Moonfall

7.

"An Indonesian plane crashed in the Bay of Bengal today with all aboard, two hundred seventy people, believed lost. Rescue operations are hampered by bad weather.

"Rebels in Patagonia admitted responsibility for the bombing of a government office building, where eleven people, including an American diplomat, were killed last week.

"Here at home, people continue to take to the roads in unprecedented numbers, frightened by reports that pieces of the Moon might fall into the oceans Saturday night. We should remind our viewers that many scientists have said that such an event is unlikely. This is Bruce Kendrick with the World Report." White House Rose Garden. 7:44 P.M.

In the evening, Henry could see the comet. It was a bright, blurry patch in the west, lingering for a short time after sunset. It would, astronomers noted, move rapidly up the sky over the next few nights.

Delivered over all networks.

"My fellow Americans,

"As you're aware, Comet Tomiko is approaching the Moon, and is expected to collide with it Saturday evening at approximately ten thirty-five P.M. eastern daylight time.

"I'm pleased to tell you that evacuation of Moonbase, and as a precaution, of the two space stations, is going ahead with all deliberate speed. We do not anticipate any difficulty getting everyone out of harm's way.

"There's been some concern about pieces of moonrock being jarred loose and coming our way. It appears that the force of the impact may be sufficient to severely disrupt the Moon. As a result there may be some debris. But there is no immediate cause for concern. Your government has been monitoring the situation, and the angle of the strike is such that scientists are confident we have nothing to fear.

"While I will not underestimate the gravity of the situation, the most serious danger we face right now is the possibility that some Americans will overreact. This is a time when we must remain calm and not allow ourselves to be stampeded by fear or rumor. We are in this together and we will come through it together. I have directed that federal agencies and military units be put on alert to render assistance, should that become necessary. Meantime, the safest place for you and your family this weekend is at home.

"Thank you very much. And good evening." Moonbase Spaceport. 11:28 P.M.

Tony had ferried two loads of passengers to L1 in record time. During the second run, the Micro completed its six-thousandth hour in flight. That imposed a series of routine service requirements on the maintenance crew. When he arrived at Moonbase, they went after it with their checklists. They examined thrusters and docking assemblies, inspected life support, and set themselves to replacing those parts that were subject to a high degree of wear. Among these parts were the actuator valves for the attitude jets.

The evacuation planners intended to abandon the micro-bus, along with the other two moonbuses, after they'd completed their mission and everyone was aboard the space planes. Consequently, much of the six-thousand-hour maintenance routine should have been unnecessary. But in the communication between the command function and the operational crews, that detail was lost.

Tony's Micro was subjected to the full treatment. Workers knew only that they had ninety minutes to perform a maintenance that normally required five hours. The result was, as one might imagine, that thoroughness was sacrificed.

Like all pure space vehicles, the Micro was equipped with a single engine and a group of attitude jets. It was fueled by a mixture of powdered aluminum and liquid oxygen. After a cumulative burn time, the jets were inclined to slag, and therefore required periodic replacement.

The jets were mounted on a bracket between ring-shaped fuel intake manifolds circling the ship. One ring carried fuel; the other, oxidizer. The pitch/yaw assembly consisted of four jets facing out, equally spaced around the ship. The roll assembly was the same except that the jets were locked in the bracket so they faced tangentially, two clockwise, two counter. The Micro had four assemblies total, pitch/yaw in front and back, roll around the center, and a fourth set mounted along the thrust axis, two forward and two back, used for fine position maneuvering.

Wherever possible, parts converged. All pipes, fittings, and manifold outlets were identical for all ferries, buses, and cargo haulers, even though the haulers used larger engines. Consequently, the piping was oversized for the smaller engines, and could deliver more fuel or oxidizer than necessary. Flow was controlled by an actuator valve. Moonbase manufactured two types of engines: large for the cargo carriers, and small for the buses. In the big engines, volumetric flow was doubled.

Because of convergence, both units looked identical. Those designed for oxidizer were rounded; those for fuel had flat surfaces. But the only way to distinguish between valves for large and small engines was to look at the part designator. There was no throttle in the vehicle; current opened the valve, lack of current closed it.

The technician charged with installing the units was a thirty-year-old engineer from the University of Texas. His name was Elias Tobin, and up until that time he had a perfect work record in a job that required absolute attention to detail. But Elias was under pressure to finish, because lubricants needed to be replaced, engine lines inspected, and the engine recalibrated. Later, an investigation team would determine that under the circumstances, the only essential task among those assigned to Elias was the replacement of the actuator valves.

He got it wrong.

Fortunately, it was not in itself a serious error.