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This question was inspired by this answer concerning rebels escaping at the battle of Endor

The answer references this piece of dialog from a new hope:

BEN

How long before you can make the jump to light speed?

HAN

It'll take a few moments to get the coordinates from the navi-computer.

The ship begins to rock violently as lasers hit it.

LUKE

Are you kidding? At the rate they're gaining...

HAN

Traveling through hyperspace isn't like dusting crops, boy! Without precise calculations we could fly right through a star or bounce too close to a supernova and that'd end your trip real quick, wouldn't it?

Here's my problem, the universe is essentially empty, stars effectively have an angular size of 0. So if you're not heading straight for any of the large bodies inside the solar system you're in (be it stars, planets or asteroid belts), shouldn't you be fine just jumping into hyperspace and fly straight 99.999999... percent of the time? That is, if all you want to achieve is get away, not get anywhere specific.

I understand why you would have a computer calculate your route if there's no particular hurry, but isn't the risk of hitting anything way smaller than the risk of getting hit by ships that are right on your tail? Or am I missing something here?

Additionally, you could perform a jump of just a few lightyears, which reduces the chances of hitting anything even more.

I'd like to see someone bring out actual estimation of encountering a sufficiently dangerous object on a 1 lightyear path between two solar systems.

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    "Or am I missing something here?" Hyperspace might effectively 'squeeze voids' yet 'expand gravity wells' (for all we know), making that 99.99% space into .01% space. – Andrew Thompson Oct 1 '14 at 13:16
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    I believe space is not as empty as you think. Also you should consider the fact that moving at speeds near c even a few atoms could make a hole in your spaceship, so you can't simply avoid planets and stars but you should stay as far as possible from any object. Galaxies are pretty full of gases and dust (this is also one of the reason why the sky is black at night: most of the stellar light is blocked by gas source), and you must take that in consideration when travelling there. – Bakuriu Oct 1 '14 at 16:31
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    "Traveling through hyperspace ain't like dusting crops, boy! Without precise calculations we could fly right through a star or bounce too close to a supernova" - You seem to have answered your own question... – Valorum Oct 1 '14 at 18:26
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    @Bakuriu That's not why the the sky is black at night. It's because the universe is expanding, which redshifts the light from the surface of last scattering into the microwave wavelengths. In fact, the sky is only black in the visible spectrum; the entire sky glows isotropically in the microwave spectrum. en.wikipedia.org/wiki/Olbers'_paradox – Brian Gordon Oct 1 '14 at 19:52
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    @Bakuriu Space is as empty as the OP believes. While there's a ton of stuff out there, there's a whole crapload more space. Even SJuan76's assertion that multiple lightyears of distance multiplied by the frontal cross-sectional area, the chances of anything being within that volume (even if you traveled several hundred or thousands of lightyears) is essentially zero. That said, hyperspace isn't space. If Hyperspace essentially folds or compresses space around the ship, then all kinds of funky things might happen. – Doc Oct 1 '14 at 23:58

11 Answers 11

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Simple answer is that it's just a plot device.

A more complex answer is that the distances between stars is actually quite vast, however the size of those solar systems, relatively speaking, isn't. So executing an "emergency" jump where all you care about is no longer being in the place you currently are should be trivial. For example, jumping 1 LY in almost ANY direction should place you safely outside of the star system you are currently in without risking collision with another star etc.

In order to make the best of it, the ships should orient themselves such that their direction is perpendicular to the systems plane. ie: point up or down with respect to the orbit of the planetary bodies. Then turn on and shut off after around 1LY of distance has been traveled. That would be about as safe as you could get.

Now the question is whether hyperspace travel requires a large gravitational body (such as a star) to be at both ends of the maneuver. This seems to be implied, and taking gravitational effects into account would make sense with the idea that it takes longer to go one direction than it does the reverse.

If so, then a destination needs to be selected and the orbits and position of various things within the local system as well as the destination need to be taken into account. By "things" I mean anything from planets on down to small asteroids or other floating junk. After all, you don't want to stop in the middle of a 100m wide asteroid. That would take a bit of time, especially if it had to rely on scanning the remote system, calculating where those items are now (versus x years ago if using light as the primary means of knowing what's there) and where they should be when you arrive.

All of that said, it should be entirely possible to have calculated potential escape routes prior to entering the initial system. Kind of like setting a way point. I'd expect such a thing to be standard procedure when entering a combat zone in case your carefully laid out plan meets with unexpected problems. Obviously they can calculate hyperspace jumps when the ships are moving, so the exact position doesn't appear to be necessary. This would change the problem from one of spending time calculating the route to one of loading the necessary data from storage; which should be trivial.

All of this, regardless of the technical issues of how big or fast their computers are or even how complicated it is to calculate, leads me to believe that the only real answer is that it was a plot device that they didn't have a real answer for but felt the idea of a retreat had to be squashed quickly in order to advance the story and keep the tension up.

In reality, a fleet met with overwhelming odds would immediately withdraw unless there was a strategic reason for sacrificing itself. In this particular scene that reason existed: weather the destruction in the hope of being able to get a shot at the deathstar if the shields were ultimately taken offline. Quite frankly, Lucas should have had Ackbar state to press the attack for that reason rather than quibble over retreating.

  • Thinking about this just a little further: Ackbar should have been fired for jumping the fleet into a combat area blind. A good admiral would have sent in a small scout force (even if it's just one a-wing or some drones) to make sure that the situation hadn't significantly changed before committing their entire fleet. – NotMe Oct 3 '14 at 18:24
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Actually, randomly jumping to hyperspace is done in an emergency without any calculations.

For example, in the Thrawn Trilogy, we find that Karrde's ship did that when running away - which is how they discovered the Katana Fleet by accident.

The problems are:

  1. Massive objects tend to pull ships out of hyperspace (which is the principle on which Interdictor Cruisers operated as well as Vong equivalents).

    Worst-case scenario is, you literally crash into a planet, destroying the ship and (in case of a capital class ship) the planet. See Pammant.

  2. (This was the one faced by Karrde's ship), you really don't have any idea where you will end, and you exit hyperspace at a random point.

    Without knowing where you are (and far from any system) - how can you navigate course for the subsequent jumps? So you have to again jump randomly, because you can't compute the hyperspace route to desired destination without knowing where you are.

  • I fail to see the first point as a reasonable concern, your second point is very valid though. Is there no way of finding calculating where you are using data about your last known position and your time in hyperspace? – overactor Oct 1 '14 at 13:36
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    @overactor your asking why they need to calculate, and now your saying well cant they just calculate? lol. simply small objects get deflected away from the ship, this is the same in startrek, stargate, ect. large objects have known paths, locations, orbits. ect. the fastest way to point b from a is a straight line, which might lead you through a star, even if the chance is small, or a higher chance is that your to close to a star. the nav computer simply follows your path and makes a few minor adjustments so you dont die. its not a hard concept. startrek does this too. – Himarm Oct 1 '14 at 14:03
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    @Himarm I meant claculating where you are after you've made the uncalculated jump. If I make a jump of 1 lightyear in a direction roughly perpendicular to the plane of orbit of planets around the nearest star, the chance I'll get too close to anything approaches absolute zero. At least, it seems like that to me. – overactor Oct 1 '14 at 14:11
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    @Himarm, in that case, why would DVK's second point be an issue? – overactor Oct 1 '14 at 14:18
  • I've only seen the movies, but it looks like once you enter hyperspace you're flying blind, with no way to make course corrections or maneuver. And, while interstellar space is almost completely empty, it's that almost you have to be careful about. There's still some non-light-emitting junk out there - planetoids, comets, etc. If a ship in hyperspace is still affected by gravity, then if you pass close to an uncharted rogue planetoid your course will be deflected to who-knows-where - probably into the nearest deep gravity well. – Joe L. Oct 1 '14 at 14:41
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From an outside view, this is simply a dated plot-device. In Star Trek the next generation, for instance, the ship computer could spend hours searching for and retrieving information. This allowed other things to happen in the episode before the data came in and revealed a plot-twist. In Star Wars, the slow computer is an excuse for building tension.

"Computers take their time" fit with the viewer's expectations at the time. It was how computer worked. But today, when google search and retrieve a global knowledge database in a second and the GPS plots my route across the country almost as quickly, we expect computers to answer quickly.

It's interesting how this shows the reader or viewer relying on real-world experiences and present-day common sense to "make sense" of the science fiction story. The flip-side is when older scifi becomes "invalid" and "nonsensical" when read by readers with plenty of first-hand experience with internet and computers. (Which is pretty much everyone these days)

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    If I have my GPS calculate a route down the street, it's pretty much instantaneous. If I have it calculate a route to the next state, it'll take a short while - probably 45 seconds (yes, Google Maps could do it faster thanks to more computing power). The longer the distance, the more it has to take into account. Trying to calculate a route to another part of the galaxy? Yeah, that's not going to be instantaneous. – phantom42 Oct 1 '14 at 13:43
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    Plus, have you SEEN Google's datacenters? Each one is the size of a small town, and they have several. A ship like the Falcon just has a little on-board computer. – Omegacron Oct 1 '14 at 14:27
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    @phantom42 &Omegacron While the answer is out-of-universe accurate, I think you misunderstand why it takes long to compute. It hasn't got to do with real distances, but route complexity. On Earth, it takes longer to compute longer routes because of the overall complexity (or lack thereof) of streets and maps. In space, it remains complex but the distances at which complexity of a map matters would be far larger. However it can be much more complex to calculate a route based on predicted paths of celestial objects and interactions with gravitational fields - that is hard and inaccurate. – mechalynx Oct 1 '14 at 17:06
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    If hyperspace calculations solve an NP-hard problem then it might take a while if n is sufficiently large whatever the power of the computers. – jfs Oct 1 '14 at 18:16
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    One does not simply solve the n-body problem. – curiousdannii Oct 2 '14 at 11:32
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While space is essentially empty, empty is relative.

  • Intergalactic space: the space between galaxies is the closest thing you will get to empty space. This space is outside of most gravity wells and matter has accumulated in galaxies so this space has nothing but the rarest of particles for thousands of parsecs in any direction.

  • Intragalactic or interstellar space: space within a particular galaxy is an entirely different thing altogether. Depending on the density of the stars in a particular galaxy, they can be an average of 4 to 400 light years apart. In some densely packed globular clusters they have been found to be less than a light year apart!

Seeing that Hyperspace travel in the Star Wars universe allows ships to traverse great distances essentially outside of normal space, there are things that still need to be considered and there are many hazards to using Hyperspace travel:

  • Potential Hyperspace Disruptions: We are not certain how massive a body needs to be to interrupt hyperspace travel. If a stellar-sized body can do it, then computations may be needed to account for any travel which passes by a known system. Supermassive objects such as black holes may cause eddies in space-time which could also affect hyperspace travel. Such obligatory computations may need to take such known disturbances into account when making a jump. It is also unclear what effect ships have on hyperspace travel, the computer may need to take recent arrivals or departures into account before calculations can be completed.

  • Galactic Stellar Movement: Nothing stands still in space. Our sun moves at 10 miles per second toward the constellation of Hercules. All stars have some degree of movement throughout the galaxy in relationship to each other. This means any attempt to target a star system must take into account angular momentum of any stars in its database as well as the jump point's angular momentum in relationship to the system the ship is leaving.

  • Known navigational hazards: Like naval ships mark regions of the ocean that are dangerous to ships, it stands to reason there may be regions of hyperspace which could be dangerous to pass through or even fly near. Such hazards would already be plotted into a good navigation system and required to be numbers to be run every time a ship left a star system.

  • Known Jump Coordinates: Good, dedicated computer systems might be able to maintain a number of existing jump coordinates and the computations necessary to get to them in areas where shipping is good, well known and the routes are kept safe and clear. I suspect the region around Coruscant, is one of the most well mapped in the galaxy, approachable from either any number of directions or depending on security protocols, approachable from only secured corridors of traffic.

  • Planetary Security or Designated Shipping Lanes: Since we mentioned security, there is also the possibility, some star systems require approach from approved corridors of traffic. Computations for such system to system jumping may require entering approach vectors or arrivals in dedicate hyperspace coordinates. Ships appearing outside those points could be considered hostile and potentially fired upon.

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Ships travelling through hyperspace are not immune to the influences of the normal space in between. Gravitational effects from stars, planets, black holes, and other phenomena would have an effect on the ships path. For example, a ship traveling too close to a black hole, supernova or star would be dragged out of hyperspace back into normal space, rapidly ending their existence as they were inevitably dragged into it.

Also, a ships destination was likely to be near a planet. One wouldn't want to emerge too close, or even within, the planets sphere of influence either. Add to that the fact that all of these objects are constantly moving at great speeds in different directions.

So while space is vast and perhaps largely empty, following a course across a great distance, trying to hit a target moving in a random direction at thousands of kilometers per second, with thousands or millions or billions of moving targets in between, would inevitably require calculating a path before you depart.

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I agree with the plot device statement. I think it would be a near instantaneous calculation to simply jump a distance equal to that of the nearest star. If gravitational fields and maybe in today's theories, the use of Dark Matter as an added hyper jump device have an effect, it would already be known as searching for the thing closest to you is always the fastest search. Jumping that short of a distance wouldn't drag you around to much because the same things are still close to you, as in, you didn't pass anything. But I'd think that passing up more stars would start to drag you around a bit.

But more plot devices crop up here because if it's that easy for you to make a short jump quickly, it's probably that easy for your pursuer to do the same. But, they'd have to find you first. :) You just have to find an empty space in a place that is mostly empty space. :)

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It's obvious that hyperspace in Star Wars is not a simple linear space, because we see a lot of evidence like this:

  • Routes that have the same length in real space can have different travel time in hyperspace.
  • Even travelling the same route in the opposite direction can take a different amount of time (this wasn't seen in the movies, though, so let's count this as a weak point).
  • A direct route can take much longer than two separate jumps with an intermediate star system.

Of course, all of those could simply be consistency failures, but in-universe, they clearly show that hyperspace is not just a smaller real space.

We can also see that while the hyperdrive can actually travel in non-direct paths, there seems to be routes that are only possible if you do two separate jumps.

The EU is also full of examples of "hidden" routes, and the EU material from early galactic exploration specifically mentions that the hyperspace routes are basically found at random, more or less - or at least that noone can calculate an optimal route between two systems.

However, it also clearly shows that the computers are simply using huge node maps. This is where the computational power of SW computers shows the underestimated growth of computers. Even with hundreds of millions of nodes with directional edges with weights, the search time on a modern desktop computer would be on the order of seconds, maximum. The truth is, most of the sci-fi that deals with old computers underestimates their amazing growth in power, and just as importantly, their incredible scaling down - what they imagined would require a whole station's worth of a computer, easily fits into a simple microchip these days.

It's funny, considering they are using robots capable of near-human thought (or perhaps even better than human), and they can't find a path in a map :)

Slightly off-topic, more hard-core and recent EU for Star Wars tends to handle hyperspace jumps in quite a different fashion. There are many cases, where ships executed multiple successive jumps to avoid pursuit - which is only really possible because the range of hyperspace sensors is very low compared to the speed of the hyperdrive. Even with the conservative speed estimates, it takes under half a second for a ship to travel the range of the sensors. This leaves very little time to do any corrections if you see some dangerous anomaly in front of you, explaining why ships mostly stick to known routes rather than just plowing through the universe :)

  • I am not so sure a modern desktop computer could calculate a route through a digraph with hundreds of millions of nodes in seconds, especially since the weight implies finding a "good" or best route. Graph calculations tend to be exponential, and can easily bring a modern desktop to its knees. Source: I recently finished an M.S. in Computer Science and actually performed such a simulation as part of my algorithms class. My Core i7 calculated a digraph a small fraction of that size and took around 12 hours. – user31563 Oct 3 '14 at 2:14
  • @Snowman Well, they're obviously not searching for the best route by far. In fact, they're trying to fly as straight as possible, regardless of whether it's the fastest way, allowing you to partition the graph a lot. It might be that the straight path is more fuel efficient, while the detour is faster, of course. But finding the absolute best isn't necessary most of the time - it might make sense when you make the same run over and over again, but that could easily be calculated offline. And knowing more about hyperspace topology would likely help a lot as well. – Luaan Oct 3 '14 at 7:49
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There are a few observations to make.

Hyperspace makes you able to travel faster from a to b. Real-space object can have influence on hyperspace

Now the question is: how does hyperspace work?

If hyperspace would be a more compressed version of normal space, then it would explain why you would need to compute a route: object that effect hyperspace would be a lot closer there, and where normal space may look vast and empty, the effects of those same objects on hyperspace would be a lot close together. So you en up with a maze of gravity-wells to navigate, and that's why you would need to compute a route.

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You need to take time to calculate in order to make the plot more exiting. If Han made the jump without any calculations he would have no time to make witty banter with Ben and Luke.

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for my 2 credits.

a few observations on Star wars Hyperspace:

  • it is not a place you can "Hang out" in. (Compare to Babylon 5 where a taskforce can wait in hyperspace for a signal the jump in.)

  • entry points need to be individually calculated. fleets are seen jumping ship by ship. Notable exception the Katana-fleet. but that was a plot point. it could as easily be achieved by linking computers and pre-calculated solutions dispensed through said computers.

  • small craft with hyperdrive can jump with the help of an astromech or precalculated coordinates they requite a lot of power/fuel to reach hyperspace. I am not sure, but I believe Wes Antilles makes a remark about not using fuel in hyperspace.(X-wing series)

  • there seems to be no way of changing direction once in hyperspace. or velocity.

  • gravitational hazards. captain solo's boast about the Millennium falcon and the "Kessel run", a route that has the Maw a black hole along it's path with an endpoint of moving tradeships, implies that the trick of efficient hyperspace travel is about avoiding gravity wells. and their massive counterparts in real space. ie the higher the ships speed the closer they can travel to the center of the well. which in turn shortens the distance traveled.

  • The technical manual puts the falcon on 0.5 past lightspeed and attributes her success on her power maneuverability and speed. and a suped-up hyperdrive and tricked out nav-system.

it would seem that the angle and direction and speed of entry into hyperspace is key for successful travel. if it is true that corrections cannot be made in hyperspace then a relative straight line needs to be plotted. and in the case of trying to escape a chasing star destroyer you will have to dodge and weave to avoid getting hit. constantly changing the variables.

On a side note:

Karrde is implying that that jump to the Katana-fleet was more an act of calculated despair then a tried and true tactic. especially since hyperdrives come equipped with a safety cut-out that drops you out of hyperspace when to close to a gravity well. the risk would be minimal. and a short distance was all they needed.

In Knight of the old republic a reference is made to a powergrab by a sith lord. where Republic hyperspace explorers were used as proof of imminent Republic invasion. there is however no saying whether they calculated the jump or just took a stab.

In regard to the space around Coruscant. The moon of Borleias lies in a system close to Coruscant. and used to be a stopover before the last leg to Coruscant. but had been ignored because of more powerful hyperdrives. it was used as staging ground for the invasion of Coruscant near the end of the galactic civil war and the later Yuuzang Vong invasion.

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This question actually has a very simple answer, and it doesnt even pertain to star wars universe:

You need to jump towards stars or other stellar objects. Because doing otherwise makes no sense:

Randomly jump to a point in space without any calculations or targeting. What happened?

Just like you said, you safely exited hyperspace without any issues, but WHERE are you? You are in a random point in deep space, far from any star system, leave aside any star.

What are you going to do now? Spend eons in cryogenic stasis to travel to an actual star system?

The vast emptiness of space which makes it safe to jump randomly, also makes sure you exit hyperspace at a point where it will make no sense to exit hyperspace at all.

Therefore, leave aside star wars universe, even in REAL life, you would need to calculate a proper exit point IN the star system you are traveling to, for jumping to make any sense.

But of course, since actually approximating any point in a star system bumps up the probabilities of actually hitting a stellar object considerably, of course you need precise calculations.

So see, its simple: Its due to practical considerations.

  • Although space is mostly empty I think the bigger issue is avoiding stars, black holes, etc. If you jump to the middle of nowhere it's no big deal -- just jump again. But if you jump into an object you're dead. – Null Oct 2 '14 at 20:42
  • What if Hyperspace relies upon gravity to work, in a fashion vaguely analogous to the way that real-life space probes are sent on slingshot trajectories around planets? If a space probe which is supposed to slingshot around the terrestrial moon and then around Jupiter misses Jupiter by a bit too much, the amount of fuel required to get it anyplace useful might exceed by orders of magnitude the amount of fuel that would have been required to reach its destination had the trajectory been calculated more accurately. – supercat Oct 2 '14 at 22:04
  • hyperspace cannot rely on gravity to work. because if there is any gravity effect on a craft in hyperspace, it would be impossible to get through the mess. ranging from stars to galactic centers. hyperspace must be relatively free of gravity, like 'another dimension'. hence you enter, you exit. it must be the complement and counterpart of space/time. say time/space if you will. – unity100 Oct 3 '14 at 0:03
  • I think the point of ending up at some unknown point between galaxies has to do with the other question linked to from this question: when the choice is "end up in an unknown location" or "die from that star destroyer" I would take a quick jump out of there where I can then take my time to plot a course someplace I really want to be. – user31563 Oct 3 '14 at 2:17
  • Yes that would be the logical course to take. its interesting why they didnt do it like that. – unity100 Oct 3 '14 at 18:50

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