CT Only: Talking M-Drive Acceleration

[atpollard]

Even a massless object has lightspeed as its top speed (in fact, it is its unique and only speed - the photon and all other particles with zero rest mass are examples).

Works for me ... so in CT, when I engage the MD the ship becomes massless and instantly accelerates to the speed of light ... Should prove interesting.

Perhaps the MD just reduces mass relative to the universe slowly so I accelerate until I am massless and travel at the speed of light. Then what happens if it continues to reduce mass and I start to have negative mass (which is the equivalent of negative energy). Will I accelerate past the speed of light?

As I understand the whole time issue (which is not very well) a trip at light speed to a star 1 LY away will take 1 year to an observer on either star, but time will stop for the person traveling in the ship. So my twin on Earth is one year older than I am. The negative time would also be for those in the ship as well. At twice the speed of light, I would arrive a year younger than when I left, while my twin on Earth will be a year older than when I left (for a 2 LY trip at 2 c).

... There you have it! The reason Civil Engineers like Newton. I have a headache.

 

[whulorigan]

Works for me ... so in CT, when I engage the MD the ship becomes massless and instantly accelerates to the speed of light ... Should prove interesting.

And it can stop on a dime from any prior speed and make right-angle turns like a UFO.

Perhaps the MD just reduces mass relative to the universe slowly so I accelerate until I am massless and travel at the speed of light. Then what happens if it continues to reduce mass and I start to have negative mass (which is the equivalent of negative energy). Will I accelerate past the speed of light?

I have always thought that would be an interesting basis for an ultra-tech Inertialess Drive - one in which the rest-mass of the ship can be "tunably" decoupled from the Higgs Field (which gives fundamental particles their intrinsic rest-masses), allowing the ship to produce a pseudo-acceleration as the inertial-mass gets "tuned down" toward zero.

An interesting consequence of negative mass would be that it experiences a repulsive force from either a positive or negative mass, while at the same time a positive mass would attract either a positive or negative mass. The result is that a negative mass and a positive mass coupled together would accelerate as a unit toward lightpseed in order to preserve conservation of momentum and energy (remember, the masses as well as the velocities will have signs in the conservation equation), which is completely counter-intuitive.

There are actually scientific papers written on this conjectural topic. See: https://arc.aiaa.org/doi/abs/10.2514/3.23219?journalCode=jpp&

As I understand the whole time issue (which is not very well) a trip at light speed to a star 1 LY away will take 1 year to an observer on either star, but time will stop for the person traveling in the ship.

And from the standpoint of the observer on the ship, he would have moved between the stars instantaneously because the distance between the stars will have shrunk to zero.

 

[McPerth]

For ANY later version I would completely agree, and I would not have brought it up at all excpt the topic is designated (CT Only).

Personally, I also IMTU view the MD as a magic box that produces an actual force and the details of the rules as simplifications. However, that is not the only valid interpretation of the rules. Particularly since how REAL gravity functions is a bit of a debated topic, never mind how imaginary super-tech functions. Perhaps the MD generates slightly imbalanced positive and negative energy/mass/gravity like the Alcubierre Drive requires, but Jump drive is more efficient for interstellar distances. I just do not know.

Being mostly a MT man (wehre mass is calclulated aside from volume, but MD stil ldepends on displacement), I've always assumed that the MD, being based on gravitics principles, uses the own generated gravity of the ship to propel it. So, as mass increases, so does produced gravity, compensating for it.

Not being an expert on physics, IDK how consistent is that idea, but it helps me to handwave the fact that the same MD can equally work on ships of the same displacement, true mass (or on why the fact of having your hold empty or full of lead) being irrelevant.

 

[aramis]

For ANY later version I would completely agree, and I would not have brought it up at all excpt the topic is designated (CT Only).

Personally, I also IMTU view the MD as a magic box that produces an actual force and the details of the rules as simplifications. However, that is not the only valid interpretation of the rules. Particularly since how REAL gravity functions is a bit of a debated topic, never mind how imaginary super-tech functions. Perhaps the MD generates slightly imbalanced positive and negative energy/mass/gravity like the Alcubierre Drive requires, but Jump drive is more efficient for interstellar distances. I just do not know.

[Your comments on OTHER massless particles is interesting. It lends credibility to the Speed of light speed limit. It is just not an irrefutable fact of the Rules, and goodness knows that Sci-Fi is all about FTL travel and handwaves.]

Except for one small issue - CT tons are Mass, not volume, as evidenced by the cargo examples.

 

[Straybow]

Actual travel FTL through normal-space will necessarily create causality problems, as FTL travel in normal space is the equivalent of moving backward in time.

We don't know this as a fact. It is an interpretation of the mathematical transformation used in analysis. Most importantly, the Lorentz transformation is subjective. The properties themselves doesn't actually change (like your note about rest mass). If there were an apparent negative time then causality would not actually be violated, only perception of order of events in differing reference frames.

When we encounter a paradox of this type, it is a signal that either our interpretation is wrong or the math is incomplete. Lorentz transformations produce an imaginary number for v>c. It is just as wrong to treat the imaginary result as "negative" in real time (and distance and mass) as it would be to treat it as "positive" in real measurements when it is neither.

The answer is probably both interpretation and math are incomplete rather than either/or. If moving FTL through normal space were possible, it would use a superset of the mathematics we currently use. The FTL math will simplify to the Lorentz equations (or very nearly so) below c, but do something else above c.

 

[Straybow]

Except for one small issue - CT tons are Mass, not volume, as evidenced by the cargo examples.

:CoW:
Not really. CT tons are not consistent with either mass or volume for most examples. Mass, displacement, M-drive, J-drive, two dimensional maps, and many other aspects of Traveller are hand-waves. Just play.

Pay no attention to the little man behind the curtain! :rant:

 

[kilemall]

I went into this issue in great detail due to peculiar aspects of the effects I wanted IMTU.

To recap- I have instantaneous jump but the travellers experience 1 week on board.

That's because I couldn't stomach jump space anymore, but wanted the staterooms and economics of passenger travel to remain the same. Having surprise jump ambushes is also very dramatic.

Since having large time-distance is not important to my universe to generate all those different worlds and their adventurousness (because it is ALL frontier past the core planets and the TC is very loosey-goosey), I don't care about the comms issue.

But I also didn't want humanity jumping across everywhere, so I have another limitation- can't jump unless the local gravitational/subspace anomalies are all charted.

That means an STL ship has to get to an area first, chart it (and keep the charts up afterwards), then jump back with the results before a system opens up.

SO I have scout cruisers- large STL ships that carry several Type S, a Frozen Watch and self-repair maintenance capability to first travel to the new frontier world.

Several issues with such a ship.

It has to carry enough life support for everyone to live for years, including the frozen watch. Since most of the distances involved are 1-2 parsecs, we are talking a LOT of supplies for 4-8 years (time dilation helps but more on that). Basically for CT prices 4 MCr per 10 people (the frozen watch normally won't count against that but we are talking about building in margins).

It has to be able to do maintenance. The Type S jump drives have to work once they get there so an unusually high capability and reliability has to be built in- and a lot of spare parts and fabs.

It has to survive frac-C travel. And being Traveller types, we don't do shields.

I had postulated a system subsumed in M-Drive and hull costs, deflectors. Idea is deflectors are a combination of mini-repulsors and fusion-based energized fields that can't stop lasers or missiles, but can deflect light particles/ionized gases.

Aramis then took us all through the numbers on particles in interstellar space, and when one is going frac-C the issue becomes not if but when you will impact. Arguably without special non-canon equipment it's suicide to run up anywhere near light speed.

So to keep my sanity and setting, I now say that those scout cruisers are maximum armored, have heavy extra deflectors, and keep a specialized sand cloud ahead of it to vaporize the vast majority of particles before they even approach the ship.

The fuel issue is not a factor for my setting. A key component has to do with lunar regolith being scraped up for He-3 for the first version of fusion, said lunar crust becomes the building blocks of a huge O'Neill cluster. So multi-year fusion reactors without the monthly fuel cost are normal, most of the fuel being carried is for accel/decel.

For reference, a couple of time dilation charts. Some people had said time stops at C and that's not quite the effect. I'm figuring something like .8C for my Scout Cruisers.

 

[kilemall]

Now for normal speed I had this set of rules, which imposes a risk/reward for speed, and environmental issues especially a mapped/supported system vs. new exploration.

Slow down, that rock can kill.

Also have a set of solar flare rules I could post, which would impact how fast you are willing to go (particularly near the star, when many such events are avoidable if one can alter course in time), and deflector rules to take the edge off all this mayhem.

[FONT=arial,helvetica]Yet another critical technology is the problem of going near the speed of light.

Redo from another post on speed limits-

Re: the upper speed limit, I'm working within CT and with the missile supplement in play.

The missile supplement is important as it gives you a hard number for what 1 hit is re: joules.

The rule states that you add a hit for every multiple of 300mm closing speed between a missile and it's target.

300mm is 3Gs or 30000 km per 1000 seconds, or expressed another way, 30km/s or approximately .0001 C.

Missile supplement missiles are 50 kg total, so I am assuming 10kg of fuel burned on average before impact, 40kg at 30 km/s.

That yields 18 gigajoules, on the boom table something like 9x the power of a TLAM-C Tomahawk warhead. So even our commercial grade starship hulls can shrug off a lot if that is the damage threshold.

http://www.projectrho.com/public_htm...The_Boom_Table

On the other hand it means that even very low pokey 1G accel to jump distance can be fraught with peril if there is debris out there.

In practice I am assuming a rock big enough to be 40kg would show up on radar and ships will simply maneuver to avoid (a primary reason why pilots are on duty). Or in an asteroid field/ring, there is a much greater change of impact and you just go slow, period.

Large rock groups like the ones that generate meteor showers would be the space-going equivalent of reefs, charted and to be avoided. Corollary is unexplored systems will be full of uncharted 'reefs' waiting to wreck fast moving ships that are not prepared.

Further assumption- the threat is likely smaller rocks or debris that is unmapped and unremarkable, coupled with the need to go faster then 3G/.0001 C.

Heh, or maybe Sand fields from ships' sandcasters.

So a more typical issue would be something 1kg or less, what's the speed limit in that scenario?

Assuming the 18GJ per hit limit, something short of that.

Playing around with the joule/impact calculator, I get 189 km/s, or .00063 C, or 18.9Gs or 1890 mm.

THAT is your absolute safety limit. Beyond that, there are risks, or countermeasures to be taken.

Never knew you were playing with death at slow Traveller speeds, did you?

Now for Big Drama and going say .1C, 30000 km/s. The 1kg impact becomes 450 TeraJoules. Divided against the 18GJ hit value, that's 25,000 hits.

Well. Go for it speedy.

The other factor is probability of impact, which should be VERY low but not impossible, rising to near probably in asteroid belts, rings, orbit, rock fields, etc.

Right now my working rolls are
* 4D(6) per week for inner planet space,
* 5D(6) per week for outer planet space,
* 6D(6) per month for deep space,
* 3D(6) per hour for asteroid belts/rock fields or
* 2D(6) per hour for planets with rings or satellite/sentient space debris.
The (6) means all die must come up 6 in order for the impact to occur.

These objects were too small to be mapped or come up on radar ahead of time. Normally mapped or large objects are avoided with an easy skill roll, surprise objects like these are avoided when possible with a challenging skill roll.

Avoidance assumes mapping or detection. If the ship is shut down for stealth, then there IS no active sensor operating, passive sensors are on an absolute minimum on capacitors, optical guidance is the main tool, and maneuver thrusters are practically manual (direct emergency link to helm, difficulty level/-4 to every maneuver).

Under stealth AND unmapped conditions (no charts available), hit probabilities go up to all 4s, all 5s or all 6s. For stealth OR unmapped situations, rolls are for all 5s or all 6s. Under stealth avoidance is impossible.

When an impact roll comes up, roll 1d6/2 to determine the strength of potential impacts, then roll 1d6 for type and consult table below.

When avoidable, roll challenging skill roll or 11+ with pilot skill, ship G rating and evade program bonuses, or agility/computer for HG. 1 hit against ship per kg per multiple of 18.9 G of impact.

1- 1-3+ kg rock mapped but nav system didn't alert, easy skill roll, or as above but 4+ with 2 as a guaranteed failure. Roll 6d6 once for rock speed.
2- 1-3+ kg rock, movement is below damage threshold, damage is only ship speed.
3- 1-3+ 1 kg rock(s), roll to avoid per rock.
4-a cloud of ice too small for detection to discover in time, impacts occur, no chance to avoid, apply as per 1-3 1kg rocks.
5- add 6d6 G speed of object(s) impact into ship, roll again for type- no limit to G increase. Ignore in asteroid belts or planetary grav wells.
6- double impact strength, roll again for type- no limit to doubling.

For unmapped rock/ice fields, I would leave that to referee imposition. Wouldn't do it very often, but it should happen at least once to the players, or NPCs the players know, and definitely at least once for hardcore scouting/frontier smuggling beyond settled areas.

Implementing something like this even if you disagree with my numbers and assumptions makes for very interesting space terrain, tactical or hide and seek play options, and a sense of 'no really you are in space and you can die' if you choose to exceed safety limits, or even just moving at all.

And this feel is what I am trying to go for in terms of making for drama, risk, etc., even in a merchant run.
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[Enoki]

Question... What about allowing ships to use their weapons to zap these small offending objects? Couldn't a ship with some point defense system aboard simply turn something somewhat dangerous like a small rock into a number of even smaller ones to avoid damage?
If you can spot it on sensors I would assume you can at least try to shoot it too...

It would be a good reason to have some armament on even a small merchant besides trying to fight off the occasional pirate or whatever...

 

[kilemall]

Question... What about allowing ships to use their weapons to zap these small offending objects? Couldn't a ship with some point defense system aboard simply turn something somewhat dangerous like a small rock into a number of even smaller ones to avoid damage?
If you can spot it on sensors I would assume you can at least try to shoot it too...

It would be a good reason to have some armament on even a small merchant besides trying to fight off the occasional pirate or whatever...

I didn't want to post the whole series, it's in my TC Universe, but yes I discuss this- if one were doing it CT style, the thing to do is constantly run Anti-Missile and Auto-Evade, treat the incoming object as an unguided missile that is not tracking per se, and play Asteroids or evade them in most cases.

These programs would only kick in for uncharted objects, in a settled system that would be only very very small rocks/ice. Otherwise flight paths would be set to avoid everything, under normal conditions.

Just a thought on this in the context of frac-C- faster you are going, less time you have to detect and avoid/shoot threatening objects since say a 2:1 time dilation would result in a 60 second alert being only 30 seconds of reaction and burn. A big reason why I wouldn't want to go much past .8C even if I had the tools to clear them.

 

[Supplement Four]

T5 to the rescue! It may not be that great of a game, but it is an awesome reference book for creative Traveller Refs. Lots of great ideas seen from the reference point of Traveller. It's like a printed volume of Marc's Ref's notes. Incomplete, maybe, and not quite ready for prime-time. But helpful to this CT Ref.



On page 365, Marc discusses NAFAL drives. Not As Fast As Light drives. There's a nice chart that shows time to the drive's max, real time, perceived time, and fraction of light speed.

The limit of standard Traveller M-Drives is 1,000 diameters (usually, the system's star). The M-Drive drops to 1% efficiency after that.

NAFAL drives are needed to go interstellar distances if the Jump Drive isn't used, and that takes....A LOT OF TIME. For example, a ship equipped with a 0.5c NAFAL drive can make it to a system 10 parsecs away in 3400 weeks (9.3 years). The occupants of that ship only age 2950 weeks (just over 8 years), due to relativity.

I labeled the thread "CT ONLY", but this is a nifty idea to bring into a CT game.