Hmm… how massive an asteroid could you safely land on Earth? Wrap it in a heat shield, put parachutes on it, divert it to hit the Earth.
You don’t even necessarily need to discount them: Fuel-efficient vehicles tend to be smaller, and hence put less wear on the roads.
Quartz, that depends on what you mean by “safely”. What would usually be considered a “crash landing” is no problem, if the thing that’s crashing is just a bunch of minerals with a little bit of disposable control hardware. You don’t add heat shields, because the whole thing is already a heat shield. The only safety issue is making sure you don’t hurt anything important here on Earth.
I would have thought a heat shield would be necessary to prevent it breaking up from thermal stress and to ensure the functioning of the parachutes. You don’t want the thing impacting at full speed.
Hence my suggestion of the Australian Outback.
I feel the same way. It was enormously satisfying to see the SpaceX Dragon mission completed perfectly.