He sat down, stunned at the fact that he'd run out of things to try. The ship lay before him like some impenetrable fortress. Several precious minutes dragged by before Ballard could again calm his spinning brain. He still had forty minutes. Had he overlooked any other possibility of getting into the ship? Slowly he walked around the _Minnow_, concentrating as he'd never concentrated before. Then as he stepped in front of the drive tubes something clicked: _The main tube was large enough for him to crawl into. If he could remove the recoil plate and hydraulic mechanism, he might be able to burn a hole through the ordinary steel bulkhead beyond._ Half-bounding and half-running, he returned from the hill with the tool box. After selecting several likely wrench sizes, he grabbed a flashlight and crawled up the tube. He wasted five minutes unscrewing the first bolt holding the plate in place. The second bolt was so corroded he couldn't budge it. Cursing he crawled out and dragged in the jackhammer, hoping the cracked 5R bit would hold until the bolt was knocked out. It almost held, flying to pieces just as there was a quarter inch to go. Frantically he somehow managed to knock the remainder out with the chuck of the hammer. But it had taken Ballard five more minutes. _Only twenty-five left._ He went out and grabbed a crowbar and pried the plate off, recoil cylinder and hydraulic fluid following like a jack-in-the-box. After cleaning out the drive tube he almost lost his reason when he discovered the cable connecting the beam to the power-pack wasn't long enough to reach the bulkhead. Fortunately he found an extension in the bottom of the tool box. _Fifteen minutes to go._ That should be just long enough. He switched on the beam. Now time seemed to race by. At ten minutes to go the bulkhead turned a cherry-red. At five minutes it was almost white. At four, the steel started to buckle. At three--the heat-beam suddenly went dead. The power-pack was empty. Ballard's reason reeled. He grabbed the crowbar and jabbed at the fast cooling metal. _Too late._ In the one minute he had left to live, Ballard suddenly became calm, reconciling himself to his end. Wearily he crawled out of the tube. At least Walton would be in for a nasty surprise, with the main drive recoil plate gone. And to make sure, he would push it off into space. With one last surge of fury he dragged up the foot thick plate he could never have lifted back on Earth, and started shoving to give it momentum. _Momentum equals velocity times mass._ Suddenly he stopped, the plate drifting on ahead of him. Now why had he thought of that? Something from his school days--he tried hard to remember--something about mass.... _Mass is a constant. Weight is a variable, but mass is what knocks holes in things--spaceships, for instance._