If you can deflect with a simple impact, it's always going to be the most reliable. If you look at the numerous things that went wrong with the Philae lander..

If you can deflect with a simple impact, it's always going to be the most reliable. If you look at the numerous things that went wrong with the Philae lander... https://en.wikipedia.org/wiki/Philae_%28spacecraft%29 https://en.wikipedia.org/wiki/Philae_%28spacecraft%29 you wouldn't want any of that to happen on a life-or-death mission. Also... a landing either requires enormous amounts of fuel or between months and years of manoeuvring time.