Is near light speed travel possible? Likely? I was contemplating the possibility of sending an interstellar probe that can produce results in a reasonable time frame.
For such a mission to be realistic, the spacecraft would have to travel at some (significant) fraction of the speed of light. I calculated that at 0.5c, it would take 14PJ of energy per kilogram. If we assume 500kg probe, that will require 7000PJ of energy. 
According to my research, that's about 2000 terrawatts, about half of the yearly electric consumption in the US.
Obviously this is enormous, but given that we can somehow provide constant trust without significantly increasing the spacecraft's weight:
Is there any fundamental reason that I'm missing that would make near light speed travel not possible?
Is there any fundamental reason that would make near light speed travel extremely unpractical/unlikely?
Edit:
I'm not asking about engineering reasons, but fundamental physics.
 A: There is a fundamental reason why it might be very, very difficult (not even mentioning the engineering). As you start approaching the speed of light, it becomes harder and harder to accelerate. At 0.5c, this would definitely become a factor. Accelerating from 1%c to 2%c is much easier than accelerating from 50%c to 51%. 
A: Research the average atoms of gas and possible dust particles per cubic meter in deep space and the kinetic impact damage of traveling at .5c through that.
A: Well fundamnetal physics is pretty solid  here, which explicitly says that $$F=\dfrac{dp}{dt}$$
$$p=\gamma(v) m_0v$$
$$\gamma(v)=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$$
$m_0$ is invariant mass.
So theoretically a spacecraft can accelerate upto any $v<c$ in accordance with the laws. The most prime difficulty is only engineering issues like:

*

*Energy source must be huge, reliable, safe, and easy to extract.

*Energy density/efficiency of fuel or whatever propulsion system.

*Spacecraft materials must sustain such massive acceleration along with i guess occupants?

*Cost of the spacecraft.

*Interstellar rocks, asteroids, rogue planets?

Currently no such technology exists, neither nuclear or conventional.
A: Yes, but what fraction are you talking about?
The most realistic albeit ludicrous idea is using sails to catch nuclear explosions. But achieving only 0.33% lightspeed.
Antimatter catalyzed propulsion assuming sufficient quantities of antimatter can be obtained offer exhaust velocities of .94c which may propel a spaceship to minimum of 0.05 to .25c given enough acceleration time.
A: There's no fundamental physical reason. Remember that speed is relative: going with 0.01c according to one frame means going with 0.91c according to another.
A: For anything with mass, it would be quite difficult since the speed of light is a limit that cannot be surpassed. On Earth, the  The Large Hadron Collider has successfully accelerated protons very close to the speed of light (because the photons have so little mass). For objects without mass (a light spot, for example), it IS possible.
