But only twenty days after the recovery and docking of the first robot ship to rise, a new sort of ship entirely came blindly up as a robot. The little space wagons hauled it to the airlock and inside. They unloaded it--and it was no longer a robot. It was a modified hull designed for the duties of a tug in space. It could carry a crew of four, and its cargohold was accessible from the cabin. It had an airlock. More, it carried a cargo of solid-fuel rockets which could be shifted to firing racks outside its hull. Starting from the platform, where it had no effective weight, it was capable of direct descent to the Earth without spiralling or atmospheric braking. To make that descent it would, obviously, expend four-fifths of its loaded weight in rockets. And since it had no weight at the Platform, but only mass, it was capable of far-ranging journeying. It could literally take off from the Platform and reach the Moon and land on it, and then return to the Platform. But that had to wait. "Sure we could do it," agreed Joe, when Mike wistfully pointed out the possibility. "It would be good to try it. But unfortunately, space exploration isn't a stunt. We've gotten this far because--somebody wanted to do something. But----" Then he said, "It could be done and the United Nations wouldn't do it. So the United States had to, or--somebody else would have. You can figure who that would be, and what use they'd make of space travel! So it's important. It's more important than stunt flights we could make!" "Nobody could stop us if we wanted to take off!" Mike said rebelliously. "True," Joe said. "But we four can stand three gravities acceleration and handle any more manned rockets that start out here. We've lived through plenty more than that! But Brent and the others couldn't put up a fight in space. They're wearing harness now, and they're coming back to strength. But we're going to stay right here and do stevedoring--and fighting too, if it comes to that--until the job is done." And that was the way it was, too. Of stevedoring there was plenty. Two robot ships a day for weeks on end. Three ships a day for a time. Four. Sometimes things went smoothly, and the little space wagons could go out and bring back the great, rocket-scarred hulls from Earth. But once in three times the robots were going too fast or too slow. The space wagons couldn't handle them. Then the new ship, the space tug, went out and hooked onto the robot with a chain and used the power it had to bring them to their destination. And sometimes the robots didn't climb straight. At least once the space tug captured an erratic robot 400 miles from its destination and hauled it in. It used some heavy solid-fuel rockets on that trip.