Topic: How do starship sensors work?

[Scottish Andy]

A quick question for you all: How can any ship sneak up on or evade another's detection while using warp drive?

My previous understanding -- which I am now suspecting/realising was probably absorbed from my tech manuals and the novels -- is partially based on Einstein's Theory of General Relativity in that subspace/FTL sensors can detect an object at long range (into light-years of distance) based on the effect that object's mass has on spacetime; the larger the mass, the more gravitational effect on spacetime, thus the longer the range it can be detected at by FTL gravity-based sensors. Thus, stars and planets can be detected from light years away but stations and ships you have to get much closer to.

The long-range sensors on Kirk's Enterprise could scan for ships to 1 parsec (3.26 ly) with immediate results in 'TOS: The Enterprise Incident', but didn't detect the Klingon ship that attacked it at the start of 'TOS Errand of Mercy'. The E-D could scan for ships out to 10 ly in 'TNG: The Wounded', but in 'TNG: Relics' the E-D didn't detect the massive gravity well of a friggin' Dyson Sphere until it yanked them out of warp!
I'm finding it hard to reconcile these for a story I'm writing, and I want to be internally consistent instead of making sh*t up as I go along. Specifically, I'm looking at where a ship can be detected and under what conditions.
So, based on what we see in the eps, do starship sensors scan into the subspace realm, or just use FTL means to scan normal space? Are the sensors mass/gravity-based, or use some other means to detect the varying types of object?

If a ship at warp speed is generating both energy, light, heat, it's own gravity, and most importantly, an intense gravity field and/or distortion of normal spacetime from it's warp drive being active, as well as using a navigational deflector to sweep microscopic space particles and debris from its path, how can any ship sneak up on another using warp drive? Conversely, if a ship cannot be detected at warp speed, how can long range sensors detect a ship at all?

I've read the Memory Alpha pages on these topics and it seems like subspace itself cannot be scanned by Fred technology. So, here are my theories. Which one (or combination) seems most reasonable?

Anything else you want to suggest within this topic. "Get a life", "You have too much time on your hands", "Who the f*ck cares you minutiae-obsessed freak!" and such like are not welcome or acceptable responses.

Andy

[Grim Reaper]

I'd really would find it odd if they can't detect objects moving at warp speed. That could result in some mighty fine collisions on high traffic routes.
Active scanning could very well be the most logical option for avoiding head on collisions and if the search field is narrow enough might explain the yanking out of warp by the sphere. But that still leaves "intersections". If they need to active scan everywhere just to avoid objects, wouldn't you make that option default in warp? So I vote for option 3 and write off the inconsistencies as plot devices.

[atheorhaven]

My belief is that the long range sensors pick up the disturbances on normal space caused by the subspace field of the ship in warp on normal space/time.

So the warp field pushes the ship into (more or less) a skin surrounding normal space and the bubble it creates can cause a small effect on normal space like an object under a pinboard pushing up normal space a little bit.  So the sensors read the bubble moving across normal space via FTL tachyons (or some such).

My opinion anyways YMMV..

[Lieutenant_Q]

In both cases that the E (E-D) didn't detect something it should have detected, I go with an unmentioned stealth device, and leave it at that.

[Commander La'ra]

The beam from the navigational deflector would be pretty easy to detect.

[Czar Mohab]

Had a long reply going at home, but long story short, a ship going fast (warp) will make more "noise". If you want it to be more stealthy, you'll need to cut the noise down somehow; maybe shutting down non-essentials, going warp 4 instead of 9.9, keeping sensors on passive, etc.

As for how a ship can detect such a vessel, they most likely would have to be looking - I would think that while traveling at warp, her sensors are limited to the basics for the spherical view ("there's something there, just don't know what, sir") while most of the "looking" would be along the path of travel.

"Faster than light, no left or right." - Tom Paris

I add that quote in as an example of the limits imposed on a vessel traveling FTL. Think about it: the main deflector has a very narrow arc and a very busy job. maybe it isn't so much that the physics prevent full power sensors at warp, but the limitations of the sensors themselves such that the most important element gets the most available power and computer time while the periphirals get what's left.

If this is an insufficient reply, I will post the work that I have at home once i actually get there.

Czar "Work sucks," Mohab

[Scottish Andy]

Larry, I'm not sure how the nav deflector actually works any more.

Previously, I too believed it was a force beam that shot directly in front of the ship to push aside interstellar dust and atoms.

Then I heard that it was just a low-power shield erected in front of the ship.

According to Memory Alpha (a source I trust), it's both:
"It performs its primary function by emitting low-power deflector shields to deflect microscopic particles and higher-powered deflector beams and/or tractor beams to deflect larger objects."

This would require a massive amount of power, especially if it is used in warp speed. Think of it, at TOS warp 8, or 512 times light-speed, the ship covers 512 light-seconds (8.53 light-minutes) per second. To project a beam ahead of the ship moving that fast to clear, say, 10 seconds of flight time ahead of them would seem to require almost as much energy as travelling at warp speed itself. Which was one of the reasons I asked this question to begin with.

How the hell can a ship sneak up on another ship, if even going at warp speed requires using the Nav Deflector? That's broadcasting on a massive scale, and easily detectable (IMHO) by passive sensors.

On a related note, I think I'm now coming down on ships still being in normal space while at warp. I mean, if they are in subspace, why would the nav deflector have to operate at all? Is there dust and atomic particles just lying around in subspace, when so much energy is required to get into FTL speeds?
No, I'm saying the subspace bubble is pulled into normal space, causing a spatial distortion or "warp" in normal spacetime, "propelling" the spacetime out of the bubble, and the ship "moves" forward on the crest of the distortion wave. *nods as he imagines Larry's head imploding*

Hmm... *grins*  This is one of the reasons I ask questions. It allows me to articulate my own thoughts on the matter and illustrate my own assumptions and knowledge so I can take the next step myself. Now that I've explained all that out, I think I have an answer. Try this on for size.

Short range sensors will pick up an incoming ship if it's not trying to hide and there's no interference. If there's a nebula, or Dath'mar's using silent running/EMCON, or the Roms have cloaked, it'll not be picked up on passives, and will require extreme proximity and/or an alert operator to notice the ship with active scans. Boom. Close range sneakiness.

If a ship is out of short-range sensor coverage, long-range readings require active scans even if it's not trying to hide. "Perform a long-range sensor sweep for other ships," and all that. If it's warping in making lots of noise (ie. max warp, shields up, active scanning), the short range passives will detect the ship at longer range than if t saunters in at warp 2 with shields down and no active emissions.

Job's a good un. I think I'm happy with that. Now, anyone care to refute or comment -- assuming all your heads didn't just explode from reading thois? 

[Scottish Andy]

I just watched 'ENT: Precious Cargo' again on Sunday -- just laying eyes on the beautiful Padma Lakshmi was reason enough -- and when the alien ship blasts into warp and disappears off the sensors within seconds, it seems they only tracked it on short-range. However, they wanted to search for its warp signature on long-range scanners, so obviously I have my answer.

This being the case, the sensors are not the all-powerful tools I thought they were made out to be. I have a good basis for my story now, but I may need to retconn my older stories to match this.