Far Trader cargo/Freight manifest questions

[mike wightman]

Which is it?

IMTU or my opinion of the OTU?

 

[TheEngineer]

Hi,

regarding our "IR-beacon in the night":

I thought about that and finally decided to check it up.

What hull temperatures or overall emission (in W) would the audience suggest for a starship ?
Goal is just to evaluate the distance in which the radiation intensity of the ship drops fairly below background radiation or any values, which could be used for detection/location.

Regards,

Mert

 

[Anthony]

For an active starship: equal to power plant output, which is 250MW/ep for CT, a bit less for FF&S.

For a starship that isn't active: equal to solar flux, which is about 1400W/m^2.

 

[TheEngineer]

Hi,

thanks for rapid reply...

active Starship:
Dont You think a bit of PP output is used for something better than just to radiate away....

Guess most of the energy is converted to thrust in our magical thruster drivers.
Perhaps we should a apply a fraction of PP output as waste radiation.
10 % ?
30 % ?
What do you think ?

passive:
Would be analogous to a mean surface temp of 123 degrees celsius ....
Is that ok ?

Regards,

Mert

 

[Anthony]

Originally posted by TheEngineer:
active Starship:
Dont You think a bit of PP output is used for something better than just to radiate away....

For the vast majority of components, no; energy sent into them eventually turns into heat. Drives are an exception. However, RL power plants are typically not more than 50% efficient, which means waste heat = PP output. Still, go ahead and assume waste heat = 1/10 of PP output.

Would be analogous to a mean surface temp of 123 degrees celsius ....

No, because it's actually 1400W x cross-section, not 1400W x area. It's actually analogous to a mean surface temp of about 0C.

Going through some math, a typical 200 dT ship:
Cross-section: probably around 200 square meters.
PP output (assumes 2G): 1 gigawatt.

Apparent magnitude at 1 AU (spread over the spectrum)
When inactive: ~26
When active: ~17

Probable limits of detection: we could build a telescope today that can spot magnitude 26 objects, if we know where to look. Scanning the sky is much much harder, but asteroid watch programs scan large portions of the sky at magnitudes of 20-22, taking a week or so to scan the entire sky, and could probably reasonably be designed to scan down to magnitude 15-17 in an hour.

 

[mike wightman]

However, RL power plants are typically not more than 50% efficient, which means waste heat = PP output.

Shouldn't that be waste heat = 0.5x PP output?
The problems with this kind of analysis are:
we don't know how efficient Traveller power plants are, i.e. how much immediate waste heat is generated; we don't have any idea of how efficient the various ship systems, especially the grav plates, inertial compensators, and maneuver drive.
So maybe the best approach is to assume the power plant produces nothing but waste heat and calculate intensity versus detection range from that and then factor in efficiency.

 

[mike wightman]

Tiger, Tiger
"glowing" bright...

 

[TheEngineer]

Originally posted by Anthony:
...
Still, go ahead and assume waste heat = 1/10 of PP output.

OK.

</font><blockquote>quote:</font><hr />
Would be analogous to a mean surface temp of 123 degrees celsius ....

No, because it's actually 1400W x cross-section, not 1400W x area. It's actually analogous to a mean surface temp of about 0C.
</font>[/QUOTE]Just used Stefan-Bolzmanns law:
M = o x T^4
Thought You gave specific radiation M with 1400 W/m^2...
How did You calc the 0 C ?

Going through some math, a typical 200 dT ship:
Cross-section: probably around 200 square meters.
PP output (assumes 2G): 1 gigawatt.

So you are assuming 100 MW waste heat in active mode ?
This reminds my of a monster thread in the TML, where people wonder, how to get rid of these amounts waste heat...
Could you present the calcs for the following ?

Apparent magnitude at 1 AU (spread over the spectrum)
When inactive: ~26
When active: ~17

Probable limits of detection: we could build a telescope today that can spot magnitude 26 objects, if we know where to look. Scanning the sky is much much harder, but asteroid watch programs scan large portions of the sky at magnitudes of 20-22, taking a week or so to scan the entire sky, and could probably reasonably be designed to scan down to magnitude 15-17 in an hour.

Do You know, which areas of the spectrum are scanned for asteroid watch ?
I guess it may be difficult to differ between an asteroid/starship, even if you detected "something" out there. Perhaps a spectrum analysation would help...

Oh, and another question as You are dealing with stellar magnitudes.
Could You describe how to convert from specific radiation intensity W/m^2 to magnitude values ?
I used to work with W/m^2 or W/sr normally.

Regards,

Mert

 

[Anthony]

Originally posted by TheEngineer:

Just used Stefan-Bolzmanns law:
M = o x T^4
Thought You gave specific radiation M with 1400 W/m^2...
How did You calc the 0 C ?

Actually, I looked it up (the 1400 W/m^2 may be slightly off), but cross-section is typically 1/4 of surface area, resulting in a temperature of 71% of what simply applying the black body equation gives you.

So you are assuming 100 MW waste heat in active mode ?

Actually, no, I was assuming 1 GW, having forgotten what I was doing.

Could You describe how to convert from specific radiation intensity W/m^2 to magnitude values ?
I used to work with W/m^2 or W/sr normally.

You can't, as they aren't the same time of measurement. Last I did the math, apparent magnitude at a range of 1 AU is 39.5 - 2.5 * log10(watts); if you're using W/sr subtract 2.75.

 

[TheEngineer]

Hi,

thanks for the information so far.
Actually I am a bit upset about physics book authors, as I try to look up the max intensity of 2.7 Kelvin radiation.
I have got 4 pretty books, 1 says nothing about it and 3 present different data or unit combinations I have never seen before.
There is a awful creativity regarding unit definitions.

Right now I have:
- 10E-6 Wm^-2mm^-1
- 1.2 Wcm^-2sr^-1
- 400 MJy sr^-1 (Jy=Jansky= 10E-26Wm^-2

So could anybody give a hint, which one is correct ?

I would be glad for any help

Best regards,

Mert

 

[mike wightman]

This may be of some use:

the power radiated per unit area (intensity) of a black body is given by the Stefan-Boltzmann law

I = sigma x (T to the power of 4)

I is in units of W/m2, watts per square metre

sigma = 5.7 x 10 to the -8 W/m2.K4 (watts divided by the area multiplied by temperature raised to the power of four), this is the Stefan constant

The total power radiated by a black body P, or luminosity L, of surface area A is

P = A x sigma x (T to the power of 4), or

L = A x sigma x (T to the power of 4)

units, watts W

radiation flux, or intensity I, obeys the inverse square law

I = L/4.pi.r(squared)

The sun has a luminosity of 4 x 10 to the 26 watts. The intensity striking the Earth's atmosphere is 1.4 kW per square metre

One last thing, Wein's Law states that for a black body spectrum the product of peak wavelength (lambda) and temperature (T) is constant

lambda x T = 2.898 x 10 to the -3 mK

Hope this helps.

 

[TheEngineer]

Hi Sigg,

thanks for the references

Besides....shouldnt we create a new topic ?
E.g.: "Sensoring/Radiation" ?

Regards,

Mert

 

[Straybow]

Hey, I tried to get this back on topic…

 

[bromdenlong]

Yeah, I was surface navy. Our berthing situation wasn't quite as tight as those WWII troopships, but the Engineering berthing area on the USS Okinawa had the volume of a 4-car garage and held 130+ guys. The Marines we carried got packed in even a little tighter than we did, but they were on board for months, not years.

Originally posted by Despasian Cruesa:
</font><blockquote>quote:</font><hr />
...Still, there's probably a reason Traveller staterooms are so large (they're immense compared to sub quarters, and big compared to modern surface ships).

Ain't THAT the Truth!!
(says the Bubblehead who spent MONTHS in a 6x4ft living space)
and drawing on that experience...
my current PCs 'inherited' partial ownership of a Kelly/Victrix Sloop converted to cargo hauling. The staterooms have all been removed and replaced with double occupancy small cabins.
Hey, crew can rough it for meesly week...jeesh!

I'm also giving the fuel option a try this time around (reducing the Jump fuel by 1/2), for many of the reasons in this thread. I want the group to ADVENTURE, not spend half the evening crunching economic numbers.

So, the sloop with the fuel space converted to cargo, and other modifications to maximize cargo space becomes profitable. Especially since the Jump-4 capability of the sloop lets the group take advantage of the higher rates for priority cargos.
Being able to cover their monthly overhead in one or two trips, means they can make the occasional jump for 'adventuring' motives...like to check out the rumor of an Ancient artifact somewhere in System X's planetoid belt....

Yeah, I know some of the realism lovers will cringe, but I'm sacrificing some logistical nightmares for enjoyment of the game

Despasian </font>[/QUOTE]

 

[jasper]

I know what a far trader is but some one mention a fat trader and free trader. Is there any difference?

 

[far-trader]

The free-trader is a 200T J1 1G merchant ship, of which the far-trader is sometimes considered an upgraded version being 200T J2 2G.

The fat-trader is the term used for the the 400T J1 1G Subsidized Merchant ship, partly because of its shape and partly because of the perception that its owner gets fat from the government subsidy. In truth the fat-trader probably makes a decent profit and it's really the 600T J3 1G Subsidized Liner that is relient on subsidies.

 

[jasper]

Thanks found the free trader in the book last night. But always read as far trader.