Jak followed as Jon walked slowly along the side of the ship, giving it a careful survey, especially toward the bottom, to see if anything on the lower surfaces appeared wrong. "I'll climb up and give the top a going-over tomorrow," Jon said as they went ahead. The _Star Rover_ was really a space-yacht. It was seventy-two feet long, and about eighteen feet in diameter at its thickest part, which was about a third of the way back from the bow. The front of the ship was bluntly rounded, and contained the control room with its thick, quartzite window-ports, and just outside that room the four bow-retarding tubes, which Jon also carefully examined when the boys reached them. Just aft of the control room were the living quarters. These consisted of the large, comfortable living room, and two small but compact bunkrooms, the bath-toilet, the kitchen and many ingeniously designed closet and drawer spaces for stowing personal belongings, clothing and supplies. Beyond these were the storerooms for food, tools and other supplies and equipment. The stern two-fifths of the ship was devoted to the storage of fuel and the various machines that drove the space-yacht and kept it a self-contained world while in space. Here were the refrigerators and heaters, the air- and water-purifiers, the generators of electricity for light and cooking and for their auxiliary motors, such as the ones controlling the airlock doors and pumps. In the lower part of the hull, under their living and control rooms and storerooms, were hydroponic tanks which not only grew vegetables and greens for their table, but which furnished oxygen to replace that unavoidably lost when the locks were opened. At the far stem were the driving mechanisms. The latter were the latest development in the atomic-powered field, and were surprisingly small for the tremendous work they did. Even Jon did not yet fully understand how they operated, although he knew how to run them. He did know they took specially-treated copper, in the form of small nuggets, and utilized the tremendous force locked within their atoms as the propelling medium by which the ship operated. In some manner these nuggets were vaporized inside the generators, into which they were automatically fed from the storage bins as needed--the power-controls regulating the speed with which they were fed into the generators. This vaporized copper was run through some sort of a modified cyclotron-type mechanism, where the binding-force of its atoms was liberated. That indescribable power then forced its vaporized particles out through the tubes--using the Newtonian law of action and reaction to propel the ship. Suddenly Jon turned to his brother. "Hey, I just happened to think. We ought to rig up a siren or something, so Mom can call us if she needs us when we're away from the ship." "Sounds like a swell idea. Can fix?"