Welcome To Mars
the Galactic Cluster trilogy
The Star Dwellers
Mission To The Heart Stars
The Quincunx Of Time
Further, the Cities In Flight Tetralogy makes sense as a "double diptych":
They Shall Have Stars
A Life For The Stars
Earthman, Come Home
The Triumph Of Time
These four titles express or evoke a prelude, a life, a return and an ending, thus a complete Wagnerian Tetralogy. Neat.
Of the ten volumes listed here, five are adult novels, four are juvenile novels and one is a collection - in fact, a very short collection if we include only the "trilogy." Of the adult novels:
two are in fact amalgamations of shorter, previously published, works;
one is an expansion, still very short, of such a work;
and another, Midsummer Century, is itself very short, less than a hundred pages of text;
thus, perhaps only The Triumph Of Time is a full-length adult novel written as a unit.
Adolph Haertel, Jack Loftus and John Amalfi are, respectively, the unifying characters of the first, second and fifth diptychs listed above. The third diptych is unified by the presence of Thor Wald in the first volume and a reference to him in the second. The fourth is unified by the presence of Dillon and Wagonner in the first volume and the existence of the Dillon-Wagonner graviton polarity generator in the second.
Black Easter and The Day After Judgement formed a further diptych with a common cast of characters but came instead to be classified and published as a single novel and as Volume II of a Trilogy. Volume III, A Case Of Conscience, comprises "A Case Of Conscience," set on Lithia in 2049, expanded as Book One, and a continuation or sequel, set on Earth and the Moon in 2050, as Book Two. Thus, of the After Such Knowledge Trilogy, only Volume I, Doctor Mirabilis, was originally conceived as a single novel.
Thus, this "diptych" analysis has enabled us to summarize or survey the contents of Blish's Haertel Scholium, Cities In Flight and After Such Knowledge.
My motto is "There is always more."