“…Numerous solution methods have been studied, including methods based on primer vector theory (Russell, 2007;Petropoulos and Russell, 2008;Restrepo and Russell, 2017), direct methods based on solving an NLP (Betts, 2000;Arrieta-Camacho and Biegler, 2005;Ross et al, 2007;Starek and Kolmanovsky, 2012;Rao, 2015, 2016), and indirect methods (Alfano and Thorne, 1994;Fernandes, 1995;Kechichian, 1995;Haberkorn et al, 2004;Gong et al, 2008;Gil-Fernandez and Gomez-Tierno, 2010;Zimmer et al, 2010;Pan et al, 2012;Pontani and Conway, 2013;Cerf, 2016;Taheri et al, 2016Taheri et al, , 2017Rasotto et al, 2015;Lizia et al, 2014). Some recent advances for indirect methods include homotopy methods (Pan et al, 2019;Pan and Pan, 2020;Cerf et al, 2011), optimal switching surfaces (Taheri and Junkins, 2019), the RASHS and CSC approaches from Section 2.5.2 (Saranathan and Grant, 2018;Taheri et al, 2020a,b), and simultaneous optimization (also known as co-optimization) of the trajectory and the spacecraft design parameters (Arya et al, 2020).…”