FTL drives: unsafe at any speed
We got to talking about space warfare last night, and I realized something pretty weird: FTL drives effect massive shifts in velocity.
Almost every FTL spacecraft, in fiction, is capable of moving between planets in different star systems. The ship starts out roughly stationary relative to planet A, and winds up roughly stationary relative to planet B. How fast are A and B moving compared to one another? How fast do stars move?
Proxima Centauri has a radial velocity (relative to the solar system's center-of-mass) of -21.7 +/- 1.8 km/s. Its proper motion vector is -3.77530 arcsec/year in right ascension, and 0.76933 arcsec/year in declination. At 4.243 light-years away, its proper motion relative to sol is 23.777 km/s. Its total relative velocity to sol is somewhere around 32.19 km/s, which is just a little faster than the velocity of the earth, rotating around the sun.
Jumping from Proxima Centauri to Sol means a ship's faster-than-light drives can effect a delta-v in real space of at least 32 km/s per jump. These are tame velocities for stellar neighbors. If Earth is headed straight for Proxima Centauri at jump time, and the ship departs from a similar planet headed towards Sol, we can assume routine jumps impart up to 91 km/s velocity differentials.
If the Millennium Falcon has a mass of roughly 1.5 x 106 kg, its FTL drives are capable of imparting 6.211 x 1015 J of kinetic energy to the ship per jump, which is roughly 2/3rds of the energy released in the impact forming Meteor Crater in Arizona. This means the Falcon could, with a single jump, put a hole in the earth roughly 1.2 kilometers across. We're talking about an independent freighter captain operating a device which routinely yields the destructive power of a fusion warhead.
If a Mon Calamari cruiser has a mass of 15 million metric tons, a similar jump imparts 6.2 * 1019 joules of kinetic energy to the hull, or roughly 14 gigatons of TNT. That's more than 100 times more powerful than the Tsar Bomba.
The Battlestar Galactica is roughly ~1400 x 500 x 180 meters, or roughly 108 cubic meters. If we assume it's ~90% air and the remainder has the density of iron, its mass is 1.4 * 108 kg air + 9.9 * 1010 kg iron, or 9.8 * 1010 kg. In the very first episode it makes 237 jumps, one every 33 minutes. If each jump can impart 32 km/s, its final velocity relative to origin could be 75,000 km/s, or 2.5% of c.
In this universe, a forty-year old spacecraft due for decommissioning is capable of acquiring 2.7 * 1026 J of kinetic energy (assuming uniform Newtonian mechanics cuz I'm lazy). That's 6.5 * 1016 tons of TNT. Almost the energy output of the entire sun in one second. We're talking 3.067 * 109 kilograms of mass converted to kinetic energy by e = mc2 (a good chunk of the Battlestar itself, if you're wondering).
Chicxulub crater is 180 kilometers across. The impact caused a megatsunami and boiled the atmosphere. We think it caused a mass extinction event. That took 4.2 * 1023 J.
If you rammed a planet with the Galactica, we're talking about an impact a thousand times more powerful.
Why bother with nukes? You can wipe out entire planets with a single ship apiece, without any concomitant radioactivity, and do it a billion times faster. There's no need to infiltrate computer systems or engage in elaborate orbital battles. Just jump in-system at 2.5% the speed of light. If you miss the planet, it's no big deal. Just jump back and give it a second go.
You don't even have to waste the whole ship. Just jump in-system, let go of a suitable chunk of rock or metal, and jump into open space before hitting the atmosphere. The only practical limit is the ablative shielding required to survive relativistic velocities in the interstellar medium, but… I dunno, magnetic fields or something.
Quit playing around. Sci-fi superweapons are easy.