In the big balloon now happily following the wheel at the end of its tether, the still-undamaged power-off fail-safe went into operation. The mirror surface behind each ruby rod rotated into its shielding position, dispersing the energy that the huge mirror directed towards the rods, back into space. Hot Rod was secure. * * * * * Mike received only one further communication from the captain. "Mr. Blackhawk," he was asked over the intercom, "is there any way that you secure the Hot Rod power switch so that it cannot be turned on without my personal authorization?" "Sure, captain, I can--" The captain interrupted. "Mr. Blackhawk, I should prefer that you not tell me or anyone else aboard the method you will use; and that you make your method as difficult as possible to discover. This I shall leave," he added dryly, "to your rather ... fertile ... imagination. "There is reason to believe that Project Hot Rod was turned on by a saboteur. Your method must be proof against him, and if he exists, he will not be stupid." The captain switched off. Mike turned to the control panel, and after a few minutes thought busied himself for some time. Then he headed for the bridge where Dr. Johnston, Chauvenseer, and the captain had dismissed the others and were utilizing every check that Dr. Johnston could dream up to assure themselves that Hot Rod was actually turned off and would remain secure at least for the duration of the flare; and trying as well to find out just what form the sabotage had taken. Without interrupting the others, Mike seated himself at the subsidiary post at the computer's console on Bessie's right, and got her to brief him while he examined the close-up display of Hot Rod. After a few minutes he reached over and increased the magnification to its maximum, showing only a small portion of the balloon, then moved the focus to display the control room entrance as well as part of the anchor tube and the cable between the two. "I think I've found your saboteur, sir," he said. The captain was at his side almost instantly. "Where is he?" he asked briefly. "Not he, sir. It. And I'm not sure just where--but look. Hot Rod's cable is taut. There's thrust on the balloon. That probably means a puncture and escaping nitrogen. "I think," he said, "that the saboteur may have been a meteor that punctured the balloon, and the nitrogen escaping through the hole it made is now producing enough thrust to keep that cable taut. Though," he added thoughtfully, "I don't see why the servos couldn't maintain the beam to Thule--though obviously, they couldn't." "How dangerous is such a puncture?" asked the captain. "How seriously would Hot Rod be damaged? How soon must it be repaired?"