ARES was only expected to fly about an hour, which does seem pretty pointless to me. A rocket propelled Mars plane is hampered by its need to carry oxidizer as

ARES was only expected to fly about an hour, which does seem pretty pointless to me. A rocket propelled Mars plane is hampered by its need to carry oxidizer as well as fuel. But it seems like you still ought to be able to get multiple hours of flight out of it -- the Rutan Voyager didn't need to carry oxygen, but on the other hand it flew for nine days. Another alternative is that you can use CO2 as an oxidizer -- Magnesium, for example, will burn in a C02 environment. Building a jet engine that runs on Magnesium is probably a non-trivial exercise, though! If you really want to build a Mars airplane, I think nuclear is clearly the way to go. I don't know how you would test it though, since we tend to frown on running unshielded nuclear reactors these days.