I love these kinds of discoveries. While poking around Dreams of Space, a compendium website of the history of space-related artwork in children's books, Ward Jenkins found this incredible, obscure 1964 children's book, Space Alphabet is by Irene Zacks, which pictures by Peter P. Plasencia. Then he tracked down a copy and scanned the whole, smoking thing into flickr.
Space Alphabet came out in the middle of the Space Race, the year Americans were able to watch the Toyko Olympics live via satellite-relayed TV signal for the first time. Which might explain why U is for the United States, and not, say the Universe or something.
I didn't find any copies on Abebooks, but there is one used library copy on Amazon. There used to be two. Sorry.
Space Alphabet set in Wardomatic's flickr stream [flickr]
Ward's blog post on Space Alphabet [wardomatic via stork bites man]
Dreams of Space: Space Art in Children's Books 1950's to 1970's [dreamsofspace.nfshost.com]