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The scenario: In the not too distant future, someone ran just the right genetic algorithm and figured out how to make a warp drive. It can travel to distant stars! The only problem is that optical technology hasn't really caught up, and the sky is big, so really the crew is only vaguely aware of the position of the largest planets in the system they are warping into.

They are on a mission of exploration, dammit, and explore they will. Presume that they show up somewhere about Earth distance away from the approximately sunlike star. Presume that there are planets similar to those in our solar system floating around (so sure, there can be a rocky planet around where Mars is, and why not a large gas giant or two out in the outer reaches, but not much further than Saturn and not much larger than Jupiter). Presume that the warp drive makes it possible to reach all of those worlds. Finally, presume that they don't have access to "planet scanners". They've got what we have - optical and radio telescopes. How do they know where the worlds are, and how do they localize themselves with enough precision to navigate?

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  • $\begingroup$ By radio telescopes, would they use radio waves? If so, couldn't they fashion a radar? $\endgroup$ – LorenzoTheSnail Apr 22 at 17:13
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    $\begingroup$ Related worldbuilding.stackexchange.com/q/63414/30492, if not even duplicate $\endgroup$ – L.Dutch Apr 22 at 17:15
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    $\begingroup$ What is exactly the question here? They simply use the optical telescope to look for them... I mean, here on Earth you can look at the night sky with the naked eye and the brightest things (after the Moon obviously) will probably be planets. I can find Mars by looking at the sky, seeing a brightish-red dot, and aiming my telescope at it. Hell, most planets were discovered by ancient astronomers before modern optics.... $\endgroup$ – Dragongeek Apr 22 at 17:38
  • $\begingroup$ @Dragongeek Yes, but the problem of navigation is one of simultaneously locating yourself in a useful coordinate system and then mapping the location of the planets in that coordinate system. So it's not enough to just detect the bright things, one needs to know how to get there. How do you do that with an optical telescope? $\endgroup$ – Michael Stachowsky Apr 22 at 17:41
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    $\begingroup$ Take a full-sky picture. Note the brightest items. Jump a few AU in any direction. Take another picture. Tell the computer to note everything that is in a different position. $\endgroup$ – notovny Apr 22 at 17:42
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  1. Observe the star, particularly its spin. That will tell you where the debris disk (planets) are most likely to be. The star's equator is likely to be close to the plane of the debris disk.

  2. Jump to a spot well above/below the expected debris disk. Mask out the star's light. Take a 6-hour photographic exposure (or equivalent). The lines (not dots) on the photographic plate (or equivalent) are the planets, moons, asteroids, comets, and other assorted reflecting debris. Now you know which objects to study in detail, and roughly where they are.

    A second exposure a couple days later will provide enough information to rough out each object's orbit so you can find it again.

    Since few planets are exactly on the same two-dimensional plane, a third observation from an acute angle to the debris disk is a pretty good idea.

  3. Your growing ephemeris of objects in orbit should be checked by a gravity model. If an object's observed orbit doesn't quite match the model, you know that you have missed something that you should probably investigate.

  4. Look at the spectrum reflected by each object that you want to study in order to plan and prioritize detailed investigation. "Hey, this absorption pattern matches carbon dioxide."

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    $\begingroup$ Nitpick: There is no "plane of the ecliptic" until you select a planet and designate it as the "main" planet of the system. You may mean the "invariable plane". $\endgroup$ – AlexP Apr 22 at 18:39
  • $\begingroup$ @AlexP indeed. Edited. $\endgroup$ – user535733 Apr 22 at 18:43
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    $\begingroup$ The question indicates there's FTL travel. There's little/no need to spend significant time to take a long measurement. You can achieve basically any desired amount of effective time-separation between observations by using the FTL drive to move to different distances away from what you're observing. With FTL, you can choose nearly any time at which you want to observe. You also, inherently, have effectively cheap space transport (at lest relatively), which allows you to have whatever size observation array your technology supports (e.g. want a 100AU array, it's just an engineering problem). $\endgroup$ – Makyen Apr 23 at 2:53
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    $\begingroup$ @Makyen sure, there are lots of clever ways to obtain the answers a bit faster. This answer is deliberately simple so folks can see the underlying reasoning without the distraction of too many miracles. $\endgroup$ – user535733 Apr 23 at 3:37
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    $\begingroup$ @Makyen True, but the question doesn't say the cost of using the drive. Maybe the fuel is very expensive, or maybe it takes many days to charge, or maybe jumps are inherently risky, or maybe it's limited by mass and can only carry limited fuel. As for your other point, even if there was no limit on how much mass can jump, you still have to get the equipment into orbit first (unless you can jump from Earth), so there's a cost to that. $\endgroup$ – Withadel Apr 23 at 6:15
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Navigating around the star and planets could be done simply with optics.

They would be able to compute their polar coordinates very accurately with respect to the local star by observing the star's new location relative to the background stars after each warp. They would also be able to easily use the inverse square law to compute their new relative distance from the star based on its new brightness. That would be aided greatly if their warp drive technology allowed them to control the distance travelled during a particular warp, within say at least 1 AU accuracy. (Presumably, this is the case since "the warp drive makes it possible to reach all of those worlds".) In which case they would only need to make a few triangulating warps to know their precise distance from the star from that point forward.

With their precise solar system coordinates knowable it then becomes a straightforward matter of discovering and fixing the planets. Full sky optical scans after a few warps around the star should be able to easily fix the interesting bodies again using triangulation.

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The ship would consult its star map.

We already have telescopes and other devices to observe and detect distant objects. By using this method, we have been able to gather plenty of data about not only our own system but others as well. If the warp drive existed, the logical next step is to strap it to a huge telescope designed to detect in-system objects (the same way we observe planets in our system), then have the telescope jump to each star system, observe the planets, come back to Earth with data (it's faster than beaming radio waves!) and repeat.

The information can be packaged into databases and sold to ship captains. There's no need for individual ships to go into uncharted space and reinvent the wheel.

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Stereoscopic view of the system, and triangulation.

Arrive in the system.
Take one high-resolution optical image of the system.

Jump in any direction by a distance of a few AU, not directly towards or away from the sun(s).
Take a second high-resolution optical image of the system.

The difference between the two images are the suns, planets, moons, and larger asteroids.

As you know the location of your two observations very exactly, and the number of object will be relatively low and usually visually distinctive, it is a trivial case to use triangulation to determine their exact position, and a rough estimate of their size.

Now sit at your second location for a while, and take a third high-resolution image of the system. This will give you a very good idea of the current motion of the detected objects.

You may miss out on the very distant and faint objects this way, for example the same technique used in our solar system with current (portable) telescope and computer tech, would easily detect the planets from Mercury to Saturn, but might miss Uranus and Neptune(they are so far out that the motion may not be enough) and will almost certainly miss Pluto and all but the very largest of the asteroids.

You may also miss anything that was obscured by the Sun(s) in either of the first two images, but you are rather likely to know that you missed something (it will be in 1 but not both of your first 2 images) , just not where it was. One more observation from a suitably picked third viewpoint should clear this up.

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