@misc{indiciaedb663aaf608c,
  title = {The State of Space Propulsion Research},
  author = {Sackheim, R. L. and Cole, J. W. and Litchford, R. J.},
  year = {2006},
  url = {https://ntrs.nasa.gov/citations/20070008232},
  note = {Source identifier: 20070008232}
}