I like a SciFi setting where Portals are the primary means of FTL transit, essentially destructive replicators that disassemble the entrant at one portal, transmits their quantum structure via entangled particle communication, and reassembles them on the other side. The consequences of this are that matter/energy balance must be carefully managed on both sides with stockpiles of raw material to replicate with and the energy to drive it being essential.

Now this method has an obvious flaw, as it doesn't account for traveling to new sectors of space. As such, an alternative method was developed for exploration. This amounts to a mass driver driven by a singularity. An autonomous vehicle amounting to a hardened Portal with interplanetary grade thrusters and a special counter-balance is built and deployed in a system close enough to a singularity to allow transit to it within a few months time.

A vector is calculated with quantum precision. A follow vehicle launches with the FT module held with in it. As the vehicles approach the singularity and gravity acceleration takes hold the follow vehicle fires a high intensity beam array serving to both revers it's own thrust, accelerate the FT module, and provide a protective channel for the module to approach within. High velocity particles are a major threat approaching a singularity, they must be deflected.

The FT module accelerates as it approaches the singularity, beginning orbit, as it orbits the counterweight section is thrust down away from it closer to the singularity, akin to a space elevator, using the same beam tech as the follow vehicle. The counterweight accelerates faster than the FT Module, while cintrepetal force creates a slight outward vector. The vehicle approaches relativistic speeds. Once in the target velocity range, generally 80% of light or .8LS, an antimatter annihilation charge is set off at the base of the FT Module severing the counterweight and propelling the FT module out of orbit and onto its final trajectory. The mother of all slingshot maneuvers.

If the FT Module is release from the gravity well successfully, is on-vector, and has survived functional, the portal onboard is activated, converting mass from the vehicle into subatomic particles to feed the beam and further thrust the vehicle until the thrust-midpoint of transit, by which point the vehicle may have approached 90%+ LS depending on the distance of transit. At this point the the beam is inverted, firing in the other direction to decelerate the FT Vehicle. Typically the target will be another highly massive body, such as another singularity or neutron star, which will be used to decelerate and re-vector towards a local system where another antimatter annihilation charge is used to overcome escape velocity and achieve orbit.

The FL Vehicle may then be commanded via entangled communicator to use its Portal to construct harvester drones to harvest mass from local space until enough mass is gathered to replicate an expeditionary vessel.

Given that none of this process is FTL, it takes many many years between launch and arrival of a portal in a new system. So the question is, who is in command when it finally arrives? What has culture, politics, and biology done in the meantime?

It is a good setup for either side of the portal, on the one hand you have PCs as expeditionary forces heading into an unknown system after many years of process to get there. On the other side you have a Stargate type scenario where a portal ship is discovered in local space. Where could it lead?

In both cases there is the opportunity for a fun bit of Deus Ex Machina, as you must decide just how autonomous the portal ship itself is. Are they dealing with a sentient ship that has been on a solitary transit for years of its own relative time, but centuries of outside time? An anachronism of the old order. Is the portal an inscrutable presence with only the need to feed itself mass and perform its function... and your team doesn't have the codes or features of it's masters? Or even, is this just a fancy automatic door which activates as soon as any being approaches close enough to be sucked in and spit out at wherever it was last programmed to route to? Leaving the PCs in suspense on this point is a lot of fun.

#FTL #TTRPG #SciFi #GM #SWN #StarsWithoutNumber #Starfinder #Traveler