@misc{indiciaeb20a8123b81f,
  title = {Mars surface sample return missions via solar electric propulsion},
  author = {Spadoni, D. J. and Friedlander, A. L.},
  year = {1971},
  url = {https://ntrs.nasa.gov/citations/19720005139},
  note = {Source identifier: 19720005139}
}