Yeah see, if you're at 99.9999% the speed of light, you cant just keep accelerating at 9.8m/s^2. Every second that passed, you would have to add 9.8m/s to your total speed, which.. you know, increases your speed, and would one day hit 299792458 m/s.
you dont get to 299792457.999999999999 and keep adding .000000009 (or w.e.) m/s of velocity, because if you did then you wouldnt be accelerating at 9.8 m/s^2 anymore, correct? Also, if you're asymptotically accelerating, that means your acceleration curve isnt linear, so you're not always accelerating at 9.8m/s. right?
You're failing to understand special relativity - from YOUR perspective on the Earth, you cannot tell by any means how fast you're going - so you can always go another 9.8 m/s faster in the next second. It's a fundamental tenet of relativity.
From the perspective of some hypothetical being off to the side of the world, watching it fly by - there would be a problem with adding 9.8 m/s of speed every second - because the world would soon be moving faster than light - which is not allowed.
What THEY see is that as the earth moves faster and faster, so we get this weird phenomenon of "time dilation". It appears to our observer as if time itself is slowing down on the Earth...everyone's clocks are going slower and slower - their heartbeats slow down - chemical reactions go slower. EVERYTHING S-L--O---W----S------D----------O-----------W------------------N.
And that solves the problem. From our perspective, we do gain 9.8m/s every second - but from the outside observer's perspective, those seconds are happening less and less frequently.
That slowing of time is what prevents the earth from EVER reaching the speed of light. It's like one day we're going at 99% of lightspeed, the next day we're at 99.9% but our clocks are running 10x slower so after the next day (on earth) we're only at 99.99% and the clocks are running 100x slower the next day 99.999% and 1000x slower...then....
So we happily believe we're accelerating without limits and because we can't see beyond the little bubble of our skies - our actual speed is indeterminate...it might as well be zero...so this can go on forever.
From the point of view of an "outsider" the clocks on Earth are almost at a standstill - they tick only once every trillion years maybe. Speed is still getting closer to lightspeed - but the pace of that acceleration has slowed to an almost complete standstill.
In the "real" universe, this would soon become problematic because with our clocks ticking so slowly from an outsider perspective - the "heat death" of the universe would happen before we here on Earth could have breakfast.
But as far as the FE'ers are concerned, our little bubble of life is all that there is in some infinite void of nothingness...there is nothing in the outside universe to come to an end.
Fortunately - this bleak picture is complete hogwash because they can't explain simple stuff like how the moon looks from three different perspectives or how sunsets, tides or a bunch of other things can happen...but that's another thread.
The bottom line (from a committed RE'er) is that you CANNOT defeat UA on the basis of lightspeed limits.
You CAN, however demonstrate that it would take an infinite amount of energy to make it work - and that it doesn't explain variable gravity or the tides.