Free The Eternal Flame by Greg Egan

but knowing your position was something else entirely. The ancestors had had their sun and their sister worlds to help them navigate, but if the travelers wanted to leave the Peerless without losing their way they would have to create their own guiding lights, on a scale commensurate with their intended journey.
    Viviana set the triggering time on the clock beside the launch plate. It was impossible to choose the beacon’s trajectory as precisely as they’d need to know it, but the timing of its launch would be enough to ensure that it was traveling in more or less the right direction. Viviano reached into the beacon and disengaged the safety lever, allowing sunstone and liberator to enter the flare chamber the next time the air valve was opened. Then they both moved back behind the plate, out of harm’s way.
    Tamara watched by starlight as the launch clock’s three fastest dials spun toward the chosen alignment. The figures on her skin tingled with recognition just before the faint shudder of the springs reached her through the rock. The beacon shot clear of the ramp and plummeted out of sight. Tamara rushed forward to the edge and peered down, but the machine was already invisible, a speck of darkness lost among the star trails. She glanced back at the clock and pictured Roberto’s fingertips on the same dials spinning beside the observer’s bench: one hand following the time, one on the scope’s coordinate wheels. At the other end of the Peerless another colleague would be doing the same.
    When the flash came Tamara raised an arm to cover her eyes, though the light was already fading before she’d moved a muscle. Powdered sunstone burned fast and bright; Roberto would have been using a filter, but the stab of light would have burned the measurements at his fingertips into his brain. Tamara was dazed and half-blinded, but now she could believe that the beacon’s light would be visible across the void, even through the Gnat ’s modest instruments—so long as nothing broke, nothing jammed, and no speck of orthogonal matter turned the machine into a fireball before the Gnat had even been launched.
    There was no point waiting for the second flash; the rotation of the Peerless was tipping the ramp up, hiding the beacon behind her. But Roberto and his opposite number would have dozens of chances to repeat their measurements, triangulating a whole series of points along the beacon’s trajectory before the machine switched to its dormant state. After that, the next flash wouldn’t come until a stint before the Gnat ’s launch.
    Viviana and Viviano were already headed back to the airlock with the empty trolley. Tamara stayed at the edge of the ramp, one hand around her safety rope, gauging its reassuring tension. She would not be embarking on a fool’s mission; they would not be going blindly into the void. Long before the journey began they would have wrapped the space around them in light, in geometry, in numbers.

    The wheat-flowers were opening as Tamara strode along the path that ran down the middle of the farm, the limp gray sacs unfurling until the petals’ red glow filled the whole chamber, overpowering the moss-light from the walls and ceiling. A faint scent of smoke hung over the field but no sign of the burn-off was visible.
    Tamara reached out to brush the plants’ yellow stalks with her fingertips. Though the crops rose and fell, the farm itself seemed ageless, unchangeable. But she remembered her grandfather telling her that in his own parents’ life-time the sheer wall of rock on her left had been a soil-covered field. There had been no low ceilings then, no second, third and fourth farms stacked above them; no one had planned for centrifugal gravity when they’d first carved these chambers out of the mountain. Tamara sometimes found herself scandalously wishing that it would be as long as possible before the engines were fired again, sparing any of her immediate descendants the tedious job of