[Spaceships] Radar ranges in space

[Michael Thayne]

Recently, I've been looking at old 3rd edition rules for creating vehicles and spaceships, and one thing that really sticks out is how much weaker the range of active sensors such as radar is in space. In 4th edition's Spaceships, even at TL7 an SM+5 ship's Enhanced Sensor Array gives you a radar range of 30,000 miles for $60k (which also pays for ladar, infrared telescopes, and comms with a range of millions of miles). In contrast, in THS Classic (which is definitely higher TL than TL7!), the largest available radar weighs 40 tons and costs $3 million, but only has a range of 10,000 miles in space. Vehicles is closer to THS Classic in this regard than it is to Spaceships.

Which approach is more realistic? My initial seems to favor 3rd edition. It's important to note that Spaceships get their impressive sensor range from electronics that are a small % of their mass. David has said that dedicating 1 system slot to a sensor/comm array does not mean that the array is actually 5% of the ship's mass. So that 30,000 mile radar is well under the 1.5 tons you might naively calculate it to weigh. By contrast, I've heard of real-world radar satellites in LEO weighing over 10 tons.

Thoughts? Is anyone willing to go to bat for Spaceships here?

[Anthony]

Fundamentally, detection with sensors requires a minimum signal, and a minimum signal to noise ratio. Optical sensors have massively increased range in space because the background noise is something like 9 orders of magnitude lower than it is in atmosphere. This is less significant for active sensors because signal strength diminishes with the fourth power of range for active sensors; in general active sensors are a poor choice for initial detection at any significant range in space, though using it for ranging on an already detected signal allows you to focus and thus greatly improves range.

[Michael Thayne]

How much of a range improvement are we talking about here, if we want a realistic rule? Vehicles gives +4 to target for "prior contact", which could include say, trying to detect with active radar something previously detected by passive IR. This is equivalent to roughly a 5x increase in range, which I don't think quite gets you the ranges in Spaceships. Maybe if you add an additional fudge factor for the fact that in spaceship combat your target is assumed to be large.

[Anthony]

Originally Posted by Michael Thayne

How much of a range improvement are we talking about here, if we want a realistic rule?

For radar in space, I don't know. The bonus for prior contact can easily be 10+.

[Ulzgoroth]

I'd think that should depend on your hardware - if you know just where the target is you're probably making the beam as narrow as your emitting antenna permits. Might be relatable to the telescopic vision stat that Spaceships provides, even though that's intended for the optical systems.