One critical development since O'Neill's day was synthetic food production. The old island designs were driven by the need to provide vast amounts of farmland to feed the indigenous population. His cylinders had been given multiple-wheel crystal palace geometries and elegant necklaces of agricultural modules so they would be self-sufficient. The new designs discarded all that baggage. All they needed was a couple of refinery modules to process excrement back into protein cells. The starship companies still kept the idea of a central garden park; that kind of open space was acknowledged as a primary psychological requirement for the crews that would have to spend months if not years up in the islands. And that much biota was a reasonably cost-effective fail-safe air regeneration system. But the rest of it, the luxurious landscapes, meandering freshwater lakes, the giant windows with their fans of mechanically swiveled mirrors, Caribbean climates and nuclear family neighborhoods of open-plan Italian villas—that was all condensed and modernized.
Centralis, which was Z-B's primary Lagrange point facility, adopted a plain cylinder geometry, five hundred meters in diameter and one kilometer long. Its apartment complexes were as cramped as any low-rent city skyscraper, only these were ring-shaped, occupying the lower fifty meters of each circular endwall. The garden between them, like any urban park, was overutilized and overmaintained. Shrubs and trees grew tall and spindly on the thin layer of crashed rock sand that passed for soil, the fusion-powered plasma tube running along the axis never providing the right level of UV. But it had ponds with fountains and expensive koi carp, and picnic tables, and a jogging track, and baseball diamonds, and tennis courts. Although it took months for the Johnny-come-latelies to pick up on the Coriolis-driven double curve flight of balls.
Radiation shielding, too, was a constant worry beyond Earth's protective atmosphere. The only true defense against gamma rays and high-energy particles was mass, big fat solid barriers of it. Centralis was given a rocky external shield two meters thick, which was encrusted with black radiator fins. There were a few gaps through, for the axial corridors connecting the main cylinder to the nonrotating docking net at each end, shafts for the pipes carrying fluid to and from the fins, and the observation gallery.
Constellations traced a slow curve outside, although the portal was always in view. It hung fifty kilometers off Centralis's rotation axis like a blue pole star. Simon knew where it was only from the cluster of colony trains keeping station around it, slim silver bars agleam with reflected sunlight, forming their own tight little cluster.
He used his DM to receive sensor feeds from the trains, closing his eyes to be greeted with the sight of the portal directly ahead. A simple ring five hundred meters in diameter, it looked like a toroid of black hexagonal netting encasing a weak-glowing neon tube. The sight of one never failed to inspire him, reaffirming his faith in Z-B and all its endeavors. A portal was the most sophisticated, and expensive, technological artifact that the human race was capable of constructing. Only Zantiu-Braun had the facilities, money and determination to build them. Portals were one-shot wormhole gateways. Rather than the continual spatial compression that ordinary starships generated for themselves to fly through, these opened a wormhole down which any vehicle could travel. It took a phenomenal amount of energy, correctly applied against the fabric of space-time, to create the rift. The combined fusion generators of twenty starships wouldn't be able to produce a fraction of the power necessary. So Z-B manufactured an isomer based around hafnium 178 and boosted it up to its K-mixing state; the subsequent decay to its ground state produced the amount of energy required to distort space-time once it was correctly channeled and focused. But the isomer was incorporated into the solidstate wormhole generation mechanism itself, which meant that once the decay was complete the whole edifice was not only useless but highly radioactive as well. You couldn't take it apart and refill it with a fresh isomer. A new one had to be built each time.
That one-shot limitation meant Z-B had to extract the maximum amount of use from every portal. As a result, they'd designed the colony train, a spacecraft every bit as crude as an orbital-transfer vehicle, but on a much larger scale. They had the same type of engine system, fusion generators powering high-thrust ion rockets, sitting at the base of a kilometer-long girder tower. Simple enough to build, they were assembled in the redundant starship yards floating in attendance around Centralis.
The fleet of colony trains that Simon could view through his sensor feed were fully laden with descent capsules, as if the tower had been swamped by metallic barnacles. Each of the 840 capsules was an identical cone, six meters wide at the base, coated with a silvery ablative foam that would allow them a single airbrake into a planetary atmosphere. They carried four people and all the basic equipment they'd need to start life on a new planet from scratch.
To qualify for a berth, the colonists had to be thirty or younger (that is, of childbearing age) and have an appropriate stakeholding in Z-B. It was a qualification that millions of people still strove for, even though the portal worlds were nothing like the original interstellar colonies. There would never be a follow-up, no second portal delivering supplies to expand the colony, no regular starship flights from Centralis. After they arrived the colonists were on their own. If they wanted to get back in contact with Earth and the other developed worlds, they had to build their own FTL vehicles. Best estimates put that level of financial and industrial ability being achieved at least a century after the founding flight, and probably a lot longer.
As financial analysts never tired of pointing out, Z-B's portal colonies were extremely risky ventures. In an age in which most interstellar flight was now concerned with asset-realization missions, Z-B's attitude seemed almost anachronistic, especially as it was itself heavily involved with asset realization.
Simon observed the colony trains patiently, waiting as the small digital timer on the rim of his vision counted down the minutes left until activation. When it came, there was little physical evidence. The blue light of the portal ring brightened by two orders of magnitude as the isomer cascade was initiated. The aperture turned blank, obscuring the stars that had been visible in the center. Slowly the blue luminescence contained in the ring began to seep inward, forming a solid sheet of photons. It twisted in an instant, distorting backward and opening into a seemingly infinite tunnel. The intensity of the light withdrew until the wormhole walls were defined only by a faint violet haze that neither camera nor eye could quite bring into perfect focus.
A whole grid of script tables displayed by his DNI provided Simon with more information than he wanted about the wormhole's stability and its endpoint coordinate. The target was Algieba, a yellow giant binary system 126 light-years distant. Easily the farthest out that any kind of colony venture had been attempted; it was just approaching the range of the current portal capacity.
The portal operations AS picked up the beacon signal left behind by the explorer starship, allowing it to confirm the endpoint coordinate was within ten million kilometers of the target planet, an Earth-equivalent world orbiting the smaller of the two stars. It flashed a go signal to the colony trains.