I Never Knew That

"Inconstant Star" (see previous posts).

It is possible to track a spaceship through empty space:

(i) it is known that a kzinti Swift Hunter warship started to return from the artifact surrounding a mini-black hole to Alpha Centauri but did not arrive there and almost certainly changed course towards 61 Ursae Majoris, the sun of Kzin;

(ii) it can be calculated when the ship is likely to have set off and also to have changed course;

(iii) the interstellar medium of hydrogen, helium and a few higher elements is about one proton per cubic centimeter;

(iv) screen fields deflect the medium into a smooth flow away from the ship;

(v) radio telescopes can, across several parsecs, detect the quanta emitted by excited atoms and also the long tunnel of nearly total vacuum remaining for years behind the ship;

(vi) Rover, unlike the Swift Hunter, can move through hyperspace, taking readings at different points;

(vii) the readings, interpreted by a computer program, should give an identification from which it will be possible to "...measure a parallax and obtain a fix." (p. 256)

So it is possible to follow a trail across light years through empty space. Information about mini-black holes and the interstellar medium is not specific to the Man-Kzin Wars series but is applied to that series by Poul Anderson and is recognized by readers as the kind of background material that is deployed consistently throughout his hard sf novels and series. We are in the same conceptual territory as when interstellar explorers venture through a "starfog" and a dark nebula in the concluding story of Anderson's Technic Civilization History.