A couple more papers on the topic: http://www.sciencedirect.com/science/article/pii/S0273117711005783 http://www.sciencedirect.com/science/article/pii/S0273117

A couple more papers on the topic: http://www.sciencedirect.com/science/article/pii/S0273117711005783 http://www.sciencedirect.com/science/article/pii/S0273117711... http://www.sciencedirect.com/science/article/pii/S0273117710006964 http://www.sciencedirect.com/science/article/pii/S0273117710... Note the authors include the founder(s) from back when they were at NASA.