Active scanners

[Jak Nazryth]

In the core book under Radar/Lidar, page 143, it states "If a ship is using active sensors, it is easier to detect (+2 DM to sensors checks) but detects more about its surroundings."

My question... does active sensors....
1) Give all other ships in the area a +2 for detecting the ship using the it's active scanners, but if they fail the role, do not realize that somebody out there is actively scanning?
or...
2) All other ships AUTOMATICALLY realize somebody is using active scanners, and then get a +2 for pin pointing the location of the scanning ship?

Followup question...
Page 144 core book lists visual, thermal, and EM, but they are not listed on page 108 so I'm assuming they come standard in all electronic sensor packages.

[locarno24]

1) Give all other ships in the area a +2 for detecting the ship using the it's active scanners, but if they fail the role, do not realize that somebody out there is actively scanning?
or...
2) All other ships AUTOMATICALLY realize somebody is using active scanners, and then get a +2 for pin pointing the location of the scanning ship?

If you pick up an active 'ping' it's pretty easy to back-track and get a bearing. However, any active scan must diminish in perceived intensity with distance (and assorted anti-detection games - frequency-hopping radar and lidar, very-short-duration pulse, etc, which I'd expect to see on a ship with stealth fittings) so there must come a range, or a level of background noise, where you don't 'hear' it.

Hence I'd go for option 1. Otherwise you have the question of 'what do you consider all other ships' - even things outside nominal sensor range?



Followup:

EM - at least EM that's not visual or thermal - is essentially RADAR/LIDAR, which as noted is universal.

Visual is....well....visual. There will be an external viewport or camera somewhere. As to thermal - never explicitely mentioned but the receive half of LIDAR is a sensitive trainable photometer (it kind of has to be), so it's not impossible that a sensitive IR camera might be part of the fit too.

[cetiken]

I would go with option 2. Mostly biased on my experience with sonar on submarines rather than any real knowledge of radar /ladar or or the rules.

[locarno24]

SONAR's an odd one, though - between thermoclines and the sea bed it's a lot easier to get echoes and refractions of sound such that you can't backtrack a contact to point-of-origin - it's just "out there, somewhere".

Radio, IR and Laser light through a vacuum are very much line of sight only things unless you're in some sort of refractive/reflective dust cloud or other bizzare phenomenon

[Jak Nazryth]

Since Traveller scanning ranges are so darned short, relatively speaking (the moon is extreme range) I think anyone "pinging" (sorry I'm at work and not looking at the book) at very long range+ (I think that is the longest range listed) and beyond you will not automatically notice but still get a +2 to detect the "ping". If a scanning ship is within the listed ranges, then you automatically pick up the "ping" and get a +2 for locating the ship actively scanning.

[phavoc]

As far as I know, the use of active radar/scanners should make you appear like a beacon at a greater distance than your scanners will work. Passive scanners have a much greater range, but the active scanner will tell you what is lurking in your immediate range.

But when it comes to space and the potential distance that sensors can be actively acquired, well, I don't have an answer for that. Plus the fact that space is full of background radiation and other things that can affect detection ranges... Guessing, I would say that passive sensors have 2-3 times the range of active sensors.

Of course active radar will give you better warnings and detection of inbound missile attacks, and ships and all that fun stuff.

[locarno24]

Guessing, I would say that passive sensors have 2-3 times the range of active sensors.

Certainly, a passive sensor can detect an active sensor at ~twice that active sensor's range (because the energy in the 'ping' must be able to travel out and the 'echo' back if it meets something, so if it doesn't it can travel out and keep going - or remain detectable, which is the effectively the same thing)

[snrdg121408]

Hello all,

Detection of active sensor systems depends on the type of transmission method and frequency being used.

Detection of active systems using radio frequencies, lasers, and other similar energy depends on how they are being transmitted. An antenna rotating and transmitting in a 360 degree circle will be detected by passive sensors by everything with in range. Take the antenna and sweep in a 60 degree arc, then the ships closest will be able to detect which direction the active system is coming from. Ships outside the arc, depending how far to the side, may or may not pick up the transmission

Sonar on the other hand uses sound energy transmitted into a liquid medium. Under ideal conditions an underwater passive sensor in the water is turned and when the operator determines loudest noise can say the sound comes from the direction sensor is pointing. Adding other measuring devices and maneuvering the sensor platform can give approximate range. Of course, as a couple of people here mentioned, the physics of sound in water can cause the information to be wrong. The right salt density, temperature, and depth to the sea floor can make a contact 60 or more miles appear to be right on top of you. On the other hand different conditions make the contact sound further away when in fact it is on top of you.

Active sonar provides both an accurate range and bearing, unfortunately the noise also lets everyone know you are there and a bearing to look at. There are ways to minimize the detection, but someone, if they are awake, will know something is up.

snrdg121408 (aka Tom R)

[mattman]

Here's what we do: I made up my own rule for this at one time. It's made for some fun tension especially in wild space if they have a reason to need those extra DMs:

When passing through a system as part of the normal travel routine, the players have a choice of passive or active sensors.

The choice of passive is treated as normal and causes one roll by the ref on the Space Encounter table on p. 139 Core Rulebook as is normally done when transiting through system space.

The choice of active causes one roll by the ref on the Space Encounter table in addition to N more rolls by the ref on the Space Encounter table where N is the player-selected sensor die modifier. It can be a number 1 to 4. Players have chosen to "up the broadcast power" to improve the scan by picking this sensor DM to be from +1 to +4. Each extra DM is a roll on the encounter table. +1 to +2 is safe for the sensors but +3 to +4 cause a hit to the sensors as they burn out should a difficult comms or engineering-electronics test fail.

Given that some of those encounters on the Space Encounter table are unavoidable, it gets a bit risky to do this

[snrdg121408]

Here's what we do: I made up my own rule for this at one time. It's made for some fun tension especially in wild space if they have a reason to need those extra DMs:

When passing through a system as part of the normal travel routine, the players have a choice of passive or active sensors.

The choice of passive is treated as normal and causes one roll by the ref on the Space Encounter table on p. 139 Core Rulebook as is normally done when transiting through system space.

The choice of active causes one roll by the ref on the Space Encounter table in addition to N more rolls by the ref on the Space Encounter table where N is the player-selected sensor die modifier. It can be a number 1 to 4. Players have chosen to "up the broadcast power" to improve the scan by picking this sensor DM to be from +1 to +4. Each extra DM is a roll on the encounter table. +1 to +2 is safe for the sensors but +3 to +4 cause a hit to the sensors as they burn out should a difficult comms or engineering-electronics test fail.

Given that some of those encounters on the Space Encounter table are unavoidable, it gets a bit risky to do this

Howdy Weasel,

To me a ship entering and/or transiting a system is normally going to be using active sensors to navigate. Ships and planes are using radar and communications equipment. There are two reasons why a ship may not be using active sensors which are

1. The systems have failed for some reason.
2. The ship is trying to avoid detection for some reason. An example might be the ship has been hired to run a blockade.

However your home brewed rules do appear to add a little extra something.

Thanks for the reply.

[Rusty_Unycorn]

Here's how I do it:
1) You have your transponder. All civilian ships have those active. It broadcasts your ship name and such.
2) If that's active, then why not have your sensors be active. It can get hard to find little pieces of debris in space on passives, and fixing damage is expensive.
So, merchants and liners are going to be running with active sensors. Warships are going to do that, unless they're lying in wait for someone. Pirates are almost never going to bring their active sensors up unless they have to.
Of course, this does bring up the transponder issue...

[far-trader]

Of course, this does bring up the transponder issue...

Well, it's a given that there is an off switch which merchants and other honest Captains can avail themselves of if needs dictate. Naturally the autolog will continue to record flight data and passive sensor readings, and flag the exception for review at the next decent port of call (Class A or B Starport or a base). If you're lucky the local inspector will find no criminal intent and stamp your exit visa. If you're not so lucky then they may find cause to impound the ship, jail the crew, bring charges, hold you over for trial, etc. etc... innocent or not

And naturally ships without transponders may still be detected, and will be treated as unfriendly. Any failure to follow directives of local defense forces will probably mean a quick death if the ship is a threat, or an expensive rescue if not.

Then there are the ship's (pirate usually) running faked transponders to worry about.

[Karl Tenh]

Funny thing is that transponders don't usually broadcast. They produce a response when they receive an interogation signal (usually from a radar pulse).

So a merchant ships is going to be running silent, not "broadcasting here I am" with an active transponder. If someone else pulses them, the transponder will squawk. At which point they should know that someone is actively scanning them and take a look themselves. If they see the other ship because of it's transponder, it's probably not hostile, since the navy, custom's and other civilian ships don't mind if their seen.

A pirate would be running dark, hoping that any return without a transponder pulse will be misinterpreted as space junk. Or they will be using a modified transponder code that squawks something else. A really crafty pirate will try and steal the custom's officials transponder code Of course, that's the reason that they use high end encryption for those types of things

[Captain Jonah]

I use active sensors giving a +4 to detect and a +8 to be detected though my detection table goes out to a light hour. I also give bonuses and penalties based on size, current drive power etc so you can detect people far outside OTU detection distances. Traveller makes detecting other ships a bit like wandering around in thick fog swinging a stick, by the time you find something you are about to bump into it.

In civilised systems Transponders are on all the time which counts as an active location beacon hence +8 to be detected, it tells everyone where you are and makes it easy to be found in emergencies of when the customs boat flies past. Having active sensors makes you no more detectable and a lot safer. Though this means active radar for civilian ships. Having active Lidar/targeting will get you a very quick visit from the SDBs.

Running without a transponder and then being detected on a patrol ships sensors gets you a visit from something well armed very quickly.