@article{Wittmann2000,
  author    = {Wittmann, Klaus},
  title     = {Overview of Space Operations at DLR},
  year      = {2000},
  language  = {en}
}
@article{WittmannKehrWillnecker2000,
  author    = {Wittmann, Klaus and Kehr, J. and Willnecker, R.},
  title     = {Decentralized Payload Operations Concept for Columbus},
  year      = {2000},
  language  = {en}
}