Sensor Drone Design

Using GURPS sensor rules if missile are allowed to utilize stealth technology and emission cloaking they become effectively undetectable at anything resembling useful ranges. This is especially true of missile which use some kind of gravity drive system, such as the B/G Engine, which itself is not highly detectable, except using a gravscanner. Gravity emission masking, which is available at TL A makes even that method of detection ineffective.
The answer in the New Diasporia universe is the use of sensor drones. To detect stealthed missiles a sensor net, consisting of hundreds of sensor drones are deployed. Such nets are deployed as far forward, that is as close as possible, to the perceived threat.
The goal is to deploy a sensor array that missile will have to physically pass. Optimum deployment forces missiles to approach  the sensor drones at a range of no more than 10 to 20 thousand miles at least half a million miles out from the fleet. This will give almost 11 minutes response time for anti-missile launch. As for many of the game mechanics of New Diasporia I have pillaged freely from other GURPS science fiction space based games. The Sensor array Rules are based on the home brewed rules for GT Sensor Arrays by Kenneth Witt located at John G Wood's elv GURPS Traveller site.
As with all my designs I run against the GURPS 3rd Edition TL progression limits. For most technology GURPS assumes that items which are developed in a specific TL cost half as much in the next TL and weigh half as much. Two Tech Levels after their introduction they weigh a quarter as much and their costs is again halved. They may also become more effective. Beyond that no improvement is seen. As one can see in the case of many devices this is not reflective of reality. Computers are an excellent example. Moore's law seems to have no boundary. Room sized at TL6, PC size at TL7, cell phone size at TL8, perhaps pin size at higher TL's. The cost was reduced at an even greater scale.
Rather than limiting progression to two tech levels I allow progression to continue. Since New Diasporia TLA is equivalent to GURPS TL14 in many areas, for sensors designs I continue to reduce sensor cost, mass, and volume for every Tech Level until TL14.
On this basis numbers for TLA sensor systems are:

PESA	TL	Scan Rating	Range	Hex	Mass	Volume	Cost
	A	51	4.5M	450	46.875	1.25	75

AESA	TL	Scan Rating	Range	Hex	Mass	Volume	Cost
	A	51	4.5M	450	4.45	0.5625	1.22

Gravscanner	TL	Scan Rating	Range	Hex	Mass	Volume	Cost
	A	42	.45M	45	0.703125	0.225	8.0

Using the modified sensor rules there is a +3 scan if >100 sensor platforms are used. If 300 sensor drones are deployed to cover a band of space between the attacking ship and the defender then the mass, volume and cost will be spread over 300 drones. Additional cost of the drone will be the B/G engine, Nuclear Power Generator, three laser communicators and a robotic computer brain. Individual drones will have radical stealth and emission cloaking.
Each drone will have a PESA  2.08 cuft sensor package, costing P2500, a AESA 1.0 cu ft sensor package costing P40.75, and a Gravcanner .375 cuft sensor package costing P5.6. Scann ratings for the whole system will be PESA:54, AESA:54 and Gravscanner:45.
A roll less than 4 on 3x6d will result in detection of a single 500mm missile. Obviously if 100 missiles detection odds are rolled the chance that some of them will be detected is almost a sure thing. So much so that a roll isn't necessary. Because the net is dispersed ignore the scan rating limit of size+36. Its actual size will be greater than size+36, but since each drone must be detected separately (for targeting purposes at any rate) this limit is unimportant.
Such a sensor net requires a signal processing program in a complexity 7 computer in the control node. The node is usually a forward deployed fighter or battlerider, although it can also be a destroyer or destroyer escort, which have the further benefit of being able to deploy the sensor net themselves.