He would have to go to Sirius and he would have to reach it the first try or never. If he could emerge into normal space at the proper distance from Sirius he would have power from it to operate the communicator. The _Thunderbolt_ would come at once when it received his message and swallow the little _Argosy_ in its enormous hold. The return to Earth would be the swift one through the warp and the Slug cruisers, so bold in pursuit of unarmed interplanetary ships, would quickly cease to exist. At 13:53 Sirius would be somewhere in or near the bow of the ship. The ship would not have to be moved more than two thirds of its length--twenty meters. He could do that by releasing part of the air in the shuttle room through the sternward airlock. How much air? He tried to remember long-forgotten formulas. So many cubic feet of air at such and such a pressure when released through an opening of such and such a diameter would exert a propulsive force of.... Hell, he didn't know. And not even the computer would be able to tell him because there were so many unknown factors, such as the proportion of the ship's mass lost to the Slug blasters, the irregular shape of the airlock opening, the degree of smoothness of its metal.... He made calculations with pencil and paper. He would have to move the ship with extreme precision. A light-hour short of the proper distance put him too far from the sun for it to power the communicator, a light-hour beyond put him in the sun's flaming white heart. One light-hour out of eight point six light-years was approximately one part out of seventy-five thousand. He would have to move the ship with an accuracy of point aught three centimeters--one hundredth of an inch. _One hundredth of an inch!_ He laid the pencil back down, almost numbly. He could never open and close an airlock and move a mass of thousands of tons with an accuracy of a hundredth of an inch. The very thought was wildly fantastic. He was already far closer to Sirius than he would be if he tried to get any closer. And that was over eight light-years from it. He looked at the chronometer and saw the hands had already reached 13:20. Thirty-three minutes left to him. Sirius was near--soon it would be in the bow of the ship--and Sirius was eight point six light-years away. How could he move the ship a certain distance accurate to one hundredth of an inch? He couldn't. The answer was blunt and ugly and irrefutable: he couldn't.