Alright, so I got the same beef with Einstein as Tesla did. Now don't get me wrong, I don't think relativity should be thrown out the window, it's great theory from a relativistic viewpoint. But I think once we begin to consider deep space travel, with near zero relativistic drag, I don't see why it can't be realized relative to Earth. Kind of like warp speed (PS That's a graph from a test where light goes faster than light). I believe the Pioneer Anomaly is better explained by breaking conservatively accepted science, and allowing the speed of light to be a variable!
Similar to how you can solve E=mc² to be "c = sqrt( E / m )" when in deep space, where we are void of energy, solar winds, solar gravity, celestial bodies, the deep void that is outer space simply becomes a sort of light vacuum if you will and 3 degrees Kelvin becomes becomes nothing for any sort of advanced ion propulsion system. Even if you take the results from the Lunar Laser Ranging Experiment:
you'll notice that photon response varied from near instantly! To around 2c. The average, mean and median equal'd c. Which is why it's such a great constant when viewed from our position in this solar system. And as far as I've investigated, no light speed experiments have been conducted on any deep space probes.
I believe I have a solve for all of this, but rather than get into a debate about my "crack-pottery science" I'd like an honest debate about light-speed, constant or variable and is it a limit?