Uslada means “sweet,” though the exact form of the word given in the names list I found it in, сладкоголосая (sladkogolosaya), isn’t anywhere I could find in either side of my thick Russian-English dictionary. It’s probably some form of the word which can’t really be translated. However, the word uslada itself is an obsolete word meaning “delight” or “sweet.” This isn’t an invented Soviet name, but a modern Russian name.
Uryuvkos is an invented name that came a bit after the heyday of these modern Soviet names. It means “Hurrah, Yura’s in space,” from the phrase Ura, Yura v kosmose. This is obviously a reference to Yuriy Alekseyevich Gagarin being the first person to enter outer space in 1961, which totally humiliated the Americans during the space race.
http://panzercentral.com/forum/viewtopic.php?f=96&t=36301 (penultimate post)