As I write this, the news reports are full of talk about 'UFOs' being shot down by the US air force, and whilst there is currently no indication that these objects are extra-terrestrial in origin, the idea has thrown up an interesting engineering challenge. Let's pretend for a moment that aliens have flown 400 light years to pay us a visit. If they possess the resources and technology required to make such a journey, I think it highly unlikely they would be vulnerable to anything we could throw at them. So, let's imagine the shoe's on the other foot and try to design the kind of landing craft we would need if we were contemplating a visit to a strange new world. Firstly, we'd want to make it durable. This craft will need to deal with unpredictable weather and the stresses of atmospheric entry, not to mention the attentions of the locals. So, we won't be using anything analogous to the Eagle lunar lander, which was basically a thin-skinned bubble of aluminium balanced on a rocket engine. Nor will we be using something like our existing space shuttles, whose heat-resistant tiles would be seriously compromised by a sustained burst of canon fire.
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