Land Navigation
- Thread starter HSlam
- Start date
fusor said:
You are judging the difficulty of the task by how difficult it is for a 21st-century computer/radar combination. o course it's not a trivial task for a 21st century tech. Using a satellite that has the power output of a microwave oven crammed into the smallest possible physical package.then transmitting its data over a ridiculously low bandwidth signal to a computer that should have been retired 15 years ago.However The slow down doesn't come from the radar...it's the processing power of the computer translating the radar returns into useful data.
for a radar unit and computer system built a few centuries from now...yeah it's a trial task/plotting the moon shot is a trivial task, detailed, and precise requiring a decent bit of modeling software.... but trivial in terms of workload for the computer. these are computers that can perform calculations to control a starship through a jump sequence that fold spindles and mutilates the laws of physics. taking into account the relative motion of two separate star systems, which are moving in multiple axis at extreme velocities, as well as account for such things as the expansion of time/space....compared to that mapping a earth sized hunk of stone and water is relatively trivial.
As for the radar....
If a radar system has the resolution and output strength to track a ship the size of a football pitch across a million Kilometers of open space, with the resolution to identify it has the resolution and output power to map a planet from say 100,000Km you don't need down to the centimeter resolution....not for a useful map.And I didn't not say it would be an instant, it could take several loops around the planet but its not like they have to hide their actions from the local defense squadron...mapping a planet is seldom a criminal offense.andtho OP mentioned unexplored/unsettled so in theory if it took several days there would be no problem.
He's been to the 57th century.[/quote]
Oh crap I've been discovered.....the temporal oversight committee is going to have a cow....
No, I am jus making a slightly educated guess based on what I know about radar, the computing power required to create accurate models of objects, and modeling software.....besides If I Had ben to the 57th, I'd still be there hitting the talk show circuits and lecturing on life on pre starlight earth..or touring with a circus as the incredible man ape form ancient Earth....
Reynard said:
It could in some cases - if the water was particularly shallow. But on a water world it's more likely that the water would be kilometres deep - possibly even tens of kilometres. On a frontier (or newly explored) world it would be rather difficult to drop buoys that could be securely anchored to a solid surface that is kilometres underwater. The problem is similar to that of a gas giant (where of course there's nothing to anchor a buoy to) - for Jupiter three different longitude systems (I, II and III) are used depending on whether a feature is near the poles or equator (I and II) or using the magnetosphere of the planet (III), all of which have different rotation rates. Though even for gas giants it's arbitrary: As described at http://vgrmag.gsfc.nasa.gov/planetary.html , the zero meridian is defined based on where Voyager (or earth) was at a specific time. So things can get very complicated on such worlds.
wbnc said:
Ah, so you're just armwaving and making baseless assumptions then. Not everything is going to be turned into a trivial task by magical 57th century supertech that can be used to armwave every physical issue away. Physics still has to be deal with and is still a limitation.
I mean, sure, big radar systems could be used to map planets from afar - we've done that with Aricebo on Earth and got pretty good planetary-scale radar images even from millions of kilometres away ( http://www.naic.edu/~pradar/radarpage.html ). But that's Aricebo - a 305m wide fixed radar dish on Earth. Not a poxy little spaceship that isn't built for the task. And the computing power may not be an issue, but it still takes time to gather the data, and someone has to analyse and interpret it too (unless you have AI expert systems that replace the ship's crew? Or do you want your computer to tell the PCs exactly where the object they're looking for is?). And you need to get data at the appropriate resolution too - it took a year of orbiting (1792 orbits) for the Magellan probe to produce a radar map of (83% of) Venus at hundred-metre resolution scales ( https://en.wikipedia.org/wiki/Magellan_(spacecraft)#Orbital_encounter_of_Venus ).
But I guess in your setting all spaceships have gigantic Aricebo-sized radar dishes on them and don't care about being blindingly bright targets to passive sensors by broadcasting megawatts of radio waves (what a great idea for exploring an unknown world!), or they carry complex synthetic aperture setups that can be used to map surfaces at metre-scale resolution from millions of kilometres away?
Tenacious-Techhunter
Mongoose
Pictures from Space of the Earth’s oceans often reveal some very interesting, and very identifiable, features.
Some useful ones for planets that are “fully flooded”:
Hydrothermal Vents
Tectonic Borders
Ocean-Floor guided low temperature Currents
Phosphorescent Reefs
Tropical Algal Blooms
Some useful ones for planets that are “fully flooded”:
Hydrothermal Vents
Tectonic Borders
Ocean-Floor guided low temperature Currents
Phosphorescent Reefs
Tropical Algal Blooms
Tenacious-Techhunter
Mongoose
fusor said:
“Resolution” is a TL question. How much higher does Resolution go up by for each TL? Until you can answer that, you can’t say he’s wrong. Regardless, even poor resolution images are useful. Since their data already has all the resolution landing on the planet the first time needed, they only need enough resolution to find a match to a known series of images... which isn’t a hard machine vision problem at all, even at poor resolutions (it’s harder to identify, say, pictures with cats in them).
Tenacious-Techhunter
Mongoose
Condottiere said:
The place on that planet where it was noon on the day the Emperor was actually born would be a good example of an arbitrary zeroth longitudinal arc defined by software.
Tenacious-Techhunter
Mongoose
HSlam said:
With Hyperspectral Imaging alone, there’s always a feature. Throw in a bunch of other sensors, and you’ll always have some big glowing something to peg as a reference, so long as you turn on the right filter. And leave a navigation beacon in geosynchronous orbit with that spot that can respond with what sensor filter settings to use.
Tenacious-Techhunter
Mongoose
fusor said:
The number of orbits required was a function of the desired resolution of the final complete image and of the aperture required to take images at that resolution with the required technology available at the time. The entire planet doesn’t need to have been mapped... they just need enough detail to go back to where they’ve already been... that isn’t a lot of detail.
Take a map of the Earth... how much resolution does it take to pick out the right continent, or the right ocean, from that map? From there, how much detail does it take to pick out the right region? And so on, and so on, until you’re at where you’ve already been.
Tenacious-Techhunter
Mongoose
Traveller already has rules for mapping out an entire planet... but that’s a red herring, and here’s why...
Those maps aren’t just navigation maps... they’re also value assessments on the scientific, agricultural, economical, archaeological, and strategic value of that planet.
“Oh, there are some interesting flora and fauna, and some fancy minerals...”
“Good soil for planting... this could be a new colony!”
“Nuts to that! Strip-mine this bitch for the magnificent resources!”
“Easy now... those figures carved into the rocky desert floor have tremendous archaeological value...”
“You’re all wrong... this planet is of tremendous strategic value... as a foothold into the Imperium! Long live the Zhodani Consulate!!!” *zap*
Mapping all this valuable data takes time, even in a polar orbit, which is why the Scout Service uses drones put into other polar orbits to supplement the recordings of the ship itself. But, for basic navigation, all that nonsense is overkill. As you approach the planet over a few days, you capture supersampled data, and if the computer doesn’t give you a recommendation you like on where to place your coordinate system, you fast-forward through a day’s cycle for each of your filters until you find a sufficiently obvious bright spot. And there’s your zero longitude.
Those maps aren’t just navigation maps... they’re also value assessments on the scientific, agricultural, economical, archaeological, and strategic value of that planet.
“Oh, there are some interesting flora and fauna, and some fancy minerals...”
“Good soil for planting... this could be a new colony!”
“Nuts to that! Strip-mine this bitch for the magnificent resources!”
“Easy now... those figures carved into the rocky desert floor have tremendous archaeological value...”
“You’re all wrong... this planet is of tremendous strategic value... as a foothold into the Imperium! Long live the Zhodani Consulate!!!” *zap*
Mapping all this valuable data takes time, even in a polar orbit, which is why the Scout Service uses drones put into other polar orbits to supplement the recordings of the ship itself. But, for basic navigation, all that nonsense is overkill. As you approach the planet over a few days, you capture supersampled data, and if the computer doesn’t give you a recommendation you like on where to place your coordinate system, you fast-forward through a day’s cycle for each of your filters until you find a sufficiently obvious bright spot. And there’s your zero longitude.
fusor said:
The Magellan probe had a 3-meter dish...which were leftovers from the voyager program...and only had solar cells generating 1200 watts, and had around 225megabytes worth of memory...of course it took forever to map the surface with that hardware...the weather radar, on a Gulfstream private jet is more advanced. And compared to an Airforce J-Stars capabilities Magellan's radar is about as advanced as an abacas.
aArifical aperture radar uses hardware not much different than any other radar, the software is the key not the hardware, and I do imagine it would be fairly common software for anyone doing survey, or recon work..such as a crew trying to locate a freaking four-acre w island out of thousands of islands. It wouldn't be as good as a purpose built survey package mounted on a scoutship, but it would be good enough to generate a useful map.
Of course, I was making assumptions....I missed The Semester they were teaching planetary survey technology at the Fleet academy.......I based my assumptions(and that's all anyone can make without access to a TARDIS) on the progress made between the 1940s and current levels of technology in a smooth progression. And, I was being conservative by using a smooth progression for hardware and software.
Well, the sensor does not even have to be "really really good", it only has to be of the right type.HSlam said:
The best way to discover features on a planet covered by a featureless layer of lava, sand or water is a gravimeter which measures variations in the planet's gravity field. The problem with gravimetry is that one cannot distinguish well between variations caused by topography (e.g. a mountain) and variations caused by the presence of an above average mass (e.g. an uranium lode), but if one just needs any kind of feature for navigation this does not really matter. Gravimetry is already a well developed sensor technology today, and a civilization which routinely uses gravitics technology will certainly include a gravimeter in its starship sensor arrays.
Condottiere
Emperor Mongoose
Mapping out an empty planet would be one of those boring tasks entrusted to an autonomous drone.
I was reminded that the whole problem with frontier planets/lifeless planets/large moons etc would be two fold. Identifying a zero longitude is all well and good, but whatever your using as a navigational aid while traveling the surface also has to be able to find that zero line. So, in the case of a "featureless" world your traveller needs to have something in his possession that can reference whatever your ship or drone sensors used as a reference.
If it relies on the ship or drone in orbit then whatever tech its using is little better than current GPS - assuming it has to maintain line of sight with the ship or drone. If its inertial or gravimetric then it still needs to communicate with the orbital sensor long enough to establish reference to the established zero line.
Of course, if the zero line can be seen by the mark 1 eyeball then you can navigate with compass and a sundial.
If it relies on the ship or drone in orbit then whatever tech its using is little better than current GPS - assuming it has to maintain line of sight with the ship or drone. If its inertial or gravimetric then it still needs to communicate with the orbital sensor long enough to establish reference to the established zero line.
Of course, if the zero line can be seen by the mark 1 eyeball then you can navigate with compass and a sundial.
Condottiere
Emperor Mongoose
Ley lines.
rust2 said:
It can account for topography (there's a correction that can be done for that, because in most cases you'll know the topography is there). What gravity surveys can't differentiate well is a deep, dense body vs a shallow less dense body - those would give the same gravity signal. You'd have to know something about the local geology to be able to rule one or the other out. You can still use it to determine the presence of mass concentrations (or voids) though, even if you can't pin down how deep they are very well.
rust2 said:Theoretically, yes, but in real life it can become quite complicated. For example, the scientists know perfectly well that the Alps are there, but to create a detailed gravimetric map of their area is still a nightmare.fusor said:
If you're talking about such large scales then there'll be isostatic corrections for mountain ranges. if you're looking at smaller scales within there then the local topography can be accounted for (but yes, it'll be a bit more complicated - but they could handle it well enough when I studied the topic 25 years ago, they can probably handle it better now).
The point is you're not going to get a pinpoint "x-ray" style map using gravity. You'll get a broad idea for what's underneath the surface (hopefully made more likely by using it in conjunction with geological and other geophysical surveys) but you're unlikely to get exact depths to precisely defined objects. Gravity is useful with other surveys, but (like any survey) of limited use on its own.
fusor said:
You are right even though you got your terminology backward.... Remember a Large Scale Map is a detail Local map, While a Small Scale Map is a more general Regional map. As Large and small are all about the fractional scale....
Now to answer the original question of How to Navigate on a world without a detailed work up.
1st Traveller answer is to be in possession of a Inertial Compass which keeps track of your starting location.
2nd would be to possess the Navigation Skill, a watch and some sort of log, then one rough figure both latitude and longitude from a known starting point.
As for setting local geographic zero pick your favorite method for your game. I believe in that in general in the Imperium that baseline is set to the main downport of a world.
