92 réponses à ce sujet

[Foofad]

http://www.projectrh.../rocket3au.html

Read, and be enlightened.

[JulianusApostate]

What really gets me, is you said "a nebulae". Nebulae is the latin plural of nebula.

[LZIM]

didymos1120 wrote...

Two, how many ships with mirror finishes have you noticed?  Sure, they all reflect light to some degree, but I can't think of one silver hulled classic SF style ship appearing in-game ever.  Three, you probably wouldn't want to be so reflective if you plan on fighting around plentiful sources of light: your lovely shining vehicle will make a lovely, stand-out target.  Four:  visible light ain't the only radiation a star produces anyway.

Actually the better ones. Have you seen Flight of The Navigator? It isn't just cool looking and highly efficient. It's reflectively and stealth like shape make it cool (cold) and as hard to detect because it is deflecting energy though in a broader spectrum like stealth arcraft would radar energy. But you can consider a ship like that being made of a meta material that can go from reflective to absorptive if they wanted to suck in stellar radiance or just ambient energy (for engines and power).

As far as our crappy space vehicles, it's a matter of requirements. Some things are highly reflective to keep humans and component safe from radiation from solar radiation and interstellar radiation, while others have paint on top of reflective materials. The point being you don't have black space ships that absorb star light and radiation and are insulated inside they would cook anything inside like an oven. Consider it like standing in bright sunlight on the top of a windless cold mountain top dressed in a thick black parka. The insulation keeps your heat in, for starters so you won't lose heat to the thin atmosphere very quickly, and the black surface absorbs heat and passes it though the insulation heating you up even more.

But the alternative to radiating energy, as I edited into my post, is that while you're flitting around in space you'd want to absorb as much energy as is practically possible instead of radiating it. 1. you'd be recharging your engine instead of carrying limited amounts of fuel, 2. absorbing energy instead of reflecting it makes you harder to see. The technology and practices in the game are extravagantly wasteful. I'd hope that any space faring humans eventually manage will be more practical, making use of inertia (if it's possible) or directing radiation, or EM in some way to manipulate local space (warp fields) without burning fuel or releasing ionized plasma (which is still a fuel).

So if anything being too highly reflective makes you a target. You'd have to absorb ambient energy and direct it inwards on top of energy from engines and weapons systems. So Mass Effect's combat scenarios aren't necessarily wrong, they are just ambiguous. If you're already in combat you obviously did the stealth part wrong and should stop doing it so you can fire more. In addition to becoming as reflective as possible, which you want in combat anyway which dumps the effectiveness of directed energy.. leaving mass and matter.. if you're sufficiently far away.. just move your ship out of the way (space combat is kinda stupid at long range on targets that have functioning engines and that are energy reflective). 

[LZIM]

didymos1120 wrote...
visible light ain't the only radiation a star produces anyway.

So, if you put an infrared lamp in front of a mirror.. would the material heat up?

That's a good question.

Reflective means reflective.

If you put laser light on a mirror.. would the material get hot? Compared to laser light on a black rock. Or again, infrared light on a black rock.

--

And besides the dumb matter slugs which this game seems to be so fond of.. missiles that can direct themselves and move faster than a ship so they can't just move aside were once the stapple of space combat themes (Wing Commander, Battlestar Galactica, Project Sylpheed). I don't really get why Mass Effect doesn't have them, but that point is moot since they don't have much space combat to speak of and none playable.

Modifié par LZIM, 22 février 2010 - 05:35 .

[Bob5312]

Flash_in_the_flesh wrote...

Space can't help you to cool down, only you yourself are passively emitting radiation.

Every body radiates energy thus passively reduces its temperature. I'm saying that space won't help you to cool down. Object can cool down only thanks to it radiating its own energy. There's no exchange of energy between objects because perfect vaccum is empty, its nothing in there, thus it's not an object. Vaccum is a perfect thermal isolator. It won't cool down any object, the object is cooling down itself by radiation.

Does vaccum has zero temperature or none? I guess you can call nothing something, thus zero is something yet there's nothing. This way we are back at the point of vaccum being or not being an object. In linked explanation there's a gas in perfect vaccum which radiated its energy to the point of absolute zero. This way vaccum achieved the state of absolute zero temperature but is it still a vaccum if there's a gas in it? Does the vaccum has zero temperature or the gas? Semantics and pretty fun discussion. Sadly it leads to nowhere.

Of course, there is no such thing in real life as a perfect vacuum, not even in the empty space between galaxies.  The entire universe is bathed in low-energy photons (called the cosmic microwave background, a remnant of the big bang) that for all intents and purposes functions as a gas with a temperature of ~2.7 K.  Even without this background radiation, there is still an energy associated with the vacuum due to quantum fluctuations; this cannot be removed, even in theory.  There is no way to ever get a system to zero temperature, in theory or in practice, ever.  You certainly can't do it by radiation: eventually thermal equilibrium will be reached at a non zero (though potentially very small) temperature.

Regarding what the codex says, I had assumed that the reference to heat dissipation being more difficult near a star was due to the incident radiation from the star dominating the energy loss due to 'black-body' radiation from the ship (ie, the ship absorbs more heat from the sun than it radiates).  I haven't actually done any calculations to see if this is reasonable, but as a rough guess:
 
Given that the solar constant is 1400 watts per square metre (the amount of energy per square metre per second incident from the sun at the Earth's surface), the surface of a ship would already be absorbing a great deal of energy from the star.  Given Stefan's law for the energy radiated by a hot body, for the ship to be in thermal equilibrium (for it to re-radiate the absorbed energy from the star) it must have a temperature of about 400 K (125 degrees Celcius, or 260 degrees Fahrenheit).  This is hot enought to boil water, and certainly hot enough to cook any crew inside without insulation and a heat dissipation mechanism.

This assumes the ship does not reflect any energy: if you paint it white you could probably drop this by a hundred degrees or more.  Nevertheless, the ship is already several hundred degrees hotter just by being near a star than it would be in deep space. 

We can't really go any further since we don't know how much heat energy is generated by firing the weapons, operating the kinetic barriers, and so forth, but it is not unreasonable to assume that this might be the dominant source of heat, and therefore have a significant impact on a ship's ability to stay in combat.

I have made a number of simplifying assumptions (fully absorbent ship, no other sources of energy, etc), but I don't think these affect the conclusions significantly.  Also, just looking up the temperature of the moon online puts it at 107 degrees celcius when in direct sunlight (the calculation actually holds for any object in direct sunlight in space) which fits fairly well with this estimate.  Presumably, the ship can manage this heat as our spacecraft do today, but firing weapons and other combat activities overwhelm the ship's ability to dissipate heat.

[The Demonologist]

This thread feels like nerd porn.



I love us.

[Locane256]

Delta426 wrote...
The difference between good, immersive science fiction and crappy star trek, is the science part.

Amen!

[didymos1120]

LZIM wrote...

didymos1120 wrote...

Two, how many ships with mirror finishes have you noticed?

Actually the better ones. Have you seen Flight of The Navigator?

 

Yeah, I have.  It also happens to not be Mass Effect, which is the subject of discussion... and which has a distinct lack of shiny silver ships.

Modifié par didymos1120, 22 février 2010 - 07:38 .

[Nemesis7884]

you morons! all can be explained by MAGIC! oh no...thats da...aaa sorry wrong genre

[didymos1120]

LZIM wrote...

didymos1120 wrote...
visible light ain't the only radiation a star produces anyway.

So, if you put an infrared lamp in front of a mirror.. would the material heat up?

That's a good question.

Reflective means reflective.

Yes, and A is A.  And?  Everything visible is reflective to some extent.  Some things reflect radar...some don't.  Some will reflect UV, others won't. Reflectivity, like much else, is relative. 

If you put laser light on a mirror.. would the material get hot?

Eventually, yes.  Unless it was a perfect reflector of that particular frequency, photons didn't also carry and transfer momentum, and quantum effects in general didn't exist.  It'd be a terrible way to heat something, but it would heat.

Compared to laser light on a black rock. Or again, infrared light on a black rock.

Compared to the rock, it would just take a very long time to hit a high temperature.  As to infrared: depends on what the rock was made of (this also goes for the mirror above).  Just 'cause it's black to visible EM doesn't mean it also absorbs infrared.  Plenty of materials can reflect infrared radiation.

And besides the dumb matter slugs which this game seems to be so fond of.. missiles that can direct themselves and move faster than a ship so they can't just move aside were once the stapple of space combat themes (Wing Commander, Battlestar Galactica, Project Sylpheed). I don't really get why Mass Effect doesn't have them, but that point is moot since they don't have much space combat to speak of and none playable.

Well, one, BSG 2003 also had "dumb matter slugs".  Most of the weaponry shown, either of the personal or ship variety, used shells and bullets.  Two, ME does have self-propelled weaponry:

Disruptor Torpedoes:

Disruptor torpedoes are powered projectiles with warheads that create random and unstable mass effect fields when triggered. These fields warp space-time in a localized area. The rapid asymmetrical mass changes cause the target to rip itself apart.

In flight, torpedoes use a mass-increasing field, making them too massive for enemy kinetic barriers to repulse. The extra mass gives the torpedoes a very sluggish acceleration, making them easy prey for defensive GARDIAN weapons. So, torpedoes have to be launched at very close range.

Torpedoes are the main anti-ship weapon used by fighters. They are launched from point-blank range in "ripple-fire" waves reminiscent of the ancient Calliope rocket artillery launchers (thus their popular nickname "Callies"). By saturating defensive GARDIAN systems with multiple targets, at least a few will get through.

As far as "missiles that can direct themselves and move faster than a ship" specifically...no, nothing is said about them (though missiles in general do, and are used, as can be gleaned from the Codex entry for GARDIAN systems, the Disruptors above, and all the missiles various people and machines shoot at you in the games). And I say, with fairly good reason:  if they move that fast, they don't really need to alter course.  No one could do anything about it if they just traveled in a line, but that's pretty much what dumb and cheap mass accelerator slugs do inside their effective ranges anyway.  Also, read that description above:  ship-borne kinetic barriers will repel stuff that isn't packing a lot of mass, so I could easily see missiles like this being impractical in terms of required eezo to counteract the mass during travel, or the reactor needed to artificially increase the mass of a smaller projectile being too large to make it worth bothering, or (partially or completely) defeating the purpose by virtue of adding too much plain old boring matter-associated mass to the weapon.  I see similar issues with an FTL capable missile that could pursue a fleeing vessel.  May as well just build a fighter or cruiser that can do the same thing as well as perform in other roles, and, more importantly, is reusable (seeing as normally vessels don't just launch, fly into stuff, and then blow up).  Not to mention all the problems involved in tracking and targeting things moving FTL, as those systems are still stuck with light-speed signals (again: all there in the Codex).

Modifié par didymos1120, 22 février 2010 - 08:33 .

[didymos1120]

LZIM wrote...

But the alternative to radiating energy, as I edited into my post, is that while you're flitting around in space you'd want to absorb as much energy as is practically possible instead of radiating it. 1. you'd be recharging your engine instead of carrying limited amounts of fuel

And to accomplish said recharge would result in yet more heat and so on and so forth.  So, the rest is moot.  Your ship would become an oven in fairly short order.

[RobbertDewulf]

Naughty Bear wrote...

I am slowly touching myself. I love it when you ladies talk dirty.

Jeez.

[Jewsapalewsa]

ImperialOperative wrote...

Here y'all, go edumacate yourselves.

OP, your arguaement appears to be inavalid according to NASA scientists. 
Follow this link

[khaos974]

There were several good explanation of the codex entry in this thread for eg Bob5312 is accurate, but somehow I feel that it is not clear for everyone.

There are two ways to transfer heat (as in Q), through any kind of radiation (yes, visible light and not infrareds only does heat off things) or through any kind of material. It is called respectively radiative heat transfer and convective/conductive* heat transfer.

Deep space or even a nebula (which has a very low density on reality) can be reasonably assimilated to a perfect vacuum. As such, any kind of conductive/convective heat transfer is equal to zero.

So any variation of temperature inside a ship** in is due to the quantity of heat it loses and it gains through radiative means. Let's look at the sources.

Gains : background radiation, internal sources (guns, power plants, general inefficiency of machinery)
Losses : black body radiation (simply put any material body emit radiation depending on its temperature***)
In a star system, near an inhabited planet the background radiation would in fact be solar radiation (~1400W/m^2 for Earth), in deep space with cosmic background radiation at 3K it would be 0.000005W/m^2****.

All other factors being equal, a starship heats up a lot faster in a battle inside a star system, so the codex is correct.

Finally, each piece of machinery has an energy conversion efficiency under 100%, whatever energy is lost (can't changed into a usable form eg movement for a car engine) is automatically converted to heat. Compare this heat with the black body radiation heat loss and you'll know whether you have to lose more heat or use a heater in your starship.

AND don't forget the NOTES.

*Conduction is the transfer of heat by direct contact of particles of matter and convection is the transfer of heat energy within a fluid or between a solid surface and a neigbouring fluid. For the purpose of this explanation they are grouped together. Space is indeed a giant insulator for those kinds of transfer, it is on the other hand a perfect conductor for radiative transfer.
**Inaccurate, I should write thermal energy, I just wanted to simplify. Same for the ship which is here considered as a closed system. Releasing ultra hot gases would be some kind of forced convection but not exactly.
***See Stefan–Boltzmann law
****Again Stefan–Boltzmann law, and the energy flux received should be corrected with the albedo, but it's not relevant in this case. And I did not pay so much attention to the units, if I am wrong tell me.

Modifié par khaos974, 22 février 2010 - 10:11 .

[Taiko Roshi]

Delta426 wrote...

Farkingrouse wrote...

Its only a game... calm down.

The difference between good, immersive science fiction and crappy star trek, is the science part.

+1. Well said good sir.

[D4rk50ul808]

I read this whole thread and still don't know if my Shepard needs to wear his snuggy in deep space or not, this did not help me at all.

[kelsjet]

Hopefire wrote...
you don't get crossover of heat across a vacuum

Riiiiiight. So I guess all that HEAT I feel on a warm summers day is in fact not coming from the SUN after traveling 8 or so light minutes through the VACUUM OF SPACE to the EARTH.
I must be making it all up, right?

/rollseyes

By the way OP, physics > you.

[Anacronian Stryx]

kelsjet wrote...

Hopefire wrote...
you don't get crossover of heat across a vacuum

Riiiiiight. So I guess all that HEAT I feel on a warm summers day is in fact not coming from the SUN after traveling 8 or so light minutes through the VACUUM OF SPACE to the EARTH.
I must be making it all up, right?

/rollseyes

By the way OP, physics > you.

No the point is that the heat you feel on a warm summers day would be several thousand times higher if the sun wasn't surrounded by a truly poor conductor of thermal energy - Vacuum.

Somebody mentioned Apollo 13 and that's a great example, The Apollo space crafts had no heating devices because they didn't need any, They were in the icy cold of space in a paper thin shell and all they needed was their instruments/computers running to give enough heat to survive, It was only when Apollo 13 started to shut down their equipments that they got in trouble getting cold. 

[Sgt Lindog]

interesting article that might help with this argument, while i know we are talking about space ships and not human bodies the principle remains the same:

http://imagine.gsfc....ers/970603.html

[guru7892]

If you can Overclock an intel i5 670 processor to over double it's clock speed and calculate 2^32 (4,294,967,296) digits of pi in under 6 seconds; you can find a way to dissipate heat in outer space after firing a laser cannon.



oh, and its the future...

[WrexShepard]

I think that they were saying that a battle in a solar system will heat them up faster due to being bombarded by solar radiation. They'd still be in a vacuum, but they'd heat up even faster.

[Vena_86]

Well, according to Mass Effect 2 you can take a walk in vacuum with nothing but a breathing mask, covering a part of your face. That is more problematic than a codex line imo...

[Tony_Knightcrawler]

didymos1120 wrote...

RinpocheSchnozberry wrote...
So how come the crew of the Apollo 13 mission almost froze to death?  Not trolling, honestly curious.

Because it was designed assuming certain levels of average power use, and therefore to shed heat at a proper rate for that level.  When they were forced to operate well below that normal level (i.e., use as little power as humanly possible) heat was being shed faster than it was generated, so the temperature dropped quite low.

Yeah. The heat generated by their bodies and the rocket was absorbed by the entire body of the rocket, which radiated that heat in infrared light. Little heat, big radiator. A human in a vacuum wouldn't suffer the same fate because his body would create heat faster than it would lose it.

Also, it probably has something to do with the fact they were leaking. You know, the whole gas pressure/temperature thing. PV = nrT

But I don't want to do that math.

[medlish]

Dr. Eric Christian...
But the thermal radiation is ALWAYS there, and that is what a spacecraft uses. To get rid of heat, you can point thermal radiators at the dark sky, and to warm up you can point at the Sun or Earth. The Sun warms the Earth through radiation, not convection or diffusion.

Near stars heat you up no matter what you do. Thus the codex is right.

Furthermore the way to get rid of heat are thermal radiators. So in space battles you would need massive thermal radiators pointing at dark sky to get rid of the heat.

[didymos1120]

guru7892 wrote...

If you can Overclock an intel i5 670 processor to over double it's clock speed and calculate 2^32 (4,294,967,296) digits of pi in under 6 seconds; you can find a way to dissipate heat in outer space after firing a laser cannon.

Yes, well, try that trick in a vacuum chamber and enjoy your new lump of fried semiconductor.