A Farewell to Traveller

[rust]

I believe that gravimetric sensors detect mass - is this right and are there any ways to hide from gravimetric sensors?

Current gravimetric sensors can detect tiny differences in mass, but they
still have a very low spatial resolution. Unless the object moves against a
background, like a submarine moving through water, it is very difficult to
detect. A submarine resting on the sea floor could probably only be detec-
ted if the sensor operator had very good data about this part of the sea
floor from previous measurements, otherwise it could hardly be distingui-
shed from a rock.

Once gravimetric sensors with a much better spatial resolution have been
developed, it would most probably require futuristic gravitics technology to
hide from them, as far as I understand it no current technology would make
it possible.

 

[DFW]

I'm a newbie in this respect. I believe that gravimetric sensors detect mass - is this right and are there any ways to hide from gravimetric sensors?

All I know about current mil ones in subs is that they aren't used to detect enemy subs at any decent range. In Traveler, no.

 

[Rick]

I'm a newbie in this respect. I believe that gravimetric sensors detect mass - is this right and are there any ways to hide from gravimetric sensors?

All I know about current mil ones in subs is that they aren't used to detect enemy subs at any decent range. In Traveler, no.

I didn't realise they were used to detect other subs at all - I thought they were used for navigation, as a replacement for GPS systems.

 

[DFW]

I didn't realise they were used to detect other subs at all - I thought they were used for navigation, as a replacement for GPS systems.

They aren't unless the sub is right under you... They also aren't used as a replacement for GPS really either. There are now even more precise inertial guidance systems in place. It can be used as an infrequent check against the inertial system.

 

[rust]

I didn't realise they were used to detect other subs at all - I thought they were used for navigation, as a replacement for GPS systems.

I do not think that the use of gravimeters for the detection of sub-
marines has already gone beyond an experimental development
stage, this would require that there is a secret military technology
which is far more advanced than the civilian gravimetric technology
used by, for example, the big megacorporations for their oil and na-
tural gas exploration. With what they have now the range would be
very short and an identification impossible, all the sensor operator
would know is that there is some object out there.

 

[GamerDude]

And another problem under the sea: Communication!

Radio does only work for a few meters under water or using stuff like ELF with a very low data bandwidth. Sound powered systems work within limits but are prone to influence from the environment and not up to data transfer either. Some laser coms should work (Blue/Green IIRC) but laser is highly directional and "must hit the target" unlike radio that, even as a "directional" beam is a cone.

Unfortunately I have to repeat what I said about a year ago on The Traveller Mailing List.... ELF doesn't really work underwater (along with the entire lower bands). This was proposed by a long time"GURPS Traveller" expert as a way to set up an "internet" on total water planet but I provided much more for him.

Here are two links and a quote
Radio Wave Propegation

Wikipedia on ELF

Military communications
The United States Navy utilized extremely low frequencies (ELFs) as radio band and radio communications. The Submarine Integrated Antena System (SIAS) was a research and development effort to communicate with submerged submarines.[9] The Soviet/Russian Navy also utilized ELFs for submarine communications system, ZEVS.[10]
Explanation

Because of the electrical conductivity of seawater, submarines are shielded from most electromagnetic communications. Signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data transmission rate of a few characters per minute and, to a lesser extent, the one-way nature due to the impracticality of installing[dubious – discuss] an antenna of the required size on a submarine (antennas need to be of exceptional size for the users to achieve successful communication). Generally, ELF signals were used to order a submarine to rise to a shallow depth where it could receive some other form of communication.

Difficulties of ELF communication
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. This is because the antenna must be at least a substantial fraction of the size (in at least one dimension) of the wavelength of the frequency of the EM waves. Simply put, a 1 Hz (cycle per second) signal would have a wavelength equal to the distance EM waves travel through a given medium in 1 second. For ELF, this is very slightly slower than the speed of light in a vacuum. As used in military applications, the wavelength is ~299,792 km(~186,282 mi) per second divided by 50–85 Hz, which equals around 3,527 to 5,996 km (2,192 to 3,726 mi) long; by comparison, Earth's diameter is around 12,742 km (7,918 mi). Because of this huge size requirement and, to transmit internationally using ELF frequencies, the earth itself must be used as an antenna, with extremely long leads going into the ground. Various other means are taken to construct radio stations with substantially smaller sizes, such as electrical lengthening.

 

[rust]

While a VLF/ELF communications network between sea floor habitats
(not vehicles) would technically be possible, it would be a truly stupid
idea: The data transfer would be slower than morse code, and for less
money than the cost of one antenna system a fibre optics cable could
be laid between two habitats, providing a far better and far more re-
liable data transfer than any kind of radio system could do.

 

[DFW]

The data transfer would be slower than morse code, and for less
money than the cost of one antenna system a fibre optics cable could
be laid between two habitats, providing a far better and far more re-
liable data transfer than any kind of radio system could do.

Use Meson communicators

 

[rust]

Use Meson communicators

I was thinking of something more realistic, like for example
long range telepathy ... 8)

More seriously, this is a description of the US Navy's VLF an-
tenna array in Cutler in Maine:

Each array consists of six diamond shaped panels supported by 13 towers. The system was
designed to allow transmission by one array (single) or both arrays (dual). The central tower
of each antenna system is 304 m (997.5 ft) tall. It is surrounded by six 266.7 m (875 ft) tall
masts, placed on a ring with a radius of 556 m around the central tower. The remaining six
towers of the array are 243.5 m (799 ft) tall and placed on a circle of 935.7 m (3070 ft) around
the central tower.

And this for miserable 200 baud.

 

[far-trader]

Use Meson communicators

I was thinking of something more realistic, like for example
long range telepathy ... 8)

How about courier sharks (ala courier pigeons)...

...with frickin laser beams attached to their heads!!

:twisted:

 

[rust]

How about courier sharks (ala courier pigeons)...

...with frickin laser beams attached to their heads!!

:twisted:

Yep, blue-green laser cannons ... 8)

 

[Rick]

I like the idea of sea floor habitats - but realistically, I would think most of them would have surface stations above them. It would be cheaper to run a cable to a surface station and have the communications net be above the water.

 

[GamerDude]

While a VLF/ELF communications network between sea floor habitats

Dude I'm sorry but go read the articles on Wiki, then go read any five books on Radio Communications Theory. This is what I did for *twenty years* in the US Air Force.

The size of antennas needed for ELF/VLF AND the piss poor propagation those frequencies have through water, make them a non-starter.

Unfortunately at least within the Traveller community this idea of ELF/VLF for some kind of real communications keeps floating around, anyone reading the science knows it ain't happening.

Hate to say it but, it's true and you don't have to believe lil 'ol me.

 

[rust]

I like the idea of sea floor habitats - but realistically, I would think most of them would have surface stations above them. It would be cheaper to run a cable to a surface station and have the communications net be above the water.

Yes, this is how I handle it in my setting. It also has problems,
the cable has to be strong enough to withstand the surface wa-
ves and at the same time light enough to avoid self destruction
because of its own weight, but these problems can be solved.
The advantage of this system is that it can also communicate
with surface ships, aircraft, spacecraft and a highport in orbit,
while a network of sea floor cables can only connect the habi-
tats on the sea floor. A well settled water world would probab-
ly have both systems.

 

[rust]

The size of antennas needed for ELF/VLF AND the piss poor propagation those frequencies have through water, make them a non-starter.

This is why I called it technically possible,
but a truly stupid idea. :wink:

 

[E.D.Quibell]

I like the idea of sea floor habitats - but realistically, I would think most of them would have surface stations above them. It would be cheaper to run a cable to a surface station and have the communications net be above the water.

What's wrong with undersea cables along the sea bed? It's what we do for global communications now.

Best regards,

Ewan

 

[rust]

What's wrong with undersea cables along the sea bed? It's what we do for global communications now.

They are fine, but you need an additional system for the connection
with whatever is above the ocean surface (floating starport, ships,
aircraft, spaceships, satellites, orbital starport ...), sea floor cables
alone could not do that.

 

[BFalcon]

They could with tethered buoys that link the seabed network with commsat uplink? any "high" ground would be suitable in order to limit the length of cable. They'd be clearly marked on any navigational maps and possibly have "noisemaker" beacons strung onto the anchoring chain to provide an additional safeguard.

Communications would be the same as modern subs (not entirely sure of all the details, but they can communicate underwater, probably using the ELF systems) and any additional data uplinks would probably be possible either through surfacing and linking to the commsats or diving until you're in range of one of the "ground-net" uplink stations.

This could give you a good balance between "completely out of contact for any information" and "being able to get your players some relevent information without being too annoying".

 

[rust]

Tethered buoys work well, you just need a smart buoy which dives
a few dozen meters for a while when there is a storm on the surface
and the waves get too strong, and in the case of a long cable several
buoys along the length of the cable to reduce the weight.

Another idea the players developed for submarines are "message tor-
pedoes" which dive to the surface, transmit their message, wait for an
answer, and then return to the submarine to deliver it. This is more li-
ke an exchange of e-mails than real time communication, but good
enough for many purposes.

ELF (see above ^^) is not a good option, and in the case of submari-
nes purely a one way communication from the ELF transmitter to the
submarine, without an opportunity to answer by ELF. Plus, it is incre-
dibly expensive, for the cost of one antenna array you could build a
copy of the Eiffel Tower.

A theoretical option, one which I have not yet researched, is a hypothe-
tical ocean layer which could transmit sonar signals ("sonarcom") over
thousands of kilometers - whales are rumoured to use it, and marine
engineers are researching its use, but reliable data are difficult to find.

 

[BFalcon]

Can you send radio signals through water at all?

The trouble with sonar is the echos... it could easily scramble the data packets to the point where you could never be sure if the data you received was corrupted or not, even with error detection methods - especially with 100's of such communications going on. Used for an emergency "all frequencies, all units" SOS call would be suitable though...

The message torpedo is a good idea, but how does it find its way back to the right ship? I think they'd be better off not being lazy and surfacing. If nothing else, a ship-borne commsat buoy that they can raise the last few hundred metres or so would be a plan. You could use high-tech alloys or composites for the "cable", so would be secure enough... and could be used in any kind of storm.

You don't need the networked commsat to sink in the event of a storm, unless you want it to be unavailable to the players once in a while... a long enough cable that allowed a degree of drift would be enough to compensate for tides and wave amplitude. Remember that you'd probably have maybe a dozen such uplinks at most over the whole globe - some of which may well be on dry land (possibly built into a spaceport and/or an uplink to the highport), so it would be reasonable to place a 30-mile radius around it where no surface vessels may enter (or would need to be especially wary) and where even submerged vessels would need to be very cautious. For one thing, it introduces another hazard for players...

I do wonder if something like carbon fibre weave wouldn't be suitable for the cable "chain", to be honest... it wouldn't rust and if enough layers were used, would be incredibly strong, yet light. If you were to build air pockets into the design too, might be enough to make it (nearly) neutrally buoyant...? Otherwise you'd need to check on the chains regularly to ensure that they hadn't rusted.