i.

Sue Fisher tried to force herself to stay awake. Three more hours of this. If only something would happen!

But nothing ever happened in Orado Port Control. Once in a great while a starship would arrive — an event scheduled usually years in advance — or somewhat more frequently one of the inter—system shuttles or the few private vessels would want to dock. Mostly, though, it was just the automated manufacturing pods, bringing raw materials from the asteroid mining operations to be sent down the beanstalk to the ground, or collecting manufactured cargo or key materials from the ground and distributing them around the system.

If I actually had to do anything, that would make it less boring. But all of that was automated. The only reason she was there — the only reason anyone would be here on the Port Control Deck — was that regulations stated that a qualified human observer would be present at all times in case of emergency. AIs could handle virtually any situation a human could — usually better. It would take something extraordinary to make the AI even consider cutting a human into the loop, or for Sue to decide to override the machine herself.

And the last time there had been an emergency in Orado system had been —

ERRRRT! ERRRRT! ERRRRT! ERRRRT!

Sue snapped out of her half—daze, adrenalin washing through her in a cold tingle that drove subtle spikes into her gut as she focused, triggering a situational download to her retinals.

The first thought she had was a starship? There isn’t one due for at least six months, the Explorer’s Compass out of Vellamo.

But the second thought was spoken, as enhanced imagery from the distributed telescopic array materialized. “Oh my God.”

It was one of the Initiative line of colony vessels, immense transports three kilometers long and over a kilometer wide that carried colonists and cargo to and from the now dozens of colonial worlds that could be over a hundred lightyears from old Sol. Sue had seen Initiative class ships twice before, beautiful graceful spindles with a perfect, sparkling circle of a habitat ring standing out from the central body.

"The reason I asked to speak with you here, in this place, is to tell you that something has broken."

Perhaps we are meeting in the heart of the Tabernacle, with you in the vestments of the High Priest and me in the raiment of the ArchDeacon of Engineering. Or maybe we are on the bridge of our great vessel and you're wearing the glittering dress uniform of a ship captain, with me your engineer. There are countless other possibilities — from business suits to no clothes at all! — but my fear in every case will be the same.

It's not my fault!

"Please don't excommunicate, execute, or recycle me!"

I am not going to try to blame our ancestors. Whether I am reading from scripture, logs, or reports, I will attempt to convince you that failures have occurred before, and they simply happen no matter what. After all, we have been travelling in the vacuum of space towards our destination star for a very long time.

"Raise not your staff to me, I beseech you, Your Eminence! Lord Captain, please sheath your sword! I meant no disrespect to the Designers. Their near-zero operational failure rate is miraculous, but even 'near-zero' is not zero, especially over centuries of operation. The reliability level that they did achieve merits admiration, if not adoration."

#

The worldship designers may or may not use religious tracts, but they would certainly rely on Redundancy, Diversity, and Margin when choosing and sizing essential systems.

Redundancy has long been recognized as a critically important design element. Indeed, the mantra of the nuclear engineer is, "Redundancy is good. Redundancy is good." Worldship designers would be expected to hold it in even higher esteem. Nuclear power plants generally have two one-hundred per cent capacity, physically independent groups of systems (called a "train") for each safety function. A worldship might have three or more. Redundancy allows removing a safety train for inspection, testing, and maintenance. If one train fails during an accident, another full capacity safety train is there to save the day and, on more than one occasion, it has.

Diversity is an important social imperative, but it's an even more important design one. No matter how reliable a given machine may be, relying on only one design creates vulnerability to the phenomenon called "common mode failure." Extrapolating from an historical scenario, if four helicopters are needed to complete a desert operation, an inadequate sand screen design on the engine intake would doom the mission no matter if eight — or eight times eight! — identically vulnerable choppers were dispatched. Similarly, a materials defect (e.g., tainted lubrication oil) could simultaneously fail all machines that used it. Even diversity in location is important, as demonstrated during the recent accident at the Japanese Fukushima Daiichi Nuclear Power Station. The designers of the coastal Fukushima plant had placed all emergency power sources in basements, despite flooding being a possible common mode failure risk. The extended duration of worldship transits would make their creators even more sensitive to design diversity.