esampson
SOC-13
CT ships also ran on energy with no fuel input. The thing that most makes them seem reactionless is that they interact with large gravitational fields. However if that's the case then why are Lifters ever needed?
"That thing's gotta have a tailpipe."
- Thread starter jcrocker
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I'm afraid you have a gross misunderstanding of what would be reactionless.
Hence your confusion.
Do you have an actual point to make other than simply dismissing his point?
Does T5 explain how a gravity drive works? If not then energy from the fusion power plant might be used to manufacture a graviton particle that is accelerated out the tailpipe ... perhaps even an anti-graviton particle that has both a reaction mass (for F=MA) and a gravitational repulsive force that pushes the ship away from it. Until gravity is fully understood (in Traveller), anything is possible.
Now, personally, I think the rules suggest a 'magic black box' that you plug in and it somehow makes the ship move. Yet if the rules are not specific, then anything is possible.
With respect to the pictures vs the design rules, I think that the artists got it right ... they intuitively recognized that a spaceship needs a rocket motor. It is a visual imperative. The 1977 rules talked about the reaction thrusters (or so I have heard).
Lycanorukke
SOC-13
I don't think they're reactionless. On p365 the blurb on how they work...
"Maneuver drives interact with gravity to move spaceships. Parts of the drive reach out and grab the gravity of a world or a star and push against it to make the ship move. Isn’t that neat?"
So essentially they use the star/world as reaction mass, and hence are not reactionless.
So maybe the 'nozzels' are focusing elements that link to into the worlds grav field (pushing against a planet 1000 Diams away isn't bad), or simply a cowl to stop things/people from wandering into the focal point of the drive and making a mess.
Edit: I vaguely remember the 'Repellertron' in the Tom Swift novels did the same thing. Pushing/Pulling against a planet to move.
Drakon
SOC-14 1K
On submarines, carbon dioxide is removed from the air and pumped overboard. But it does not go out a simple pipe, because that makes a submarine easier to spot.
Instead, CO2 is pumped through a diffuser. Externally, it resembles a flat section of hull, with dozens of tiny holes. From a fair distance, you probably wouldn't distinguish the holes.
Maybe it does have a tail pipe, but it doesn't look like one.
As for neutrinos, that would be dependent on which technologies the fusion plant utilizes. Something like a Tokomak type of reactor would spew neutrinos in all directions, (if I am understanding the process correctly). Something along Polywell lines would have more of a neutrino beam effect, along the axis of injection, with very little emissions off axis.
Instead, CO2 is pumped through a diffuser. Externally, it resembles a flat section of hull, with dozens of tiny holes. From a fair distance, you probably wouldn't distinguish the holes.
Maybe it does have a tail pipe, but it doesn't look like one.
As for neutrinos, that would be dependent on which technologies the fusion plant utilizes. Something like a Tokomak type of reactor would spew neutrinos in all directions, (if I am understanding the process correctly). Something along Polywell lines would have more of a neutrino beam effect, along the axis of injection, with very little emissions off axis.
Gravitic drives might actually use the system itself as reaction mass, and thus not be truly reactionless, but generally, yeah, I tend to agree with your syllogism.
esampson
SOC-13
No. I have a quite clear understanding of what 'reactionless' means in this context. It means that the drive works through a violation of Newton's third law (for every action there is an equal and opposite reaction), that being that to move itself forward it does not have to send mass in the opposite direction. You have the action but lack the reaction, hence 'reactionless'.
In the case of ships travelling in space mass that is ejected from the ship in order to propel it forward is even termed 'reaction mass'. By and large we tend to use 'reaction mass' and 'fuel' synonymously. That is not always the case however. One example would be the Dawn probe which technically has no fuel, using a photovoltaic array, and which uses xenon gas as reaction mass. Another example would be a nuclear thermal rocket in which the fuel is radioactive material while the reaction mass is hydrogen which the radioactive material superheats.
Merely because a drive works through the translation of gravitational forces does not mean it is automatically reactionless. Perhaps the redirected gravitational forces are used to propel a reaction mass such as hydrogen. Obviously in the case of Traveller this does not occur as ships do not appear to need to carry reaction mass, but the example should illustrate that a gravitational drive does not have to be reactionless.
The various drives are described on page 363 in T5, granted they aren't exhaustive essays on the principles but for me they say enough to see how they work.
M-Drives interact with Gravity to produce vectored movement and are the in system drive of choice. This is why they are bound by the 1000D limit and only function at 1% outside of that.
Lifters, are anti-gravity hull plates that negate local gravity and allow limited lateral movement. Only good within 1D of a gravity well and good for only 50kph.
G-Drives are less efficient versions of M-Drives but work in the same way and are limited to 10D.
NAFAL drives are an even more inefficient version of the M-Drive.
M-Drives interact with Gravity to produce vectored movement and are the in system drive of choice. This is why they are bound by the 1000D limit and only function at 1% outside of that.
Lifters, are anti-gravity hull plates that negate local gravity and allow limited lateral movement. Only good within 1D of a gravity well and good for only 50kph.
G-Drives are less efficient versions of M-Drives but work in the same way and are limited to 10D.
NAFAL drives are an even more inefficient version of the M-Drive.
Nope. It is incorrect to say that it is a violation. The 3rd Law simply states what happens as a result. It DOESN'T state that movement is impossible without the 1st condition. I think this is perhaps where your confusion lies.
To clarify. A violation would be if you lit off a rocket and there was no equal and opposite reaction.
I didn't think about it this way until Wil and Lycanorukke mentioned it... it is exactly Newton's Third Law that is in effect here: the M-Drive pushes against the planet's (and/or the star's) gravity field, and the ship, being much much smaller, is propelled. Or repelled? (Or even "rappelled"?)
But, the point is those steenking tailpipes. As atpollard noted, they are "correct". And it wasn't just the artists, but rather Game Designers' Workshop itself, that intuitively recognized that "a spaceship needs a rocket motor". It is a visual imperative. And more correctly, artist, namely the great Chadwick himself.
andycowley
SOC-10
I hate to add fuel to the fire ..... but here eis what Wikipedia has to say on the subject of reactionless drives ... and no, I'm not a physicist so will not be definding any of the statements made herein 
NOTE; I searched the entire T5 BBB for the word 'reaction' or 'reactionless' but found no matches ... I therefore conclude based upon the above quote and the BBB that all the Maneuver Drives described in T5 are reaction drives ....
NOTE; I searched the entire T5 BBB for the word 'reaction' or 'reactionless' but found no matches ... I therefore conclude based upon the above quote and the BBB that all the Maneuver Drives described in T5 are reaction drives ....
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Hence, it is incorrect as there are no rocket motors on most Trav ships.
I think that's exactly the point we've narrowed that part of this discussion down to: the drives are not reactionless, using a nearby gravitational field for propulsion, but neither do they emit any sort of exhaust that we traditionally think of, since they do not react on contained fuel. They might emit something, but they might not. Something else might do the emitting.
With those rocket-like nozzle-like things in the back of starships, it seems as though something is being emitted from them. Might be waste heat. Might be neutrinos. Might be "jump flux particles" or some other fake thing. Might be magical.
Or might they simply be the port(s) where waste helium from the Power Plant is vented? We are presuming (based on appearance) that the ports are associated with the M-Drive.
Or they may simply be some type of protective cowling for when the ship is in port/dirt-side (I believe someone already suggested something to this effect upthread).
esampson
SOC-13
Actually, it does. The movement of the rocket can be viewed as either action or reaction (with the thrust taking the correlating position).
Newtons third law does not state that for some actions there is an equal and opposite reaction. It states that for every action there is an equal and opposite reaction. It is, according to the third law, impossible for forward motion without mass being pressed in the opposite direction. When you walk forward the Earth is pushed back by an equal and opposite amount. It is simply that the mass of the Earth is so many orders of magnitude greater than yours that the amount it is pushed 'back' is many orders of magnitude less.
Even sails make use of action/reaction, pushing air (or other forces) in the opposite direction. It is simply that the amount of force exerted in the opposite direction is not enough to completely overcome the momentum of the medium and so the medium is slowed rather than stopped.
Let's at least be honest about those 'vents' (as some have proposed) on the back of the ships ... they look almost exactly like the back of a jet engine. To argue that they are just some minor vent for waste gasses invites giggles in response.
I think that it was TNE where they bit the bullet and re-imagined that the grav magic simply reduced the inertia of the ship so a reaction drive could achieve Traveller performance levels.
If you really think that the ships have no thrust and the MD pushes nothing against nothing (or against the whole universe, take your pick) then you should really start designing ships that reflect that reality ... the official "classics" do not.
I think that it was TNE where they bit the bullet and re-imagined that the grav magic simply reduced the inertia of the ship so a reaction drive could achieve Traveller performance levels.
If you really think that the ships have no thrust and the MD pushes nothing against nothing (or against the whole universe, take your pick) then you should really start designing ships that reflect that reality ... the official "classics" do not.
esampson
SOC-13
The positioning of the nozzles and shape of the nozzles would really only make sense if they are for some sort of propulsion. As devices for getting rid of waste heat they wouldn't make any sense because you wouldn't want to constrict them. While it is conceivable to have something at the back of the ship that has to be shielded you would want that shielding to flare out rather than constrict.
Additionally the fact that they are all placed on one side of the ship would tend to indicate thrust. As devices which are used as some form of emitter you could have them facing in any direction, and in fact would probably want to have them facing opposite each other in order to prevent emissive pressure from shifting the ship (assuming you have more than one).
Neither of these points is meant to be read as 'ships must have engine nozzles'. These are simply observations that the nozzles we see in the art really would have to be related to propulsion (assuming they aren't some weird form of airlock or something). If we accept that ships do not have some sort of exhaust thrust then they are pretty much an artist's mistake.
mike wightman
SOC-14 10K
CT '77 edition implied in the fuel use section that fuel was being burned to produce accelerations, at least 288 of them if the power plant is fully fuelled, and in the non-starships section it mentions all non-starships consume fuel at 10kg per G of acceleration for 10 minutes.
HG first edition flat out states the maneuver drive is a fusion rocket.
Artists producing images for such vessels are going to put rocket exhaust ports in the diagrams.
Revised CT ('81 edition, TTB, ST) and HG2 dropped the references to fuel use and the statement about fusion rockets. But by then we already have four years of artwork showing exhausts
HG first edition flat out states the maneuver drive is a fusion rocket.
Artists producing images for such vessels are going to put rocket exhaust ports in the diagrams.
Revised CT ('81 edition, TTB, ST) and HG2 dropped the references to fuel use and the statement about fusion rockets. But by then we already have four years of artwork showing exhausts
Of course, you are right. And Mike's post clarifies CT for us:
1977: M-drives burn fuel, of course. How? Who cares?
1979: M-drives are fusion rockets.
1981: M-drives do not burn fuel.
(Perhaps due to cans of worms being opened up when every ship is a big fusion gun? But then every ship is a big fusion bomb anyway...)
1992: Ships have High Energy Plasma Recombination rockets, which burn LOTS of fuel.
1996: HEPlaR burns lots of fuel, and M-drives do not burn fuel. Both are available.
2008: M-drives tacitly do not burn fuel.
2012: M-drives do not burn fuel. HEPlaR and other rockets are supplemental, and a bit apocryphal, although draft material exists.
And so we know why the art is the way it is. And even though M-drives are now gravitic thrust-plate-like things, the art is still iconic, and something I can't see being un-done, no matter how anachronistic it is.