Changes from previous version:
-added small gas giants
-removed radar signature for gas giants (gas giants absorb
radar)
-added rules for minerology/"prospecting"

Executive summary:
Detection ranges in an empty hex for a "typical" sensor (PEMS-13, AEMS-11) are as follows:
 

Object		Passive Range	Active Range
200-m iceball		50,000 km	500,000 km
Small Gas Giant		100 AU	-----
(1 billion years old)
Small Gas Giant		3 AU	-----
(5 billion years old)
Large Gas Giant		3000 AU	-----
(1 billion years old)
Large Gas Giant		300 AU	-----
(5 billion years old)

Small military sensors (PEMS-13.5) multiply ranges by x3; big military or science sensors multiply range by x10. These imply that almost all large gas giants will have been charted by the Imperium but that small gas giants will often have escaped detection.
 
 
 

In more detail, here are signatures on the FFS2 scale for all these objects:
 

Object	Passive/Vis	Passive/IR	Active
Rocky asteroid	0.5	0	0.5
(habitable zone)
Rocky asteroid	1	1.5	0.5
(inner zone)
Rocky asteroid	-0.5	-2.0 *	0.5
(outer zone)
Rocky asteroid	-2.5	-5.5 *	0.5
(Oort cloud or empty hex)
C-type asteroid	0	0	0.5
(habitable zone)
C-type asteroid	0.5	1.5	0.5
(inner zone)
C-type asteroid	-1	-2.0 *	0.5
(outer zone)
C-type asteroid	-3	-5.5 *	0.5
(Oort cloud or empty hex)

* indicates that science-grade sensors get an additional +0.5 to detect these objects using passive/IR.

Rocky asteroids are greyish (albedo 0.2 - 0.3).
C-type asteroids are dark asteroids (albedo 0.05) mostly consisting of carbon compounds.
Comet nucleii and Kuipter belt objects roll 1d6; on 1 use the rocky asteroid values, on 2-4 use the C-type values, on 5-6 use c-type with an additional -1 to visible signature. (Ice exposed to cosmic rays becomes extremely dark.)
 

These values assume a 1-m radius asteroid. For larger or smaller asteroids use the following modifiers:

Asteroid Size modifiers:

Asteroid Radius	Passive/Vis	Passive/IR	Active
1 m	-2	-2	-1
10 m	-1	-1	-0.5
100 m	0	0	0
1 km	1	1	0.5
10 km	2	2	1
100 km	3	3	1.5

For people who want to do prospecting, a detailed mineralogical scan requires a second roll at the original detection difficulty, +2 difficulty levels for a non-science sensor, and 1 full 30-minute turn in which the sensor looks only at the target.

(In more precise DSR terms, scanning for minerals reduces the signature by 2 points and requires a roll on the usual detection table, at +2 difficulty levels for a non-science sensor. Note that the reduction of 2 points is usually offset by the tracking-already-detected target modifier (+1.5) and the scanning-a-single-arc modifier (+1.0))
 
 

Gas giants in empty hexes or Oort clouds use the following chart:

Object	Passive/Vis	Passive/IR	Active
Small Gas Giant	2	+3.5 *	**
(0.05 jupiter mass, 1 billion years old, empty hex)
Small Gas Giant	2	+2.0 *	**
(0.05 jupiter mass, 1 billion years old, empty hex)
Large Gas Giant	3	+5.0 *	**
(1 jupiter mass, 1 billion years old, empty hex)
Large Gas Giant	3	+4.0 *	**
(1 jupiter mass, 5 billion years old, empty hex)
Very Large Gas Giant	3	6	**
(5 jupiter mass, 1 billion years old, empty hex)
Very Large Gas Giant	3	+5.0 *	**
(5 jupiter mass, 5 billion years old, empty hex)
Brown Dwarf	3	8	**
(40 jupiter mass, 1 billion years old, empty hex)
Brown Dwarf	3	7.5	**
(40 jupiter mass, 5 billion years old, empty hex)

* indicates that science-grade sensors get an additional +0.5 to detect these objects using Passive/IR.

** gas giant planets and brown dwarfs have radar signature sufficiently low that they have not yet been measured from the Earth, and I'm not sure how to calculate them; in all practical circumstances the target would be detected visually or in the infra-red first. Some gas giants may have moons or rings (active signature +0.5 to +4.0) that will be detectable instead. (Roll 11+ on 2d6 to have reatined a moon, +1 for large gas giants and +2 for very large; roll 1d6/2 for the moon's active signature.)

Small gas giant numbers are extrapolations due to the lack of evolutionary tracks for objects below Saturn's mass.
 
 

Detection can be calculated using the Definitive Sensor Rules (available on the web or via email.) In essence, one adds the sensor sensitivity (from FFS2 or the conversion notes in the DSR) to the target signature and subtracts the range to calculate the "signal":

Signal = Sensitivity + Signature - Range + modifiers

and then compares to the following chart:

SIGNAL	active detection	passive detection
	task	task
<0	(target cannot be detected under any circumstances)
0	Impossible	Impossible
0.5	Average	Staggering (TNE: Formidable)
1	(automatic detection)	Average
1.5		Easy
2		(automatic detection.)

Ranges are taken from the following chart:

Range:				RANGE
km	BL Hexes	T4 name	T4.1 name	term
<=500			regional	8
<=1,600				8.5
<=5,000			continental	9
<=16,000	0			9.5
<=50,000	1-2		planetary	10
<=160,000	3-5	VS		10.5
<=500,000	6-16	S	far orbit	11
<=1,600,000	17-50	M		11.5
<=5,000,000	51-160	L		12
<=16,000,000	161-500			12.5
<=50,000,000	501-1600			13
<=160,000,000	1 AU			13.5
<=500,000,000	3 AU		interplanetary	14
<=1,600,000,000	10 AU			14.5
<=5,000,000,000	30 AU		outsystem	15
<=16,000,000,000	100 AU			15.5
<=50,000,000,000	300 AU		oort	16
<=500,000,000,000	3000 AU			17
	30000 AU			18
	100000 AU	1/2 parsec		18.5
		1 parsec		19
		3 parsec		19.5
		10 parsec		20

So, for example, a typical scout (Sensitivity=13.0) scanning for a rocky asteroid (passive (vis) signature = 0.5) at a range of 1 AU would have a signal of (13.0) + (0.5) - 13.5 = 0.0, for an Impossible task to detect the asteroid.

A labship with a science-grade PEMS-14 looking for old gas giants in an empty hex would have a signal of 14.0 (sensor) + 0.5 (empty hex science bonus) + 4.5 (signature with science bonus) - 19 (range) = 0.5, a Staggering task.

Remember the following modifiers to sensor sensitivity (taken from the most recent version of the DSR) based on sensor location:
 

Sensor Location	Passive/Vis	Passive/IR	Active
Inner zone	-0.5	-0.5	0
Habitable zone	0	0	0
Outer zone	0.5	0	0
Oort cloud/empty hex	1	+0.0 (normal)	0
		+0.5 (sci-grade)

(The full DSR also includes modifiers for long scans (1 day) and for scanning only a single arc, which if combined allow a +1.0 for taking 2 weeks to do a scan.)

© 1997 Bruce Alan Macintosh
html by Charles R Hensley