Standard maneuvering coordinate system?

[Matt123]

If the plane for all the planets is not the same (or there are significant variation on it), I guess the main world should be used as reference too, for the same reasons given above.

That kinda flows well & is easy to grasp. I will use that principle for all systems IMTU, ta.

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The other consideration is whether in-system travel should use different reference points to jump travel.

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Why would that be needed?

As I understand jump (I may well be wrong, off course), the jump points depend on gravitatory fields, and that's why they change all time and must be calculated for every jump. If so, and as the most used ones are the ones arround the main world (IMHO), this reference method would work quite well.

Without being able to mathematically determine one objects relation to another you are going to struggle to compute a jump. A means of determining that relationship is a given.

My observation was merely that it might make sense for both the in-system references & galactic references to be the same.

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And a final thought, when measuring your location in degrees relative to the sun, while on approach to earth, to how many decimal places must you measure to get a +/- 10m3 accuracy?

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I guess quite a lot...

But why do you need such accuracy? IMHO sensors would make quite less accuracy acceptable.

Not everyone wants to openly approach shipping lanes or rely on domestic nav aids which can be switched off at any time. Calculating jump for example will require mathematically accurate knowledge of your present location and the desired destination. How accurate I don't know, 10m3 is only a guess, but whatever the degree of accuracy required it will be a known quantity & 10m3 is as good a guess as any.

Regardless, I was only curious as to how many decimal places a degree would need to determine a spot at earth orbit distances. My maths ain't up to it

 

[Orr]

As I understand jump (I may well be wrong, off course)...

Your parenthetical aside is an entirely accurate because you are entirely wrong.

Traveller is not Starfire and Traveller is not The Mote in God's Eye. Traveller is Traveller.

There are no "jump points" in Traveller. Rather than there being a certain point where jump can only be attempted, there are any number of points from which you can choose to jump.

Instead of jump points, Traveller has jump limits. Once you clear the jump limit you can jump from any point you choose. Those jump limits have nothing to do with gravity either, they're purely dimensionally based.

As for accuracy requirements Matt mentioned, jump is accurate to within 1,000 kilometers per parsec jumped. Seeing as a parsec is 3.086 e13 kilometers, being able to plot your exit point after traveling that distance to within 1 e3 kilometers implies a certain precision.

 

[McPerth]

Your parenthetical aside is an entirely accurate because you are entirely wrong.

Traveller is not Starfire and Traveller is not The Mote in God's Eye. Traveller is Traveller.

There are no "jump points" in Traveller. Rather than there being a certain point where jump can only be attempted, there are any number of points from which you can choose to jump.

Instead of jump points, Traveller has jump limits. Once you clear the jump limit you can jump from any point you choose. Those jump limits have nothing to do with gravity either, they're purely dimensionally based.

Aside from the possibility (that I fully accept) that I am wrong in the concept, it seems I didn't express well what I meant.

You're right the expression jump points was perhaps not the best I could use. When I used it I didn't mean fixed points from where you must jump, but, as I undertand traveller, to enter acurately to jump, you must place yourself (and your ship, of course) into a precise vector on a precise place at a precise time. That is the task of the navigator, to find where, when an in wich vector you must be to make the jump you want.

Those vectors for jumping are not fixed (if they where you wouldn't need a navigator, as they would surely be somewhat marked), and, AFAIK, canon doesn't tell us what determines them, or under what circumpstances they change.

Even so, canon tells us gravity interferes with them (that's the reason you must be at 100 diameters from any body to safely jump), and IIRC also tells us the multiple dimensions the jump represent, and used for jump, are not fully understood. So I assumed the best way to calculate the vector needed is by the gravity influence on them, more than by a not fully undertood dimensional based calculations.

As for accuracy requirements Matt mentioned, jump is accurate to within 1,000 kilometers per parsec jumped. Seeing as a parsec is 3.086 e13 kilometers, being able to plot your exit point after traveling that distance to within 1 e3 kilometers implies a certain precision.

Never readed that data. Can you please tell us where can we found it?

Not that I doubt it, just curiosity.

BTW, forgive me to fix you, but you expressed wrongly the equivalence for a parsec. Correct equivalence is 3.086 x (10^13) (quite more than as you expressed it, and so reinforcing your point here).

 

[hdan]

Quick note: 3.086e13 is the same thing as 3.086 x (10^13).

 

[steventirey1985]

Quick note: 3.086e13 is the same thing as 3.086 x (10^13).

I was going to post saying that is not correct, but after a bit of looking, it is correct:

Most calculators and many computer programs present very large and very small results in scientific notation. Because superscripted exponents like 107 cannot always be conveniently represented on computers, typewriters and calculators, an alternative format is often used: the letter E or e represents times ten raised to the power of, thus replacing the × 10, followed by the value of the exponent. Note that the character e is not related to the mathematical constant e or the exponential function ex (a confusion that is less likely with capital E); and though it stands for exponent, the notation is usually referred to as (scientific) E notation or (scientific) e notation, rather than (scientific) exponential notation (though the latter also occurs).

So 3.086e13 is the same as 3.086 x (10^13)

 

[McPerth]

Then forgive me my mistake. I understood 'e' meant 'elevated to'.

 

[FreeTrav]

Again with an esoteric question: Does Traveller have some sort of standard method of determing the direction of movement of a ship in terms of its coordinates like is used by aircraft or ships on Earth? Or can one be recommended. It sometimes is nice to be able to give players this sort of a thing as a problem to solve. It is sort of a "Let's see some navigation and piloting skills since your character has them...." sort of thing. :devil:

For interstellar navigation, you really only need to do the equivalent of identifying which "hex" you're in on the map. For that, the (documented) Ring/Ray system is adequate.

The real issue is when you're in a system. For that, I'd use a standard spherical coördinate system - that is, {r, θ, ϕ} - but rather than measuring θ and ϕ in degrees or radians, I'd measure it in grads or centigrads (100 grads is one-quarter of a full circle), carried out to a sufficient number of decimal places to provide the required resolution at the orbital distance of the mainworld.

r=0 is, obviously, at the system barycenter. θ=0 is the line from the barycenter to the center of mass of the mainworld. ϕ=0 is the average plane of the system.

There is an exception to the definition of θ=0. If the mainworld is a satellite of another world in the system (e.g., Regina in orbit about Assiniboia), θ=0 is the line from the stellar system barycenter to the barycenter of the planet-satellite system that contains the mainworld. If the mainworld is an asteroid belt, θ=0 is the line from the system barycenter to the center of mass of the asteroid hosting the main starport (or hosting the administrative center, which I figure is likely to be the same place).

You may also need to report a vector of motion. This also uses the {r, θ, ϕ} notation, where r is the speed (always positive), and θ and ϕ are both zero along the line extending from the system barycenter to your ship, your vector θ is tilted at your location ϕ relative to the system θ=0, and your vector ϕ is in the same plane as the location ϕ.

Reporting verbally (assuming you're using English, or YTU's Galanglic is close enough to English) is always in the format <LOCATION-or-VECTOR> <distance-or-speed> AT θ BY ϕ. For locations, distance is reported in millions of kilometers (Mkm, EM-KAY-EM), to sufficient decimal places to provide mandated fineness of resolution; for vectors, speed is reported in kilometers per second (kmps, KAY-EM-PEE-ESS). Numbers are pronounced digit by digit, so FIVE-ZERO rather than FIFTY. ϕ is the only component that can be negative; if it is, pronounce MINUS, e.g., -92 is MINUS NINE TWO. The decimal point is pronounced POINT.

An example report might be "This is IRMS EMPRESS MARAVA, LOCATION 102.586 EM-KAY-EM AT 117 BY 385 VECTOR 50 KAY-EM-PEE-ESS AT 0 BY -5."

 

[Orr]

... as I undertand traveller, to enter acurately to jump, you must place yourself (and your ship, of course) into a precise vector on a precise place at a precise time.

You have the cart before the horse.

The navigator's calculations do not produce a specific "vector-point-time" where the jump must take place, rather the navigator selects a point at which jump will be initiated and makes his calculations accordingly. The point selected is usually, but not always, the point the ship can reach the earliest.

Putting it another way, the navigator doesn't announce "We can only jump to Regina from this point at this time on this vector.". Instead the navigator announces, "The earliest we can initiate a jump to Regina is from this point."

As for vectors, canon states that vectors are retained through jump. (Something which raises a whole host of questions in itself.) Because of this vector retention feature, there can be situations where a ship may want to create a vector in the departure system which would be useful in the arrival system. While several canonical adventures have included this wrinkle, most written examples of travel to/from the points where jump is initiated have ships beginning/ending at "rest".

Even so, canon tells us gravity interferes...

Canon says nothing of the sort. You're confusing fan-efforts with actual canon.

Marc Miller, the creator and owner of the game, has spent decades regularly shooting down any attempt to link gravity to the 100D jump limit. He has repeatedly said the limit is dimensionally based and that we must simply take it as an article of faith. While text in various sources mentions that gravity seems to play some sort of role, Miller steadfastly refuses to explain just how it occurs and steadfastly prevents anyone else from explaining how it might occur.

Without an explanation that can be turned into a rule, we're left with the dimensionally based 100D limit and nothing more so you can leave gravity aside.

Never readed that data. Can you please tell us where can we found it?

Miller's essay on jumpspace from JTAS issue #24. Find it and read it, it will clear up a lot of things for you.

BTW, forgive me to fix you...

As others have already explained, there's nothing for you to "fix".

 

[Matt123]

You have the cart before the horse.

That seems a little nit-picky, there is little difference between McPerth's statement and your 'correction'. I certainly do not see any evidence in McPerth's statement that indicates he believes there is only one opportunity to jump out of a system.

Miller's essay on jumpspace from JTAS issue #24. Find it and read it, it will clear up a lot of things for you.

Ta for the referance. I'll enjoy reading it.

Just taking a quick skim though I find..

Entering jump is possible anywhere, but the perturbing effects of gravity make it impractical to begin a jump within a gravity field of more than certain specific limits based on size, density, and distance. The general rule of thumb is a distance of at least 100 diameters out from a world or star (including a safety margin)...

It seems MM and McPerth agree.

 

[McPerth]

You have the cart before the horse.

The navigator's calculations do not produce a specific "vector-point-time" where the jump must take place, rather the navigator selects a point at which jump will be initiated and makes his calculations accordingly. The point selected is usually, but not always, the point the ship can reach the earliest.

Putting it another way, the navigator doesn't announce "We can only jump to Regina from this point at this time on this vector.". Instead the navigator announces, "The earliest we can initiate a jump to Regina is from this point."

As for vectors, canon states that vectors are retained through jump. (Something which raises a whole host of questions in itself.) Because of this vector retention feature, there can be situations where a ship may want to create a vector in the departure system which would be useful in the arrival system. While several canonical adventures have included this wrinkle, most written examples of travel to/from the points where jump is initiated have ships beginning/ending at "rest".

I think I was not again able to express well what I meant, but I try not to make my posts several pages long.

When I said 'a precise vector' I don't meant 'a single precise vector', but that the vector you try to enter jump must be very precise (hence the need of a good computer and a good navigator).

You may enter the same jump (from system A to system B) from everal ectors on system A, but they must be precise, in vector, posiiton and time.

Inv V&V, on the sidenote 'The Vilani Hero' (page29), talks about Commodore Maun Ugadushda ordering the ships in his comboy to jump to 'Immediatly jump using any available jump vector'. That poins that you can ener jumpspace from nearly anywhere on a system, but not with free jump vector choice. So if you want to use a precise jump vector (and so make a controlled jump to wherever you want to go, not just leaving a dangerous situation), you must choose the right place and time.

Canon says nothing of the sort. You're confusing fan-efforts with actual canon.

Marc Miller, the creator and owner of the game, has spent decades regularly shooting down any attempt to link gravity to the 100D jump limit. He has repeatedly said the limit is dimensionally based and that we must simply take it as an article of faith. While text in various sources mentions that gravity seems to play some sort of role, Miller steadfastly refuses to explain just how it occurs and steadfastly prevents anyone else from explaining how it might occur.

Without an explanation that can be turned into a rule, we're left with the dimensionally based 100D limit and nothing more so you can leave gravity aside.

Miller's essay on jumpspace from JTAS issue #24. Find it and read it, it will clear up a lot of things for you.

I've done my homework and readed it (BTW, i was also wrong when I said i've never readed it, I've done, but too long ago to remeber).

Aside from the quote Matt gave us above, there are several more quotes in this same article that seem to point against what you say that gravity does not affect.

On page 35 this article:
Gravity has extraordinary effects in the function of the jump drive (...) the transition cannot usuly take place withn the stresses of a gravity well (...) the turbulence created by the gravity well makes the result unpredictable (...)

And in page 37, under Special Types of Jump is a full subsection about Gravity Well Effects.

EDIT That does not mean MM has not changed his mind since then (after all more than 25 years have passed since JTAS #24 was published). I've readed nearly all that I could about CT and MT (not as mucha about other versions), but sure there's many matherial I have not had the oportunity to read.END EDIT

Also, thoughout the article talks about how small is the understanding Imperial physicians have about the alternate universes that allow jump.

As others have already explained, there's nothing for you to "fix".

I already apologized for my misunderstunding and my mistake in this, but I don't mind to do apologize again.

 

[Orr]

It seems MM and McPerth agree.

No, they don't. The difference is rather subtle however.

Miller wrote that gravity effects jump, other writers have written that gravity effects, and fluff/descriptive text has presented that gravity effects jump. That gravity somehow effects jump has been known since the game was first published.

Here's the subtle bit so pay attention.

What has been missing for over 30 years is just HOW gravity effects jump and just HOW that effect can be translated into actual rules beyond the 10D/100D limit requirements. What has also taken place for over 30 years is Miller gently shooting down any and all attempts by anyone to "quantify" or "explain" or otherwise turn into a rule just how gravity effects jump.

We've been repeatedly told to take as an article of faith that jump limits have something to do with gravity and that we should only employ dimensionally-derived jump limits. We're told gravity plays some role and we're also told to ignore gravity's role because the dimensionally-derived limits model that role well enough.

Whatever care navigators must take concerning gravity in their jump calculations is inherent in the 100D limit requirement.

Summing it all up, the game's owner and creator says gravity's effect on jump are inherent in the jump limit requirements and no other explanations are necessary. Clear the limits and gravity is no longer a concern so, because you initiate jump beyond the limits, gravity is not a part of a navigator's jump calculations.

 

[Orr]

Inv V&V, on the sidenote 'The Vilani Hero' (page29)...

Fluff text is not a rule anymore than art is a rule. In fact, fluff text ignores rules as often as art does.

That poins that you can ener jumpspace from nearly anywhere on a system, but not with free jump vector choice. So if you want to use a precise jump vector (and so make a controlled jump to wherever you want to go, not just leaving a dangerous situation), you must choose the right place and time.

You're confusing the real space vectors which are retained through jump with the "vector" a ship follows through jump space.

Jump masking and jump shadows mean that some points at which you can initiate jump are not points from which you can jump to certain destinations. In that case, your choice of jump initiation point will depend on the potential for jump masking/shadow issues. Some points may be "clear" and some points may not be "clear". (I'd left jump masking and jump shadows out of the discussion because they only add complexity to the situation and you're already confused enough.)

As for time, I'll explain again that time only figures into the question of which jump initiation point which A) clears the local jump limit and B) is free of any potential jump masks/shadows for a given destination you can reach the earliest.

Aside from the quote Matt gave us above, there are several more quotes in this same article that seem to point against what you say that gravity does not affect.

I'm explained the subtle part to him and I'll repeat it for you.

Gravity plays some role. Miller says that gravity play some role. Miller has also spent 30 years actively preventing anyone from turning that role into a RULE. We do not calculate field strength, body densities, tidal forces, or any of the other suggestions made over the last 30 years regarding gravity's role. All we calculate is a dimensionally-derived limit which Miller tells us models gravity's role.

Once the ship clears the limit, gravity is no longer an issue.

And in page 37, under Special Types of Jump is a full subsection about Gravity Well Effects.

Once again, that page contains descriptions about how ships will be destroyed or jump attempts will fail. That page contains no RULES regarding however and we're told the many negative consequences can be avoided by clearing dimensionally-derived limits.

Also, thoughout the article talks about how small is the understanding Imperial physicians have about the alternate universes that allow jump.

And that is the peg on which Miller hangs his hat. Jump is barely understood in the game so Miller needn't provide any meta-game explanations beyond what he has already provided.

Summing up again; Miller states that gravity effects jump in some manner and, because gravity's effect on jump is folded into the jump limits, Miller also states that gravity's effect on jump should be ignored. Once a ship clears the jump limit, gravity is no longer a concern.

 

[McPerth]

Returning to the main matter of the thread, does anyone know what kind of references/method real Space Agencies use today for 'rockets' (I don't dare to say spaceships, and now I don'f recall any better word) they launch and that cannot be refered only to Earth (voyager, etc)?

I don't have any idea about that, but maybe can give us some light about the subject, or at least some idea from people more in the matter than myself (an I guess most of us).

 

[Icosahedron]

I doubt if current methods would be of much help. I think today we just use distance and direction from ground control, or distance along a predetermined path. Spaceflight isn't free enough to need a proper co-ordinate system yet.

 

[Dragoner]

Dead reckoning and do the math is how I think it is done now.

 

[BytePro]

o:

Ouch... ok... I'm gonna wade in here.

In real life, we use an Inertial Coordinate System to define positions in the solar system. The 'fixed' origin is the center of mass of the system. This is not the 'center' of the sun, which actually would vary even more. Note that last - because the center of mass is only fixed in the sense that the precision (accuracy) one needs is acceptable. EVERYTHING in the universe MOVES. And gravity is the motive force (you know, that thing Traveller generally handwaves away )

A planet's position relative to a solar system's center of mass is handy (ephemeris) and many other elements are needed to define position in such a system and to establish 'bearings' per the OP question. That is way too much to explain in a post not to mention I know I'd butcher things explaining so I'll start with these tidbit's for now (maybe someone with better writing skills can attempt to simplify things...).

NASA uses the DSN (Deep Space Network - collection of antennas) for determining position and fairly accurate relative speed via measuring differences in frequency shifted signals for interstellar navigation. In addition to several other methods and numerous models. (Others use a similar concept I image). Plans are to use Very Long Baseline Interferometry in the future (distant space based elements added to the network), though I don't believe anyone is there yet...

For interstellar game, using extremely distant (extra galactic preferably) pulsars/quasars - which provide highly visible reference points and extremely accurate timing would almost invariable be used in navigation, even within solar systems. There has been some recent innovations in this area, btw.

And yes, lots and lots of digits of precision are necessary - space is huge and things travel, well, fast!

In RL, navigation and positioning is an iterative, refinement process. No one thing is used. Space probes generally rely on onboard instruments (cameras) to obtain more accurate positioning information as they near their destinations - as Earth based systems can only provide so much accuracy and information about the masses and their motion in the solar system (remember - everything is in motion and gravity is driving it...).