Ok not based on the 90s TV show don't worry.
Thinking recently of a new AU
Instead in the 3060s a Merc unit went missing with their Monolith DropShip - a full search finds nothing it's put down to a miss-jump.
In truth that's exactly what happens but using the age old sci-fi story telling plot device the unit is sent back in time - to 2012. They appear at the nadir point of the Sol system. Sensors confirm they are in the Sol system however no defence stations no WarShips no DropShips in the system at all and the only transmissions they detect are low radio waves emanating from the third planet.
Burning in system they discover a small space station in low orbit (the ISS) and hundreds of what appears to be satellites both commercial and military.
That's as far as I've gotten so far because I'm sticking on a few points.
a) would they use their JumpShip to head into deep space and just disappear building their own colony far away thinking better not risk the timeline?
b) try to communicate with the planet? Finding hundreds of individual nations many at war with each other.
c) attack, try to make their own bandit kingdom.
On the flip side what is Earth's reaction to the ISS suddenly going dark, hubble exploding in space, maybe the satellite network disappearing completely then big stompy robots supported by armour and infantry attacking the planet.
Would they go nuclear and try to take out these invaders regardless of where they were? Or would it turn into modern technology's range advantage against BattleTech's superior armour and individual unit size?
Alternatively
What would be Earth's reaction to a Conquistador (big ass plane) landing at London, JFK or LAX Airports and a 100ton Atlas stepping off it asking for a new employer? Would these mercenaries be accepted and taken under contract maybe with the agreement of sharing tech or would modern military leaders convince the politicians to attack and try to wipe them out.
Anyone got any ideas?