Absolute zero speed in space

Just ranting and thinking out loud here...I came up with this yesterday in the shower and I just have to get it down to get my mind around it. I'd be interested to get feedback on this, too (I'll enable comments on this post).

As I understand it, it's very difficult to determine when you're 'not moving' in a spacecraft, because the question is always, "in relation to what?". Frequently, for craft originating from Earth, the speed is relative to the surface of the earth, so geo-stationary satellites are considered to be "not moving". However, I believe it's also common for satellites that leave Earth orbit (think the Voyager crafts) to begin using the Sun's position to determine their speed - the sun considered to be stationary in this case. However, the Sun is orbiting the center of our galaxy in one of its arms, right? And the galaxy itself is moving away from the center of the universe rapidly, along with all the other galaxies out there. So how can you determine what is actually standing still? A guess on my part...maybe it's that point at the center of the universe.

But something else I believe I understand to be true is that the speed of light in a vacuum is a constant, regardless of the speed and direction of the object that gave off the light. That's something that seems simple at first, but when you start thinking about the applications and implications, it's actually pretty profound. Think of it this way...if you're standing in the back of a truck that's driving 25 mph, and you throw a ball forward at 50 mph, ignoring air resistance, the ball will actually be traveling at 75 mph, assuming that you consider the surface of the earth to be your stationary reference point. Likewise, if you throw it backwards at the same speed, the ball will be traveling at 25 mph, but the opposite way. However, to the person in the truck, it looks like the ball is leaving them at 50 mph both times, because they are their own stationary reference point. Basic Physics...you with me so far?

OK, now think of a flashlight on some space vessel. If they're going impossibly fast, say 1/2 the speed of light, and give out a beam of light, the light still "only" goes the speed of light, no matter which way you shine it. That means that if the light is traveling in the same direction as the craft, it would only leave the craft at 1/2 the speed of light, since their speed is also 1/2 the speed of light in the same direction, but a person floating in space (assuming they're "not moving") would see the light traveling at the speed of light, and the craft at 1/2 that speed behind it (assuming you could see a beam of light in a vacuum, which you can't).

Interesting, but where am I going with this?

One more bit of data I want to throw out there is (if I'm not mistaken) the Sun is approx. 93,000,000 miles from the earth, and we travel the circumferance of the circle described by that radius in around 365 days, or around 8,760 hours. That means that the mass of Earth is orbiting the Sun at somewhere around 66,705 mph. The speed of light is around 670,616,629 mph.

I know it's possible to measure the time light takes to travel a known distance, even on Earth, though you have to account for the matter the light is traveling through. It seems to me that, at midnight at a point on Earth, you're traveling about as fast as you ever do on Earth, since you're adding around 1,000 mph at the equator to that above speed for the Earth's rotation. Now, say at midnight you were to measure how long it look for beams of light to travel exactly 50 miles, and get reflected back to their origin, when emitted in at least each of the four cardinal directions (though ideally this would be done in all six cardinal 3-d directions from a geostationary satellite). If the speed of light is a constant, you should see a time difference in how long it takes the light to return from each of the directions, since the light going West can be expected to actually leave your station 67,705 mph faster than the one going North, and 135,410 mph (twice the above number) faster than the one going East, since that point on the surface of the earth is traveling that fast toward the East, and the velocity of the light emitter does not impact the speed of the emitted light. The motion of your base station on Earth has actually closed some of the distance toward the light that started out going East while it was in transit.

That all assumes that the Sun is stationary in the universe, which we've already established it is not. Therefore, it seems to be that by analyzing discrepancies in the time it took the light to cover that distance in each direction from the analysis above, you should be able to triangulate the direction toward the point in the universe that, according to the beams of light, is actually truly stationary. Maybe it's been done, I don't know. It just seems logical to me.

Edit: Oops, I mis-spoke here. I didn't mean to say that you could triangulate an object which was itself absolute-stationary, I meant that you could use the vectors to figure out which direction and how fast you'd have to travel from the point and time you took the measurements to be absolute-stationary yourself.

One more implication the absolute speed of light has is very much rooted in the theoretical - bodily light-speed travel. If we accept for a moment that lightspeed is an absolute inviolatable boundary of speed, let's assume that we can develop craft to travel at 1 mph slower than the speed of light. The interesting thing is that since neither Earth, nor the Sun, nor our galaxy are absolutely stationary, there would appear to be an 'upstream' and a 'downstream' direction to space travel. It wouldn't matter where you launched from, since you're going at near that theoretical (and absolute) speed, it would take you longer to travel from some point A to point B than back from B to A, since though they are stationary with respect to each other, they are actually moving along the same vector with respect (speed and direction) to absolute stationary. Unless, of course, both points B and A are themselves at absolute stationary, which is highly unlikely in this universe of ours.

So at what speed of craft would traveling from B to A change from taking the same amount of time as from A to B over to taking different times? I suppose it's at whatever speed your craft is being physically prevented from going faster by the speed of light barrier, rather than by function of limitations in its design (engine thrust, etc). At that point we'll need a new way of talking about speed. Of course, that's quite a while from now :) And of course, throw the theory of relativity in there and start telling me that it would take the same amount of time because time actually slows the faster (is that absolutely faster or relatively faster?) an object is moving, and the whole second part of this monologue just disappears.