Re: Return to No Stealth in Space

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?

One factoid I recall hearing is that if the space shuttle's
engines (the ones on the orbiter itself, IIRC, not the boosters)
were operating out at the orbit of Pluto, we'd be able to see them
back here on Earth through telescopes. Say the shuttle's engines
emit 10^8 W worth of heat (rough estimate based on the mass of
the fuel and a burn lasting a few minutes), and all of that heat
ends up as radiation, then we have ~10^27 photons/second. A
1 m2 telescope would catch ~100 photons/s, which I think is
plenty, provided you have a high enough magnification to cut
the signal-to-noise ratio, and you know when and where to aim it.

Cranking similar numbers from your scenario, I get 10^36 photons/s,
and 10^3 photons/s in a 1 m2 telescope. The problem is that you've
got a star there as well. I think diffraction of the star's image
is probably going to produce so much background noise that you'd
never be able to pick up the signal from the ****p. I think it's the
same physics that prevents us from directly imaging planets orbiting
other stars.

This is all assuming visible light. If the thing emits copious
radio or gammas or something, then I think it's a whole different
ballgame.