On Wed, Feb 24, 2016 at 05:57:56PM +1100, Greg Chalik wrote:
> We can spot very small objects very far away from orbital telescopes
> now though....

We can usually only detect moderately large, well-lit objects, when
they're close to us.

The sort of problem I presented requires the ability to scan the whole
sky down to about magnitude 41.  Hubble's limit of about 31 might seem
close, but it's an exponential scale which means that the starship's
sensors would need to be ten thousand times more sensitive than the
multibillion dollar HST at its most sensitive (with most narrow field
of view and longest accumulation times).

The light reflected from such an object would be so faint that each
square metre of sensors would receive only a single photon per week.
You would need many photons to establish that this wasn't just noise,
and likely at least dozens of such above-noise detections to correlate
the same 'hits' along its trajectory and determine that it was not
just a much more distant background object.  Meanwhile, also
processing and rejecting detections of most stars within about a
hundred million parsecs (about a hundred quadrillion of them).

I think it's impractical to expect that of rugged, portable starship
sensors, even at TL15.

- Tim