Participatory technology assessment (pTA) is a method to gain public perspective about issues related to engineering and technology. pTA can be particularly useful in informing technical decision-making. We will discuss an experiment in using pTA to inform early engineering decisions. In partnership with NASA, the Expert and Citizen Assessment of Science and Technology (ECAST) network conducted a pTA-based forum on NASA's Asteroid Initiative, which includes the Asteroid Grand Challenge and the Asteroid Redirect Mission. 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 the demographics of each state. The full forums included sessions on asteroid detection, planetary defense, NASA's Asteroid Redirect Mission, and Mars exploration. This paper focuses on the Asteroid Redirect Mission (ARM) deliberation. Citizens were given background information about two options for performing the ARM mission that, in 2014, NASA was actively assessing before making a downselect decision. Option A involved capturing a 10m diameter asteroid, redirecting it to lunar orbit, and sending astronauts to investigate and sample it. Option B involved capturing a several meter diameter boulder from the surface of a much larger asteroid, and likewise placing in lunar orbit and sending crew. In this paper, we will assess values and perceptions participants had about Option A and Option B. These results were shared with NASA managers in December 2014 prior to their making a downselect decision about which option the agency should pursue for ARM. While the public did select Option B as their preferred way to perform the ARM mission (which aligned with what NASA later chose), the more important results from the deliberation included the illumination of citizen values and perceptions concerning ARM.