The Celestial Frontier

When Voyager 1 mysteriously crashed three hundred years after launch Humanity discovered that what they'd been calling the Oort Cloud was in fact an immense sphere of solid crystal enveloping the Sol System. Since then they have been continuously attempting to breech it, to no avail. Over the centuries they've advanced, invented technologies, terraformed planets, and gradually filled their system, but still the Crystal Sphere remains impenetrable.   The Star Courtiers left Earth thousands of years ago; among the stars they attained power and knowledge beyond anyone else in Humanity. They have settled into a quiet place in the galactic order, content to observe the happenings of the universe without interfering. They have, however, had one major impact: because of them the Crystal Sphere was built. The Courtiers are peaceful but the rest of Humanity are not, and so the Sphere was built to contain them and keep the galaxy safe. The Courtiers have been debating since whether they should help their brethren escape.   Meanwhile four people – Aurora, Amethyst, Aerule, and Isan – have fallen foul of the powers that be and escaped to the Celestial Frontier, the edge of Humanity's advance. They are explorers, and their exploration will drive them to the edge of the Sol System, and then to breech the Crystal Sphere.   Wandering between all this is Cathal, a madman and a living myth. No one knows where he came from and few believe he really exists, but wherever a story is happening, there he is.