# Interstellar flight and navigation



## Jojo999 (Feb 11, 2009)

I've been pondering the questions/thoughts below for some time regarding interstellar flight.  IF there are other intelligent races in our galaxy, perhaps the reason we have no solid, definite proof of their existence or visits is because interstellar flight is just not possible (or practicable)?

Assuming Einstein was correct and one can't ever travel faster than the speed of light and further assuming that we wanted to travel to another star and could reach near light speed in a reasonably fast time period, has anyone given any thought to how you would actually navigate to the destination?

*Stars are not where we on Earth see them to be!* If you could somehow jump say 100 light years from Earth instantaneously, nothing would be where you thought it was as the stellar objects have moved relative to the light from them that reached the Earth.  If you start from Earth in a light speed capable ship and merely point at where you want to go, you are looking at where the star was at some point in the past (how much in the past depends on how far away the star is from Earth).

So your destination is now somewhere else in the heavens from where an Earth person would see it.  For all we know, it might even have gone nova or there might be another star in the way now.  Even the very closest start system (Alpha Centuri) is 4 years away at light speed and who knows what might have transpired to it in the last 4 years?

Also necessary to consider is what would happen to a material space ship moving at near light speed if it were to hit something, like an asteroid, planet, moon or star?  The space ship would probably be destroyed.

So with a light speed as a maximum limit, it would seem that you would (1) only reasonably be able to travel to very close star systems from any point and (2) need some sort of real-time stellar location calculation computer with an en route object detection and avoidance system that would function at near light speed, which (3) would require some major computer power (which is not in existence at this point) to somehow track the object you want to get to while constantly updating the flight path/course as you got ever closer and avoiding objects in the way.

Ursula K. Le Guin's Hainish novels have people traveling at near light speed in ships (potentially out-living their families and friends by many hundred or thousands of "real" years if they traveled often enough) but communication at light speed, world-to-world proved so difficult, she was forced to invent the Ansible for instantaneous communication.  However, she never addressed the mechanisms of how a ship would navigate the universe at near light speed.  Have any other SF authors done so?


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## iansales (Feb 11, 2009)

Alastair Reynolds novels also feature NAFAL travel. Other novels containing non-FTL interstellar travel include *Dark Sky Legion* by William Barton, the Astropolis trilogy by Sean Williams, the Orphans trilogy by Sean Williams & Shane Dix, and *Vast* by Linda Nagata.


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## Boneman (Feb 11, 2009)

Although Orson Scott Card didn't address it in the early books, he does come up with an interesting idea in the latest "Ender in Exile." Basically the ship travels foward, and any debris it meets, usually small, there's an instant reaction and it coverts it to energy via Nuclear Fusion which is used to drive the ship on. Course hitting an asteroid don't count. Or rather he doesn't mention it. 

If you read all the Dune, series, you just need a spice-saturated navigator who can see into the future, and guide the ships (which fold space, rather like folding a piece of paper, so you bring two points close together) past all the debris etc - simple!


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## Omphalos (Feb 11, 2009)

Check out Tau Zero.  Technically the ship in that story never reaches lightspeed, but the relativity effects make it look like it does.


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## Leo (Feb 12, 2009)

Stars don't move that fast relative to each other, and astronomy is getting better at modeling that motion - at least for the nearby ones. Plus no foreseeable technology seems to allow accelerating the ships at more than a tiny fraction of light speed. So, navigation shouldn't be that tricky I guess.
It does look like stellar systems are very isolated islands indeed, I find that a bit depressing, but it can also be viewed as a challenge to move out of our old den


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## Jojo999 (Feb 12, 2009)

Leo said:


> Stars don't move that fast relative to each other, and astronomy is getting better at modeling that motion - at least for the nearby ones. Plus no foreseeable technology seems to allow accelerating the ships at more than a tiny fraction of light speed. So, navigation shouldn't be that tricky I guess.



Let's say you wanted to go to a star that was 100 light years away.  The position of the star in NOW has changed in the 100 years it has taken it's light to reach us.  Additionally, in the 100 years or so it would take a NAFAL ship to reach the star, it has moved further.  And as I said in the OP, the star might have exploded or been in a collision with another star or ....

We probably know the star direction and velocity so calculating its NOW position should not be difficult.  BUT remember, we would also have to calculate all the other stars in the general vicinity, making the task more complex (so we don't run into any other stars on the way there).  IN a dense nebula, this could get pretty hairy.

I just find this a fascinating problem.  Now if we had a telescope that could look through a wormhole and see the universe in real time....


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## Boneman (Feb 12, 2009)

> By Jojo999
> _Now if we had a telescope that could look through a wormhole and see the universe in real time.... _




Yeah, mine broke some time ago.........now we have to use imagination, or a kaleidoscope.....or writers like you to describe it for us, so we go "Wow, so that's what it will look like!"


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## Leo (Feb 15, 2009)

Jojo999 said:


> IN a dense nebula, this could get pretty hairy.


Some cases might be trickier, but I still think the biggest problem will be not the modeling of star motion but the dealing with undetected dust and stuff. Even if the ship goes at "only" 0.001c the relative kinetic energy of any bit of rock will be tremendous. Bring up the force fields 
Yes, I too would love to see the universe without all that LTD (light travel delay)... What was the cheat code for god mode again?


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## reiver33 (Feb 16, 2009)

I think it was SNAFU....

If I remember correctly from Tau Zero (haven't read that in over thirty years), the relative mass of the ship becomes so large that it 'outweighs' anything it hits by a factor of lots. I was never quite sure about that, as it would be the relative density which would determine who gets a kicking...


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## Leo (Feb 17, 2009)

The cheat code doesn't work... As a nostalgic of the quark era, I run an older version of the universe 
The relativistic mass and kinetic energy increase should affect the impinging dust as well since Relativity is reciprocal. But then maybe weird things happen to density.


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## ManTimeForgot (Mar 23, 2009)

Don't know where to start really so I will just throw stuff out.  (Read Jack McDevitt.  The guy is very good at applied future science and thinks of quite a few contingencies).  I also recommend Ventus by Karl Schroedder (sp?).  It's quite the amazing book on AI.


1) Stars don't go nova suddenly unless a very serious accident occurs.  We can tell which stars are nearing the end of their existence fairly easily, so, presumably, us (or a more advanced alien race) in the future, will simply avoid traveling to those coordinates with a dying star/black-hole nearby.  Though, I imagine that pulsars would be rather useful for navigation and location purposes.  *Side note* To get a "spontaneous" nova out of a star you need to inject a ball of iron (or some other non-fuseable material) about the size of mars (or possibly greater, not like we have ever done the experiment) into the core of the star.  But once you start even caring about interstellar travel modeling stellar trajectories is something you look into and it isn't that difficult to gauge speed and direction of a star with sufficient time observing it (and during travel you should reasonably be able to make corrections to your trajectory given enough computing power).

2)  Practical travel at a significant fraction of the speed of light through normal space will require a high-powered and practical forcefield of some kind.  We are experiment with electroplating a plasma to metallic substances; combined with high intensity magnetic fields and high intensity computer controlled lasers you could get something reasonably approaching a "force field."  This sort of thing would require an incredible amount of computing power to accomplish, but that leads to...

3) Traditional computing power is going to hit a plateau soon.  Minimalization of computer chips using semi-conductors will soon become as small as we can make them without interference from meso and nano level "influences" rendering the project unable to be completed.  Modern computers will take a serious backseat once practical Atomtronic computing becomes available.  It is quite feasible that only a few years after practical Atomtronics is available that we will master microfluidics and genetic engineering such that we will be able to invent practical organic computing.  Organic computing will be a huge leap forward.  Imagine a computer that has as its sole purpose to make itself smarter and answer questions...  If by the time organic computing comes around we haven't figured out AI I will be greatly surprised (self-associative networks and heuristic analysis combined together with enough processing power and a goal to understand and interact with the environment can't be that far from completeness).  And then there is the gold-standard of computing: Quantum Computing.  Once you have this you are boss.  There just isn't a problem complex enough that we can currently imagine that this baby wouldn't cut through in any reasonable amount of time.  Qubits: instead of being 1-0 run the entire range of answers from 0 to 1 (so 10% no is just as valid to a quantum computer as 100% yes and no; as a side note: Atomtronics are capable of multistate answers too, but no where near as many as quantum computing).  So computer controlled defense systems and navigation isn't much of a problem.  Human pilotting is an emergency measure (as seen in McDevitt's books).


You need a very serious amount of energy to start exploring vast swaths of space in person.  This is why a viral strategy, using communications and self-assembling structures, becomes much more viable for gathering information and long-term relocation planning.  However, once you start getting into the energy range of harvesting the combined output of multiple solar systems or a galaxy or two, then you can start thinking about fold space and string manipulation.  Once you can do that its basically like magic.  Don't like your current point space?  Have the universe change state so that you are elsewhere.  Don't like the current material/energy in front of you?  Make it something else.


Long-term practical exploration of space, given our current technical ability or something comparable, is going to require automated repair systems and quite a bit of engineered algae (lichen or something similar) that will convert materials into oxygen, hydrogen, or carbon as needed.  It would also be really great if lasers became practical enough to use as high-grade mining and refining tools (simultaneously that is; with sufficient temperature materials of different densities will separate: i.e. float atop one and other), so that repair systems had a steady stream of available iron, nickel, aluminum, and cobolt to work with.


MTF


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