Kerbal Engineering Systems

However, consider that the impactor was likely also made of the same density stuff as the rest of Kerbin...

After Matt Lowne couldn't manage a seaplane SSTO, I decided to actually build one that works. Presenting: the Kingfisher-class. It's not entirely stock (those tail fins and the little winglets and elevons attached to the forward pontoons are from Airplane Plus), but I think it's the best looking SSTO I've ever made. Plus, it has room for ten kerbals and decent Delta V in LKO to get to stations or interplanetary vehicles. Video Craft file

Oh no not another asteroid challenge for me to have to do

Alright, first post on the KSP forums! Here's my concept. It's called the Asteroid Redirection System (creative name, I know), and it's an ICBM-inspired asteroid redirection vehicle integrated with a launch vehicle. The launch vehicle has a Clydesdale booster as a first stage (with two liquid fueled Twitch engines for roll control, and in my headcanon these are hypergolic engines that use storable propellant) to allow for long-term storage of the launch vehicle in a silo until a potentially hazardous asteroid is detected. Upon detection, launch is commanded, the silo opens, and the vehicle is propelled out of the silo by a small "zeroth stage" consisting of Flea boosters. The zeroth stage detaches, allowing the first stage to fire, taking the stack up to a suborbital trajectory. A second stage powered by a Woolfhound AJ10 engine (again, since it's modeled after the real AJ10, which uses storable hypergols as propellant, my headcanon is that this engine uses storable propellant) propels the system into orbit, and then performs the Kerbin ejection burn out to the target asteroid. The second stage remains attached throughout the "chase phase," in which the spacecraft maneuvers towards the asteroid and fine-tunes the encounter. The final use of the second stage is to begin braking upon arrival at the asteroid mere months after launch. The second stage then separates, and the Redirection Vehicle (RV) continues the braking burn with a high-efficiency nuclear thermal engine (my headcanon on this one is that the fuel would be loaded into the RV within the last few minutes before launch, much like the upper stage on a Falcon 9). The RV then approaches the asteroid and gives it a slight nudge to ensure that the asteroid is on a safe trajectory. The RV remains attached to the asteroid in case any further hazard mitigation maneuvers are required, and to track the asteroid to enable longer-term mitigation (i.e. moving the asteroid farther away from Kerbin with a larger vehicle) and possible exploitation of the asteroid.