Details on how M-Drives work

[aramis]

What are the external effects of the drive? What happens to someone standing next to the ship when they fire it up?

Per Marc, it's pretty rough.

T5 B2 p113, paraphrased: the jump drive operates on all the tonnage within its field. Anything besides the ship (or someone physically in contact with the ship) automatically misjumps.

T5 B2 p120, Paraphrased: The ship itself loses performance as if all the items in its bubble are part of it. If this reduces below the plotted jump, it's treated as an astrogation failure. If it reduces below J1 Jump drive failure does major damage to the drive, and spends a random time in jump...2-12 days. It also puts you on target...

Note that aiming for the 100D limit with larger drives (say, Hop 1), you can't actually plot a 3 Parsec hop course, but you can plot a course which will intersect the desired world's occultation, the random time in jump may mean it's not there, and you go full distance.

(Edit: I realized I misread and was thinking JD.)

Thruster plates/MD in CT, MT, and T4 have no reaction. THe plates themselves are pushed by their action, and move the ship mechanically.
Fusion Rockets in CT Bk5-79 are lethal weapons. Which is probably why Jeff Swycaffer's Exonidas Spaceport includes a repulsor beam to land ships.

 

[Proneutron]

Seems...odd that they go 1G to 6G in tech 8-10, IIRC, but then hit a firm limit forevermore...) as well as, likely, some sort of velocity limit . . . not sure if I can justify it, but that's life in the slow lane.

MgT has higher G ratings for small craft...

 

[Proneutron]

What are the external effects of the drive? What happens to someone standing next to the ship when they fire it up?

Not good. If you were standing next to the ship when it lifted off you'd be pulled by the same Gravity well at the same rate as the ship. Eventually dying of freezing and hypoxia as you went towards orbit.

 

[BRover]

MgT has higher G ratings for small craft...

Never seen a copy . . . hence my ignorance.

 

[Timerover51]

Go for for it! And if anyone knows all the different Cannon data from the carious versions of Trav that would be cool. Aramis already added the thruster plate data from MT?

I assume the "Dean Drive" for my maneuver drive, and require that the power plant number match the maneuver drive number on all ships. For small craft, I go with the Dean Drive as well, along with a power plant of Type A, depending on the G-rating.

Edit Note: The Dean Drive should be considered Tech Level 6 or 7, as it was developed in the late 1950s to early 1960s.

 

[mike wightman]

No, you are talking about a DIFFERENT usage of gravity. What NASA describes as a warp drive. Which is ENCASING the ship is a bubble of space time that is then moved. That is not how a gravity well works. Two different uses for gravity altogether.

It is exactly how gravity works.
Gravity is warped spacetime.
If you warp spacetime you have an affect that you can call gravity.

A gravity well as you call it is a geodesic in curved spacetime...

 

[mike wightman]

MgT has higher G ratings for small craft...

TNE, MgT and T5 all raise the maximum performance for all craft.

 

[Grav_Moped]

My vision (rather fuzzy) of maneuver drives is that of creating a gravity "ramp" (bubble?) so the ship falls down it--higher Gs having a steeper "hill"--with the ship floors/ceilings having (flat) grav-modules for internal gravity. Hence the limit is volume (or length?) rather than mass, since all the stuff in the field fall at the same acceleration.

So, yeah, a "warp" drive, but limited--max 6G (or thereabouts. Seems...odd that they go 1G to 6G in tech 8-10, IIRC, but then hit a firm limit forevermore...) as well as, likely, some sort of velocity limit . . . not sure if I can justify it, but that's life in the slow lane.

The 6G limit is because the Traveller universe was created to use six-sided dice.

On a more serious note, 6G is pretty much about as much as humans can handle for 10 minutes in an acceleration couch. This would make artificial gravity an optional feature in ATUs (you can have it if you want, or you can get all crunchy-SF and make every ship a tailsitter/skyscraper without different rules). Limiting missiles to 6G appears to have just been a play balance decision.
Perhaps there's an in-universe limit to how strong an artificial gravity field (uniform enough for humans to tolerate) can be generated regardless of tech level. It's probably more complicated than that, though.

In Classic Traveller, there wasn't a velocity limit. That came later -- and even then, it's not so much a velocity limit as a "distance available in which to accelerate" limit. And that was pretty much only imposed to keep people from turning 1000 metric ton (100 displacement ton) Scout/Couriers into planet-cracking relativistic deadfall ordnance. (Q: How many Ewoks does it take to destroy the Death Star? A: One, with sufficient velocity.)

 

[Panzerkraken]

I've toyed with limiting the utility of reactionless drives by saying that they're limited to an acceleration of M x(perceived gravity), based on this formula.

 

[Proneutron]

I've toyed with limiting the utility of reactionless drives by saying that they're limited to an acceleration of M x(perceived gravity), based on this formula.

What is "perceived gravity"?

 

[Drakon]

What is "perceived gravity"?

Gravity is not a force like, well other forces, it is a "pseudo-force" it is an apparent force we see as an object follows a "geodesic" in space and time. This is the big thing with Einstein.

A geodesic is the straightest possible line on a surface. On a flat plane, a geodesic is a straight line. On a curved surface, a geodesic may curve, because of the distortion in space time around massive objects.

All of Newton's laws still apply. But while Newton assumed that space and time were a fixed and "flat" structure, Einstein saw that if one allowed space and time to bend, gravity, what we see and feel as gravity, falls right into your lap.

Matter creates distortions in the space-time manifold. Objects trying to move in a straight line, end up in orbits and deflections and such because of the bends and curves in space and time.

There is a form of chess that is played on a circular table. All the pieces move the same, but it is possible to "orbit" the board, be able to attack a piece from around the table. All the rules are the same as regular chess, just the board is different. And that difference creates a whole new game.

 

[Proneutron]

Gravity is not a force like, well other forces,

I understand physics. I asked what he meant in the context of that post. Rather than just saying gravity... Thanks though for your time.

 

[kilemall]

I'll throw my current conception out there, those that can make use of it great, those that find it distasteful are advised to not use it or worry about my 'doing it wrong'.


I have the M-drive creating a gravitic bubble around the ship which has the primary effect of causing the ship to 'weigh much less' then it would normally against local space-time. Side effect is it also bends and messes with IR, EMF and other output such that ships are less detectable then they would be 'barefaced' emitting into cold empty space.

Then the heat coming off the fusion reactor powering this drive is ejecting superheated and when actually moving super-accelerated gasses, as such the nozzles on the end of the ship are more exhaust stacks then reaction jets.

Most of the time the ship is just venting heat, but when it's time to move the exhaust IS pushing the ship in a reaction mode, just that the ships 'weighs' grams on the kilogram and a lot less reaction mass is needed to create vector.


Increased Gs are simply higher tech more powerful grav fields that cause the ship to 'weigh less' and get more delta vee per second.



The grav bubble is not practical for planetary vehicles, so they are grav-neutralizing and ultimately grav-thrusting. Earlier orbital craft have reaction drive and planetary have whatever atmosphere drive is possible, ultimately later TL thrusters take over.

Both inertial compensation and artificial gravity ends up being developments of grav thrust tech.

 

[Panzerkraken]

What is "perceived gravity"?

In the sense of the gravitic force calculation,

F=G(m1*m2)/r^2

converted from the result(in kg*m/s^2) to m/s^2 based on the mass of the smaller body (usually m2).

Effectively, the Grav engines work fine as long as you're in a gravity well (stellar or planetary), but they lose effectiveness when you're outside one much faster than the base rules.

Assume 100dT craft, with a 2G M-Drive, and a density of 6T/dT, for a mass of 6x10^5kg. At surface level on Earth (5.972x10^24kg), it has a perceived gravity of 9.8m/s^2, and with a 2G drive, would have an acceleration of 19.6m/s^2. Based on the above, the two objects would cease to have a gravitic relationship at:

(Setting F to 0, reconfiguring)

r=SQRT(G*(m1*m2)

r= SQRT(6.67x10^-11*6x10^5*5.972x10^24) = 1.549x10^10m, or about 15 million km. It's a quadratic relationship, so you can eyeball it along a standard square of x slope for how the thrust falls off.

The thing is, for a given craft, you can have the G*m2 calculation already completed, and just do a quick calculation of the relative weight of the planet. In our case, the Gm2 number is 4.002x10^-5, so if we want to calculate the slope out from Mars (6.39x10^23kg) we just plug that into the equation in place of the mass of Earth for

r=SQRT(6.39x10^23*4.002x10^-5) = 5.056x10^9m, or about 5 million km.

the same would hold true for the Sun (once you leave the planetary wells, you may still be within the Solar gravity well) and the calculation becomes:

r=SQRT(1.989x10^30*4.002x10^-5 = 8.921x10^12m, or 8.9 billion km, somewhere in the neighborhood of 60AU is where the drives would fall off to nothing.

Notably, the drive would be more efficient the closer you get to heavy bodies (such as the sun) so as long as you keep out of the corona, you could potentially get a huge boost while travelling in-system by passing within a few million km of the sun. It's horribly slow (in Traveller terms) otherwise.

For instance, at about the orbit of Mercury, assuming you're not in the influence of other bodies, that 2G M-Drive would have an effective acceleration of .08m/s^2, but moving to half the distance (~30 million km) would increase the effective thrust to 408 km/s^2. Solar slingshots become a serious THING.

So.. all that is pretty much to say I like doing math. d= .5at^2 is the same as calculating the stat mods in MgT to me, so I like to complicate things sometimes.

Edit: I left out the units in a lot of the calculations. G cancels a lot (because it's in N) and most of the rest are in meters.

Edit 2: Corona, not Heliosphere. Heliosphere extends out to 120AU, so not what I meant...

 

[Panzerkraken]

I realized after the fact that I let myself get sucked down the well without addressing the simpler formula that I linked in the first post Proneutron replied to. AND when I was originally thinking about this, I was planning to use that simpler calculation because it doesn't require a lot of big numbers like the masses of planetary bodies or the gravitic constant (G).

g(h) = g(0)*(R(e)/R(e)+h)^2

So what that's saying is that the force of gravity at a given altitude (g(h)) is calculatable based on the square of the altitude. So to calculate the gravity at 100km, take g(0) to be 9.8m/s^2, and R(e) to be 6.378x10^6m. Plugging numbers in becomes:

g(h) = 9.8m/s^2*(6.378x10^6m/6.378x10^6m+1x10^6m)^2= 7.32 m/s^2, or about .75g.

At 1000km, the perceived gravity for earth by that calculation is 1.4 m/s^2 or .15g.

The calculation simplifies the process I described in the previous post by quite a bit. So that 2G M-Drive scout I was talking about there would have 19.6m/s^2 at sea level, but would drop off to 14.6m/s^2 at 100km altitude and at 1000km would be down to 2.8m/s^2 of acceleration. At 10000km it would be down to .0352m/s^2, but at that point the Solar gravity well would have kicked in, for 1.06m/s^2 and you would use the Solar data until the craft reached a different gravity well.

Why? Because ever since the first time I read Have Space Suit, Will Travel, I've thought that multi-g constant acceleration made the solar systems too small. Space is big. If you have jump drives, they should matter for in-system travel as well.

 

[Straybow]

No, you are talking about a DIFFERENT usage of gravity. What NASA describes as a warp drive. Which is ENCASING the ship is a bubble of space time that is then moved. That is not how a gravity well works. Two different uses for gravity altogether.

It is exactly how gravity works.
Gravity is warped spacetime.
If you warp spacetime you have an affect that you can call gravity.

A gravity well as you call it is a geodesic in curved spacetime...

I don't think so. If this is stemming from Alcubierre, it isn't gravitic at all. It smooshes space ahead and re-expands space behind. Technically, the ship isn't moving, nor is the space around the ship moving, per se. The vessel and its warp field are translocating in reference to outside objects but have no acceleration. It seriously messes with frame of reference calcs.


It's fairly certain no communication can pass through the warp field where space is being smooshed (I'm sure that is exactly the technical term), so you can't see where you're going. Communication through the re-expansion side is also doubtful. So, if photons can't penetrate it kinda removes any FTL physics paradoxes.

 

[Proneutron]

I don't think so. If this is stemming from Alcubierre, it isn't gravitic at all. It smooshes space ahead and re-expands space behind. Technically, the ship isn't moving, nor is the space around the ship moving, per se. The vessel and its warp field are translocating in reference to outside objects but have no acceleration. It seriously messes with frame of reference calcs.

Exactly. A "warp" drive isn't creating an external grav well in front of the ship to fall into.

 

[mike wightman]

No, it is warping spacetime - the clue is in the name warp drive, or are you claiming the warp bubble doesn't warp the spacetime around itself?

And any warping of spacetime we perceive as a gravitational affect.

 

[aramis]

No, it is warping spacetime - the clue is in the name warp drive, or are you claiming the warp bubble doesn't warp the spacetime around itself?

And any warping of spacetime we perceive as a gravitational affect.

That's not what I've seen...

... the XYZ set remains flat even though gravity curves motion in it; some argue that that is due to compactified additional dimensions in a parallel brane.

We don't know for certain how Alcubierre's theory would resolve, but it may not be as gravity. And the good Dr. doesn't think it is a gravitic effect.

If it were expressed as gravity, then the warp drive is only good at low sublight, because of the potential for tidal stress to spaghettify the ship. Even still, 10 PSL means mars in 2-4 hours. Alan Dean Foster used the idea of a generated well ahead of the ship, but his was way more of a thermodynamics violation than Traveller's Fusion Plants.

Alcubierre's drive isn't expected, if it works, to result in acceleration, merely motion while activated, dropping you back to inertial space when turned off, with the same moment and vector as when initiated relative to where you started, but translated along a line by having moved the circumscribed volume of space.

This can be problematic; you need to drop out at a point that will result in falling into a relatively good vector; if you can't, you'll need to make multiple short warps in the right spots to bleed off the velocity via gravitation, but then you're accelerating something else.

 

[Proneutron]

If it were expressed as gravity, then the warp drive is only good at low sublight, because of the potential for tidal stress to spaghettify the ship.

Yes, I hadn't even considered tidal force as a fly in that ointment.

My Grav M-Drives are limited to 5%c