@ARTICLE{topputo2014survey,
  author = {Topputo, F. and Zhang, C.},
  title = {{Survey of Direct Transcription for Low-Thrust Space Trajectory Optimization with Applications}},
  journal = {Abstract and Applied Analysis},
  year = {2014},
  volume = {2014},
  pages = {1--15},
  number = {Article ID 851720},
  doi = {10.1155/2014/851720}
}