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 Post subject: Visibility of Ships
PostPosted: Sun Jan 21, 2007 10:32 pm 
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I was getting out of my car tonight and happened to see a couple airplanes flying overhead...

That got me wondering if a ship with an AVT style drive would be visible to the naked eye for observers on a planetary surface (when under thrust, and at an altitude equivalent to LEO).

Would it be? Under cruise thrust? Combat thrust?

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 Post subject: Re: Visibility of Ships
PostPosted: Sun Jan 21, 2007 11:02 pm 
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Jonathan Brase wrote:
I was getting out of my car tonight and happened to see a couple airplanes flying overhead...

That got me wondering if a ship with an AVT style drive would be visible to the naked eye for observers on a planetary surface (when under thrust, and at an altitude equivalent to LEO).

Would it be? Under cruise thrust? Combat thrust?


Assuming the drive plume is radiating in the visible light range, combat thrust would definitely be visible.

Cruise thrust probably would be.

Easy way to work it out - you can see the lights of cities on the night side of the Earth. The total drive output of an AV:T ship cruise drive is about 3/4 of a terawatt, which is more power output than NYC uses.

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 Post subject: Re: Visibility of Ships
PostPosted: Sun Jan 21, 2007 11:22 pm 
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Ken Burnside wrote:
...which is more power output than NYC uses.
And all in one place instead of spread out over however many square miles...

So equivalent to a dim star? Bright star?

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PostPosted: Sun Jan 21, 2007 11:23 pm 
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Well, it'd be the one that's moving...

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 Post subject: Re: Visibility of Ships
PostPosted: Mon Jan 22, 2007 12:01 am 
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Jonathan Brase wrote:
Ken Burnside wrote:
...which is more power output than NYC uses.
And all in one place instead of spread out over however many square miles...

So equivalent to a dim star? Bright star?


Well, the ISS is a dim star moving visibly across the sky.

This would be a VERY bright star moving across the sky.

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PostPosted: Mon Jan 22, 2007 1:14 am 
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Ken, you need to move somewhere with cleaner air. ;-)

Every time I've gone out to look at the ISS, it's been pretty bright - usually as bright as Sirius. Once or twice it's been brighter than Venus, they only explanation I have is that the sun must have reflected perfectly off the solar panels towards me.

Those of you who haven't seen the ISS with the naked eye, I highly recommend it. NASA has a page on their spaceflight website that calculates the viewing times and directions so you know when and where to expect to see it.

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PostPosted: Mon Jan 22, 2007 12:50 pm 
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Matt Picio wrote:
NASA has a page on their spaceflight website that calculates the viewing times and directions so you know when and where to expect to see it.


The page in question is here.


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PostPosted: Mon Jan 22, 2007 4:35 pm 
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0.75 TW of sun-spectrum light, at a distance of 1 AU, has an apparent magnitude of about 10. At a distance of 1,500,000 km, that becomes apparent magnitude 0. Cruise drives don't mostly produce sun-spectrum light, and a lot of energy goes directly into the exhaust, to it's more like apparent magnitude 0 at 300,000 km.

At a distance of 40,000 km (geostationary) it would be the third brightest object in the sky (after the sun and the moon). At a distance of 300 km (near earth orbit) apparent magnitude is -15, making it several times as bright as the full moon, and it will cast discernible shadows.


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PostPosted: Mon Jan 22, 2007 5:16 pm 
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I can see traffic control regulations taking into account as to when a ship is allowed to orbital burns.

Or when ships in orbit could create a spectacular light show for the holidays. An orbital Fourth of July celebration, for example. :D


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 Post subject: Re: Visibility of Ships
PostPosted: Mon Jan 22, 2007 5:47 pm 
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Ken Burnside wrote:
This would be a VERY bright star moving across the sky.


VERY bright!

Darn. Beaten to it by Anthony. FWIW I did some BOTE calculations of my own. So, just to add to Anthony's numbers, here are a few more...

These are for a Gen1 torch pulling 1g (0.852 TW Power Output - and I'm assuming this is all visible)

7.04 Km away it'll be as bright as the sun.

Here are some other samples distances and the object it'll be comparable to (with apparent visual magnitude in brackets):
5 100 Km Full Moon (-12.5)
213 000 Km Venus at brightest (-4.4)
465 000 Km Jupiter at brightest (-2.7)
820 000 Km Sirius (-1.47)
1 640 000 Km Vega (0.04)
1 950 000 Km Betelgeuse (0.41)
4 030 000 Km Polaris (1.99)
25 600 000 Km Naked eye limit (6)

So under combat thrust you could see it over 1/6 of an AU away with the naked eye.

Other Yard Sticks:
Distance Intensity Apparent Prose
m Wm-2 Magnitude Description
1 6.78E+10 -46.0 Too Close!
10 6.78E+08 -41.0 Still too Close
100 6.78E+06 -36.0 The other end of a Rafik's mast
1000 6.78E+04 -31.0
10000 6.78E+02 -26.0 About half as bright as the sun at 10 Km (half a hex)
100000 6.78E+00 -21.0 LEO
361000 5.20E-01 -18.3 ISS Perigee
437000 3.55E-01 -17.8 ISS Apogee
41640000 3.91E-05 -7.9 Geostationary Orbital Radius
35786000 5.29E-05 -8.3 Geostationary Orbit from Earth's Surface
384400000 4.59E-07 -3.1 In Moon orbit
1.5E+11 3.01E-12 9.8 1AU

As you can see, even combat in (low) orbit around the moon would be perfectly visible even in twilight, being brighter than Jupiter.

(Sorry the formatting hasn't held - it was all in neat columns!).

Simon*


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 Post subject:
PostPosted: Mon Jan 22, 2007 5:51 pm 
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Anthony Jackson wrote:
0.75 TW of sun-spectrum light, at a distance of 1 AU, has an apparent magnitude of about 10. At a distance of 1,500,000 km, that becomes apparent magnitude 0. Cruise drives don't mostly produce sun-spectrum light, and a lot of energy goes directly into the exhaust, to it's more like apparent magnitude 0 at 300,000 km.

At a distance of 40,000 km (geostationary) it would be the third brightest object in the sky (after the sun and the moon). At a distance of 300 km (near earth orbit) apparent magnitude is -15, making it several times as bright as the full moon, and it will cast discernible shadows.


Wow... So I suppose the sky would turn noticably bluer (I know that the full moon makes for a sky that is definitely less black than a new moon)... And it would be even brighter than the airplanes that originally got me musing on the subject.

How much would the exhaust stream radiate? Would most of the light come directly from the engine (in which case I could imagine that it might not be visible unless the angle was right), or would there be a glowing "contrail" (so to speak).

OK, what about combat thrust... If cruise thrust in LEO is brighter than the full moon, combat thrust must really be impressive. Any discernable heat effects? (I doubt it, but I had to ask). EDIT: OK, somebody answered the question about combat thrust before I even posted it....

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"I don't like your attitude."


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 Post subject:
PostPosted: Mon Jan 22, 2007 6:13 pm 
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Dan Glass wrote:
I can see traffic control regulations taking into account as to when a ship is allowed to orbital burns.

Or when ships in orbit could create a spectacular light show for the holidays. An orbital Fourth of July celebration, for example. :D


Which I suppose is why Winch says that you wouldn't have tramp freighters in such an environment.
I still think you could, but I think tramps, foreigners, and other ships whose captains or crews might not be considered entirely trustworthy would need to be routed off to stations well away from inhabited planets...

Speaking of which, what would the effects be (for both cruise and combat thrust) of aiming your torch straight at a planet and opening the throttle? (Other than putting yourself at the top of planet XYZ's Ten Most Wanted list).
I can imagine lots of radiation hitting the surface. Maybe some visible effects? I have a feeling the atmosphere would stop the exhaust from actually making it to the surface, but I don't really know enough about that...

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Co-pilot to pilot as their plane, half rolled over, hurtles toward the ground at a 45 degree angle:
"I don't like your attitude."


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 Post subject: Re: Visibility of Ships
PostPosted: Mon Jan 22, 2007 6:17 pm 
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Location: Dallas TX
Simon Hunt wrote:
Ken Burnside wrote:
This would be a VERY bright star moving across the sky.


VERY bright!

Darn. Beaten to it by Anthony. FWIW I did some BOTE calculations of my own. So, just to add to Anthony's numbers, here are a few more...

These are for a Gen1 torch pulling 1g (0.852 TW Power Output - and I'm assuming this is all visible)

7.04 Km away it'll be as bright as the sun.

Here are some other samples distances and the object it'll be comparable to (with apparent visual magnitude in brackets):
5 100 Km Full Moon (-12.5)
213 000 Km Venus at brightest (-4.4)
465 000 Km Jupiter at brightest (-2.7)
820 000 Km Sirius (-1.47)
1 640 000 Km Vega (0.04)
1 950 000 Km Betelgeuse (0.41)
4 030 000 Km Polaris (1.99)
25 600 000 Km Naked eye limit (6)

So under combat thrust you could see it over 1/6 of an AU away with the naked eye.

Other Yard Sticks:
Distance Intensity Apparent Prose
m Wm-2 Magnitude Description
1 6.78E+10 -46.0 Too Close!
10 6.78E+08 -41.0 Still too Close
100 6.78E+06 -36.0 The other end of a Rafik's mast
1000 6.78E+04 -31.0
10000 6.78E+02 -26.0 About half as bright as the sun at 10 Km (half a hex)
100000 6.78E+00 -21.0 LEO
361000 5.20E-01 -18.3 ISS Perigee
437000 3.55E-01 -17.8 ISS Apogee
41640000 3.91E-05 -7.9 Geostationary Orbital Radius
35786000 5.29E-05 -8.3 Geostationary Orbit from Earth's Surface
384400000 4.59E-07 -3.1 In Moon orbit
1.5E+11 3.01E-12 9.8 1AU

As you can see, even combat in (low) orbit around the moon would be perfectly visible even in twilight, being brighter than Jupiter.

(Sorry the formatting hasn't held - it was all in neat columns!).

Simon*


Actually, I think by the time you could take a measurement at a distance of 1 meter (assuming you survived, which... isn't likely), you'd already have been blown back a kilometer or so by the exhaust stream... So you'd measure the magnitude as equal to that at 1 km... :D

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"I don't like your attitude."


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 Post subject:
PostPosted: Mon Jan 22, 2007 6:23 pm 
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Jonathan Brase wrote:
Speaking of which, what would the effects be (for both cruise and combat thrust) of aiming your torch straight at a planet and opening the throttle?

Annoying the locals. Possibly some aurora-like effects. Nothing significant will reach the ground.


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 Post subject:
PostPosted: Mon Jan 22, 2007 6:44 pm 
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Anthony Jackson wrote:
Jonathan Brase wrote:
Speaking of which, what would the effects be (for both cruise and combat thrust) of aiming your torch straight at a planet and opening the throttle?

Annoying the locals. Possibly some aurora-like effects. Nothing significant will reach the ground.

Would there be any audible effects at ground level? I could imagine hot gas hitting the atmosphere at however many kps could create quite a noise, but I don't know if it would make it all the way to the surface. (it would be an awful lot of hot gas... I once did a calculation on a similar drive and got something in the "tons per second" range for mass flow...)

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"I don't like your attitude."


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