Questions about sensors, comms, signals, etc.

[ochd]

More newbie questions, please:

- I had in mind that my players' ship had been bugged, such that it was secretly transmitting its location. Would such a thing be able to be picked up once the ship emerged from jump space (eg, from the scout base hundreds of thousands of kms away)?
- Which then raised the question, are starports able to detect which ships jump into their systems -- 100 diameters away? Further? (According to the core rulebook, ship sensors are only minimally effective, if that, at more than 50,000km range, but maybe that's just for starships.)
- What sort of things in space would interfere with sensors, comms transmissions, etc? Solar flares?
- And finally (for now): visual sensors only give minimal detail at very long and distant ranges. Is "enhancing" those images feasible? ie, the usual sci-fi trope where a computer is used to give a lot more detail to an obscure image.

Any advice gratefully received.

Thanks,

Dan.

 

[phavoc]

Since we are talking about distances in space, a ship's 'bug' would need some power in the transmitter if it expected to be heard - assuming nothing special on the receiving side. Space probes today are able to get away with very low power transmissions because the receivers are big, but more importantly they know exactly WHEN and WHERE to look.

It might actually be more clever to bury the 'bug' signal in the regular comm traffic. If the ship is trying to run quiet and has turned off it's transponder then it should detect the EM emission from itself. A laser/maser wouldn't be detected if you could shield the transmitter on the hull. Then again unless it knew exactly where to send the pulse, it won't get received either.

Jump flashes aren't really discussed in the books. Nor is the detection side. In other genre's, ships exiting hyperspace/jump space leave a signature, and the faster and or bigger the ship is when it leaves the bigger the 'flash'. Systems looking for ships coming out of jump should be able to use passive sensors to detect that - and larger (population wise and tech wise) systems would deploy more and larger passive detectors - if only for safety.

You may need to hand-wave some of the things here and come up with something you like. I have some stuff on jump flashes, but it's not complete.

 

[Jak Nazryth]

Pavoc took the words out of my mouth.
A bug small enough not to be physically noticed without a good Recon check, would use the ships own power and communications systems. Otherwise something that small wouldn't be able to get very far... possibly not even through the hull.
This isn't like many Sci-Fi movies where a button sized bug and instantly be detected many light years away.

That's how one of my players used to track a ship.
He did a computer hacking on a target ship and loaded a sub routine into the ships computer.
When the Astrogator entered the coordinates of it's next jump target, the sub routine would activate the comms system and send out a compressed burst just as the J-Drive would begin to kick in. The micro burst was designed to be obscured by the energy surge of the jump bubble, a fraction of a second before it formed.
It worked pretty well. The players were able to track the target ship for several systems until it lead them to the prize... "A secret base".

Anyway, that is one way to bug a ship.

 

[AnotherDilbert]

HG, p24 introduces two new range bands, Very Distant and Far. At Very Distant range sensor tasks gets more difficult (giving stealth a chance). At Far range sensor information is further limited.

I would assume a reasonable starport has at least as good sensors as good starship sensors. So they can see you, but not with any detail, just a blip on a screen, but they might miss you if you are stealthy. I don't think they can identify a ship, at least not at Far range.

I would assume that visual sensors already have enhanced the sensor feed as far as possible. You might get a little more detail with a really powerful computer?

 

[steve98052]

Physics can answer some questions for you. Angular resolution is proportional to the wavelength divided by the aperture. A smaller resolution is better, so smaller wavelengths and larger apertures (optical telescope diameter, radio telescope baseline, etc.) are better.

As a point of reference, the Hubble Space Telescope has an aperture of 2.4 meters, "sees" visible light (400 to 700 nanometers wavelength plus some infrared and ultraviolet wavelengths, and is rated at a resolution of about 1/10 arc second (which I think refers to green light, since it would be sharper in ultraviolet and less sharp in infrared).

If you aim the Hubble at a point 100 Earth diameters away, that resolution works out to about 620 meters, so anything smaller than that would be just as featureless point. To resolve details more sharply would require a larger aperture (or aperture synthesis), a switch to X-rays or gamma rays, or fudging laws of physics. Of those, aperture synthesis seems like the most plausible.

The other issue is that imaging a distant ship is only part of the problem. You also need to notice it against the background of stars, which can only be done by a collection of wide angle imaging devices -- and then it will only notice objects bright enough to be brighter than the noise in the system (including electronic noise in the sensors, dirt in the optics, and interplanetary dust).

When it comes to using advanced technology to get better at sensing things like that, the greatest advantage is probably that manufacturing gets cheaper, so you can install more sensors.

 

[ochd]

Thanks for the replies.

It worked pretty well. The players were able to track the target ship for several systems until it lead them to the prize... "A secret base".

That is actually one method that crossed my mind. So, where were the players relative to the target ship? When they followed the ship to the next system, how did they locate it before it jumped to the next system?

Cheers,

Dan.

 

[ochd]

HG, p24 introduces two new range bands, Very Distant and Far. At Very Distant range sensor tasks gets more difficult (giving stealth a chance). At Far range sensor information is further limited.

Ah, completely missed that -- I only looked through the various sensor suites in HG. That little boxed section answers some of my questions, thanks.

Dan.

 

[Condottiere]

Part of the transponder signal?

That would be more of a hack.

 

[Jak Nazryth]

Thanks for the replies.

It worked pretty well. The players were able to track the target ship for several systems until it lead them to the prize... "A secret base".

That is actually one method that crossed my mind. So, where were the players relative to the target ship? When they followed the ship to the next system, how did they locate it before it jumped to the next system?

Cheers,

Dan.

It was a kidnapping ring. The players investigate a missing CEO's kid that included a ransom note. After lots of role-play and skill checks, they made good progress, and determined that an old scout ship was being used to ferry high value captives off world. It was modified to include a brig. In any case, the players came up with the idea of how to track the ship. Since the system was crowded with thousands of ships coming and going, their ship was just "one of the crowd" but followed the scout at a distance (their sensors were better than the old scout) but close enough to pick up the burst communication. Then they simply went to the same system and finally located the scout ship and followed it at a distance to the hide out located in an abandoned mining station on a small moon. They returned to the original system, reported the location to the CEO who hired them, and eventually got paid for their work. A private merc unit jumped to assault the base. The players joined the fight, they were in charge of sneaking in and rescuing the kid napped victims while the merc unit took on the small but determined group of well armed pirates. They managed to rescue the CEO's kid, and several others being held for ransom. Got a good paycheck.

 

[ochd]

Got a few more questions:

- I was thinking of having a specialist "stealth" ship (the hull equipped with emissions absorption grid and stealth, as per HG pp12-13) sneak up on the players. Even with these hull options absorbing radar and lidar and disguising heat emissions, would it still be easy to spot at the shorter range bands using visual sensors, for anyone who was looking?
- If you have spotted a ship just on visual sensors, but not with radar, lidar, etc. then are you still able to target it with missiles?
- If such a ship was picked up on radar/lidar/other sensors, is it possible for the sensors to lose it again -- ie, would you make the players roll sensors checks periodically, or once successful is that it?

Thanks again.

Dan.

 

[AnotherDilbert]

The rules makes no difference between types of sensors, either you detect the ship or not.

In other words, stealth means making the ship difficult to spot in all EM spectra, visual and radar alike. A stealthed ship is probably non-reflective matte black in appearance, and quite difficult to see in space against the black background.

 

[AnotherDilbert]

- If you have spotted a ship just on visual sensors, but not with radar, lidar, etc. then are you still able to target it with missiles?

"If it bleeds, it can be killed"
Corollary: If you see it you can shoot at it...

- If such a ship was picked up on radar/lidar/other sensors, is it possible for the sensors to lose it again -- ie, would you make the players roll sensors checks periodically, or once successful is that it?

I would not make additional checks until something changed. If the target passed behind a moon or the range increased enough to make the task more difficult, it would have to be reacquired.

 

[ochd]

Cool, thanks for the advice.

Dan.

 

[simonh]

It’s very easy to misunderstand just how huge space is and just how tiny even the biggest ships are. For an example, the Apollo missions left 1 square meter reflectors on the moon so we could bounce lasers off them to measure the distance to the moon. The laser is beamed through a telescope to maximize it’s beam strength at long range. Even so, the beam is 7 km across by the time it reaches the moon. The reflected signal is a continent across. They have to run the experiment, continually transmitting the laser signal for many hours in order to pick up enough of the reflected signal to get a result. Detecting anything at planetary range, unless it’s planetary size or you already know where to look, is extraordinarily hard. The planet Neptune was only detected due to gravitational perturbation of the orbit of Uranus, and it's a gas giant.

 

[locarno24]

If you aim the Hubble at a point 100 Earth diameters away, that resolution works out to about 620 meters, so anything smaller than that would be just as featureless point. To resolve details more sharply would require a larger aperture (or aperture synthesis), a switch to X-rays or gamma rays, or fudging laws of physics. Of those, aperture synthesis seems like the most plausible.

Definitely. The biggest advantages of a TL12+ world is the ease of access to orbit and computing power; putting a few dozen networked sensor satellites to generate a virtual aperture baseline a sizeable portion of an orbit across is pretty easy with a couple of air/rafts and commercially available TL12 computing power.

The ability to field distributed, networked sensors (even if the individual sensor is no more capable than the one on a starship) is the biggest advantage of an 'emplaced' system, and means that most of the time, a starport has a much better 'look' into the surrounding system than even a high TL warship parked in orbit.

 

[steve98052]

The laser is beamed through a telescope to maximize it’s beam strength at long range. Even so, the beam is 7 km across by the time it reaches the moon. The reflected signal is a continent across.

The job is getting more difficult with time too, because the retro-reflectors are aging. NASA stopped its rangefinding, but two other organizations are still doing it. A couple of things that make it work are the precisely monochromatic nature of the laser light used and the extremely short pulses. That way, a narrowband color filter and a time-band shutter block all but the expected pulses of light.

The planet Neptune was only detected due to gravitational perturbation of the orbit of Uranus, and it's a gas giant.

Even so, Neptune is not difficult to see with binoculars if you know where to look. And Uranus is visible with unaided eyes in a good dark sky.

. . . Of those, aperture synthesis seems like the most plausible.

Definitely. The biggest advantages of a TL12+ world is the ease of access to orbit and computing power; putting a few dozen networked sensor satellites to generate a virtual aperture baseline a sizeable portion of an orbit across is pretty easy with a couple of air/rafts and commercially available TL12 computing power.

Computational complexity is the main reason we didn't get optical aperture synthesis until the late 1990s, even though we had radio aperture synthesis in the 1950s. However, the glass still needs to be there. It takes a bunch of telescopes to accomplish much with aperture synthesis, and they have to be positioned precisely to be able to measure the phase of the light -- and it still takes actual aperture to gather enough light to see dim objects.

So the short story is that if a ship comes in quiet, it will not be detected. One result is that an attack fleet doesn't really need coordinated jump. It can just jump into the system over the course of a few hours, leaving power plants on idle and maneuver drives off, then turn on the power when the admiral decides the time is right.

 

[ochd]

It’s very easy to misunderstand just how huge space is.

Ain't that the truth. Refereeing Traveller these last couple of months has been a good exercise in re-education

 

[ochd]

So, some more starship comms related questions, this time about a ship's ID:

- Assume a starship gives a call sign (Free Trader Beowulf) when it communicates with other starships, but also a more formal serial code and number (eg, the scout ship in High and Dry has SC000... or something). What kind of data would be available to another ship captain receiving that id (limitations of non-FTL transfer of information aside)? Make and model, I guess, but also current owner? registered crew? recent flight history?
- If a crew then wanted to change their ship's call sign, eg to avoid detection by the authorities, what kind of difficulty rating and timeframe would you give that? I'm thinking formidable (14+) but maybe even that is too easy.

Thanks again,

Dan.

 

[phavoc]

So, some more starship comms related questions, this time about a ship's ID:

- Assume a starship gives a call sign (Free Trader Beowulf) when it communicates with other starships, but also a more formal serial code and number (eg, the scout ship in High and Dry has SC000... or something). What kind of data would be available to another ship captain receiving that id (limitations of non-FTL transfer of information aside)? Make and model, I guess, but also current owner? registered crew? recent flight history?
- If a crew then wanted to change their ship's call sign, eg to avoid detection by the authorities, what kind of difficulty rating and timeframe would you give that? I'm thinking formidable (14+) but maybe even that is too easy.

Thanks again,

Dan.

I would assume starship transponders work the same way as ship transponders do today. There is something called AIS (Wiki entry here) that does something for ships. I believe the aircraft tracking version would be the same. See below for the data broadcast by AIS.

I don't see the need for registered crew, or flight history. The design of the Imperium, with it's multiple levels of independence preclude the idea that the state requires that level of details from all it's citizens all the time. If the Imperium were more autocratic and dictatorial then yeah, that might be more along the lines of what you would expect. Otherwise standard ship name, course, speed, & destination should be enough.

It gets me thinking, if a ship is in distress, are there going to be automated messages for medical emergencies, quarantine, hijacking, etc?

Data broadcast by AIS

An AIS transceiver sends the following data every 2 to 10 seconds depending on a vessel's speed while underway, and every 3 minutes while a vessel is at anchor:
The vessel's Maritime Mobile Service Identity (MMSI) – a unique nine digit identification number.
Navigation status – "at anchor", "under way using engine(s)", "not under command", etc.
Rate of turn – right or left, from 0 to 720 degrees per minute
Speed over ground – 0.1-knot (0.19 km/h) resolution from 0 to 102 knots (189 km/h)
Positional accuracy: Longitude – to 0.0001 minutes
Latitude – to 0.0001 minutes
Course over ground – relative to true north to 0.1°
True heading – 0 to 359 degrees (for example from a gyro compass)
True bearing at own position. 0 to 359 degrees
UTC Seconds – The seconds field of the UTC time when these data were generated. A complete timestamp is not present.

In addition, the following data are broadcast every 6 minutes:
IMO ship identification number – a seven digit number that remains unchanged upon transfer of the ship's registration to another country
Radio call sign – international radio call sign, up to seven characters, assigned to the vessel by its country of registry
Name – 20 characters to represent the name of the vessel
Type of ship/cargo
Dimensions of ship – to nearest meter
Location of positioning system's (e.g., GPS) antenna on board the vessel - in meters aft of bow and meters port or starboard
Type of positioning system – such as GPS, DGPS or LORAN-C.
Draught of ship – 0.1 meter to 25.5 meters
Destination – max. 20 characters
ETA (estimated time of arrival) at destination – UTC month/date hour:minute
optional : high precision time request, a vessel can request other vessels provide a high precision UTC time and datestamp

 

[AnotherDilbert]

- Assume a starship gives a call sign (Free Trader Beowulf) when it communicates with other starships, but also a more formal serial code and number (eg, the scout ship in High and Dry has SC000... or something). What kind of data would be available to another ship captain receiving that id (limitations of non-FTL transfer of information aside)? Make and model, I guess, but also current owner? registered crew? recent flight history?

I would assume the Imperial Internet (as cached by your local Library software) has more information available than currently. The only caveat is that the information might be months old.

- If a crew then wanted to change their ship's call sign, eg to avoid detection by the authorities, what kind of difficulty rating and timeframe would you give that? I'm thinking formidable (14+) but maybe even that is too easy.

IIRC, all ships in Imperial space are required to have an Imperial transponder that is quite difficult to tamper with.

It might be possible to steal some other transponder and have several transponders, but only one turned on, giving you several identities to choose from...