@book{GrundmannHallmannSchaefer1983,
  author    = {Grundmann, Reinhard and Hallmann, Willi and Sch{\"a}fer, Horst},
  title     = {Entwicklung eines einfachen Windmessgeraetes fuer Entwicklungslaender},
  publisher = {FIZ Energie, Physik, Mathematik},
  address   = {Eggenstein-Leopoldshafen},
  pages     = {137 S.},
  year      = {1983},
  language  = {de}
}
@book{LeyWittmannHallmann2009,
  author    = {Ley, Wilfried and Wittmann, Klaus and Hallmann, Willi},
  title     = {Handbook of space technology},
  publisher = {Wiley},
  address   = {Chichester},
  isbn      = {978-0-470-69739-9},
  pages     = {XIII, 882 S. : Ill., graph. Darst.},
  year      = {2009},
  language  = {en}
}
@book{Hallmann2015,
  author    = {Hallmann, Willi},
  title     = {(Meine) Erinnerungen an Jesco von Puttkamer : zusammengestellt anl{\"a}sslich des Todes von Jesco von Puttkamer am 27. Dezember 2012},
  publisher = {Pro BUSINESS digital printing Deutschlang GmbH},
  address   = {Berlin},
  isbn      = {978-3-86460-271-9 ; 3-86460-271-8},
  pages     = {178 Seiten},
  year      = {2015},
  language  = {de}
}