Tom Corbett, Space Cadet: The Revolt on Venus

On term break from Space Academy, Tom Corbett and Roger Manning accompany their pal Astro to his native planet Venus for a well-deserved rest. There the cadets plan to hunt the biggest game in the star system, but their vacation is soon interrupted when the intrepid crew of the Polaris stumble across a secret plot to overthrow the Solar Alliance. Lost in the Venusian Jungle, unable to contact the Solar Guard, separated from their ship and each other, the hunters have now become the hunted: caught between the heavily armed forces of a would- be tyrant mad for power ... and the tyrannosaurus Astro wounded years earlier — thirty tons of terror mad for revenge. (Book 5 in the Tom Corbett series.)