@misc{indiciaeb0df91657cf8,
  title = {Earth-Approaching Asteroids as Targets for Exploration},
  author = {Shoemaker, E. M. and Helin, E. F.},
  year = {1978},
  url = {https://ntrs.nasa.gov/citations/19780021079},
  note = {Source identifier: 19780021079}
}