469
xkcd #2865: The Wrong Stuff
(imgs.xkcd.com)
Alt text:
The phantom found Edward Everett Hale a century too early; by the time we invented satellites, the specifics of his 'brick moon' proposal were dismissed as science fiction.
I guess the idea is that if a competent engineer had been in charge of the Trojan Horse project, the ancient Greeks would've used an aluminum frame with a mylar fabric covering.