I'm a science fiction writer, as yet unpublished. I really like to try to get as much of the science right as I can. I'm working on a story in which an asteroid hits a kilometer long spacecraft that is loaded up with 130 30m long 10m diameter tanks. They hold hydrogen and oxygen (in separate tanks, of course). The ship is hit by a nickel-iron asteroid that's also about a kilometer across and quite hot. (It went through the upper part of Earth's atmosphere, leaving a nice trail of fire, before exiting back out into space.) If I have a smaller space craft nearby, how much lead time does it need, and how fast does it need to go, to avoid being blown up? This all happens about 36,000km from Earth. How much lead time would I need for my smaller ship to dive towards Earth and get around back behind it before debris could reach it? Finally, any idea how much velocity a kilometer-wide asteroid would lose if it went through the atmosphere as I've described? Currently, I'm assuming the asteroid hits the atmosphere with a velocity of about 60 meters per second, gets to within 8k meters of the surface, and exits with a velocity of about 18 meters per second. Any help with these questions and how to figure the answers would be greatly appreciated.