A geometric sans-serif with origins in a recurring typographic style found on old sci-fi novel covers, especially second-hand Isaac Asimov books published by the New English Library.
This turned out to be Avant Garde, the classic yet devisive typeface originally designed by Herb Lubalin in 1970 as a logo for the magazine of the same name. Later to be expanded into a full font by Lubalin and Tom Carnase and released by ITC.
Nebule was begun from a similar foundation of only uppercase characters. The wide, circular shapes of letters such as /O/, /C/ and /G/ are intentionally contrasted with the narrower upright shapes of the /H/, /E/ and even semi-round /B/ and /P/. Apexes and vertexes are left sharp on shapes such as /A/, /N/ and /V/, being allowed to overshoot the cap height and baseline.
The /S/ is allowed a little more leniency, relaxing from a harsh geometric outline to flow more naturally, while the /R/ and /Q/ follow more conventional forms than their inspirational counterparts. A subtle constrast between the vertical and horizontal strokes is retained, helping to reduce the mechanical feel of a strictly geometrical structure.
Ligatures are perhaps one of the most fun parts of designing a typeface, but easily the most self-indulgent and potentially superfluous. Following Avant Garde's hedonistic lead, over twenty discretionary ligatures were initially drawn for the uppercase alone.
Once work on the lowercase began, it quickly became evident that a similarly decadent approach was in order, though these would all need to flow from the conventional forms of the standard ligatures of /i/, /f/ and /l/. Lowercase /l/ and /t/ soon began extending to wrap around adjacent circular letters and this idea bled over to /j/. Work was stopped at this point before all remaining descenders were pulled into this indulgent gravity well.
In keeping with its science fiction heritage, the additional alternate forms for angular letters of /A/, /M/, /N/, /V/ and /W/ are provided for discretionary fitting with compatibly-angled neighbours, as well as a straight-based /S/ for the most 90s of sci-fi treatments. Lowercase alternates include a tilted /e/ and matching straight-based /s/, along with the equivalents of angled letters /v/ and /w/ as well as /y/ just for completeness.