Sensors and Transponders
A strong argument for no sensors used in the official Classic Traveller rules points to transponders. By Imperial Law, transponders continually broadcast the ship's ID and relevant information. When a ship emerges from J-Space in a system, it's bombarded by contacts--all transponder signals broadcasting ID and current position.
Military vessels have transponders that can be adjusted to broadcast as if the Navy ship were another vessel or be turned off all-together. But, all civilian ships must incorporate a transponder that constantly broadcasts and cannot be switched off.
Of course, the military grade transponders find their way to the grey and black market, and they can be had for a price. The penalty for being caught with such a device is high and can include imprisonment or forfieture of the ship or both. One would think that corsairs with such a transponder would have an edge over the civilian traffic the pirates prey upon, but in actuality, the opposite is true. Modern sensors are good enough to detect a ship long before it's within any range to do much damage to a civilian vessel (accoriding to Classic Traveller rules, its easy for a civilian ship to detect out to one-half light second or 150,000 km), and if a ship approaches without a transponder broadcast, it is perfectly legal to blast that vessel from the sky. Corsairs have learned to be more crafty, either by broadcasting a false signal (which still doesn't overcome the the problem of sensor dectection range) or finding position on a vessel by hiding behind a moon/planet/asteroid/satellite in space.
There is another strong opinion posited by Classic Traveller players that, even with transponders that can be switched to silent mode, modern starship sensors will be able to detect other vessels just by the heat of their drives to a distance far greater than that of space combat (but this opinion conflicts the Detection Range listed under Classic Traveller space combat rules).
Either way, sensors and game statistics on sensors are moot. They're considered part of a ship's equipment, and are needed for various tasks associated with the ship. But, with all ships broadcasting position all the time, ship's sensors is something that doesn't need to be addressed. Classic Traveller assumes all ships are known and plotted on the gaming board when the starship combat scenario begins.
On the other hand, DGP has published sensor rules for Classic Traveller in their product
Grand Survey. If you can find this out of print CT item, it is well worth buying--every page stuffed with very useful information you can use in your game. Also look for DGP's companion publication
Grand Census. Together, they're two CT products that every CT GM should be able to reference for his game.
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Not that it would be that important to you, but in my game, I use both ideas above. I use the constant-broadcast transponder idea, and I use the DGP sensor rules on the rare occasions when sensor checks must be made. I find the two approaches quite agreeable with the Official Traveller Universe as well.
EDIT: Just to clarify. Sensors were not "omitted" from Classic Traveller. They were just deemed unimportant for space combat. See Book 2 pg. 13: Scanners, detectors, and sensors are mentioned, all as part of the bridge and basic starship controls. Sensor dectection range is listed on pg. 32 of Book 2.
1st Edition Traveller used different detection ranges than what is listed in 2nd Edition. You can view those detection ranges
HERE.
EDIT 2: Power Projection FLEET, a Traveller starship combat game, addresses the use of sensors in Traveller by stating this: "Space is vast, almost entirely empty and very, very cold (just a few degrees above absolute zero) such that even gases freeze solid. A ship's drives have to emit a lot of energy to provide any reasonable thrust, so the energy from a manuvering ship is very easy to detect against the super-cold background of space.
"Even if a ship turns off its drives, it has to maintain a reasonalbe internal temperature for its crew; it containst a power plant which has to power a lot of electrical equipment (life support, computers, etc.). These systems all emit heat (as a waste by-product) which must be shed from the ship to prevent it building up and cooking the crew. Even a carefully contructed 'stealthy' ship must find a way to get rid of this energy, and can therefore be detected using the advanced military sensors avaialable to Traveller ships.
"The problems astronomers have detecting potential Earth-impacting asteroids might make you think it's easy to hide in space. However asteroids are typically as cold as the space around them, vary enormously in how bright (reflective) they are, and current telescopes and their asocieted computers only allow us to scan limited sections of the night sky relatively slowly.
"Traveller ships have far improved sensor technology and computer processing power, plus ship sensors don't suffer the warping and attenuating effects of viewing space through a planet's atmosphere.
"In summary, in [Traveller], its is generally pretty easy to detect the presence of other starships and extact a fair amountof information as to the ship's type and status, based on its energy emissions."
