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"That thing's gotta have a tailpipe."

J

jcrocker

SOC-13
A starship flies along, merrily fusing hydrogen in its power plant and jump drive - and forming helium.

Does it vent the helium? Do ships leave a "contrail" of really hot helium? Do the passive IR sweeps become really important in unfriendly systems? "Conn, this is sensors, I've got a cluster of five hot helium trails at bearing two-two-seven, but no IFF or transponders at that bearing."

Or does it tank the gas, so they don't give their position away? Does the Imperial Navy have a lucrative sideline inflating party balloons? Or is that more of a Scout thing?
 
jcrocker said:
A starship flies along, merrily fusing hydrogen in its power plant and jump drive - and forming helium.

Does it vent the helium? Do ships leave a "contrail" of really hot helium? Do the passive IR sweeps become really important in unfriendly systems? "Conn, this is sensors, I've got a cluster of five hot helium trails at bearing two-two-seven, but no IFF or transponders at that bearing."

Or does it tank the gas, so they don't give their position away? Does the Imperial Navy have a lucrative sideline inflating party balloons? Or is that more of a Scout thing?
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Well, given that a lot of your 'flying along' is done in jump space there wouldn't be any contrails at that point. When you jump in there's a great big honking signal, so you would need to be really far out of the system to hide that. At that point I would think that the gravitic signature of the engines would probably be the most noticeable thing. A big ship might be burning a couple of dozen tons of hydrogen per day, which would be pretty spread out over its trail, but those engines would be exerting massive amounts of energy.
 
esampson said:
...A big ship might be burning a couple of dozen tons of hydrogen per day, which would be pretty spread out over its trail, but those engines would be exerting massive amounts of energy.
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Right, granted it would be a thin trail of helium, but since it would be venting product from a fusion reaction, I'm guessing it would be very hot. I'm not a nuclear physicist, I don't even play one on tv, but there's a graph in the wikipedia article on the topic that talks about reaction rates vs temperatures as measured in billions of degrees kelvin. Yes, it has a 10 to the -2 in the scale, but that's still in the millions of degrees.

http://en.wikipedia.org/wiki/Hydrogen_fusion

I'm not saying the exhaust gas would still be quite that temperature when vented, or that it would stay that way for long, but to a high tech IR system, even a wisp of gas a few thousand degrees would stand out like an arc lamp.

Is that what anti-piracy patrols are, looking for hot plumes of helium without a friendly transponder at the head of it?

Or is this just something that would have to be hand-waved away? Would it skew play balance too much, give too much away?
 
You can always jump in behind a planet, hiding your jump flash from the mainworld. Then you only have to worry about sensor pickets.

As far as waste heat management, it seems just as likely that by TL 9 or 10 there's ways to store that in a storage-sink, for recycling at an appropriate starport... or jettisoning as a decoy.
 
Well ACS and Space Combat say that all ships have Hot Spots and defines them as any Maneuver Drive and any Power Source, so that means there must be exhaust or radiator ports on the ship.

Gas or exhaust plumes I'm not sure about. Three questions spring to mind:

1). How quickly will a hot gas cool.
2). How quickly will the plume disperse (related to 1.)
3). What volume and density of gas/exhaust escapes (and how quickly will it match the background levels in space).

If your sensor is looking for radiant heat, won't the actual ship (and those hot spots) be the bigger source compared to the plume?
 
Reban said:
Well ACS and Space Combat say that all ships have Hot Spots and defines them as any Maneuver Drive and any Power Source, so that means there must be exhaust or radiator ports on the ship.
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Not necessarily ports. Could be "radiator strips" all over the ship. The long and short is that the ship will be a very bright spot (IR band) against the black (cold) of space.

You can't hide unless you get behind something and hope that the locals are too low TL or, too stupid to have system wide observation devices.
 
Also neutrino emissions from the power plant - presumably omnidirectional?

(But, what ARE those things that look like rocket nozzles at the ends of all our starships, anyway, if not for hot particle emissions?)

Just glancing at the sensors list gives us plenty of ways to detect a ship.
 
robject said:
(But, what ARE those things that look like rocket nozzles at the ends of all our starships, anyway, if not for hot particle emissions?)
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Those are the mistake an artist makes when they don't understand the game rules. ;) All too common.
 
pendragonman said:
No no no. Those are the speakers that the VROOOM! sound comes from in atmo.
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Only in an atmo?

Surely sufficiently advanced tech would eliminate the need for annoying things like having an atmosphere for sound propagation.
How else would you hear all those 'woosh', 'engine rumble' and 'pew pew' noises as the ship flies past in space? ;)
 
If the Thrusters run on plasma (rather than on electricity), via some catalytic reaction, then those nozzles might be the thruster's exhaust vents. This would also explain the reliance upon fusion power plants. (Given the power outputs, fission plants are more efficient use of volume and credits...)
 
aramis said:
If the Thrusters run on plasma (rather than on electricity), via some catalytic reaction, then those nozzles might be the thruster's exhaust vents. This would also explain the reliance upon fusion power plants. (Given the power outputs, fission plants are more efficient use of volume and credits...)
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As depicted, they are too large for that. It's just a mistake.
 
They're a placebo for the passengers. Nobody would pay for passage on a ship with no obvious visible engines, right?

No wait, they're lens flare generators for the benefit of the visual effects crew.

They're required for legacy support of ancient launch pads.

Clearly they have something to do with religious observation.

Back on topic: A recent design I am toying with puts the helium back into the fuel tanks in order to maintain pressure. There's still the problem of what to do with the waste heat, though, so I think venting to space is probably more reasonable.
 
Midgardsormr said:
They're a placebo for the passengers. Nobody would pay for passage on a ship with no obvious visible engines, right?

No wait, they're lens flare generators for the benefit of the visual effects crew.

They're required for legacy support of ancient launch pads.

Clearly they have something to do with religious observation.

Back on topic: A recent design I am toying with puts the helium back into the fuel tanks in order to maintain pressure. There's still the problem of what to do with the waste heat, though, so I think venting to space is probably more reasonable.
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Why would you want to maintain pressure? As long as you maintain 1 atm it isn't like the tank will implode (unless the tanks are built in some strange manner where there is outside force being exerted on the tank to keep it from exploding). And at 1 atm the tank is basically empty. It would contain .12% of the original fuel.

At one point I had thought about having ships trap the helium since hey, there must be some applications for it beyond balloons, since it's a Noble gas, but then I realized that since many cities are powered by fusion there probably is no shortage of helium. In fact given how much hydrogen a ship burns through I suspect a ship's engine isn't even particularly efficient and most likely the majority of the 'waste' is still hydrogen. A fusion plant burning 2 tons of hydrogen per month should probably be enough to light up a planet assuming any sort of real efficiency.
 
HG_B said:
As depicted, they are too large for that. It's just a mistake.
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I don't know. They look like they are in the same general neighborhood of ship to nozzle ratio as the ion thruster on the Dawn space probe. It doesn't seem inconceivable that whatever technology is being used might require nozzle of comparable size (the issue of how thrust is produced is pretty much ignored in most versions of Traveller. In TNE it definitely was done with reaction mass and in T5 the method is a magical 'gravitic drive' that keeps us from saying exactly what the requirements are, but it is possible to extrapolate that those drives are not silent devices that effortlessly lift ships to orbit because otherwise there would be no need for Lifters).
 
esampson said:
I don't know. They look like they are in the same general neighborhood of ship to nozzle ratio as the ion thruster on the Dawn space probe. It doesn't seem inconceivable that whatever technology is being used might require nozzle of comparable size (the issue of how thrust is produced is pretty much ignored in most versions of Traveller. In TNE it definitely was done with reaction mass and in T5 the method is a magical 'gravitic drive' that keeps us from saying exactly what the requirements are, but it is possible to extrapolate that those drives are not silent devices that effortlessly lift ships to orbit because otherwise there would be no need for Lifters).
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In most versions it is a type of grav reactionless drive. Hence, no rocket type nozzles needed. It is simply a case of an artist who has no understanding of the ship design paradigm. It isn't ignored in most versions.
 
Really? Because I can't find any reference to how maneuver drives work in CT, beyond things such as they draw power from the power plant. I'm not saying the information isn't there. Just that I can't find it.

In MT it is specified that maneuver drives are reactionless, but by then we had lots of artwork with ships with nozzles.

In TNE the drives quite definitely were not reactionless. You actually had to set aside reaction mass when you designed the ships.

I've got no idea how drives worked in T4.

Lastly in T5 the drives are once again 'gravity based', but it is never said they are reactionless. Don't ask me how a gravity based drive might be producing a reaction because I couldn't tell you, but then again I couldn't tell you how a gravity drive works in the first place. What I can tell you is that apparently you can't just run your maneuver drive on low power and use it to move yourself about over the starport because that's what Lifters are for. It seems a little hard to believe that you can't control the engines well enough to do it so it seems as though the answer must be that there is some form of deleterious effect to people in close proximity.

In all fairness this doesn't necessarily mean thrust. It could be that the m-drive works on a related but slightly different mechanic than the lifters (hence the differing radii where they cut out) and that their mechanic is harmful to unshielded people within a short distance or something.

So in 4 of the 5 versions of Traveller I'm seeing one where it is clearly reactionless, one where it clearly isn't, and two where it is unknown. Unless I am both missing something in CT and T4 says that the drives are reactionless that doesn't constitute 'most versions'. (I am not including Mongoose Traveller or GURPS Traveller because I lack the books an because their canonicity is not completely established).
 
esampson said:
I've got no idea how drives worked in T4.
Click to expand...

T4 had it both ways: there was HEPlaR, and there was reactionless. Whatever that meant.

Lastly in T5 the drives are once again 'gravity based', but it is never said they are reactionless. Don't ask me how a gravity based drive might be producing a reaction because I couldn't tell you, but then again I couldn't tell you how a gravity drive works in the first place. [...]

So in 4 of the 5 versions of Traveller I'm seeing one where it is clearly reactionless, one where it clearly isn't, and two where it is unknown. Unless I am both missing something in CT and T4 says that the drives are reactionless that doesn't constitute 'most versions'. (I am not including Mongoose Traveller or GURPS Traveller because I lack the books an because their canonicity is not completely established).
Click to expand...

CT is murky on the issue, but seems to imply some sort of waste energy or gas being expelled out the tailpipes.

And for T5, although they do appear to be reactionless (they run on energy with no fuel input), nevertheless the Scout/Courier, Traders, Yacht, Safari Ship, Merchant, Corvette, Corsair, and other Adventure-Class Ships do seem to all have tailpipes. Thus something is going on somewhere. Perhaps power plant emissions, then.
 
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