Space and Sensor information

[TheEngineer]

Hi !

Anthony, wouldn't a well cooled ship surface (e.g. below 100 K), cause much lower radiation values than those You noted as detection limits ?

Even a 300 K blackbody radiates "just" around 460 W/(m²s), so small ships are near to the limit.

Anyway, I don't consider general detection of even small cool passive bodies as a major problem, especially assuming future tech sophistifications.

What maybe is an issue, is to do that in a limited time frame, like a combat round.
Its not so much the question, if something could be detected, but how much time it takes.

Perhaps one method to enter areas quite undetected, is to use system resident small objects as carriers. Takes a while, but IMHO a battery powers vessel is very hard to locate here.

TE

 

[Anthony]

Originally posted by TheEngineer:
Hi !

Anthony, wouldn't a well cooled ship surface (e.g. below 100 K), cause much lower radiation values than those You noted as detection limits ?

For as long as it remains cool, sure. However, unless you assume a device that violates the second law of thermodynamics (note that canonical black globe generators do so) it won't be able to remain cool for very long. If you painted a scout ship black and cooled it with liquid nitrogen, it would have an exposed surface of maybe 50 square meters, absorbing about 70 kilowatts of heat, or about 250 MJ/hr. That will use up more than a ton of liquid nitrogen coolant per hour.

 

[TheEngineer]

Yeah, thats right.
We talked about heat capacity problems quite often in the TML and perhaps here too

Guess we noted, that liquid hydrogen is a pretty heat storage, but I don't remember the numbers.
On the other hand, I tried to figure out the capacity of the ships capacitors lately and came out with 780 GJ/kl. Here it would just need another magic device to transform low level heat into a what-ever capacitor energy.

Well, the other option would be to transfer heat to backside and radiate it away via normal hull(would work at perhaps 450 K). Huh, another "hot" topic....

 

[Ptah]

Originally posted by Anthony:
I was playing around with photon counts when trying to do a sensor guess for another purpose. Assuming a 1 arcsecond resolution and 4 bytes per pixel, a complete sky map is ~2 terabytes. Assuming a 1 meter telescope and 10 seconds integration time per frame, Vlim should be 20-22 (and this limit is large noise-related); the total time to scan the sky will be a couple of hours. The apparent magnitude of a source at 1 AU is roughly 39.5 - 2.5*log10(watts), so the minimum detectable signal will be in the 10-100 megawatt range. Which is enough that ships can credibly not be spotted at an AU. The problem is that, given jump drives, detecting objects beyond about .03AU (15 light-seconds) isn't terribly important, and that drops the minimum detectable signal to 10-100 kilowatts, which it is more or less impossible for a ship to avoid (for objects in the life zone, sunlight heating the hull will do the job).

This somewhat exceeds the capability of any current modern sky scan system, but would be buildable today if someone wanted to spend the money.

Note that, if you wanted to take a closer look at something previously detected, Vlim probably increases by 5 or so, making the limit under a megawatt at 1 AU.

Anthony good stuff, will copy and save for future reference. If i read this correctly your estimate of detectability is for a 10 sec scan time (i.e. integration of signal for 10 seconds)? That's pretty good especially since we are talking current tech. Also if I understand correctly the couple of hours for the entire sky is based on a single detector?

 

[Valarian]

Originally posted by Anthony:
For as long as it remains cool, sure. However, unless you assume a device that violates the second law of thermodynamics (note that canonical black globe generators do so) it won't be able to remain cool for very long. If you painted a scout ship black and cooled it with liquid nitrogen, it would have an exposed surface of maybe 50 square meters, absorbing about 70 kilowatts of heat, or about 250 MJ/hr. That will use up more than a ton of liquid nitrogen coolant per hour.

Anyone know what Helium would be like as a liquid coolant? Could be a use for all that fusion plant byproduct. Pump the Helium gas exhaust in to the space between outer and inner hull where it could cool and reduce the heat footprint. Viable?

 

[mike wightman]

Originally posted by Ptah:
</font><blockquote>quote:</font><hr />Originally posted by Anthony:
I was playing around with photon counts when trying to do a sensor guess for another purpose. Assuming a 1 arcsecond resolution and 4 bytes per pixel, a complete sky map is ~2 terabytes.

Also if I understand correctly the couple of hours for the entire sky is based on a single detector? </font>[/QUOTE]What would happen if the entire hull was studded with smaller sensors?

 

[Anthony]

Originally posted by Ptah:
Anthony good stuff, will copy and save for future reference. If i read this correctly your estimate of detectability is for a 10 sec scan time (i.e. integration of signal for 10 seconds)? That's pretty good especially since we are talking current tech. Also if I understand correctly the couple of hours for the entire sky is based on a single detector?

Yeah, single detector and conventional telescope. You'd need upwards of a hundred square degrees of coverage to scan the sky in an hour.

 

[Anthony]

Originally posted by Valarian:
Anyone know what Helium would be like as a liquid coolant?

Yes. It would be lousy. Nitrogen has a heat of vaporization of 800 kilojoules per ton. Helium has a heat of vaporization of 20 kilojoules per ton. Hydrogen has a heat of vaporization of 450 kilojoules per ton.

 

[princelian]

Anthony's quite correct - LHe doesn't have the heat capacity to handle the load. You'd need <insert high-tech impossible material here> to use as super-coolant or something.

The problem is that if you tried to retain all that 5-600 K blackbody power, you'd overload your system and blow up eventually.

...using 21st Century physics, of course...

Leaving Travelleresque "needs-to-be-plausible physics" behind, one could have a higher-dimension heat sink where the heat is radiated at vibrational levels not accessible to our technology. The heat goes away, but not in "normal" dimensions....putting a bit of Traveller-speak into it, you dump heat into J-space or something.

The problem with this approach is that if you posit a higher-dimensional-space dump, you can also posit a higher-dimensional-space sensor array that can see it. If you assume it's J-space, though, nothing "here" can see anything "there," so it's undetectable.

Maybe it only works at >100D, too, and gets less efficient the closer you get to a planet, making it easy for the pirate to hide at 102 D and jump you before you can engage the J-drive, but pretty hard for any ship to hide closer to the planet.

(I'm just BS-ing here, btw. Nothing real-world-physics based here.)

The bottom line is that, as GM, I want:

</font>

• For it to be possible to hide a ship at reasonable ranges.</font>
• For good enough sensors to pierce this stealth.</font>
• For good enough stealth technology to hide it again.</font>
• And so on.</font>

All of that is needed for "strange and unidentified sensor ghosts" to pursue the party's ship; for the party's ship to sneak in close to the pirate base; for pirates to ambush them just as they are about to set the Heroic Plan in action because they have a military scoutship in their little pirate flotilla; etc.

Ships have to be difficult to detect at range, have means to make themselves (by action or by being designed for stealth) harder to detect, and have means to detect sneaky b*st*rds trying to ambush them.

Hence, a feel like in the Honorverse, where technologically-equal opponents might or might not ambush one another [as seen in the Manticore training exercise/wargames Honor kicks so much butt in] and where a technological edge makes all the difference [as seen in most Manticore-vs-Haven encounters].

Furthermore, for whatever physical reason, BIG ships need to be easier to find than small ones. The 100,000-ton freighter cannot hide; the 400-ton hunter/killer can. The 250 kton dreadnaught, even one designed for "stealth," should show up and have a real tough time evading pursuers' sensors. It's 1000 ton destroyer escorts, however, should be harder to "see."

You can find rulesets out there that deal with sensors, range, and how much intel is available at those ranges. Star Fleet Battles, for example, has rules for this. At extreme range, all you have is a blip. Later, you can tell the blip's size class (SC2 = capital ships and SC7 = shuttle/fighters, for example). Eventually, you start figuring out nationality and class and if you're close enough, subclass.

Finally, IMTU, when a ship enters or leaves J-space, it "rings" the hyperspace-sensitive jump capacitor crystals of other vessels and installations. This makes ships detectable at considerable ranges when they emerge from hyperspace (bigger signal) or enter hyperspace (smaller signal because the energy is "pushed" mostly into J-space). This is analagous to the "hyper footprint" of the Honorverse, but I was using this mechanism long before I read On Basilisk Station.

This is, if you're reading my older posts about detecting jumpspace, backwards from how I described it - entering ships were making more signal than departing ones - but I had my thinking backwards. ARRIVALS are spectacular (and detectable) things; departures less so.

 

[Ptah]

Originally posted by Sigg Oddra:
</font><blockquote>quote:</font><hr />Originally posted by Ptah:
</font><blockquote>quote:</font><hr />Originally posted by Anthony:
I was playing around with photon counts when trying to do a sensor guess for another purpose. Assuming a 1 arcsecond resolution and 4 bytes per pixel, a complete sky map is ~2 terabytes.

Also if I understand correctly the couple of hours for the entire sky is based on a single detector? </font>[/QUOTE]What would happen if the entire hull was studded with smaller sensors? </font>[/QUOTE]I think that is the exact solution to faster scans, just brute force increase of numbers. You'll also want extra scaners around after taking a few hits. Basically each sensor, properly placed, will bserve a different arcsecond of sky. To simulate TL advance you might increase the signal-to-noise discrimination and teh arcsecond view. Maybe a factor of 2 to 10 per TL depending on how you view such things.

 

[Ptah]

Originally posted by princelian:
Anthony's quite correct - LHe doesn't have the heat capacity to handle the load. You'd need <insert high-tech impossible material here> to use as super-coolant or something.

The problem is that if you tried to retain all that 5-600 K blackbody power, you'd overload your system and blow up eventually.

...using 21st Century physics, of course...

I concur.

Leaving Travelleresque "needs-to-be-plausible physics" behind, one could have a higher-dimension heat sink where the heat is radiated at vibrational levels not accessible to our technology. The heat goes away, but not in "normal" dimensions....putting a bit of Traveller-speak into it, you dump heat into J-space or something.

The problem with this approach is that if you posit a higher-dimensional-space dump, you can also posit a higher-dimensional-space sensor array that can see it. If you assume it's J-space, though, nothing "here" can see anything "there," so it's undetectable.

Exactly MTU solution with respect to being able to dump heat, or at least enough of it, into J-space.

Maybe it only works at >100D, too, and gets less efficient the closer you get to a planet, making it easy for the pirate to hide at 102 D and jump you before you can engage the J-drive, but pretty hard for any ship to hide closer to the planet.

(I'm just BS-ing here, btw. Nothing real-world-physics based here.)

I like the 100D idea. Yeah BSing but imagine what talking about a laser in terms of 19th century physics would sound like.

Pretty solid BSing as it can preserve game balance requires as little postulating of new physics as possible adn relies on new physics already needed by the game, i.e., FTL travel via J-Space.

The bottom line is that, as GM, I want:

</font>

• For it to be possible to hide a ship at reasonable ranges.</font>
• For good enough sensors to pierce this stealth.</font>
• For good enough stealth technology to hide it again.</font>
• And so on.</font>

All of that is needed for "strange and unidentified sensor ghosts" to pursue the party's ship; for the party's ship to sneak in close to the pirate base; for pirates to ambush them just as they are about to set the Heroic Plan in action because they have a military scoutship in their little pirate flotilla; etc.

Ships have to be difficult to detect at range, have means to make themselves (by action or by being designed for stealth) harder to detect, and have means to detect sneaky b*st*rds trying to ambush them.

Hence, a feel like in the Honorverse, where technologically-equal opponents might or might not ambush one another [as seen in the Manticore training exercise/wargames Honor kicks so much butt in] and where a technological edge makes all the difference [as seen in most Manticore-vs-Haven encounters].

Furthermore, for whatever physical reason, BIG ships need to be easier to find than small ones. The 100,000-ton freighter cannot hide; the 400-ton hunter/killer can. The 250 kton dreadnaught, even one designed for "stealth," should show up and have a real tough time evading pursuers' sensors. It's 1000 ton destroyer escorts, however, should be harder to "see."

You can find rulesets out there that deal with sensors, range, and how much intel is available at those ranges. Star Fleet Battles, for example, has rules for this. At extreme range, all you have is a blip. Later, you can tell the blip's size class (SC2 = capital ships and SC7 = shuttle/fighters, for example). Eventually, you start figuring out nationality and class and if you're close enough, subclass.

...

I like it. It also helps support a small ship universe for merchants, smugglers and pirates. Maybe those merchant ships are 200T to avoid detection by pirates. Same for the 400T patrol ship, all the better to sneak up on pirates with.

 

[RandyT0001]

Here is a picture of Earth from Saturn made by Cassini's wide angle imaging science instrument (telescope).

The ISS comprises two telescopes:
Wide Angle Camera: a 5.7-cm aperture f/3.5 refracting telescope with a 3.5° field of view and an angular resolution of 60 microradians per pixel.

Narrow Angle Camera: a 19-cm aperture f/10.5 Cassegrain telescope with a 0.35° field of view and an angular resolution of 6.0 microradians per pixel.

Each has a 10242 pixel CCD detector, fitted with spectral filters that rotate on a wheel to view wavelength bands from 0.2 microns to 1.1 microns. The Wide Angle Camera has 18 filters ranging from 380 to 1100 nm, and the Narrow Angle has 24, from 200 to 1100 nm. The ISS data system allows many options, including on-chip summing and data compression.

Sounds like it's a very small telescope. It made this image by picking up reflected light from the Sun. Just think what could be done with a few more TL's advancement.

Anyway.........

 

[princelian]

Randy, that's the light being reflected from the whole planet, admittedly at 8.83-odd AU.

And in response to the earlier post about detectors that can sense one photon/second, I believe (correct me if I'm wrong) that these are photomultiplier tubes (PMTs), which employ high voltage (10,000 V or more) to set up a cascade effect from a single photoelectric collision. We use them to detect a single gamma ray strike on a sodium iodide scintillation detector, for example.

Know what happens if the power's on and you expose the PMT to ambient light? It immediately burns up from an overload of photoelectric collisions, each one setting off its own cascade of electrons.

So sure, you can have a ship's sensor capable of seeing one photon, and starlight will immediately burn the thing up, not to mention such things as an explosion close aboard. Or a torchship's light. Or the system's primary.

 

[Anthony]

Originally posted by princelian:

And in response to the earlier post about detectors that can sense one photon/second, I believe (correct me if I'm wrong) that these are photomultiplier tubes (PMTs), which employ high voltage (10,000 V or more) to set up a cascade effect from a single photoelectric collision.

Nope, those are CCDs, close relatives of the things in your digital camera (though the ones in your digital camera are not as sensitive). They are routinely used in astronomy.

 

[Lochlaber]

Why would a fusion generator of either type be radiating such huge amounts of heat. A hot fusion plant would 'supposedly' be in a magnetic bottle which could withstand the elemental forces underway inside of it, without causing a huge explosion, melting the people next to it, etc.. Again, from what little I understand of cold fusion, it creates no heat and directly converts it's energy output into electricity.

Using the nuclear submarine again as your target. If you were able to see that sub outside the orbit of Neptune, why did neither cold war opponents simply put IR satellites up to watch for the other guy? Atmospheric problems could have been handled by simply using the same Orions or other sub hunters with their MAD gear. I've seen IR pictures of subs being brought into port and they don't look like the huge IR sources everybody seems to think they are. They are big but I would have imagined by this discussion, I could read by their IR light and they aren't that bright. When you start adding in refractory shells, this should hide the heat even more.

The final thought I have is, how many sensors can you operate and/or afford and of what types. Even with the hundreds of observors, i.e. astronomers of all types, they can only cover only a small part of the night sky. Sheer distance only increases the area a single sensor can cover on a regular basis.
Take the nuclear submarine, why were they able to hide if supposed detectors could find them in deep space but not in the ocean?

 

[Ptah]

Originally posted by Lochlaber:
Why would a fusion generator of either type be radiating such huge amounts of heat. A hot fusion plant would 'supposedly' be in a magnetic bottle which could withstand the elemental forces underway inside of it, without causing a huge explosion, melting the people next to it, etc..

The magnetic field contains the plasma and keeps it from coming into direct contact with the walls. However, the magnetic field does not stop radiative heat transfer (i.e., infrared radiation) from leavinf containment.

Now maybe we can contain that heat with the same thing we use to focus lasers in Traveller. The problems are actually rather similar. If it is to be a field containment or field focus I'd vote for magnetic monopoles. Theoretically possible (in fact they are in the theory of electromagnetism just never observed), probably with a vanishing small lifetime in a normal environment but maybe longer if artificially created.

Again, from what little I understand of cold fusion, it creates no heat and directly converts it's energy output into electricity.

First, cold fusion is not real, so you can make it what you wish. However if it operated as you describe above (no heat) it would probably violate the laws of thermodynamics by converting work (the reaction) 100% without generating heat.

[mini-rant]
Cold fusion is not real. It's more sci-fi pie in the sky than jump space. I've read the actual paper and we even discussed it in several seminars at Berkeley. The biggest thing people don't realize is that the "fusion" reaction these guys say never produced energy. IIRC tey postulated that "if" the binding energy of hydrogen-metal complex was "x" then they would have generated lots of energy. The thing is, the binding energy is not x or anywhere near x. It's like psotulating that if the gravitational constant was one-enth its present value I could fly, sure but that isn't the value.
The sole basi for their conclusion that "fusion" occured is some neutron readings IIRC. These are hard to do, since they are looking for low numbers, due to background. These guys were inorganic chemistists (again IIRC) so they were not familiar with making these measurments as a nuclear physicist or nuclear chemist might be.
[/mini-rant]

Using the nuclear submarine again as your target. If you were able to see that sub outside the orbit of Neptune, why did neither cold war opponents simply put IR satellites up to watch for the other guy? Atmospheric problems could have been handled by simply using the same Orions or other sub hunters with their MAD gear. I've seen IR pictures of subs being brought into port and they don't look like the huge IR sources everybody seems to think they are. They are big but I would have imagined by this discussion, I could read by their IR light and they aren't that bright. When you start adding in refractory shells, this should hide the heat even more.

A good comparison. THe difference is the attentuation of signal by water and the power levels of a nuclear sub are orders of magnitude smaller than a Traveller ship. In contrast, the ranges involved in Traveller are orders of magnitude larger. That last point is important to keep in mind when people think things can't hide in space. The sheer distances are beyond what we are used to imagining.

 

[Anthony]

Originally posted by Lochlaber:
Why would a fusion generator of either type be radiating such huge amounts of heat.

First of all, there are theoretical limits to the efficiency of a power plant; for thermal power plants (including fusion) the limit is equal to the ratio of the temperature of the source to the temperature of the heat sink. For cold fusion, the temperature of the source is pretty low, and the credible operating regime is pretty narrow, so 25% is about the limit (meaning heat output of 3x power output). For hot fusion, in theory the efficiency can be pretty high, in practice more than 50% is unlikely (heat output = power output). If you had a direct gamma to electricity converter you could theoretically have very high efficiencies

Secondly, anything that uses power also produces some waste heat.

Using the nuclear submarine again as your target. If you were able to see that sub outside the orbit of Neptune, why did neither cold war opponents simply put IR satellites up to watch for the other guy?

First of all, it's not that bright; nuke subs don't routinely use gigawatts of power (even a Traveller starship is not easy to spot from beyond the orbit of Neptune). Secondly, atmospheric problems are extremely hard to deal with, particularly if the object is also on the ground; detection ranges for objects on the ground drop by a couple orders of magnitude. Third, atmosphere gives you options for non-radiative heat elimination. Fourth, water stops IR, so a sub underwater can't be detected by its IR emissions.

 

[Scott Martin]

Originally posted by princelian:

<SNIP>... these are photomultiplier tubes (PMTs), which employ high voltage (10,000 V or more) to set up a cascade effect from a single photoelectric collision.

Photomultiplier tubes are still in common use for mass spectrometers, since the "cascade" is triggered by a collision event, which a CCD cannot directly detect.

They do have severe issues with shot noise (generally a thermal effect) as well as any contamination in the vaccum environment in which you want them to live. Since high vaccums take a lot of energy to create (and energy == waste heat) this is obviously an interesting design "challenge"

<Edit> which is why CCD's are a much better bet for light detection: they only react to light, so they have better signal/noise ratios, largely by having a lot less noise...</Edit>

Scott Martin

 

[avi.hecht]

There were attempts to locate submarines by their IR signature - it was not very successful, but is doable in costal waters. The problem is that water absorbs the radiation and diffuses it, by the time it reaches the detector (on the surface) it has spread through the heat is dispersed through a large body of water. In addition the temperature difference between the environment and the submarine is smaller than that of a fusion plant in outer space.

 

[Lochlaber]

Space should be as able to hide a object's heat signature from millions of kilometers away, as water a few hundred feet deep. An equivalent is a candle a mile away, you aren't going to see it with an IR scope depsite the size of your detector. Space is cold, so any heat disappating from the ship, should be dispersed by the same natural forces at work in water.

The problem with your fusion plant creating such a huge heat signature is the simple fact it would kill the crew. From what I have seen of the few partial successes with controlled hydrogen fusion, is that the heat was fully contained in the magnetic bottle and that containment is what makes it a controlled reaction, not an uncontrolled one. If the heat wasn't held by the bottle, you would simply have a fusion heat bomb, not a reactor.

As for the cold fusion, yes it is a theoretical pipe dream. However that theory postulated that you could provide huge amounts of power without requiring the continuous fusion reaction that needed to be contained. This in reply to the poster who said that a cold fusion plant would be even easier to detect than a hot fusion plant.