Sensors in space

Since the current topic of discussion is about distances in space (in
particular, the 100 diameter limit), I's like to pose another related
question: How do you handle sensors in space?

In combat, a sensor ops roll has a difficulty profile according to
whatever sensor array you happen to be using, modified by Sensor Ops
skill or computer model and range. The range DM is -1 per square (or
25000 km). That means that even with a Simple sensor ops task and a
model 9 computer, anything beyond 450000 km is invisible. Here's how I
arrived at that number:

	 Best dice roll:  12
	 Computer model: + 9
	 -------------------
			  21
	Number required: - 3
	 -------------------
	  Maximum range:  18 x 25000 = 450000 km
	   (in squares)

That seems totally unreasonable to me, especially when some of the
sensor packages have a Interstellar range.

Notice that any planet size 5+ can't even detect ships out to its 100
diameter radius (without the help of navigation satellites, etc). That
seems really bizarre.

I don't _think_ I've missed anything entirely obvious, have I?

- - - Iain.