The Primitive Tech equivalents of Radium Drive and Empyrean Sail are Nuclear Thermal Propulsion and Nuclear Thermal Propulsion (redundancy intentional).

Cutting Edge Primitive Tech (CEPT) uses alchemically enriched “clean” uranium fuels. Currently, production is only really implemented at the fighter / shuttle scale (less than 5000 cubic meters displacement), with rated flight times of less than 12 hours before refueling is necessary. Pre-Arrival Kravyad spaceflight used much less efficient fuel (that was additionally much more toxic from a radiation-poisoning perspective), but was used for surface to orbit, and orbit to orbit spacecraft. Even if one of those vehicles were recovered and rehabilitated today (or built by renegade production facilities), performance would only approximate 1/10^th that of Empyrean Sail – so a Maricha to Subahu orbit would take on the order of 60 – 100 days instead of the approximate week that the trip take by Empyrean Sail now, with fuel accounting for 90% or more of the vehicle mass.

CEPT designs allow for Andhaka or Outcaste pilots, and the transportation of significant numbers of travelers of either class. CEPT designs in larger scale craft likewise provide for the comfort and safety of those travelers on intrasolar journeys. While unscrupulous transportation concerns may be tempted to falsify the designation, a potential of a dozen Andhaka to destabilize flight control functions tend to keep vendors honest.