T4 Only: Some people say no stealth in space, a discussion.
- Thread starter warwizard
- Start date
Don't forget to account for the blue shift your approach vector is going to give your emissions. ECM devices are known to frequency shift and boost the pings of active sensors to give misleading blue/red shifts so the enemy gets misleading approaching or receding vector info.
Marcatlas
SOC-12
Ok, so you park your ship in front of a big sensor array. That doesn't get you anywhere. 1st you have to get to the cluster (which means you'll be detected getting there.). Jupiter's upper atmospheric temp is about 1000 c, so you'll show up as a cold spot. But, you have to get to Jupiter first, and that will mean you are detected going there. So, you haven't gained any advantage...
Timerover51
SOC-14 5K
I assume that this search gives you no range data. Also, how accurate is the bearing at distances of say 100,000 or more kilometers?
Marcatlas
SOC-12
One sighting (one line) would only give any range info if you knew the absolute magnitude of the object. Like if you know the absolute magnitude of a star. Otherwise it's unknown until you can get a 2nd line on it. Here's an excellent explanation of how you would do this if you were in a spaceship. Measuring distances
Spinward Flow
SOC-14 5K
A single detection is never enough.
You need MULTIPLE detections (over time) to establish a plot vector and range.
That's a minimum of 2 sensor sweeps to (1) detect and (2) verify.
3+ sensor sweeps are even better (as we all know, right?).
So for the sake of illustration purposes, let's say that a routine "condition green" passive scan around your ship requires 4 hours to complete a full ~41,000º scan of the entire volume of space around your craft. That means that if a "blip" appears in 1 scan, it's going to at least another 4 hours before you can get a second passive scan for that "blip" and start being able to make some vector plot assumptions about it.
"One ping only" may work for ACTIVE sensors, but you need more than a single contact for PASSIVE sensors.
This is why in astronomy, for exoplanet and comet hunting for example, you need to have (at least) 2 verified detections, not just 1, to confirm the presence of an exoplanet or comet.
But once you have a blip, you can focus on the blip. You don't need to do an entire sky scan for it.That's a minimum of 2 sensor sweeps to (1) detect and (2) verify.
3+ sensor sweeps are even better (as we all know, right?).
The point is that you point your radiators towards the sensor cluster and pump in heat to match the background while adjusting to take care of the dopplar shift (blue shift if closing, red shift if going away.) Please note that this is really difficult to pull off as there are multiple external radiation sourses that will be reflecting from your hull, the best way to manage that is to reduce the reflection's absoloute magnitude, so there is less energy there to be detected. Try to think of this as positioning a truck with a bank of headlights facing out of one side and position yourself in line between the setting sun and the mk 1 eyeballs that you do not want noticing you as you sneak over the last ridge. Measure the sunlight intensity on your other side and adjust the output of the headlight bank as the sun sets. This trick only works against sensors in a direct line with you and the sun.
Marcatlas
SOC-12
The point is, if you start moving in space you WILL be detected if someone is looking for it.
Spinward Flow
SOC-14 5K
The word "IF" is doing all the heavy lifting that assertion ...
So if your sensor sweeps "do this" ... and you're not completely sure of what you're looking at (until it's too late) ...
mike wightman
SOC-14 10K
Look at in the IR spectrum...
Spinward Flow
SOC-14 5K
Drive at night if you want to be in a collision.
Be functional if it breaks lidar speeding guns.
Well this is the T4 FF&S military ultra black hull coating, to the Mk 1 eyball it turns a 3D shape with highlights reflecting from nearby visable light sourses into a 2D rectangle indistinguishible from a painted sheet of cardboard, at least till you are 90% closer and can spot the corrigated end of the cardboard (unpainted). Yes it converts visable light into IR via blackbody radiation, but as noted upthread that is inefficient in radiating energy. To me that sounds like a very weak IR signal which needs a lot of antenna surface area or nearby presence to establish a detection. The reflectivity of visiable light is .00063 or about 3 orders of magnitude or about a -1.5 mod on detection of visable EM spectrum RAW (to the best of my memory).
But the issue is not reflection of (active) sensor signal. The issue is that the craft will be brightly glowing to (passive) sensors in infra-red due to its temperature (~ 290K +), just as a piece of metal heated somewhat hotter will be glowing bright red-orange and visible to (passive) sensors (such as your eyeballs), or that same metal heated extremely hot will melt into a liquid and be glowing yellow-white.
Spinward Flow
SOC-14 5K
So I went and looked up what the peak wavelength for 290K black body radiation was using an online calculator.
The answer for 290K comes back as being 9992 nanometers.
For reference, optical "red" is 610-710 nanometers.
Infrared is the 760-1,000,000 nanometers wavelength range.
Commonly used subdivisions of the infrared ranges are:
- Near-infrared = 750 to 1400 nanometers
- Short-wavelength infrared = 1400 to 3000 nanometers
- Mid-wavelength infrared = 3000 to 8000 nanometers
- Long-wavelength infrared = 8000 to 15,000 nanometers
- Far-infrared = 15,000 to 1,000,000 nanometers
Ah, but how big/bright would it be on a sensor scan at 0.5 light second = 150,000,000m distance from the sensor?
If we assume a 50m long craft (note: 400 ton Subsidized Merchants are 46.5m long according to LBB S7, p21) then simple trigonometry calculator yields a scanning angle of 0.000019098593171027798º resolution.
Or to put it more politely, a sensor resolution of 0.0687549354157 arc seconds to detect.
For reference, the James Webb Space Telescope has a resolution of:
Another source says:
In other words, being able to detect "something warm" in the 50m long size range at 0.5 light second = 150,000,000m distance would be "challenging" even for the James Webb Space Telescope which is optimized for near/short/mid-wavelength infrared observations.
If the emitter is "small enough" ... it's going to be difficult to spot at long distances ... even if it is "brightly glowing" in a specific EM band.
Save that if the emitter is moving, particularly at an angle that crosses the sensor, then the craft is no longer 50m. Rather. it's 50m * exposure time of the scanner long. Obviously it's less bright per pixel, but there's more pixels to detect. And if the craft isn't moving, the sensor can move to get a similar effect.
