@misc{indiciae2bdf1d2de042,
  title = {Manned orbital operations - An economical approach to space utilization},
  author = {Smith, T. D. and Tschirgi, J. M.},
  year = {1971},
  url = {https://ntrs.nasa.gov/citations/19710061333},
  note = {Source identifier: 19710061333}
}