I think I will defer to the experts.
The question hasn't been put to NASA yet as far as I have heard.
Until it is I see no reason to doubt these people, who are the ones who said it was possible:
John Logsdon, director, Space Policy Institute at George Washington University
Donna Shirley, instructor of aeronautics engineering at the University of Oklahoma and former Mars exploration manager at NASA
Alex Roland, chair of the History Department at Duke University and former NASA historian