I figure we could get a Falcon Heavy filled with rocks or something launched in a hurry. But, I did the math, and like you say, all we could do is watch. Assum

I figure we could get a Falcon Heavy filled with rocks or something launched in a hurry. But, I did the math, and like you say, all we could do is watch. Assuming the standard asteroid density of 2000 kg/m^3 [1], a 260 m diameter asteroid has a volume of 4/3 * pi * 130^3 = 1.84e10 m^3. Falcon Heavy can lift 16818 kg to a transfer orbit to Mars [2], which I assume is basically what it can do to reach an asteroid coming at us. A normal speed of space probes (without gravity assists) seems to be about 25,000 mph = 11600 m/s. Thus, it has a momentum of about 1.95e8 kg*m/s. Assuming we hit the asteroid perpendicular to its motion, transferring all our momentum into transverse velocity, that is 1.95e8 / 1.84e10, or approximately 0.01 m/s. To ensure a miss, it would need to travel the whole diameter of the earth, 6.378e6 m, which would take 6.378e8 seconds, or about 20.2 years, which is the amount of time before impact we would need to hit the asteroid. We would probably have more success hitting it head on. Since the earth is moving at about 3e4 m/s, we only need to delay the asteroid by 213 seconds. The minimum speed of an asteroid impacting Earth is 1.1e4 m/s, so we would need to move it backwards 2.343e6 m. This allows us to hit it slightly later, only 7.3 years ahead of time (in the best-case scenario). Assuming it could vary by a factor of two, we would need up to about a 14 year lead time. [1] https://en.wikipedia.org/wiki/Standard_asteroid_physical_characteristics https://en.wikipedia.org/wiki/Standard_asteroid_physical_cha... [2] https://en.wikipedia.org/wiki/Falcon_Heavy https://en.wikipedia.org/wiki/Falcon_Heavy [3] https://en.wikipedia.org/wiki/Impact_event https://en.wikipedia.org/wiki/Impact_event