The Slow Speed of Light

[Supplement Four]

One thing I've noticed with some Traveller players is that distance is not accounted for with communication. We forget that communication, in the game, travels at the speed of light. Therefore, with the distances typically involved in the game, there is usally a time delay between messages.

Sometimes, this is a few seconds. And, sometimes this can be hours--depending on the distance involved.

A ship exits J-Space, for example, and then makes contact with the starport. Well, if J-Space exit is just at 100 diameters, then communication is probably instantaneous. But, when a ship makes an in-system voyage, or has to exit J-Space a great distance from the target world, or is traveling through an asteroid field, then most likely there will be some time delay when communicating at a distance.

Crafty GM's can use this as a heck of a drama-laden device. :devil: Especially, if the GM wants to somehow isolate the players.

A device I've used in the past is to have the PCs in jeapordy (during an emergency, or a pirate attack, or something of the like), and be in contact with the starport, able to see the good guys with the sensors.

For example, the PC's are in-bound some great distanct to the main world when they are set upon by a corsair vessel. As the PC's ship is disabled and boarded, the PC's are in constant communication (with appropriate time delay, of course) with the starport.

The problem is: The starport is too far away to do anything about it. All they can do is watch!

Heck, the starport is probably recording the transmission. They see who the corsairs are--they just don't have a ship that can make it to the spot in time to save the PCs. Even at 3Gs, it may take hours to reach the PCs, depending on distance.

I've also done the reverse: Had the PCs witness a pirate attack or some disaster on scanners, but the data is hours old. They acutally witness the attack, but, in this scenario, it is they who can do nothing about it. Even at full G thrust, the corsairs would be long gone before the PCs could arrive.

It can be a clever and intriguing push or pull for an adventure.





Another, semi-related, idea I've used in a game before happened in my last Traveller campaign. The PCs had entered an asteroid system and were fell upon by the bad guys. One of the players asked if there were any other ships on the scanners. Sometimes, I'll let this type of thing be reflected by chance, as I did that time, allowing the player to roll higher dice to see if the scanner showed a close ship.

Yes, there was a ship! But, then I figured if the ship was traveling towards the starport (in which case it might be able to help the PCs as it would be around the same velocity, depending on the vessel's M-Drive). As fate would have it, the ship was coming from the starport, down the space lane corridor, to exit the asteroid field and make jump. These asteroid contained a particular radioactive ore that interfered with Jump process (a -1 on the roll for misjump...not much, but enough to keep ships clear of the field when jumping).

Long story short, the ship was heading in the opposite direction, and since the PC ship was on one end of the journey, the random ship was actually slowing down (past the trip's mid-poing and decelerating).

I figured it's speed...and it was moving too fast to do anything to help the PC's! I figured it would be in range for two space combat turns (about 30 minutes), and that's all.

That was kinda cool--a very neat session. The PCs were in dire need of help. They were outgunned and being boarded. And, this ship flys by with the ability to help--yet there is nothing it can do because it cannot change vectors fast enough.

The ships passed each other in the night. One in need of help, and the other wanted but unable to affect help.





One other thought on this: I wonder about sensors. I mean, if a ship is on a long in-system journey--say, from Saturn to the Earth--that ship is hooking 'em. It's moving. Even at 1G acceleration, it's average velocity on this trip is quite high.

Moving at that speed--how effective are sensors? The ship is certainly not moving anywhere close to the speed of light, but it is moving at quite a speed. And, it will take hours to effect a vector change.

Say a piece of space debris is in the way--will be in the way as the ship and the rock's path intercept.

First off, the ship is at point A, sensing out to point B. The rock is at point D, and the ship and rock intersect at point C.

A=======================B=====C=====D

Because the ship is moving so fast--can sensors keep up with that kind of speed?

 

[aramis]

1G (OTU G) = 10.m/s/s
1 hour = 3600.s
1G-Hour = 36000m/s/s = 36.km/s/s
C (OTU) = 300,000.km/s
1 G-Hour = 0.00012 C
a G-Day is 24 Ghours... or 0.00288 C (actually, less, as time dilation starts to be measurable. Or 0.288PSL

Not enough to seriously deter sensors. You'll get some NICE doppler shift....

keep in mind: Bat sonar routinely tracks objects up to Mach 0.07 or so 50MPH dragonflies can be tracked by bats.

 

[Icosahedron]

I don't think S4 was talking about sensor distortion, just asking if by the time you've detected a lump of rock in your path, it's too late to avoid it - like driving too fast in fog.

I can't be bothered doing the calculations just now...

 

[Supplement Four]

I don't think S4 was talking about sensor distortion, just asking if by the time you've detected a lump of rock in your path, it's too late to avoid it - like driving too fast in fog.

Exactly. On a journey from Saturn to Earth, there's a rock that will get in the path. This rock is 7/8ths the distance to Earth.

Acceleration to mid-point. Deceleration to end-point. the ship will be decelerating and really have no real means of maneuver. It will take the ship hours to make a vector change.

How does the ship avoid the rock? How does the ship detect the rock from the distance at the beginning of the journey (at Saturn) so that it can plan around it?

My point: Once a long, inter-system journey is launched in Traveller, there is no way to make vector changes. Not quick ones, anyway. How good are sensors? Can they detect cold rocks 7/8ths the way to Earth from Saturn? If not, do starships just rely on the vast emptiness of space each time they make an inter-system journey? The few times something like that happens, it's just chalked up to un-avoidable accidents?

It seems to me that, by the time the sensors detect the rock, the ship will not be able to maneuver out of its path in time to avoid it.

 

[Gadrin]

One thing I've noticed with some Traveller players is that distance is not accounted for with communication. We forget that communication, in the game, travels at the speed of light. Therefore, with the distances typically involved in the game, there is usally a time delay between messages.

Sometimes, this is a few seconds. And, sometimes this can be hours--depending on the distance involved.

Yes, that's why when those NASA or ESA broadcasts are made, they usually talk about the time lag between when something lands and the data arrives on earth via radio.

One other thought on this: I wonder about sensors. I mean, if a ship is on a long in-system journey--say, from Saturn to the Earth--that ship is hooking 'em. It's moving. Even at 1G acceleration, it's average velocity on this trip is quite high.

Moving at that speed--how effective are sensors? The ship is certainly not moving anywhere close to the speed of light, but it is moving at quite a speed. And, it will take hours to effect a vector change.

I assume that the setting already takes this into account...

So a scan via sensors (with whatever resolution) will show possible objects in the path, may reduce a trip down to a speed that it can accelerate, then decelerate then scan, then repeat... So the trip may be at 1G for X minutes or seconds, then 3G for Y minutes or seconds and so on...in other words the distance may be covered in smaller spurts.

When you think of how far the various current Earth missions have gone and several have gone without a hitch (no collisions, no micro-meterorites reducing them to swiss cheese) then it's fairly safe to say its a reasonable journey at any speed.

Obviously there are always exceptions, and that's what separates a Pilot-1 from Pilot-5, all that experience with dealing with various types of obstacles.

Do current NASA probes have sensors ? Or do they just hope for the best ?



>

 

[flykiller]

... that's what separates a Pilot-1 from Pilot-5 ....

I'd say navigator. plotting safe courses is his job.

most systems will have been surveyed several times over several hundred years, and all the major meteor clusters and streams (like the perseids) will be noted and avoided. outside of those space is somewhat empty.

note than in our system the gas giants are said to sweep up a great deal of in-system debris. systems with no gas giants may have significant amounts of litter that impose major vector limits.

supp-4's observation that location/vector matching may take hours is very valid, both for rescuers and for pirates, and imtu the vilani and imperials have centuries of experience dealing with this. if a world has significant traffic then there are designated jump ingress and egress zones that have an sdb or two on-station, and any ship that loiters near the zones for no announced and authorized reason will be queried. if the zones aren't mandatory, or if they're not established, then of course jump ingress and egress may take place anywhere - but then it's the pirates that have the location/vector matching problem.

 

[far-trader]

Space is big. Really really big. Your ship, and presumably the rock, are small. Really really small comparatively. The odds of a random collision are tiny. Really really... you get the point

Now, IF (big IF, really really... starting to annoy you aren't I ) there is a rock on an intercept that you can detect you probably will. With lots of time to limit the probability of it actually hitting you. You don't need hours to make a vector change sufficient to avoid the intersect. Unless the "rock" is changing its vector every time you do

Even the slightest change of your vector will open up a lot of space between the two.

The hard part in the scenario will be the actual detection.

From a single point of observation (your ship) you will have to have the rock with apparent movement from your point of view. Anything except mostly head on (or directly behind you) due to its lack of apparent motion. It's nearly impossible to detect a small object coming straight at you in space. Adding observation points outside your own helps eliminate blind spots. Not "blind" because you can't "see" there (though that may be the case, especially when trying to look where your drives are pointed) but because objects in that area may not have apparent motion to make them detectable, until it's too late.

Once you do spot the object, and recognize it as something not already tracked and catalogued (i.e. safe, as the navigator will have avoided any close encounter paths with such, if they are any good and not pressured to take the risk for a faster path). Then you have to continue observation (and possibly ask other observers to assist) to track it's position to determine just where it is and what its vector is before you'll know if it's a threat or not, and if it is just how to avoid it. That's what will eat up your time. Not your actual vector change. Until you know what its path is any vector change you make is as likely to hurt you as help you. In that you may unwittingly change you vector to make the collision more likely. Though as noted it's extremely unlikely anyway, so an early vector change is most likely to simply delay you unneccesarily.

 

[far-trader]

...Do current NASA probes have sensors ? Or do they just hope for the best ?

They generally avoid areas of known high risk and play the odds (see "Space = BIG++" ) And they wouldn't be able to change course anyway. Any vector change they have is mapped out way ahead of time for the mission. To use it to avoid a potential collision (even if it were imminent and they detected such) would mean the mission is lost anyway so what's the point.

But even when they took the Cassini probe through Saturn's rings the odds of a collision were very small. They weren't particularly worried. And that's several orders of magnitude more "populated" than an asteroid belt. And an asteroid belt is several several orders of magnitude more populated than the rest of the solar system. A random collision in space is so unlikely as to be insignificant. It falls in the realm of referee fiat if you ever want it to happen to the players. Not saying it never happens. Given thousands of years and who knows how many spacecraft flying about it's bound to have happened many many many times. But the odds of it happening to the characters in their lifetime (never mind just the game period) is practically nil.

 

[Gadrin]

But even when they took the Cassini probe through Saturn's rings the odds of a collision were very small. They weren't particularly worried. And that's several orders of magnitude more "populated" than an asteroid belt. And an asteroid belt is several several orders of magnitude more populated than the rest of the solar system. A random collision in space is so unlikely as to be insignificant. It falls in the realm of referee fiat if you ever want it to happen to the players. Not saying it never happens. Given thousands of years and who knows how many spacecraft flying about it's bound to have happened many many many times. But the odds of it happening to the characters in their lifetime (never mind just the game period) is practically nil.

That's what I thought.

GURPS requires a minimum "armor" on a starship of 100 to handle debris and dust and what have you, otherwise that's it.

That 100 is nothing compared to warships; so it was gauged to cover the basic "travel in space" jaunt.



>

 

[Commander Truestar]

One thing more germine to one of the orignal questions...

In a set of sessions earlier this year my players entered an area of deep space via jump and set about their 'evil plot' happy they were in the middle of no where with bladders full of H to pump into the regular tanks...
Well, a deal of time into their 'evil plot' they pick up a tachyon wave!! Someone else has arrived!!

(Ironic looking gent pops up in a baloon saying "How Ironic!")

Well, now the players have to find out what they are dealing with and activate all Passive sensors to see what they are reading. Sadly, at the speed of light, even the most basic info is not even registering and won't for some time. Indeed, even listening for simple things like transponders don't happen for hours on end.

So what's a player to do? Start rushing! Make mistakes! Break things and use up resources...not to mention time...

So finally they get hit by a full sensor sweep! The other guy has gone active sensors. This gives teh players some info and tells them that sitting quietly at passive sensors is not gonna keep them hidden. So the order is given, "light 'em up!" Now the most important piece of information they will get is an aproximate distance. This is because the time it takes the sensors(moving at the speed of light) to hit the tartget and fly back can be pumped through some basic calculus(with an estimate of the bogie's speed) to determine where they were when hit and are now...

Eventually, after hours of "strategic pinging", they get an actual voice message!!(let the negociations begin!). Soon the players have set someone to monitor voice traffic and they send an answer. It will be hours back and forth with one guy responsible for monitoring the comms recorder and playing back the message after it surprises everyone by arriving.
This and sensor ping responses give the players a reliable idel of the speed and vector of the bogie even though it is coming right for them(Shoot it ned! its coming right at us!)

Finally the comms range is such they can get video but nothing will be normal because now they have secured from scurrying about their mission and are now working on firing plots and weapons estimates. Not only are few things certain except their bogie's course and intentions but they must appear much the same to their visitors. So they decide to prepare a "surprise gift".

Working with their best numbers, the players launch a few waves of missiles programmed to go inert until signaled, then home in on any local(Yes Pinkey, a relative term) power source and play "seek and boom".

The odds are astonomically high, the tension is so thick you can barely cut it with monomolecular wire(careful about those knuckles) and then it comes to the time to send the signal to the missiles.....

and then you wait...


and then you wait...


and then you wait...


and then you pray cause the clock ran out on the signal(suggesting if your math was right you just activated your "mines").

So now you are praying that:
1: one of those very expensive missiles is close enough to the intruder to track it
2: it has enough of a eye on the target to lock and track
3: it has enough fuel to chase and reach the admittedly slowing target
4: it can get close enough to the blip designated "enemy" before the blip designated "enemy" changes it's designation to "firing on the players now that we are in
range"

and finally, you pray to the void you'l return to that any missile that "strikes" does enough damage to give the players the upper hand in the battle to come once the blip designated "now S-O-L" enters direct energy weapons range.

In our case, I gave a set of rolls to make and the players rolled incredibly well and managed to put two missile right down the ship's pitot tube(private pilots form the 17's/80's may recognize this term).

So BOOM and no more enemy after all that hours beween contact insanity


As a GM I found it very fun

Marc

 

[Starviking]

Not CT, bit I recall a TNE article in Challenge about the time-lag in sensors. The major point was that a ship jumping in-system can immediately see all that's going on in the system, but the people in the system can't see anything until the light from the incoming ship's arrival has reached them.

Of course, 'tachyon waves' mess that up a bit

 

[dean]

I like the author CJ Cherryh's postulation that inside all the "civilized", inhabited systems, there are a series of buoys positioned across the system that provide incoming ships with the latest available, albeit time-lagged, information on the system, including positions and velocities of all know ships in the system.

Uninhabited/backwater systems will lack this system, of course, unless the Scouts saw reason to establish it because of the systems importance as a route.

 

[kafka47]

I thought this was covered already in the thread on Flight Plans or Jump Tapes. Flight Plans would be filed with the appropriate authorities would dictate the point of precipitation from Jump Space. I try always ensure that it is more than 100 diameters as just at 100 diameters is premium space that Main world can charge premium credit for the privilege.

Flight plan precipitation points are part of the package that one must carry with them when departing a system and is first thing the transponder squawks at traffic control in the new system. So that everyone within a J-6 radius of World A can safely jump with an infinitesimal small change of collision.

Sort of like how pilots of ships know which berth their ship must dock in...well before departure.

 

[Commander Truestar]

Not CT, bit I recall a TNE article in Challenge about the time-lag in sensors. The major point was that a ship jumping in-system can immediately see all that's going on in the system, but the people in the system can't see anything until the light from the incoming ship's arrival has reached them.

Of course, 'tachyon waves' mess that up a bit

That kinda depends on where in space you are and how you define starport services.

IMTU Port Quality is very important.

Start with an X Class port: If the IISS or IN put a becon there to direct you to a proper contact you are lucky. Otherwize, what you know is what you can see as broken down by light seconds away in distance bands.

Working up towards C Class ports you will get only what is logical(so a low service system on a main traffic route will have some Imperial placed beacons and other systems or IN patrols)

C Class ports: Will publish ingress and egress jump area designations for local space to A) giving access the port proper B) giving access to the gas giants. Defining these zones insures that arriving ships won't suddenly precipitate from jump right on top of departing traffic. Ports with heavier traffic may maintain multiple zones and these zones are advertized to all ports so that navigators plotting jumps into those systems will be aware of the arrival/departure restrictions. Depending on the traffic and other variables, the port may have deployed repeater beacons.

Repeater Beacons: These are actually base level robots that deploy in a given location in the system(which means they maintain that position relative to the solar system so they will both adjust their positions with planetary orbits and send requests to the port when they need fuel.
The beacons serve traffic by: 1: receiving broadcast traffic schematics, news, alerts and other important data the port is putting out. 2: performing the intial "Scan and ID" on arriving traffic in ordeer to aid with customs, inspection, arrival berth planning, port defense, etc...
The more traffic a port has, the wider a network the port will "Want" to maintain. The actual size of their network will be based on the port's economic ability to afford to deploy and maintain the network.

A and B Class ports:
Add Naval and SDB squadrons not on passive duty to the C Class ports. Also add corporate specific beacons and comms traffic.

In a large part, you can consider it similar to driving cross-country. As you leave a city you leave a dense radio-space filled with all sorts of Stations serving a very diverse spectrum of needs and consumers. Once you get out into the suburbs, the radio traffic density drops and gaps in frequencies become apparent. Out in the large countryside gaps between cities, you have huge gaps in the dial as there are significantly less stations.

Following this model, if a major national story breaks in one place it will quickly be picked up and broadcast across the network to all stations. If a local story breaks out, it will be broadcast locally quickly but not spread much even as a sideline story on other stations.
THe only difference to the model is that there will be a spider-web like pattern of delay based on the travel of the signal between beacons at the speed of light. Once the "news" reaches the port(or an outer-support station deployed for the port), it gets configured for rebroadcast and spreads to the appropriate part of the web

Examples will be:
Arrival in Regina System bound for Regina Prime:
The IMS Broken Credit precipitates from jump and her bridge crew set about post-jump procedures. As they make their inboard system checks the interferance from dissapating jump energies fades... Once that is gone, the comms officers(or officer responsible for comms as well as other things) begins receiving comm and data traffic being broadcast by Regina System Port Authority. This includes a schematic of all traffic in this "pie section" of the system as well as Port and legal updatesa and military or security advisories.
At the same time, the Credit's transponder code has been picked up as well as her apparent course and heading.

Immediatly the local craft in this small part of the system are aware of the Credit and everything local to the Credit is viaible on the bridge screens out to twice normal civilian scanner range. She also receives automated instruction for the approach vectors to all Civilian serving facilities in general(IE: if you are making for Regina Prime take heading A, if you are headed for Assinbola Polar Orbit facilities, take vector B, if you are heading for Regina IV facilities...)

As time continues, the signal that the credit has arrived gets to one of the outer port support stations and a local traffic controller sends a message to the Credit aking what her intentions are. By the time this message gets to the Credit, her arrival has been noted at the main Port traffic control and a provisioner is considering where she can be berthed in all the facilities she may want to arrive at. At the same time, the Credit is showing up on all civilian displays in the pie section of the system she is inhabiting.
When the Credit replys, that reply is routed back to the outer support station who takes responsability for guiding her into her primary approach vector to her intended port facility. That tech may or may not have received a list of facilities with open berths sent to them from the main port provisioner.
Eventually the port tech on the support base and the credit are in regular(if broken by time lag) contact and the port has hard confirmation of The Broken Credit's intentions[she may just be here to hang in space waiting for another ship to make a "deep space transfer" of cargo, may be heading to a port or have some other intended destination in the Regina System]. That tech can assist the Credit's crew in their arrival details while forwarding the hard data from the ship in-system to the main port.
Main port workers can contact the intended destination of the Credit and make provisioning for berthing(orbital shuttle serviced position or downport) or docking(orbital hard-dock).

I could go on with the description but you get my admittedly long winded point.

Marc

 

[Patron Zero]

Buoys & Lighthouses

One would think that in the heavier traveled spacelanes there would at the very least be navigation buoys 'anchored if not dedicated lighthouse installations.

IMTU such was facilitated by a network of information broadcasting beacons, each being a small independently owned and operated 'radio' station much like one might find along a forgotten stretch of modern American highway.

I found having manned beacon points gave the spaceways a bit of substance rather than parsec after parsec of emptiness and void. The broadcast stations also would act as 'drop off' points for ships carrying data 'consignments' (read as express route mailbags) which could be transmitted ship to station or physically delivered by way of message 'torpedo'.

In the most remote of sectors, the buoy stations could act in a limited capacity as general store and/or 'roadside' diner to provide sustenance to weary starship crews.

I found having a place to stop just to have a fresh cup of joe and 'read' the local newspapers before going deep in system quite comforting.

 

[Magnus von Thornwood]

Because I am so annoying...

....

So finally they get hit by a full sensor sweep! The other guy has gone active sensors. This gives teh players some info and tells them that sitting quietly at passive sensors is not gonna keep them hidden. So the order is given, "light 'em up!" Now the most important piece of information they will get is an aproximate distance. This is because the time it takes the sensors(moving at the speed of light) to hit the tartget and fly back can be pumped through some basic calculus(with an estimate of the bogie's speed) to determine where they were when hit and are now......

Does anyone here understand that active use of sensors, pinging away is going to be detectable by the prey long before the hunter is getting anything back that they can use? It being a fact and a sad one for active pinging hunters that the prey can hear them far beyond the range of return because the energy that the hunter is sending out travels farther than people think and loses enough energy that it can't get back to the actively pinging hunter but now the prey knows that they are being hunted and where the hunter is. This is why the Silent Service relies so much on passive search functions, you can't hear passive but active can be heard from way, way out.

If I were your players I would have checked the signal strength and done the math and been like "OK, Mr. Badguy just told us where he is and now we got like 2 hours before he's actually in range to detect us, so let's be real careful and get done and jump the hell out of this potential Charlie Foxtrot before he knows we're here." But that's just cause I am annoying and read lots of sub stuff.

 

[Commander Truestar]

If I were your players I would have checked the signal strength and done the math and been like "OK, Mr. Badguy just told us where he is and now we got like 2 hours before he's actually in range to detect us, so let's be real careful and get done and jump the hell out of this potential Charlie Foxtrot before he knows we're here." But that's just cause I am annoying and read lots of sub stuff.

Yes and there is something else you missed, but which I alluded to in my scenario...

When the Hunters got the active ping back they knew "Where the bad guy was WHEN THE PING Bounced back".

While the energy blast of active ping tells the bad guy:
1) there are hunters in-system
2) what direction the hunters are in

It does not tell them much more. They can not do the math on decay without knowing how much power the hunter put into the sensor "ping" so the badguy is limited too. That is one of the things sub guys have an advantage in..they know their opposite numbers gear pretty well and know the medium absolutly. As well, their AO map is finite.

The thing you missed on the good guys side, as stated above, is... When the hunters get their data back, they have an idea wher teh sensor/bad guy intercept took place. Only continued sensor data, which will be skewed due to relativistic effects, will give the hunter an idea what the baddie did once it was pinged.

That said, if the light-time lag is an hour decreasing to 30 min, then the hunter has to reply on their knowledge of strategy(friendly and enemy) and educated(or experienced) guesses to figure out where the baddie is going and what they are doing.

IMTU, this is part of where Ship/Fleet tactics skills come in. Navigators with that skill are prized IMTU because they can do the math and can work cross-skills and apply theory

Marc(yeah, I run a tight game > )

 

[Magnus von Thornwood]

Yeah well....

I said I read a lot, not I do a lot, and yes I know there is a big difference. Still, I wouldn't have gone active in response to an active ping and actually if the Sensors and Tac officers know their stuff they should be able to suss out the type and such of the offending ping and work out the math as most of that stuff can be found in a good copy of Jane's, but again that's just Mr. Armchair speaking.

Of course Mr. Armchair does happen to have a copy of Jane's ASW book.

 

[aramis]

Marc:

With 4 antennae, at "corners" of a tetrahedron, one can 3D triangulate source of ping, and by ratio of decay, decay of ping (and thus imply distance fairly accurately).

For 2D, a 3 antennae array can do a full 2d 360° sweep.

Thus that active ping gives rough range and a fairly accurate bearing.

Keep in mind that signal drop off over distance is an exponential function, and thus the differential as a fraction of the stronger signal antennae's power gives the position on the curve distance, AND the timing differential between the antennae gives the bearing. By knowing where in the curve one falls, one can back-calculate the signal strength at source, as well.

 

[Starviking]

That kinda depends on where in space you are and how you define starport services.

IMTU Port Quality is very important.

Good points Marc, but I was referring to 'Ship' and 'System' ideally - i.e. given the constraints of the Einsteinian universe. System sensors will, of course have an effect.