Prof. Reynolds, as usual, has the gist of it correct, but some clarifications are in order.
The Su’suumi field (named for its discoverer, Su’suumi Niet’sii) is not “radiation” per se. It is a shell or bubble, theoretically of zero thickness, which defines the interface between the ship and the rest of the Universe. When the Su’suumi field is active, its contents are inertialess (and therefore not subject to the Einstein limit) with respect to the outer world.
When the ship is operating in free space, the Su’suumi field is allowed to take its “relaxed” or minimal-energy configuration, which is a sphere centered on the engine — actually, on the hyperrotation center of the zee-coil within the engine — large enough to encompass the entire ship. Use of the relaxed configuration within atmosphere is no longer permitted, because interaction with atmospheric atoms produces a bright glow or light related in some ways to Cerenkov radiation that can interfere with sensors needed for safe operation. In cases where covert operation is indicated, this also obviously increases the visibility of the ship undesirably. Longer-wave radiation of sufficient intensity to produce effects similar to that of “EMP” is also produced, which interferes with electric and electronic devices at some distance.
For atmospheric operations the Su’suumi field is “tensed”, that is, drawn in tightly into an envelope that follows the contours of the ship, approximately 1 – 1.5 gliltz (30-45 cm) from the conductive surface of the hull. In the “tense” configuration the field approaches its theoretical limit of zero thickness, which reduces its interaction with atmospheric atoms to nearly zero. That almost eliminates parasitic light generation, and by manipulating the strength and configuration of the field nearly any amount or wavelength of electromagnetic radiation can be generated. The ship is “stealthed” by setting the field to produce light precisely equal to that of its background.
Maintaining the tense configuration requires a great deal of power, which reduces the time the ship can spend in atmosphere. Previous incidents in which ships were visible to ground observers were due to the assumption on the part of the researchers that Earth’s planetary population was pre- or non-technical, thus incapable of recognizing the ship as what it was and not having devices that could be affected by the secondary radiation of the Su’suumi field. Ships were therefore operated in relaxed mode to save power. That assumption has now been corrected, and tense mode is used for all in-atmosphere operations.
The Blackbird Incident was the result of a mistake made by a trainee pilot who fat-tentacled the controls, allowing the Su’suumi field to relax briefly. Z’ir has been disciplined and the ship has returned to free space, where they will review the requirements for atmospheric operation using Mars as a practice ground. The University regrets the incident, and offers assurances that all possible precautions will be taken to avoid any more such.