# Time-Delay and Signal Mechanics

Today is the first of two parts talking about how the time delay in Slower Than Light works.  Today I’m going to be writing about how signal strength and distance are abstracted, and how those create interesting interactions.  Tomorrow there will be a video using one of STL’s prototypes, as well as a special surprise.

I know I’ve been accused of being obsessed with numbers in some places, and this post isn’t going to help that impression.  If you’re just looking to see the mechanics in action, you can skip this post entirely and just watch tomorrow’s video when it goes up.

Signal Mechanics

The basis of the way information flows around the galaxy in Slower Than Light is electromagnetic signals that move at light speed.  Every signal in the game has two properties relevant to its propagation: the location it originated from, and its strength.  Signals get weaker further from their source by the inverse square law.  To make math easier for users (and developers…) the base signal strength of each transmitter is its strength at 1 light-year from the source.  That is to say, if a transmitter on a colony or a starship has a stated strength of 100, the signal will have a strength of 100 one year later when it reaches 1 light-year’s distance from the source.  It will have a strength of 25 when it reaches 2 light-years away a year after that.  By the time it has traveled 10 light years, it will have only a strength of 1.

The second component of the system is a receiver.  When a signal reaches a receiver, if the receiver’s sensitivity is lower than the signal’s strength, it can read and decode the message and either update its own database or forward the message along.  Because transmitters and receivers can have different ratings on different planets, it is entirely possible for a colony to be able to hear another settlement, but not be heard by them.

Figures 1 and 2 show how this relationship works.  Earth here has a 100 strength transmitter, while the colony 10 light-years away only has a 70 strength transmitter.  Both have a 1 Sensitivity receiver.  If Earth sends a message to the colony (Figure 1), the signal strength is reduced to 1 by the time it arrives(100 Strength divided by 10 lightyears squared), but since the colony has a receiver with a sensitivity of 1, it can receive the message from Earth.  If the colony then attempts to respond, however, its message starts with a strength of 70, and by the time it reaches Earth it has been reduced to a strength of only 0.7, which is less than Earth’s receiver’s sensitivity, so Earth cannot hear the reply.

We resolve this communications gap with transceivers, devices that receive and re-transmit messages.  In Figure 3, a relay spacecraft with a transceiver has been place between Earth and the colony.  The relay has less transmitter strength than either Earth or the colony, but when it has the same receiver.  When the colony’s signal reaches the relay, it has only degraded to 2.8 strength over the five light-years, so the relay can receive it.  The relay then re-transmits the message to Earth with a strength of 50.  Over the 5 light-years to Earth, the signal degrades down to a strength of 2, but is still easily receivable by the homeworld.

Deep Space Radar also uses the signal medium, but slightly differently.  Each spacecraft in STL has a reflection percentage, an amount of signal strength it naturally reflects.  Deep Space Radar sends out a powerful pulse, and every spacecraft reflects a small fraction of that pulse back, called the “return”.  If the return is still strong enough to be detected when it returns to the point of origin, the target can be detected, and some information about its size, position and velocity can be derived.

Finally, the signal system is also used to collect information on other events that might be detected.  Ships firing certain types of engines to accelerate and deccelerate might be visible to colonies in the same star system.  Detonations of large weapons either planetside or in space would also be visible at some distance.  Some natural sources produce signals that can interfere with near-by transmitters and receivers.  Finally, most megaengineering projects will make a lot of noise on the electromagnetic spectrum.

Gameplay

Knowing how these signals move around the galaxy is important, but what does it mean for gameplay in STL?  At a basic level, signals come in two flavors: Normal and Urgent.  Normal  signals are just regular updates on the locations of ships, the demographics of colonies, the status of production orders, that sort of thing.  When they arrive, the player’s interface is silently updated to reflect the new information.

Urgent signals indicate something that happened that may require the player to intervene.  For instance, when a new spacecraft is detected, that is considered an urgent signal.  If the game were processing turns, it would immediately stop, give the player that message, and return them to the home screen to give orders.

When a new colony first makes contact, that is an urgent signal.  If a distress signal is received, that is an urgent signal.   All the normal messages you would expect a game to call your attention to are urgent signals.

Orders the player gives are also signals.  If the player needs to order the colony from Figure 1 to build a spacecraft, the order will take 10 years to reach the colony, at which time construction will begin.  If it took 2 years to build the spacecraft, the completion report would arrive back at Earth 12 years after that (22 years after the order was originally sent), and the orders for the ship would then take another 10 years to reach it from Earth, meaning that from the time construction was ordered to the time the ship received its orders would be 32 years.  Of course, with STL it will be possible to send a mission along with the ship construction order so that it would only take 12 years for the ship to be built and assigned orders, but without foresight, the unwary can quickly find themselves with a many-decades-long construction process.

Each colony acts as a relay automatically, so if make sure all of your colonies can talk to at least one other colony when they’re founded, you’ll have a connected network of planets that can all send messages to each other.  It might not be the most efficient method, though.  In Figure 5, we have Earth attempting to communicate with Colony 3.  Using the values for Earth, colonies, and relays given above, each world can send and receive messages to planets within 10 light-ears.  Earth and Colony 3, though, are 16 light years apart.  To get messages back and forth, they need to relay through Colony 1 and Colony 2, and each stage of that journey takes 10 years.  Thus, when Colony 3 sends updates to Earth, they arrive 30 years later.  With a string of relays across the void between Earth and Colony 3, that time could be cut down to a bit over 16 years.

Conclusion

Wow!  That was nearly 1,300 words about the way signals work in Slower Than Light.  If you read all that, congratulations!  You’ve gone above and beyond.  If you just skipped down here, don’t worry — I’ll be posting a video tomorrow demonstrating everything above to help make it clearer and help you see how these mechanics will actually play.

## 2 thoughts on “Time-Delay and Signal Mechanics”

1. Mason says:

Hmmmm… Two comments come to mind:

1) The vast majority (if not all) of all deliberate communications should be of the point-to-point variety, rather than broadcast as this article applies. If colony A is transmitting a message to colony B, then it is a safe assumption that only colony B will be in a position to potentially receive the message. Yes, a tight-beam communication will spread over interstellar distances, and there is a possibility that a ship (or other mobile entity) would happen to end up within that cone, but… The odds are very, very low that this would happen by accident and if assuming this simplifies the required calculations…

Note that this wouldn’t rule out broadcast type of communications as well — but they would be far less common (for example, broadcast would be appropriate when the target location is not known, there is no known path to the target, or the source is natural).
2) I’m not certain how necessary / useful a deep space radar system is. Passive sensing (which you also mention) is going to have *far* superior detection ranges for ships and the like (assuming that realistic propulsion technologies are used). Slowing from .25c (relative to the target system) to a point where gravity capture can occur is going to take vast amounts of energy, expended over years, and all of that energy is going to be focused on the target system, so stealth is simply impossible. The only time that this detection capability would come into play is pure fly-bys (which you wouldn’t be able to do anything about, due to the same delta-v issues described earlier) or natural objects (which can be safely assumed to be detected once they get within, say, ~2 light weeks of a manned vehicle / sensor platform). Given the above, is it really worthwhile to spend time / resources implementing active sensor technologies?