The following information is missing from the Funding section: “The authors received internal funding for this project from the China Aerospace Science and Technology Corporation (CAST): http://english.spacechina.com/n16421/index.html. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.”The authors have also provided an updated Competing Interests section: “The authors received internal funding for this project from the China Aerospace Science and Technology Corporation (CAST): http://english.spacechina.com/n16421/index.html. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.”