Tom Corbett Space Cadet #5: The Revolt on Venus:

For the young cadets of the famous Space Academy Polaris unit, whose every minute not used studying to become Solar Guard officers is spent on high adventure in space or the distant planets, a month's leave would seem to be a perfect time for rest. But they have other ideas when they plan a trip to the jungles of Venus. There they hope to hunt the most terrifying of all big game –– the mighty tyrannosaurus rex!