@misc{indiciaeca1b93c15397,
  title = {Preliminary summary of the ETF conceptual studies},
  author = {Seikel, G. R. and Bercaw, R. W. and Pearson, C. V. and Owens, W. R.},
  year = {1978},
  url = {https://ntrs.nasa.gov/citations/19790003307},
  note = {Source identifier: 19790003307}
}