Re: [FT] Some thinking on sensor and operational level games

Per Varis Casus wrote:

> Spacecraft Imaged At Long Range
> Spacewatch imaged the Galileo Spacecraft on the night of November
> 28, 1992 as it made its second close flyby of Earth.	It was 8.06
> million kilometers from Earth 
> http://www.lpl.arizona.edu/spacewatch/other.html
> range: 26.87 lightseconds

Or about 8000 MY in FT terms, at 1000 km per MU.

Thanks very much for this link - it gives us the right
order of magnitude to be looking at.

This is with a 1.8 metre telescope, through an atmosphere,
using late 20th/early 21st century technology.

I think we can agree that detection is marginal, but
definite - and that even basic identification is not possible.
There's an object there. Of about the right size. Where
we expect Galileo to be. Had we not been expecting a spacecraft
there, I doubt it would have been recognised.

Things that would improve performance:
1a) No atmosphere when looking from spacecraft
1b) Technology 200 year advance
1c) Possibly larger aperture sensor
1d) No terrestrial vibrations (big trucks nearby, earthquakes etc)

Things that would degrade performance
2a) Possibly trillions of similar-sized objects, from decoy
balloons to pieces of wreckage, some of which would be set up
to look exactly like the target.
2b) Lower integration time ( ie less than 3 days )
2c) Possibly smaller aperture ( must scan entire sky, not just a
bit of it)
2d) Vehicular vibration due to thrust, people moving inside
in microgravity, non-rigid structure, thermal differences etc.

I reckon that 1a,1c,1d are cancelled out by 2c,2d pretty nearly.
That leaves 1b vs 2a, 2b. I have no difficulty believing that
sufficiently
good sensors could exist in 200 years to actually get a recogniseable
image of Galileo at that distance. To differentiate Galileo from, say,
Pioneer 10 which looks similar would be more difficult. To be able to
read the nameplate, which says "Galileo" rather than "Decoys R Us" is
more difficult still.

Had it been spray-painted black, it may not be detectable unless much 
closer.
Wrap it in rock-coloured tinfoil, and you'd have a really hard time
telling it from an asteroid.

So I'll just ignore the the problem for now, it's PSB. Maybe they cancel
out.

<intellectual honesty mode = OFF>
Galileo masses what, a few tonnes? Call it size 0.02.
It's actively emitting telemetry towards Earth, call it the same as
an active search sensor's counter-detection range (2000).
It's civilian (ie no attempt to hide it), so multiply range by 2. (4000)
It's previously detected (ie we expected it to be there), so multiply
range by 2 again. (8000)
So I'd expect us to be able to detect a spacecraft of about this size
as a faint, fuzzy blob of indeterminate size that can be identified
as a "possibly telemetry-emitting spacecraft" at about 8 million km.
Which we did. QED The System Works, and is a good simulation of reality.
<intellectual honesty mode = ON>

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