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Active Sensor Design

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Let's have a look at active sensors. Why would you want more than one type? Bigger is better, right? Let's see.

The rules say that:

 The Range of an active sensor is equal to:
 Sensor Strength x Sensor Size x SQRT(Sensor Resolution) x EM Sensitivity x 10,000
 An active sensor is able to detect any ship of a size that is equal to or greater than its resolution at its maximum range.
 Missiles smaller than size 6 are detected as if they were size 6.
 The emissions from an Active Sensor can be detected with passive EM sensors (details yet unclear).

For this example, I'll use a Sensor Strength of 16 and an EM Sens. of 8, i.e. all sensors use the same tech levels.

Now I've designed four different sensors for different roles (I'm not saying that they are optimal for the job):

  • The ElCheapo 60 is a 300-ton (size 6) search apparatus with a resolution of 60, equal to a 3,000-tons ship. I want to stick it onto everything that flies and needs a pair of eyes.
  • The SuperSearch 150 weighs the same, but is intended to spot bigger fish at longer range. Therefore, it gets a resolution of 150 (7500 tons).
  • The Defendor XS is going to be my standard short-range sensor. Size 2 means it weighs only 100 tons, so I can stick it on pretty much any ship.
  • Finally, the R&D department is trying to sell me the idea of a small (100 tons again) low-res (10, equals 500 tons) sensor - the Multiplax V. Let's see what it can do.
 			ElCheapo 60	SuperSearch 150	Defendor XS	Multiplax V
 Sensor Strength	16		16		16		16
 Resolution		60		150		1		10
 Sensor Size		6		6		2		2
 EM Sensitivity		8		8		8		8
 Max Range in km	 59,489,024 	 94,060,406 	 2,560,000 	 8,095,431 

OK, now at what range can these apparatuses spot nasty aliens? Let's just mount them all on an obsolete ore freighter and zip over to the Mars Orbital Testing Range!


Fine. Three months later the technicians come back with lots of diagrams. What does it all mean?

At long range, the Defendor and the Multiplax don't even play. No surprise here. And the SuperSearch clearly out-ranges the ElCheapo. It can spot a 10,000-ton battleship at almost 100 million km. And that's its maximum range against all targets bigger than that, too. Obviously the best of the lot!

But wait: the SuperSearch sees big things at long range, but the smaller the target ship, the more myopic the SuperSearch becomes. To the degree that a lousy 2,500-ton missile frigate could sneak up to us and fire missiles from a mere 10 million km away and all without a single blip on the screen!

The ElCheapo with its lower resolution would spot the same attacker at about 45 million km, hopefully giving us more than enough time to react.


Next test: what if our tentacled friends launched a bunch of fast Fighters or Fast Attack Craft? Let's say the fighters weigh 450 tons (size 9) and the FAC weigh 950 tons.

Ouch. The SuperSearch probably wouldn't notice them before they rammed the main antenna. The ElCheapo does better, but a whole squadron of really small fighters could still get very close (< 1 million) before being detected. What if the are armed with short-range, high-boom missiles? Too close for comfort.

We could rely on the Defendor missile sensor, but it has a max. range of only 2.5m km, and we might want a little more warning time. And suddenly that obscure Multiplax machine begins to make some sense!


Now for the final test. Things That Go Boom are approaching from all sides and we want to shoot them down before they tear us a new airlock. How do they perform against missiles? Keep in mind that a 20-Missile-point missile (equal to size 1, or 50 tons) is considered huge by most players. Expect your typical anti-ship-missile to be much smaller. Many will be smaller than 10 MSP.

No contest here. You go with a Defendor-type sensor or you are going to Uranus. The other sensors couldn't tell a nuclear missile from a dead frog.

Finally, remember that sensor strength and therefore range scale with sensor size. Make it twice as big and it sees twice as far. You could build a monstrous size 100, resolution sensor. It would spot everything bigger than a missile at almost 130m km, and even a size-8 missile at about 20,000,000 km. Great! It's just that carrying a 5,000-ton antenna is considered a bit of a performance spoiler by most spaceship captains.

If you designed a somewhat mobile super-surveillance ship around it, it would be in the 12,000-ton range and probably take more than three years to build, at the tech levels used here. Is it worth it?

Endless possibilities...

More details you might want to know

  • Size 1 and below active sensors can be put onto civilian craft without turning them into military ships, in addition to making a handy backup for military craft.
  • You can either switch on all Active Sensors on a ship or none. A ship with two different-sized actives that wants to scan for missiles might give away its position due to the larger sensor's emissions.

Fire Controls

Fire Control are designed in the same window as Actives, but do not detect targets. They just use data from an Active to direct weapon fire.

Editable Version

An editable version of the graphs in this tutorial has been created to allow you to modify the values and experiment with different sensor configurations.

Google Sheets Link


Mor, TMarkos, Zook