A Bounty of Discovery and Beauty
In terms of scientific bang for the buck, I don't think anything beats the NASA space probes we have sent out over the years. And the more recent ones work even better and are often a lot cheaper, making them even more of a science bargain. There was a lot of noise over the loss of a couple of probes, but I think this is overshadowed by the great successes of the other ones, and even counting the lost probes, our current space probe programs are probably still cheaper overall than the billion-dollar ones like Viking and Voyager, while supplying data that is equally excellent.