Re: Return to No Stealth in Space

On Tue, 18 Mar 2008 15:01:51 +0000 (UTC), jdnicoll@[EMAIL PROTECTED]
 (James
Nicoll) wrote:

>	The assumption is not only that there is no stealth in
>space but that the people involved aren't even trying to be stealthy,
>knowing as they do that it is a waste of time.
>
>	Assume a civilization over at Alpha Centauri. Recent
>simulation make it seem possible that one or more of the stars
>could have terrestrial planets in the habitable zones. Assume
>that the native of Alpha C have spread out across their system
>using rockets much like the UberFusion rockets of old time SF:
>One Gee Forever (or until they use up their reaction mass in 
>accordance with M/m = e^delta vee/5,000 km/s). 
>
>	Let's say that the largest rockets are about the size
>of an oil tanker. A quick back of the envelope calculation
>suggests that a 500,000 tonne ****p with a mass ratio of 4 and
>an acceration of 1 G [1] and an exhaust velocity of 5000 km/s
>might have a peak power output of 5^16 Watts (plus whatever 
>for ineffeciencies).

>	Could we spot this at 4.3 LY? Would we recognize it
>for what it was?
	
Well, an exhaust velocity of 5000 km/s suggests that we're
talking about a fusion rocket or something like that, which
would have an emission spectrum similar to starlight - lots
of hot hydrogen and helium doing its thing.

Detecting that anywhere in the vicinity of Alpha Centauri is
going to be complcated by the fact that there's something
lurking around those parts that puts out about ten orders of
magnitude more energy in a Form Very Similar To Starlight.

Can we sort one from another?  Hmm.  Coincidentally, a full
Earth will reflect ~5E16 watts of starlight, so spotting a
fusion-drive supertanker operating near Alpha Centauri would
be like spotting an Earthlike planet orbiting near Alpha
Centauri, and I'm pretty sure that's not something we can do
quite yet.


Possibly the greater doppler ****ft would make the fusion drive
easier to detect, but A: I doubt it would be enough and B:
someone with really good equipment would have to look very
specifically for that sort of thing, which is the sort of
proposal that gets your request for telescope time laughed at.

Though now I'm wi****ng I'd thought of that back when I had 
two mostly unrestricted weeks with a 2.3-meter scope and a
spectrometer set up for observing thruster plumes...


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