[redsniper]

So... what? Are basing this all on currently available technology? Can't we extrapolate how much computational power will increase in the future? I mean we're already talking about ridiculously powerful propulsion systems and radiators and stuff.

[headdie]

can i just say all we have talked about so far is taking a snapshot of the sky, those readings then need to be analysed which takes human time and or additional computer processing/analysis

[Flaser]

can i just say all we have talked about so far is taking a snapshot of the sky, those readings then need to be analysed which takes human time and or additional computer processing/analysis

Not quite that difficult as space is cold, anything man-made is hot. You compare it to your charts for known objects and if something turns up it's a bogey...

...and paranoid captains will have the crew double-check the few objects in the vicinity anyway.

@Resolution debate: You don't get it. It's not about identification, it's about detection. Granted, if the bogey tries to blend into a nearby solar-body then this method won't work...

...except it will as it will likely be of different temperature.

...and using a sensor pod that's a couple of light seconds away is "impossible", you can't just make sure that a bogey can't hide in front of a solar body that way, that would be too easy. No we need some very expensive using unobtainium.

Still a sensor that's good for detecting things in deep space (in transit) would prevent all you stealth warfare scenarios as you'd see the bogeys coming in from a long way.

[Aardwolf]

Flaser, did you miss the part where a Sathanas would be smaller than a pixel, when it's only as far away as the moon? And that's something as large as a Sathanas, not a fighter or a missile.

[headdie]

not to mention once detected you need to identify the object as friendly, hostile or neutral and IFF transmissions can be faked/copied.

[BengalTiger]

Alright, since noone figured out how warm an Oscar would be to get rid of excess heat, I volunteer to spend the next few (dozen) minutes half hour to calculate it. I never did anything like this, so if I make a mistake anywhere- be sure to point it out.

The Oscar SSN has 2 pressurized water reactors, delivering about 73 000 kW each (shaft power). The highest efficiency for such a reactor is 32%. So running at full power, it'll deliver some 228 MW, of which 155ish is lost as heat, radiation, etc (let's say it's all heat to make stuff easier). If the ship's running without powering up it's nuclear rocket motors, let's assume the reactors run idling at 10% power. So that's 16 MW of heat per reactor.

So both reactors give a total of 32 MW of heat. Let's say the crew doesn't make enough energy to change the final result too much, so this is all the power that has to be radiated to space to keep our boat from overheating.
Now let's assume that the whole side surface of the ship is one ginormous radiator. The ship, as described a few posts earlier, is 154 m long, has a dia of 18 meters. That makes it's circumference around 18*3.14= 61 meters.
The total side surface, therefore is 154*61= 9394 m^2.

So we need to lose 32 MW in 9394 m^2. That's 3.4 kW per sq m.

Now, to figure out the black body temperature of our tub-of-war, I'll go ahead and use the Stefan-Boltzmann law, which states that the total power emitted from a black body (per square meter); known from now on as j is equal to the temperature^4 multiplied by the Stefan–Boltzmann constant, or sigma.

j= σT^4.
j= 3.4 [kW/m^2], σ= 5.7x10^-8 [W/(m^2*K^4)]

Therefore:
T= (j/σ)^1/4

T=(3.4/5.7*10^-8 [(1000*W*m^2*K^4)/(m^2*W)])^1/4
T=(3.4*10^8*1000/5.7)^1/4

T=494 K
Pretty dayum hot (especially when the reactor will have to run hotter than the coolant to give energy to it), and it shows how far we are from realism in our SWAGs in this thread.
It also shows that a 30% efficiency nuclear drive would totally suck on a space warship, unless it's OK to be detected pretty far away.

I'm also pretty sure that this ship would go 'below radar' for much longer than a Sathanas at nearly 300 K, so you'd really need a whole army of many thousand telescopes watching the sky to find it.

Now let's shut down the sucker completely. This time we have 100 crew members, each generating probably 500 watts of heat when sprinting from one end of the boat to the other.
That's 50 kW for 9394 m^2, or just over 5 W/m^2. The d00ds on wikipedia say that's below 100 K. If the crew drops to 50, and they sit around making 200 watts, the boat would only need a few dozen K outside to keep from overheating, making it a much harder target to find than the 280 K that was expected in the texts about no stealth in space.

Now let's assume the nose cone gets totally insulated by a few yards of aerogel (and it could, because we have a realistic temperature on the radiators on it's sides that keep it from overheating). Without a space based system of sensors, or the ship flying to Earth sideways, it's just a very small, cold asteroid.

Now I'll make the ship with a 2x larger outside surface, and make it look like a disc (with the 2 sides being front and rear; defining "front" as the direction it's traveling).

I'll put all the radiators on the rear half. They'll have the surface of an Oscar sub, and they'll radiate heat with a temperature of under 100 K with the reactor off, just like the earlier cigar shaped vessel. And just like the Oscar, it has enough cooling not to overheat.

I'll put several yards of thermal insulation on the front half (aerogel is pretty light) to keep it from overcooling. Because the radiators are on the @$$ and the temperature is stable, the front could emit no energy at all. If the logic is correct, I now have a ship which is stealth (in space) in the front.

Now try to find me before I get past you, activate, and attack.
Hell, without the Solar system being saturated in sensors, I could simply keep facing the Earth using thrusters on the rear side and remain invisible.

My warheads could be smaller versions of the ship, and they can also be launched facing Earth. They'd make it all the way to reentry without being spotted.

[General Battuta]

There's a lot of wishful thinking in there - but then again there's a lot of wishful thinking in the Project Rho calculations too. The truth is probably somewhere in between the two.

Your ship won't be able to get much of anywhere without giving its position away, but if it were launched from another rapidly moving object it might be able to coast in a stealthy fashion. Unfortunately incident solar radiation on the ship will render it thermally detectable inside about Jupiter orbit, so it better stick to the edge of the system. (Equilibrium temperature for a spherical blackbody around 1 AU is I believe somewhere near 300K).

The directional heat stealth might work at distances larger than that, though again the best the ship can do is glide.

You'd be best off ditching the crew. You could also get behind an occluding object, fire your thrusters there, and re-emerge gliding on a new vector.

[BengalTiger]

(Equilibrium temperature for a spherical blackbody around 1 AU is I believe somewhere near 300K).

True...
Earth's average temperature is 287 K. Mars has an average temperature of 210 K, and Pluto has 44- this will give a ballpark figure of how warm the side of the attacker facing the Sun will get, unless he/she/it/other is in a shadow or has a really high albedo or something. In that case it will be easy to attack- the defender's army of orbital telescopes will be far brighter than the attacker's fleet crossing Pluto's orbit. Even near Mars the attacker has a 100 K advantage vs illuminated objects orbiting Earth, and a sensor system covering the whole sky as far out as Pluto would require huge amounts of satellites (don't forget that all the data has to be processed). If they are insulated on the side facing away from Sol, they'd be just as invisible to the attacker as the attacker would be to them.

It looks to me that finding something in space isn't nearly as easy as it looks.

[Flaser]

Flaser, did you miss the part where a Sathanas would be smaller than a pixel, when it's only as far away as the moon? And that's something as large as a Sathanas, not a fighter or a missile.

No, you guys are the ones, who don't realize that for mere detection I don't need to get a "picture" at all, just a range, angle (~azimuth+elevation) and range rate. Sure, with a resolution of less then 1 pixel for freaking huge areas of space, my readings will suck - but that's fine! I've detected the bogey, I know *something* is there (I don't yet know if it's just a single source or multiple).

Even with only a single pixel to that whole area, the incoming reading will still flare compare to the environment, so I will get a definite reading that *something's* there.

Now I can slew my narrow angle targeting scope to the area and have a better look.