The Platform had become, in fact, a port in space, though so far it had had only arrivals and no departures. Its storage compartments almost bulged with fuel stores and food stores and equipment of every imaginable variety. It had a stock of rockets which were enough to land it safely on Earth, though there was surely no intention of doing so. It had food and air for centuries. It had repair parts for all its own equipment. And it had weapons. It contained, in robot hulls anchored to its sides, enough fissionable material to conduct a deadly war--which was only stored for transfer to the Moon base when that should be established. And it had communication with Earth of high quality. So far the actual mail was only a one-way service, but even entertainment came up, and news. Once there was a television shot of the interior of the Shed. It was carefully scrambled before transmission, but it was a heartening sight. The Shed on the TV screen appeared a place of swarming activity. Robot hulls were being made. They were even improved, fined down to ten tons of empty weight apiece, and their controls were assembly line products now. And there was the space flight simulator with men practicing in it, although for the time being only robots were taking off from Earth. And there was the Moonship. It didn't look like the Platform, but rather like something a child might have put together out of building blocks. It was built up out of welded-together cells with strengthening members added. It was 60 feet high from the floor and twice as long, and it did not weigh nearly what it seemed to. Already it was being clad in that thick layer of heat insulation it would need to endure the two-week-long lunar night. It could take off very soon now. The pictured preparations back on Earth meant round-the-clock drudgery for Joe and the others. They wore themselves out. But the storage space on the Platform filled up. Days and weeks went by. Then there came a time when literally nothing else could be stored, so Joe and his crew made ready to go back to Earth. They ate hugely and packed a very small cargo in their ship. They picked up one bag of mail and four bags of scientific records and photographs which had only been transmitted by facsimile TV before. They got into the space tug. It floated free. "_You will fire in ten seconds_," said a crisp voice in Joe's headphones. "_Ten ... nine ... eight ... seven ... six ... five ... four ... three ... two ... one ... fire!_" Joe crooked his index finger. There was an explosive jolt. Rockets flamed terribly in emptiness. The space tug rushed toward the west. The Platform seemed to dwindle with startling suddenness. It seemed to rush away and become lost in the myriads of stars. The space tug accelerated at four gravities in the direction opposed to its orbital motion. As the acceleration built up, it dropped toward Earth and home like a tumbled stone. 10