce might create all sorts of "pollution."

In the end it all comes down to how much you are emitting. (you can probably hide reflection and occulation by emitting!). A fusion rocket plume, you can't hide that.

Your power plant, well if you want to get "hard sci-fi" about it you don't need to hide it because your ship should melt from the waste heat if the only way your are getting rid of it is through materials based heat exchange technology.

Calculations that like to show how you can't hide based on huge power plant heat signatures typically fail to see if a ship could even exist without melting at those temperatures. If you have a way to keep the heat down so you don't melt, you may have a way to keep down the heat so you are not so easily seen.

P.S. The same also applies to things such as fusion rockets. They are often held out as "hard sci-fi" but given unrealistic thrust/impulse combos. If you do the waste heat calculation, and again be generous, such ships should melt.

All the melting problems only get worse as the ship gets smaller.

 

[Anthony]

Originally posted by Ptah:
Space is also really, really big. It is all about how "hot" your ship, or more accurately how many photons you are putting out. Spread them over a big enough sphere and they may be hard to distinguish from background and the noise on your sensors from you own ships heat, shot noise, gama rays and other things zinging through your electronics.

Yep. I actually did some research on real-world sensors before posting. If you want some comparative values, the apparent magnitude of an energy emitter is ~39.5 - 2.5log10(Watts) + 5*log10(AU), and the sensitivity limit of a typical asteroid search telescope is magnitude 20-22 in an exposure of several seconds. This implies detection of a source of 10-60 megawatts at 1 AU, which will fail to detect a spaceship running cold, or 1-6 kilowatts at 5 light-seconds, which is pretty well automatic detection.

 

[sinbadsam]

Two terms little discussed, which affect the detection performance of non optical sensors.

Sensitivity and Selectivity

Take the NASA Apollo lunar video's taken with the sensors of the time, ie TV camera.

When the "sensor" pans to the sky, where are the stars? How many stars can your MK 1 eye ball detect?
Why so few is because of the two mentioned above.

In the original TV series "Star Trek" the actors had "stains" on their clothing. But due to the above two, the "stains" could not be "seen" by the viewer at home. This cause "issues" when the series was "remastered" using current technology.

As for optical sensors, well the "Hubbel(sp)" orbiting telescope has to "focus" on what it is imaging. "Infinite Focus" just does not "cut the mustard" when imaging things of any detail. So to view an an area using a optical sensor how many "F Stops" do you need? Lets say 1000 F Stops per per minute of arc. That will increase your image processing requirements by "at least" 1000x.

The reason why I called them "theoretical poppycock" is because they are only looking at theories.

Transducing an optical image to a "Electronic" system again uses the two terms above.

I would recommend Bruce's Sensor Rules which can be found in the many Traveller sites, IIRC.

Just because he owns a game company does not make him a "expert".

This subject has been thru many iterations on the TML over the years, go and search there.

 

[Golan2072]

Originally posted by Ptah:
Your power plant, well if you want to get "hard sci-fi" about it you don't need to hide it because your ship should melt from the waste heat if the only way your are getting rid of it is through materials based heat exchange technology.

Couldn't you use water (or L-Hyd) to do this? It will explain the huge fuel usage of Traveller starships (especially when jumping). Ofcourse, that will also mean that there would be superheated vapor for sensors to detect

 

[Anthony]

Originally posted by Sinbad Sam:

The reason why I called them "theoretical poppycock" is because they are only looking at theories.

Um...no. I'm taking stats from real hardware. I am, incidentally, being quite a bit more pessimistic than Bruce Macintosh.

 

[Daneel Olivaw]

I never said that the guy is himself an expert (besides, how do we know?). I simply meant that he and other people whose work I've mentioned have done their research based on material from actual experts.

BTW, I agree - this is a great topic. It sure beats the weird looks I get at work when I say to a colleague, "So what's your opinion on the future of space-based electromagnetic sensor technology?".

Hmmm... This might help to explain why I wasn't more popular in high school.

 

[sinbadsam]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by Sinbad Sam:

The reason why I called them "theoretical poppycock" is because they are only looking at theories.

Um...no. I'm taking stats from real hardware. I am, incidentally, being quite a bit more pessimistic than Bruce Macintosh. </font>[/QUOTE]Opps my point was being made to "Daneel Olivaw".

I can tell you have looked into real hardware.

As for Bruce's Sensor Rules, we both have the same pessimistic point of view on them, just was suggesting something for Daneel Olivaw to look at.

 

[Supplement Four]

I never used Bruce's sensor rules after I played with them a few times. Whether or not the ideas behind them are accurate, from a gameplay standpoint, the rules are too difficult to use. There's too many modifiers, and you've got to calculate a "signature" for a vessel in order to use those rules.

The ideas behind those rules need to be implemented in a simpler manner.

I tackeled this a while back, about a year ago, and came up with THESE rules. I don't currenlty use these in my game (I don't currently use any sensor rules--wanted to give the DGP Sensor Rules a try, but I may go back to them.

I did use them earlier in my campaign.

But, they're an example of using "in-game" stats, with less modifiers, that allows a sensor rule to be more easily played than what Bruce has come up with.

-S4

 

[Anthony]

Incidentally, Bruce is a professional astronomer. My pessimism compared to him is because of different assumptions about field of view and image processing.