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"How would Space Fleets see each other?" Topic

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WarEmblem13 Jan 2020 7:03 p.m. PST

How would opposing fleets in space see each other? Radar would have limited usefulness in space. GPS wouldn't be available unless the fight was taking place near a homeworld and even then it's likely the satellites would be targeted first. In both Star Wars and BSG fleet actions take place at near knife fight range and almost all detection is visual. This is fine if we envision star battles looking like Jutland or Trafalgar, but how would opposing carrier fleets such as those at Midway find each other?

Mr Elmo13 Jan 2020 7:17 p.m. PST

Primarily from the dissipation of heat both from engines as well as life support.

Other factors depend on your game's reality.

emckinney13 Jan 2020 7:19 p.m. PST

Do you have realistic drives? If so, there's no problem. Telescopes and automated signal processing make it no problem. Even with drives off, the temperature of the crew areas and other inhabitable area, and the unavoidable and irreducible waste heat from the power plant make a ship so much hotter than the background that it's easy to pick out.

Radar is pretty effective, since there's comparatively little clutter and you can play tricks with long baseline synthetic aperatures (multiple ships combining precise data).

Dynaman878913 Jan 2020 7:51 p.m. PST

He mentioned Star Wars so realistic is pretty much out. Pretty much however you want it to work with Star Wars or even Star Trek type tech.

WarEmblem13 Jan 2020 8:47 p.m. PST

Alright, so the heat signature of drives and crew would stand out in space. How far would you able to detect a heat signal?

Thresher01 Supporting Member of TMP13 Jan 2020 9:31 p.m. PST


Personal logo Parzival Supporting Member of TMP13 Jan 2020 9:39 p.m. PST

Far enough that in any even semi-realistic tactical combat game, no ships will be out of detection range.

Zephyr113 Jan 2020 10:48 p.m. PST

Gravitational distortion. Mass can create little dimples in space-time that can be detected. (I'm assuming you have the tech level to do that… ;-)

Giles the Zog14 Jan 2020 3:57 a.m. PST

Nearest I've read is the Lost Fleet series (Jack Campbell ?) that had problems of spotting fleets/ships in *time*…as in sensors might detect them where they were 3 hours ago, but due to the delays they've already moved so the commanders had to second guess where they would be.

parrskool14 Jan 2020 4:56 a.m. PST

…. also david drake's RCN Series….

ScottWashburn Sponsoring Member of TMP14 Jan 2020 5:20 a.m. PST

If the ships are using reaction drives the exhaust plumes would give them away at enormous distances. A physicist friend of mine who was once in a Traveller's campaign with me calculated that a 1000 ton ship accelerating at one gee near Jupiter would have an exhaust plume that would be visible with the naked eye on Earth. :)

Mr Elmo14 Jan 2020 6:00 a.m. PST

How far would you able to detect a heat signal?

Well, the ISS is the biggest space shippy thing we have. It generates 70kw of infrared radiation. Warships may generate more but be stealthy so let's go with that.

Now the question is: how far could you detect a 70,000 watt light bulb? I'm thinking "interplanetary."

WarEmblem14 Jan 2020 6:57 a.m. PST

That is very helpful Scott and Mr Elmo, thank you.

williamb14 Jan 2020 7:59 a.m. PST

WarEmblem see this website link
click on site menu in green letters and look under space war for detection. One set of spaceship combat rules covered detection quite well. They are called Starcruiser and are available on Wargames Vault.

Personal logo Parzival Supporting Member of TMP14 Jan 2020 12:36 p.m. PST

I think it's safe to say we're all assuming sub-light speeds here. If ships can move at FTL, then forget about detection— the ships are already where they're going before any detection is possible. In fact, they'd arrive at the destination before you see them leave the departure point! Which probably rules FTL out as a reasonable thing to approximate on the tabletop.

As for the reference to The Lost Fleet series (great books), what Giles the Zog is referring to is the concept of light-lag— light (and for that matter any energy) takes time to travel from one point to another: 1 second for every 300,000 km. So anything you see/detect is actually further along in time than the light/energy which has reached your eye/sensor. Inside 150,000 km or so this is essentially unnoticeable to living things. At a distance of a full lightsecond (300,000 km) or more, you will begin to notice the delay, especially in a radio conversation— there will be a "lag" in the time between when one person speaks and the other hears. Similarly, the light (or thermal energy, or any other energy) arriving from a vessel will also have a lag— it is essentially the light arriving from where the ship was when the light bounced off it (or was produced by it). So if you're a lighthour away from an enemy vessel (1,080,000,000 km), you "see" its location as it was an hour ago, and must interpret its current position based on its speed, vector, and ability to alter the same. And if you intend to shoot it at such a distance, then you also have to calculate where the target will be an hour from that estimated position, as that's when your laser (or other energy weapon) will have crossed the distance to arrive at the target. How do you simulate this on a tabletop? Well, you don't… except perhaps to say that abstractions like "initiative" and "dice-rolling" account for the light-lag complexities.

At some point all spaceship combat games contain an unavoidable amount of handwavium. It all depends on at what point the designer starts waving the hand. (I confess to waving it pretty much right off the bat! grin)

— Howard Shirley, creator of Generic Outlandishly Big Spacefleets (GOBS!)

DyeHard14 Jan 2020 3:28 p.m. PST

The "How" would be in two ways,Passive: Telescopes, or Active: RADAR (Lidar)

Either you are just picking up whatever signal is out there, or you interrogate a target with a directed signal.

The good news, if you are near a star, it gives off tons of signal that will bounce off a target, then the question is what angel can you resolve. That is when can you tell you can something compared to background. More good news, the background can be very dark, and there is very little stuff between you and the target to scatter light.
See things like: link

To get an idea of how far you can see starts to get technical: link
But 1 part in 10^5 (2 Sec) is a rule of thumb. If you thing of a circle with the radius of the distance between you and the target, you divide that circumference by 10^5 and a ship that long would be resolved (i.e. visible).

Bigger ship can be seen from greater distance.

Far from a star you would have to either look for their increased heat compared to background or probe with a chirp that would bounce off the target and return to you. They would know you where there in one haft the time that you could possibly "see" them. So, there is some risk in this.

robert piepenbrink Supporting Member of TMP14 Jan 2020 4:57 p.m. PST

Let me get this straight. The fleets are moving into position using FTL Doubletalk Drives. Weapon systems run the gamut from extremely hypothetical to outright fantasy, and the shielding has a similar range. The first two SF systems mentioned don't appear to be compatible with one another. But we're worried about how "realistically" they could see and identify one another?

This makes arguments about the model of Dr. Watson's service revolver feel like hard science.

Invent the FTL drive and the weapons, and see whether anything you've learned to that stage suggests a solution to the intelligence-gathering problem. In the meantime, have your ship's Psionic Communications Officer let you know when he hears alien thoughts. What do you think we keep PCOs on the payroll for? (Credit to Bertram Chandler, back when SF was a branch of literature.)

Personal logo Parzival Supporting Member of TMP14 Jan 2020 5:00 p.m. PST

Don't forget that with any active detection/targeting system the process is twice as long as with passive sensors, because with an active system (Radar, LIDAR, etc.) a signal is first sent from the detecting vessel to the target. It travels to the target at light speed, strikes the target, and then returns to the sensor at light speed. With a passive system, a sensor merely receives energy already emitted or reflected from the target. So it takes twice as long for a signal to be sent and returned with an active system as it does for a passive system to receive energy directly from the target. So with an active system you get double the light-lag issueS!

Personal logo Parzival Supporting Member of TMP14 Jan 2020 5:29 p.m. PST

"FTL Doubletalk Drives." grin

But really, it is important to have figured out exactly what the game rule process is for any FTL capability.

1. Do you use Jump Gates/Jump Points/Wormholes? In other words, is the FTL dependent on arriving at a specific location in the battle space, away from which FTL can't happen?

2. Do you use "hyperspace" or a similar extra-dimensional spacetime phenomenon? If so, can ships encounter each other within this dimension? Can they engage in combat? Or is each ship effectively in its own solitary environment while in transit?

3. Or is FTL simply instantaneous— one second you're here, next second you're there? POOF!

4. Does the process of FTL leave detectable and traceable effects in normal spacetime? Is it possible to know when a ship is arriving at FTL? Is it possible to detect if a ship is preparing to activate FTL? Is it possible to detect an FTL ship traveling from point A to point B if you are an observer at point C?

Daricles14 Jan 2020 5:58 p.m. PST

Assuming realistic technology based on real world physics detection ranges are at a minimum tens of thousands of kilometers, reasonably out to many light minutes (within the solar system) and potentially extending into deep space.

It's safe to assume detection at vast ranges far exceeding any effective weapons range.

As others have noted, at these types of ranges you will know where the enemy was, where they were headed, and how fast they were moving. If you know a little about their drive capability you can calculate a movement envelope (volume of space) describing all positions they can reach in a given time frame.

Detection will be via visual/thermal detection using telescopes, which can be mounted on the ships. At shorter ranges (hundreds to thousands of kilometers) you can use radar/lidar type systems effectively.

Daricles14 Jan 2020 7:36 p.m. PST

Mr Elmo, the ISS that puts out 70kW is essentially a human sized hamster habitat in space and not a warship with dozens or hundreds of crew, weapons systems and at least interplanetary drive systems.

It's a safe bet an interplanetary warship will put out a larger energy signature than the ISS.

Mr Elmo14 Jan 2020 9:17 p.m. PST

warship will put out a larger energy signature than the ISS.

Feel free to pick a number. For a game tho, you're likely rating vessels as "passive 7" with an enemy of "detection 4".

Daricles15 Jan 2020 4:03 p.m. PST

"Feel free to pick a number"


Keifer11311 Feb 2020 8:41 a.m. PST

Assuming current technology. Space Battleship Titan is heading towards Saturn.

Pirate Ship Jolly Roger is heading from Saturn to Pluto.

How hard would it be for the Titan to see the Jolly Roger? That is, space is pretty big, would the Titan have 360 degree active and passive sensors that would just spot the Jolly Roger? Wouldn't there be a need for visual/thermal telescopes to land a "hit" on the JR, or would a modern "ship" easily detect it?

Daricles11 Feb 2020 5:27 p.m. PST

It would be easily detectable. Current ground based telescope systems on earth can scan the entire sky in a matter of hours. Some radio telescopes can scan the entire visible sky in a few minutes.

A ship in space doesn't have to contend with atmospheric distortion and would use multiple telescopes at once to complete a full sky scan in a few minutes.

At the distances you are describing the ship would stand out like a road flare on a dark night even if it wasn't actively engaged in a burn.

A few minutes might seem like a long time, but the distances involved make it inconsequential. You will see and track objects looooooong before you can engage them with any type of weapon.

Lion in the Stars11 Feb 2020 6:35 p.m. PST

Alright, so the heat signature of drives and crew would stand out in space. How far would you able to detect a heat signal?

NASA detected the reaction-control system on the shuttle firing from the orbit of Saturn(!).

How hard would it be for the Titan to see the Jolly Roger? That is, space is pretty big, would the Titan have 360 degree active and passive sensors that would just spot the Jolly Roger? Wouldn't there be a need for visual/thermal telescopes to land a "hit" on the JR, or would a modern "ship" easily detect it?

Depends on your assumptions on ship size and sensor fit.

Using ships the size of the ones in Jovian Chronicles (tens of thousands of tons), it's a trivial proportion of the ship's mass to have a significant number (say, 20+) 1m telescopes. That's about 1/10 the capability of Hubble, per telescope. And 20 telescopes gives you a pretty good % of the sky covered at any given time, without even scanning around.

Stalkey and Co24 Mar 2020 6:20 p.m. PST

super interesting thread – thanks for the great replies guys!

In wargaming terms, I think this is very much like naval battles on the ocean – depending on technology, you'll need to hide behind islands, etc. In space, I guess planets, moons, etc. I'm assuming asteroids won't work unless big enough to completely hide behind.

Another good question would be how technologically possible will be be to "jam" detection?

Again, in "near tech, present physics" not Star Wars [the BIG hand wave]. So tactically, they know you are there, somewhere, but can you interfere with the detection process enough to misguide the defense?

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