EM-Rail Ejector

The EM-Rail Ejector is a railgun-type launcher used to fire Solar Sails into orbit around a star, either to build up a Dyson Swarm or to supply a future Dyson Sphere. It works by shooting sails in a straight line at high speed, but it requires direct line of sight to the target point on the selected swarm orbit, so placement matters as much as power supply and sail logistics.

Because the ejector must “see” the point it is targeting, the planet itself can block firing, and the building also cannot be placed near other tall structures that obstruct its line of fire. To operate it, you must select a specific swarm orbit in the UI; the ejector then tracks a point on that orbit and only becomes eligible to fire when the pitch angle is between 5° and 60°. When outside that range, the machine glows orange instead of blue and its Target Status shows as inactive.

For most planets, the most practical placement is near the poles. A pole-mounted ejector usually has the best uptime because the line of sight to the orbiting sail target is least likely to be blocked, and for many common orbits it can operate for long stretches as the planet turns and revolves. For near-equatorial swarm orbits, placing ejectors around 30° latitude can maximize daily uptime: the launcher starts within firing range near dawn, reaches the ideal angle around noon, and then drops back out of range later in the day. Placing the same setup directly on the equator creates a midday gap when the pitch angle becomes too steep, while moving farther toward the poles reduces the time it can fire.

Polar swarm orbits have their own special requirements. The orbit radius must be large enough that the ejector can always maintain at least a 5° pitch angle from the pole, and the usual solution is to build two ejector stations, one on each pole, so each can cover half of the year. If the planet has meaningful axial tilt, aligning the swarm’s longitude with the northern hemisphere’s summer solstice helps the pole handoff occur correctly.

A few practical notes make large-scale sail launching easier:

• A single EM-Rail Ejector cannot maintain 100% uptime on most setups, and even averaging above 50% over a year is difficult unless the orbit and latitude are chosen carefully.
• A sorter can remove excess Solar Sails from an ejector and feed them into another rail launcher, either by belt or directly.
• Railguns fire 20 Solar Sails per minute, or 40 per minute when proliferated.
• Proliferated sails increase energy use, reaching +150% in the cited example of Mk.III proliferated sails at 4.5 MW.
• Each Dyson Sphere node can absorb up to 360 Solar Sails per minute with full upgrades, which corresponds to about 18 continuously firing ejectors per node, or 9 if the sails are proliferated.

The EM-Rail Ejector is comparable in role to the Vertical Launching Silo, but instead of sending rockets it supplies the steady stream of Solar Sails needed to keep a Dyson Swarm growing.