“Son of a bitch,” Wilson whispered. Out of all the things he’d expected to see within the Dark Fortress, a kinetic sculpture bigger than planets was not high on the list. The scale of the barrier was already hammering at his beleaguered human senses. But that at least had been a projection, energy manipulated and folded on a stellar scale, while these lattice spheres looked resolutely solid. This was matter manipulated in quantities incomprehensible to Commonwealth technology. Yet the barrier creators had produced something that from a simple visual viewpoint was almost laughably mechanical, in the truest sense of the word. He wouldn’t be at all surprised now if they were to find gearboxes with cogwheels the size of moons driving the entire edifice. “Are those strands really solid?” he asked.

“I can’t tell,” Anna said. “The electromagnetic environment in there is playing hell with the satellite’s radar.”

“That much matter would coalesce under its own gravity,” Bruno said. “They have to be energy forms.”

“Not so,” Russell immediately claimed. “There’s nothing like a terrestrial planet mass in there. And their spin rates will keep them inflated.”

“Nonsense, they’d have to be metallic hydrogen to maintain their structural integrity under these conditions.”

“So? It’s metallic hydrogen. Apart from those glowing ones, I’d say they were exotic matter. There’s virtually no infrared emission coming from in there.”

“Is the outer shell complete?” Oscar asked. “I mean, is there a corresponding hemisphere on the inside of the barrier, or is this just some giant bearing groove for those lattice spheres?”

“Good question,” Tunde said. “Anna, can you focus the satellite telescope through those grids?”

“No, sir, no way,” she exclaimed. “That haze effect around the third sphere is like looking into a gas-giant cloudscape, and it gets thicker below it.”

“Like oil,” Oscar muttered. “It lubricates the gaps between the spheres.” He realized Tunde was looking at him and smiled an apology. “Just a thought.”

“Anna,” Wilson asked. “Will the satellite survive in there?”

She let out a long breath as she stared at the main image on the twin portals. “I don’t see why not, certainly as far down as the first lattice sphere, anyway. The sensor returns we’ve got show clear space that far in.”

“Okay then,” Wilson said slowly as a sense of real enthusiasm grew inside him. “Let’s do it.”

Anna launched a second Galileo-class satellite, flying it to the entrance hole at the top of what the crew now all called the Dark Fortress. Once it arrived, she sent the first satellite inside, using the second as a relay. As it descended toward the outermost lattice sphere, the energy surges around the satellite picked up noticeably. Eventually, Anna stopped trying to compensate. At that rate she would run out of fuel in a matter of hours. So she let the little craft wobble its way forward, blurring the visual sensor pictures. Every eighty kilometers or so she would stabilize it again, and run a quick check before allowing the vibrations to build up. There was nothing to see en route, the gap between the outer shell and the first grid sphere was empty, with the satellite sensors recording it as a hard vacuum.

When it was halfway there, one of the sphere’s massive struts slid underneath the hole, eclipsing the light pouring up from the inner lattice spheres. By now the crew were successfully recording the geography of the first lattice, and were making good progress charting the second. There seemed to be no logic behind the pattern. But predicting the times of the eclipses was now straightforward.

As the satellite grew nearer to the first lattice sphere, the radar return began to improve. “That’s odd,” Anna remarked as she stabilized the satellite once again.

“Problem?” Tunde asked.

“I’m using parallax to confirm the distance to the strut we’re heading for, but there’s a discrepancy between that and the radar return. Radar places it three klicks closer.”

“Maybe that optical haze effect is throwing the parallax reading?”

She shook her head. “Clear view. There is no haze around these struts.”

The discrepancy began to rise as the satellite closed in. Then they examined the magnetic flux around the strut, seeing the force lines warp like cyclone clouds around the surface.

After a long and heated conference with the rest of the physics team, Tunde said, “Whatever else it is, the outer lattice sphere has electro-repulsive properties. The radar pulses aren’t actually reaching the surface itself.”

“Can we take the satellite in and attempt a landing?” Wilson asked.

“I wouldn’t recommend it. That repulsion force would play havoc with the electronics. We’ll have to study it from a distance.”

The Galileo satellite spent two days hovering thirty kilometers above the first lattice sphere as it rotated slowly underneath. All of its sensors’ booms were fully extended, gathering up as much information as possible. Back on the starship, the physics team worked with the engineers to try to design a simple probe that they could drop onto one of the struts. Its circuitry was all optronic, using a laser for communication; sensors were extremely limited. But even studying its flight path as it neared a strut would tell them something.

Wilson, keen to expand the exploration of the Dark Fortress, authorized its deployment. A further two Galileo-class satellites were launched. Anna and Jean Douvoir had assembled a small team of controllers drawn from the pilot-qualified on board to help remote-fly the probes. Together, they steered the twin satellites through the entrance hole, and took them down toward the first lattice sphere. Anna maneuvered the lead one into the center of a pentagonal-shaped grid, and while Jean held the original satellite fifty kilometers above as a communications booster, she fired its ion thrusters, flying it straight in toward the second lattice sphere. As it passed through the level of the struts, electronic systems suffered repeated crashes. Thankfully the multiple redundancy architecture managed to keep the primary components on-line the whole time, constantly rebooting the failed units. It released the probe and carried on.

Once it fell below the outermost lattice sphere the Galileo returned to full functionality. Heartened by that, Anna got another of her team to send the second satellite through. With both of them clear and operational, she took them in deeper still.

The probe, meanwhile, drifted steadily toward its target strut. Information zipped back along the laser link, revealing the swirling energy environment around the vast mass. Contact was lost a couple of minutes before impact. The physics team wrote that down to the repulsion force affecting the probe’s battery.

Anna’s team piloted the two Galileo satellites in toward the second lattice sphere. As they receded from the first, so the magnetic and electromagnetic squalls shrank away. It began to look as though the second lattice sphere was inert. With one satellite holding back, poised halfway between the two, Anna lowered hers in toward the edge of a strut making up a large pentagon shape. Radar return was precise, there was no magnetic field, no electromagnetic emission, the infrared signature was minute.

“Something’s slowing it,” Anna reported. The satellite’s velocity was dropping at an increasing rate, as though it were encountering some kind of atmosphere. Molecular sensors stubbornly continued to report a vacuum outside.

Anna managed to get it to within seventy kilometers of a strut surface before it came to a complete halt. She had to fire the main thrusters at full strength simply to keep it there. Without that, the satellite would have reversed its trajectory. “Something’s pushing it away,” she told the physics team.

After three days of attempted approaches at varying velocities, another Galileo satellite arrived to assist, equipped with a simple rail launcher to shoot inert slugs of different elements. It began firing. Every slug, no matter what its component atoms, slowed to a halt before reaching the strut, then began to return, picking up speed. After making both passive and active sensor sweeps of the second lattice sphere, the physics team came to their excited conclusion: “Negative mass matter,” Tunde announced at the next departmental heads meeting. “Its gravitational force is the opposite of our own, therefore anything made out of ordinary matter will always be repelled.”