Have we figured out how maneuver might work?

[robject]

I confess, I've been reading Atomic Rocket lately. I regret doing so.

Disclaimer: I am not a gearhead. But, the gearheads do intimidate me, and they say that reactionless drives are a no-no.

So, maneuver drive isn't reactionless, is it? All those rocket nozzles in the backs of ships seem to suggest it.

And no, I don't think they're fusion rockets or high-energy plasma rockets. But they are emitting something that's not particularly destructive but still enough to warrant nozzles.

I do think maneuver drives are gravitic in nature, which means they push and pull against local gravity sources.

But that's as far as I've gotten.

Gravitic, with rocketlike emitters of some sort, but not a fusion/plasma torch.

 

[Cryton]

Actually, the new drive science is working on is pretty much reactionless. Just run electricity through it, and it works. No joke. That's it.

I will see if I can find the links

 

[Cryton]

From 2016:
https://www.sciencealert.com/it-s-o...wed-em-drive-paper-has-finally-been-published

and way to much more. Just google NASA Sonny White EM Drive

And have fun with a reactionless drive

 

[Timerover51]

I have always figured that they were reactionless drives, with gravitics as a base. This is based on the fact that The Traveller Book shows air rafts and GCarriers as Tech Level 8, along with fusion, while Jump Drives appear at Tech Level 9. Now if you were using the large amounts of hydrogen as reaction mass rather than for a "jump bubble", a reaction drive would make more sense. However, you would use more boost and cruise rather than continual acceleration for getting to and coming in from a jump point. I would have to check on mass ratios in Thrust Into Space, but for very high specific impulses such as you would have with a fusion-based reaction drives, I would guess you could do quite well on maybe 10% reaction mass carried.

By very high specific impulse, I am looking at specific impulse levels in the millions of feet per second, with a cruise velocity of jump point of maybe 100,000 feet per second, or circa 20 miles per second. That would give you 72,000 miles per hour and put you at a jump point for Earth in about 12 hours.

 

[vegas]

So, maneuver drive isn't reactionless, is it? All those rocket nozzles in the backs of ships seem to suggest it.

Nah, its reactionless. Those aren't "rocket nozzles", they are for pumping waste heat off the ship conveniently pointed away from the direction of travel...

 

[aramis]

Nah, its reactionless. Those aren't "rocket nozzles", they are for pumping waste heat off the ship conveniently pointed away from the direction of travel...

Perhaps they're the PP exhaust.

 

[Condottiere]

I don't recall that gravatics provide reactionless travel, so if manoeuvre drives are based on them, you're going to feel the acceleration.

Maybe it would need to create and maintain an acceleration bubble.

 

[AnotherDilbert]

The nozzles exist because CT'77 used rockets that expelled reaction mass.

By the time that was retconned in 79-80 the classic illustrations had already established the nozzles.

MT posited that M-drives glowed as a byproduct of its normal operation.



Reactionless can mean several things:

1) A drive that is not expelling lots of noticeable reaction mass.

2) A drive that violates Newton's Third Law "for every action, there is an equal and opposite reaction."

Note that the anti-grav drive of an air/raft might be reactionless in the first sense without being reactionless in the second sense if it affects the local gravity field as a reaction to its lift. Roughly like a maglev train that hovers in and is propelled by the magnetic field, and in turn changes the magnetic field.

A regular ground car is not propelled by expelling reaction mass, yet no-one would call it reactionless given that it exerts a force on the road through the wheels, in accordance with Newton's Third.

Physics would break down and have to be rebuilt from the ground up if the second kind of reactionless drive exists, but the first kind is no problem.


We don't really know how manoeuvre drives are supposed to work. From MT we know that M-drive technology is based on artificial gravity and damper technologies and that a force pushes on the M-drive. We have no idea if the M-drive in turn affects or pushes against anything else, e.g. gravity or electromagnetic fields. Hence, we don't know if the M-drive is reactionless in the second sense.

 

[aramis]

If one goes with reaction drives, then one needs to consider the following;

• Tsiolkovsky's Rocket Equation (how fast is the exhaust)
• the incredible thirst of reaction drives for fuel.
• The very short acceleration times even "magic" levels of fuel (like TNE)
• The very huge distances involved.

So a freighter might have 10 half-hour burns, plus a single jump.
Getting to orbit takes 1-2. To the Jump point, another. 1 G-burn in TNE is 0.5 G-Hours, or 3600 seconds at 1(Traveller G) of 10 m/s². So, for various sizes, travel times on 1G, ignoring local gravity (because the only way I do calc is iteration in programming.)

Size	Diam	Jump Point	h:m:s
1	1600	160000	4:26:40
2	3200	320000	8:53:20
3	4800	480000	13:20:0
4	6400	640000	17:46:40
5	8000	800000	22:13:19
6	9600	960000	26:40:0
7	11200	1120000	31:6:39
8	12800	1280000	35:33:20
9	14400	1440000	40:0:0
10	16000	1600000	44:26:39
11	17600	1760000	48:53:19
12	19200	1920000	53:20:0
13	20800	2080000	57:46:40
14	22400	2240000	62:13:19
15	24000	2400000	66:40:0

[tc=4]1 G-burn travel times rough estimate[/tc]

It turns what was a under 4 hours for CT/MT ships into up to 2 days.

It's best for the feel of the game to have those M drives be gravitic or some form of hyper optimized EM drive.

 

[Keklas Rekobah]

My Cr0.02 worth of handwave...

1) No such thing as a "reactionless" drive.

2) Gravity is matter warping spacetime.

3) Anti-gravity is technology anti-warping spacetime.

IMTU, Sometime during Terra's 21st century, scientists "cracked the code" of how gravity works. Then they essentially reverse-engineered the principle and came up with anti-gravity (AG). By forcing a local anti-warp, they found that not only was it possible to make heavy objects essentially weightless, but with sufficient power, objects could be lifted into orbit. The only problem was, how do you keep them there?

A few tweaks of the tech, and sufficient thrust could be generated in a sort of Alcubiere "bubble" -- not enough to be useful as an FTL drive, but enough to move objects at up to 6G acceleration. For some reason only vaguely hinted at in the maths, 6G is the maximum acceleration that can be achieved using this type of drive, no matter how big the drive or how much power was involved. In fact, exceeding certain limits caused such a catastrophic failure that no trace of the ship, its drive or any of its crew was ever recovered.

The "Action" was the "opening" of the bubble ahead of the vessel and the "closing" of the bubble behind it (or something like that - look up the Alcubiere Drive sometime). The overall effect is as if someone was squeezing an orange through a flexible hose - peristalsis in a mammal's digestive tract would also be a good illustration.

Efficiency is measured in how much power goes into the AG engine versus how much mass is accelerated by how many meters-per-second-squared.

Later experiments with the AG drive showed that the "catastrophic failure" was actually something that allowed the test vessels to travel between two points in space without transiting the distance between those two point. It wasn't exactly teleportation, since some time did pass between departure and arrival - about 168 hours, give or take.

(Sometimes the difference between time in the ship and outside the ship was positive, and sometimes it was negative, so relativistic effects were apparently not in play.)

So ... IMTU, it was the discovery of anti-gravity and the means to control local gravity fields that accelerated* Terra's expansion to the stars.

(*No pun intended.)

And yes, I have read the Atomic Rocket webpages, and while their Real World science is sound, this is Traveller, and a few gimmicks must be allowed or the system - as it is written - fails to be Traveller any more (IMHO).

 

[mike wightman]

Reduce the interaction with the Higgs field and you reduce mass. Reduce mass and you can accelerate objects with less force/energy.

 

[kilemall]

Wouldn't actually reducing mass cause problems with maintaining cohesion at the least? And applying that field make artifical gravity plates a problem to do?

 

[mike wightman]

Wouldn't actually reducing mass cause problems with maintaining cohesion at the least?

Cohesion of what? At the scale of people and ships it is the electrostatic force that holds stuff together.
Project a large enough antigravity wave at a planet and it could fall apart - but that's Ancient era tech.

And applying that field make artifical gravity plates a problem to do?

Actually it makes them much easier to explain.

 

[whartung]

[*]The very short acceleration times even "magic" levels of fuel (like TNE)

Chadwick gave a talk at a convention and from the way he was talking (he did not say this directly), he's mostly convinced that the TNE numbers were too conservative by an order of magnitude at least.

Not infinite fuel to say the least, but, operationally, there's a pretty big difference between 40 "G Turns" of fuel and 400.

 

[mike wightman]

Reduce the length of a turn by a factor of ten and you get somewhere near reality. This would have the effect of slowing ships down, making insystem travel times longer and so insystem jumps become preferable, and you could finally reduce weapon ranges to more realistic performance parameters too.

Reaction mass is reaction mass, if you want to go faster you either have to throw more of it out the back or throw it out at a greater velocity/energy. Fusion rockets, and/or HEPlaR are still limited by the laws of known physics.

 

[aramis]

Chadwick gave a talk at a convention and from the way he was talking (he did not say this directly), he's mostly convinced that the TNE numbers were too conservative by an order of magnitude at least.

Not infinite fuel to say the least, but, operationally, there's a pretty big difference between 40 "G Turns" of fuel and 400.

Frank was overly optimistic. Given the Tsiolkovsky rocket equation, the HEPlaR is a high grade CPAW. One which is impossibly small. Improving it significantly results in hyperluminal exhaust.

Plus, HEPlaR doesn't draw enough energy.

 

[mike wightman]

Kzinti lesson...

'A reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive.'

 

[kilemall]

Cohesion of what? At the scale of people and ships it is the electrostatic force that holds stuff together.
Project a large enough antigravity wave at a planet and it could fall apart - but that's Ancient era tech.

Hmmm, I didn't think that one through. I'll drop that objection.

Actually it makes them much easier to explain.

This assertion I don't get. You're reducing the mass of everything in the ship, yet supposedly putting in a plate that is altering gravity in the direction of the deck floor. I have to think this would create a lot of odd situations and engineering challenges/stresses, not to mention countervailing artificial gravity fields interacting with each other.

 

[mike wightman]

Whatever artificial gravity is it is not real gravity. Real gravity is the curvature of spacetime caused by the mass/energy density in a given location.
'Gravity' simulated by spin, engine thrust of even being hoisted in an elevator is not 'gravity' but is indistinguishable from gravity except it does not cause a curvature of spacetime.

Reducing the effective mass of the stuff on board a ship means whatever force/energy effect is needed to give the illusion of a 1g environment can be much lower.

 

[AnotherDilbert]

Reduced inertia would be quite noticeable.

It would be the opposite of a low gravity environment. Instead of low gravitational pull and standard (high) inertia, you would have standard gravity and low inertia.

Low inertia would mean that things accelerate faster. If you raise your arm your natural reflexes would use too much force throwing your arm away and you with it.

It would not keep things "normal" within a ship.