Eh at this point it's become painfully apparent that a) you wouldn't know the laws of physics if they bit you on the ass and b) there's something clearly wrong with you.

So, good luck with that.

Great yeah http://www.businessinsider.com...

There was no "them", only one point.

This is remarkable. You were the one who started banging on about interstellar distances (and then interplanetary for some mysterious reason), not me.

Not in the least, I'm arguing that the heat from the exhaust would have reached negligible levels by the time whatever miniscule amount of it got around the shield, mostly due to the vast majority of it being blocked by the ship and being blasted directly backwards. And as another poster pointed out to you, the exhaust isn't nearly as hot as some might imagine. In fact I was being wildly generous with a 3 kilometer radius shield, in all probability a few hundred meters would do just fine. And even at 6km across, at 1 million kilometers distance it wouldn't be visible to the naked eye if it was a speck of dust on the fingertip. Do you understand this?

Whatever background in physics you might have had, it's a pretty small angle of the sky by now, I would say.

And yet again nobody is talking about going from Earth to Mars except yourself. Not that that would be especially difficult mind you.

The reason I asked if you were a humanities guy is because this comes across as straight from the "how to bullshit convincingly " critical theory handbook, wherein one simply keeps throwing random barely related objections at a fact in the hopes that it goes away, also much favoured by creationists. You continually refuse to address the proper physics in the article that blew project rho out of the water (and having looked over that site there's a whole lot more rubbish in there, even the few bits that have been updated since 2004), and appear to be having some sort of meltdown.

So, good luck with that.

Who said I disagreed with them?

Not that readers need it pointed out, but Mars has mysteriously entered the discussion.

Argh. You're comparing an exhaust, which rapidly cools off in space and generally acts very differently to a laser, to a laser. I don't even know where to start with that one.

Right, yeah: http://www.businessinsider.com...

You keep using that word. It does not mean what you think it means.

jackiechanwtf.jpg

I did. It's up there, in italics, marked 5, Informative, with a link to the full article, my first response to your post.

I seriously have no idea where you're getting this stuff. At 1 million kilometers a ship with a 6km wide umbrella around its midriff would occupy about one eighth of the sky that Venus does when it's at its furthest from earth. That's the size of the dot you're saying is occluding everything behind it. That's the size of the dot with negligible differences from the background you're trying to differentiate.

Oh yes, there is.

There were two sentences out of dozens in that post that I actually wrote. You're ignoring all the others quite deliberately, because they show you're wrong.

It's like the terracotta army, except straw men.

So what you're saying is that from a million plus kilometers away, a ship with a forward profile of maybe a few score meters heading directly towards someone that isn't fixated on that miniscule segment of the sky, with a several kilometer wide umbrella to disguise the exhaust bits that weren't sufficiently collimated before they cool off and become indistinguishable from the background noise, especially at those distances, this ship will stand out like a sore thumb?

And that's before we even start talking about the way you don't need to burn thrusters until you're knocking on your target's door. No drag in space, remember?

Wow.

Our equipment can't even pick up large asteroids before they're a few days away. And they're light coloured infrared emitters moving on predictable tracks at a fairly staid pace compared to the clip our spaceships must be making in order to be useful.

That's right, it doesn't go out the front where the ship is heading. And the reason everyone in the ship isn't cooked to a crisp is because it's going out the back of the ship, away from our putative target. It doesn't magically shine through the ship like a lighthouse. You do understand this, right? Now put that together with the rest of the very simple concepts under discussion and the sun may yet rise.

No, as another poster memorably put it, "it's a painfully mis-organized page of RANTING QUOTES!!! mishandling and misattributing varoius claims." The article I linked to that you steadfastly refuse to address, that's physics.

Nope. I'm claiming it can be hidden across much shorter distances under circumstances which are broad enough to be tactically useful.

Yes, that heat the article that you steadfastly refuse to address, addresses.

You're not a humanities guy by any chance? I mean do you have any clue how small of a profile we're talking about here at these kinds of distances?

No, you're deliberately and obviously ignoring the article.

Actually the problem is you putting words in my mouth and then arguing with those words. The vast majority of the exhaust will be hidden by the ship only as long as it approaches a lone target dead on. The umbrella just gives a few degrees more leeway which decreases the closer you get to your target.

You are aware that insulators and light blockers don't need to increase in mass proportional to the source being blocked right? I mean otherwise you'd need more than four walls and a roof to block sunlight. The linear progression you envisage is grasping - a lot. Not to mention that it doesn't need to be perfect, just good enough to beat the enemy's likewise imperfect sensors long enough to get close enough to strike. Dull radiation is as good as no radiation if the enemy can't tell the difference, and don't forget about the distances under discussion here.

And off we wander down the garden path again.

Okay, so you didn't read the article. Maybe you should get on that.

It's alright to be wrong, you know. Just don't end up like a creationist or a feminist clinging fiercely to disproven articles of faith.

Not in fact a bad idea. Given that there's no shock wave in space and physically directly hitting a moving target like a ship would be all but impossible, one-shot lasers on missiles might just be the way to go.

Unexpected situations like an enemy starship might throw at you, you mean? :D Also I've a deep respect for the value of instinct and experience.

That latter bit wasn't part of the article, it was just my own addition. Even without shielding you can't see the exhaust through the rest of the ship. Adding an umbrella like insulator at the back of the ship would simply reduce the possibility of detection if you weren't coming at a target head-on, or if your maneuvering depended on your main thrust being adjustable in direction. And remember this is space, aerodynamics aren't a consideration. The umbrella could be many kilometers across and of a lightweight material.

You're really not understanding what's being said. What's not being said is that you can disguise an exhaust pointed at a sensor.

Space is notoriously empty of those, hence the name. Not to say it couldn't happen but I'd imagine it would be rare.

What heat beam, you've lost me. I'm talking about the ship's exhaust. The article is talking about the ship itself.

Ideally to stop them from being picked off at a distance you'd want to be able to deliver them at close to the target as possible, even a very fast rocket is going to look pretty slow in the vastness of space, and their visibility increases if they have to maneuver to match courses with a jinking target. The question is whether or not an autonomous drone AI can do the job any better than a human, taking into account things like information warfare and EMP pulses.

Well by deep space I meant "not in orbit around a planet". You could put the factories well inside the orbit of Venus.

Yeah but you might not want to nuke the planet, taking out military centres or something could be a preferred option.

I read a rebuttal to that which was fairly compelling: http://scienceblogs.com/builto...

The equation given isn’t derived. We have no idea where they’re getting that 13.4 proportionality constant. Dimensionally it’s correct, and it’s pretty easy to derive the equation up to that constant which will depend on the sensitivity of the detector. That equation modulo some uncertainty with respect to that constant is accurate as far as it goes given a spacecraft of hull temperature T and cross-sectional area A.

I would take you through the steps of the derivation, but it would be pointless because the assumption that the hull temperature has anything to do with the interior temperature is simply flat wrong. We can prove this with a potato.

Switch your oven to the “Bake” setting at a temperature of 350 F. After preheating, put in the potato. The interior of the oven, and eventually the potato, are maintained at a constant temperature of 350 degrees. How hot is the exterior surface of the oven? Depends on how well insulated your oven is, but I can guarantee it’s a lot less than 350 degrees.

The key is the understanding the relationship between heat and energy. Put hot coffee in a thermos – the hot coffee is hot because it contains thermal energy. If the energy can’t leave, the coffee will stay hot because the energy stays inside the thermos. The outside of the thermos stays at the temperature of the surroundings. Now neither the thermos nor the oven is a perfect insulator. Some energy leaks out of the oven’s interior, cooling it down. The oven thus has to pump energy into the heating elements to make up for this loss. Equilibrium is reached when the rate of energy being put into the oven equals the rate of loss through the insulation.

For a spacecraft in a vacuum, the pretty much the only way to lose energy from the interior is by radiant heat. The higher the temperature of the outside, the higher the rate of energy loss via radiation. But the temperature itself is irrelevant, since just like the oven and the thermos it’s not necessarily related to the actual temperature inside the cabin at all. It is always and everywhere a function of the total power passing through the hull. If the temperature inside the cabin is constant, the power leaving the hull by radiation is exactly equal to the power being generated inside the hull.

So how far away can we detect a given amount of emitted power? According to Wikipedia, a telescope of 24 aperture can detect stars of magnitude 22 after a half-hour exposure. I think this is a pretty good realistic limit for detection with reasonable equipment in a reasonable time frame. Now we need to compare this magnitude to something of known power output. How about the Sun? The sun has magnitude -26.73 as seen from the Earth’s surface (smaller magnitude is brighter), for a difference in magnitude of 48.73. The exponent used for magnitude is 2.512, so the difference in power per unit area of telescope is 2.512^48.73 = 3.1 x 1019. Since the Sun radiates about 1000 watts per square meter at the distance of the earth, the smallest radiant power we can reasonably detect in our telescope is about 3.123.1 x 10-17 watts per square meter.

Our hypothetical spacecraft is radiating that power into space, evenly distributed over the surface of a sphere of radius r, where r is the distance to the detector. When that power-per-area is the same as the limit of our telescopic capability, that gives us the maximum detection range. Mathematically,

Where rho is the sensitivity of our detector. Solve for r:

So what’s the power? Well, each human on board is going to produce about 100 W just from basic bodily metabolism. Computers, life support, sanitation, and all the rest will contribute more. We might assume 10,000 watts total for a futuristic ship that’s specifically designed to emit as little power as possible. It might well be significantly lower. Plugging in, I ger r = 5.98 x 109 meters. This is pretty far, but it’s only around 4% of the distance from the earth to the sun. Practically nothing in terms of solar system distances. Even a ship dumping a megawatt of power should only be visible from a third of the earth-sun distance.

The reason for this divergence in our estimate versus the Project Rho estimate is that it takes a huge amount of energy to maintain a hull exterior at cabin temperatures. But insulation means that’s not necessary, all that’s necessary is that the power out equals the power generated in the interior.

And of course the engines can only be noticed if they're pointed vaguely in the direction of observers, otherwise the whole exterior hull would be the same temperature as the exhaust. It could be shielded reasonably well, even if you're stuck with elderly chemical engines.

Does it really matter how fast your tactical computer is when the bottleneck in performance is material limitations? A ship can only go so fast, change direction so quickly, and so on. The real problem with human pilots will be their inability to withstand enormous g-forces that a machine would shrug off, this gives automated drones a major advantage tactically speaking.

Kind of OT but I believe that Andromeda managed to depict laser small arms reasonably accurately also. Space battles needn't just be between space ships!