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Old 09-09-2021, 10:39 AM   #1
Fred Brackin
 
Join Date: Aug 2007
Default Traveller-hot reactionless or cold?

The terminology refers to a difference between some reactionless drive systems that are silent and devoid of exhaust ("Cold") and others that emit fire or bright light or some other kind of radiation ("Hot").

I've seen ilustrations that shows the back of Trav ships with ports or something with something else shooting out of them and other illustations that show a kind of "nimbus" behind the ships.

Hot reactionless goes back to the Golden Age when Lensman ships had "drive flares even though they burned no fuel and Star Wars ships have glowing back ends. Cold reactionless is characteristic of UFOs and other vehicles with silent emissionless propulsion.

So,do the grognards out there have opinions or can they cite canon on this question?
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Old 09-09-2021, 11:53 AM   #2
Anthony
 
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Default Re: Traveller-hot reactionless or cold?

Most ship designs in Traveller show exhaust ports; e.g. the Type S. Super early versions didn't use reactionless drives at all, they used fusion drives with highly cinematic performance (computed exhaust velocity around 10c).
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Old 09-09-2021, 12:11 PM   #3
Fred Brackin
 
Join Date: Aug 2007
Default Re: Traveller-hot reactionless or cold?

Quote:
Originally Posted by Anthony View Post
Most ship designs in Traveller show exhaust ports; e.g. the Type S. Super early versions didn't use reactionless drives at all, they used fusion drives with highly cinematic performance (computed exhaust velocity around 10c).
The thought comes to me that Trav must have both as the grav cars/tanks/carriers show no exhaust and it would indeed be undesireable in urban traffic.

The diference might even be conected tot he performance jump G:T had in drives beween TLs 10 &11.
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Old 09-09-2021, 12:54 PM   #4
mstlaurent
 
Join Date: Aug 2004
Default Re: Traveller-hot reactionless or cold?

Quote:
Originally Posted by Fred Brackin View Post
The thought comes to me that Trav must have both as the grav cars/tanks/carriers show no exhaust and it would indeed be undesireable in urban traffic.

The diference might even be conected tot he performance jump G:T had in drives beween TLs 10 &11.
This was always my understanding. That there were cold thrusters that were based on gravitics used by air-rafts and grav tanks and the like, and then there were hot thrusters that were used by spacecraft. Granted, I never got deep into G:T, I was always Classic, but I assumed that the difference was that the grav thrusters could only be used in a significant gravity well.
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Old 09-09-2021, 01:31 PM   #5
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Traveller-hot reactionless or cold?

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Originally Posted by Fred Brackin View Post
The thought comes to me that Trav must have both as the grav cars/tanks/carriers show no exhaust and it would indeed be undesireable in urban traffic.
Traveller has had distinct contragravity systems (which don't function in deep space, though some can reach low orbit) since very early. Those don't have reaction ports.
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Old 11-09-2021, 10:33 PM   #6
Mr Frost
 
Join Date: Sep 2004
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Default Re: Traveller-hot reactionless or cold?

I have it (mostly) cold due to the mayhem hot (let alone hot and forceful) exhaust would create at very busy ports . It is just light that would create heat if allowed to just stay inside the ship .

In my designs the colour of the exhaust does tell you something of the engines' behaviour : blue means it is thrusting , red is reverse thrust (and purple means something has gone very very wrong) with shade and brightness varying with performance . With practiced observation you can tell which direction the ships' thrust is vectored and how hard .
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Old 11-10-2021, 08:34 AM   #7
malloyd
 
Join Date: Jun 2006
Default Re: Traveller-hot reactionless or cold?

Quote:
Originally Posted by Fred Brackin View Post
Hot reactionless goes back to the Golden Age when Lensman ships had "drive flares even though they burned no fuel and Star Wars ships have glowing back ends. Cold reactionless is characteristic of UFOs and other vehicles with silent emissionless propulsion.
Note that there are different [kinds] of "hot" here. The Golden Age stuff, and I've always assumed Traveller engines, put out something comparable to jet engines or ship propellers. Something you don't want to be standing next to when they are on, but nothing even remotely close to what something that played fair with physics that had the kinds of performance envelopes these things have should have, where you'd need to be careful not to melt the city as you flew over.
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Old 11-10-2021, 06:32 PM   #8
DeadParrot
 
Join Date: Apr 2012
Default Re: Traveller-hot reactionless or cold?

My assumption has been the most power plants on Traveller ships are fusion. A quick scan of the New Era book Fire Fusion and Steel has most of the normal TL for Traveller games using fusion for power plants. TL 6-8 show fission. TL 9-16 show fusion. TL 17-21 are antimatter. (page 64).

For a space ship, it could save some space and weight to just vent the hot fusion products out the back. What's a bit more heat and helium in space going to hurt? No real thrust, basically an exhaust pipe. Standard liftoffs from a star port are probably fairly slow affairs to limit the effects of hot fusion byproducts on the tarmac.

A lot of the tech details are left rather undefined. Guessing some of the artwork shows hot vents to make the scene seem more exciting.

As far as land craft, the power could come from a very compact fission reactor or a mostly sealed Mr Fusion type thing.
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Old 11-12-2021, 03:21 PM   #9
SteveS
 
Join Date: Nov 2013
Location: near Seattle WA USA
Default Re: Traveller-hot reactionless or cold?

As I recall, the lowest technology reactionless thrusters use 2.5 times the power per thrust as typical thrusters, and GTL13 thrusters are better still (though possibly more compact rather than more power efficient). That suggests that early thrusters run hot, while typical thrusters run lukewarm. (Cold seems implausible.)

One problem throughout space science fiction is waste heat. Rather than invent yet another superscience, my handwave for that problem was that one of the effects of gravitic technology is the possibility of gravitic heat sinks. How do they work? Who knows. Maybe they're sheets of gravitationally confined plasma that can dump heat into space through blackbody radiation, at sufficiently high temperatures that the radiating area becomes manageable even for a fusion power plant. A gravitic radiator might be combined with a gravitic thruster; if so it would be very hot.

Other editions of Traveller have a multitude of maneuver technologies, including magically efficient rockets, realistic rockets (except for the heat problem), and assorted gravitic devices.
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