Participatory technology assessment (pTA) is a methodology that seeks to gain public perspective such that it can inform government decision-making. For engineering activities that are in the early stages of preliminary design, or in what Fisher et al. might call ‘upstream’ engineering, pTA can be particularly useful in informing technical decision-making. We will discuss an experiment in using pTA to inform upstream engineering. In partnership with NASA, the Expert and Citizen Assessment of Science and Technology (ECAST) network conducted a pTA-based forum on NASA’s Asteroid Initatiative and other possible missions that could follow from it (e.g., Mars). The goal of the forum was to assess citizens’ values and their preferences about potential detection, mitigation, and exploration-based technologies associated with NASA’s Asteroid Initiative. ECAST organized two citizen forums in Phoenix, Arizona, and Boston, Massachusetts, in November 2014, with a total of 183 citizens selected by ECAST to reflect to rough order the demographics of each city. The forums included sessions on planetary defense, NASA’s Asteroid Redirect Mission, and Mars exploration. This paper focuses on the Mars exploration session. Citizens were given background information about three potential Mars missions that NASA could carry out and then engaged in structured facilitated discussions about their preferences: 1) Crewed orbital mission to direct robots on the surface of Mars; 2) short exploratory crewed mission to Mars surface; and 3) establishing a permanent settlement on Mars. In this paper, we will assess values and perceptions the public had about different Mars exploration options. We will also present results on the public’s perception of mission planning needs for NASA. These results show a complex set of values that may be relevant for NASA managers examining planning to go to Mars.