(Spaceships) Implictions of the sensor rules.

[Fred Brackin]

Questions concerning how far away you should set your FTL boundary and general defense of an inhabited system came up recently in other threads and I've been reviewing the Spaceships rules and have finally organized my thoughts.

Let's begin by walking through a simple detection scenario. We'll have thesM+15 space station that orbit above a major world (and which costs hundreds of billions if not trillions of $) trying to find an SM+6 scout ship that is doing inteligence-gathering. The TL is 10, the maneuver drive is standard of "cold" Reactionless and the most common power plant is fusion.

Technically, we begin calculations with the Systems Operation (Sensors) Skill of the person performing that function for the station. Hoever, almost by defintion we know that if the orgaization running the station is "professional" their sensors guy is at least Skill-12 but how much higher is reasonable is a matter of opinion. so we'll defer that question.

So we have Skill+ SM of target (SM+6) + time spent (one half hour +5) and Telescopic Vision level of the Enhanced Sensor array (+16). So far ll those plusses look good but then we figure in possible range penalties and 75 AU (the number Spaceships uses sometimes for the FTL boundary) and we get a -75.

So we were +27 but are now -48. There's more plusses though. We get a +10 for "in plain sight" that applies most of the time (but not if you have an opperating cloaking system). Then there's a +24 for "sillhoetted against deep space" that also applies most of the time.

Finally, there is IR signature and counter measures. That's a +7 for the Fusion power plant and what could b a -10 for a Cloaking system and a -8 for Stealth. We'll assume no Cloak and the Stealth is negated for any IR signatures of _5 or above.

That leaves us at Sensor Ops -7 to spot this scout ship at 75 AU. How close does the scout need to be for you to rollv. base skill. That appears to me to be c. 2 AU using numbers from Spaceships.

This is for a relatively rosy scenario for the defense too. If the scout jumps in with the local star between himself and the station the stations 3 billion $ sensor suite can't see him at all. Then if the scout comes around the star so closely he's never seen with deep space as a background that changes a +24 to a +2 for coming at you with the star as a backdrop.

Taht -22 takes you from rolling Skill at 200 milion miles to rolling v. base skill at 4000 miles. (-43)

Things could be worse than that too. If the scout is desgned with an ausiliary power plant such as fuel cell or solar the IR signature modifier drops from +7 to +4. More importantly it sllows for Stealth measures that could give another -8. A total of -32 which makes your distance for base Skill 250 miles.

If he has a Cloak that take soff another -20 (-10 for the Cloak and you lose that +19 for In plain sight). That puts you at 200 yards. At least the scout probably can't land infiltrators on the station. Keepign him off your planet might be a lsot cause.

So you need not only this trillion $ space station to detect at c. 2 AU you need soemthing like a ring of other (perhaps cheaper) stations in a closer solar orbit to protect against that "coming at you from out of the Sun" trick. Extending your detection range out into the outer solar system is probably prohibitive.

I recommend placing your FTL boundary at no more than 10 AU. You should get good detection of real warships that far out. Putting it at 10 AU still makes it a 9 day run at 1G continuous.

Also, please will someone else check the math? I was juggling Speed/Range table numbers in my head mostly.

[AlexanderHowl]

A developed system will likely have sensors close to the FTL boundary. Imagine a system with a FTL boundary of 40 AU. It creates a sphere with a volume of 268,000 square AU. Now place a SM+6 remote buoy in each cubic AU.

Each automated buoy will have three steel armor, fifteen extended comm/sensor arrays, one control room, and one habitat. With a cost of $4M, the entire system can be covered with an expense of around $1 trillion. With 15 extended sensors each, each buoy can track 15 different targets, allowing for the monitoring of over four million targets by the entire system. A developed system with 5 billion people would have an income of $335 trillion, meaning that the buoy system would be a minor cost.

[Fred Brackin]

Originally Posted by AlexanderHowl

A developed system will likely have sensors close to the FTL boundary. Imagine a system with a FTL boundary of 40 AU. It creates a sphere with a volume of 268,000 square AU. Now place a SM+6 remote buoy in each cubic AU.

Each automated buoy will have three steel armor, fifteen extended comm/sensor arrays, one control room, and one habitat. With a cost of $4M, the entire system can be covered with an expense of around $1 trillion. t.

At TL10 your SM+6 Extended Sensor Array has 9 fewer levels of Telescopic Vision. That reduces its' detection range by a factor of 30 so you go from 200 million miles to 6-7 million.

The formula Google turns up for surface area of a sphere gives 7.07 x 10 to the 20th for a radius of 7.5 billion miles (75 AU). The simpler formula for the area of a circle gives 1.13 x 10 to the 14th in square miles.

Anyway, I'm getting 6 million sensor platforms for 24 trilion $. Still lower than i expected but still quite a lot too.

[thrash]

Originally Posted by Fred Brackin

...trying to find an SM+6 scout ship that is doing inteligence-gathering.

I'm not sure you're asking the right question. How useful are the sensors on a ship this size going to be at 75 AU? It doesn't make sense to bother, if legitimate (registered through a neutral flag of convenience) freighters approaching the main world can do better with their stock sensors.

On the other hand, what will your response be if you detect the scout? What would it take to intercept or drive off a ship that far out? If you're not going to intercept, it may make more sense to just accept that eyes are always out there in the Dark and plan accordingly. This may actually enhance interstellar political stability, using the "trust, but verify" method.

A better question is, can you detect an invading fleet in time to respond? Or, more challenging, a single militarily significant combatant (either commerce raider, pirate*, or rogue) on a fly-by attack through the inner system? This gets into where you station your system defense forces and their alert status, but you can make some reasonable assumptions (e.g., near the main world and ~6 hours to get under way).

*Pirate strategy: make a fly-by, shoot up some expensive property (like that huge station), and exit the system. Send a demand for payment to prevent it happening again.

[Fred Brackin]

Originally Posted by thrash

I'm not sure you're asking the right question. How useful are the sensors on a ship this size going to be at 75 AU? .

The scout ship would be coming much closer than 75 AU and it could do so at very little risk to itself. With the approach from sunward tactic it could get to the planet the station is orbiting.

My main interest in doing these calculations was seeing if was at all useful for a GM to set the fTL boundary as far out as 75 AU. My conclusion was "no".

[Varyon]

Originally Posted by thrash

*Pirate strategy: make a fly-by, shoot up some expensive property (like that huge station), and exit the system. Send a demand for payment to prevent it happening again.

"That's is a very nice space station you have over there. Would be a shame is something were to... happen to it."


From what I understand, a more likely scenario is to have a lot of smaller satellites spread apart and working together to function like a very large array, which gives better performance with less weight (and thus cost) than having a single solid system (or even an array spread out over a station's hull). Spaceships doesn't have any rules support for that, unfortunately, at least not to my knowledge.

[Celjabba]

Originally Posted by Fred Brackin

Questions concerning how far away you should set your FTL boundary and general defense of an inhabited system came up recently in other threads and I've been reviewing the Spaceships rules and have finally organized my thoughts.

Let's begin by walking through a simple detection scenario. We'll have thesM+15 space station that orbit above a major world (and which costs hundreds of billions if not trillions of $) trying to find an SM+6 scout ship that is doing inteligence-gathering. The TL is 10, the maneuver drive is standard of "cold" Reactionless and the most common power plant is fusion.

Technically, we begin calculations with the Systems Operation (Sensors) Skill of the person performing that function for the station. Hoever, almost by defintion we know that if the orgaization running the station is "professional" their sensors guy is at least Skill-12 but how much higher is reasonable is a matter of opinion. so we'll defer that question.

So we have Skill+ SM of target (SM+6) + time spent (one half hour +5) and Telescopic Vision level of the Enhanced Sensor array (+16). So far ll those plusses look good but then we figure in possible range penalties and 75 AU (the number Spaceships uses sometimes for the FTL boundary) and we get a -75.

So we were +27 but are now -48. There's more plusses though. We get a +10 for "in plain sight" that applies most of the time (but not if you have an opperating cloaking system). Then there's a +24 for "sillhoetted against deep space" that also applies most of the time.

Finally, there is IR signature and counter measures. That's a +7 for the Fusion power plant and what could b a -10 for a Cloaking system and a -8 for Stealth. We'll assume no Cloak and the Stealth is negated for any IR signatures of _5 or above.

That leaves us at Sensor Ops -7 to spot this scout ship at 75 AU. How close does the scout need to be for you to rollv. base skill. That appears to me to be c. 2 AU using numbers from Spaceships.

This is for a relatively rosy scenario for the defense too. If the scout jumps in with the local star between himself and the station the stations 3 billion $ sensor suite can't see him at all. Then if the scout comes around the star so closely he's never seen with deep space as a background that changes a +24 to a +2 for coming at you with the star as a backdrop.

Taht -22 takes you from rolling Skill at 200 milion miles to rolling v. base skill at 4000 miles. (-43)

Things could be worse than that too. If the scout is desgned with an ausiliary power plant such as fuel cell or solar the IR signature modifier drops from +7 to +4. More importantly it sllows for Stealth measures that could give another -8. A total of -32 which makes your distance for base Skill 250 miles.

If he has a Cloak that take soff another -20 (-10 for the Cloak and you lose that +19 for In plain sight). That puts you at 200 yards. At least the scout probably can't land infiltrators on the station. Keepign him off your planet might be a lsot cause.

So you need not only this trillion $ space station to detect at c. 2 AU you need soemthing like a ring of other (perhaps cheaper) stations in a closer solar orbit to protect against that "coming at you from out of the Sun" trick. Extending your detection range out into the outer solar system is probably prohibitive.

I recommend placing your FTL boundary at no more than 10 AU. You should get good detection of real warships that far out. Putting it at 10 AU still makes it a 9 day run at 1G continuous.

Also, please will someone else check the math? I was juggling Speed/Range table numbers in my head mostly.

2 questions :

-First, why do you scan from a station in orbit instead of several dedicated observation satellites like the planned TL8 NEOSM situated at various Lagrange point to avoid blind spots ?

-Second, I would add a bonus for the computer doing the initial image analysis - assuming you don't actually roll the sensor skill of the dedicated computer

You describe not a "rosy scenario" but pretty much a worst case, imho : one single sensor in planetary orbit, no computer support to detect a ship at 75 AU .
That said, I agree that in a setting without in system FTL, setting the FTL boundary at 75 AU basically cripple detection and defense unless you have *many* units available for both.

[thrash]

Originally Posted by Fred Brackin

The scout ship would be coming much closer than 75 AU and it could do so at very little risk to itself. With the approach from sunward tactic it could get to the planet the station is orbiting.

Yeah, about that: do you really think the planetary space traffic network (if nothing else) will be that blind for an entire sector? This tactic depends on having all the relevant sensors concentrated to a very small solid angle relative to the star, which is exactly what the network won't do for that very reason.

Position two sensor platforms at the main world-star L4 and L5 points, focused between the star and the main world. Now your scout is back to "silhouetted against deep space" values for its approach.

[thrash]

Originally Posted by Varyon

From what I understand, a more likely scenario is to have a lot of smaller satellites spread apart and working together to function like a very large array, which gives better performance with less weight (and thus cost) than having a single solid system (or even an array spread out over a station's hull).

Phased arrays have the resolution of an antenna the size of their spread, but still only the sensitivity of their combined detector areas. In this case, sensitivity is more important.

[Andreas]

Originally Posted by Fred Brackin

At TL10 your SM+6 Extended Sensor Array has 9 fewer levels of Telescopic Vision. That reduces its' detection range by a factor of 30 so you go from 200 million miles to 6-7 million.

The formula Google turns up for surface area of a sphere gives 7.07 x 10 to the 20th for a radius of 7.5 billion miles (75 AU). The simpler formula for the area of a circle gives 1.13 x 10 to the 14th in square miles.

Anyway, I'm getting 6 million sensor platforms for 24 trilion $. Still lower than i expected but still quite a lot too.

By substituting some more accurate numbers in your calculations, I get a bit less than 4.5 million sensor platforms, which is a bit less expensive.

Then there is the question of skill. This all assumes that you only detect when rolling against base skill right? While you wrote that you wanted to defer that question, by assuming that you are rollinga gainst base skill, you would be assuming pretty low skill levels. That is even more the case if the people operating the sensors gets large bonuses for rutine tasks (which kind of makes sense, how would they know if what they just detected the presense of is hostile, friendly, or just a simulated signal to test them?).