It was not unreasonable. Tapping the ionosphere for power was something like pumping water out of a pipe-well in sand. If the water-table was high, there was pressure to force the water to the pipe, and one could pump fast. If the water-table was low, water couldn't flow fast enough. The pump would suck dry. In the ionosphere, the level of ionization was at once like the pressure and the size of the sand-grains. When the level was high, the flow was vast because the sand-grains were large and the conductivity high. But as the level lessened, so did the size of the sand-grains. There was less to draw, and more resistance to its flow. However, there had been one tiny flicker of auroral light over by the horizon. There was still power aloft. If Bordman could in a fashion prime the pump, if he could increase the conductivity by increasing the ions present around the place where their charges were drawn away, he could increase the total flow. It would be like digging a brick well where a pipe-well had been. A brick well draws water from all around its circumference. So Bordman computed carefully. It was ironic that he had to go to such trouble simply because he didn't have test-rockets like the Survey uses to get a picture of a planet's weather-pattern. They rise vertically for fifty miles or so, trailing a thread of sodium vapor behind them. The trail is detectable for some time, and ground instruments record each displacement by winds blowing in different directions at different speeds, one over the other. Such a rocket with its loading slightly changed would do all Bordman had in mind. But he didn't have one, so something much more elaborate was called for. A landing-grid has to be not less than half a mile across and two thousand feet high because its field has to reach out five planetary diameters to handle ships that land and take off. To handle solid objects it has to be accurate, though power can be drawn with an improvisation. To thrust a sodium-vapor bomb anywhere from twenty to fifty miles high, he'd need a grid only six feet wide and five high. It could throw much higher, of course, and hold what it threw. But doubling the size would make accuracy easier. He tripled the dimensions. There would be a grid eighteen feet across and fifteen high. Tuned to the casing of a small bomb, it could hold it steady at seven hundred fifty thousand feet, far beyond necessity. He began to make the detail drawings. Herndon came back with half a dozen chosen colonists. They were young men, technicians rather than scientists. Some of them were several years younger than Bordman. There were grim and stunned expressions on some faces, but one tried to pretend nonchalance, and two seemed trying to suppress fury at the monstrous occurrence that would destroy not only their own lives, but everything they remembered on the planet which was their home. They looked almost challengingly at Bordman.