How NASA uses paired comparisons to plan the mission to Mars
Happy 4th of July weekend!
We all face important decisions every day, but few of us will ever be asked to make the life-or-death choices necessary to plan a manned mission to Mars. It’s notable, then, that when NASA was confronted with deciding on a life support system for the spacecrafts that will transport astronauts to the red planet and the moon, they fielded a paired comparison survey to twenty five experts across the agency. In honor of our Independence Day, here’s a brief dive into America’s exploration of the final frontier.
In a paper presented in 2018 at the International Conference on Environmental Systems, NASA planners recount their use of Analytic Hierarchy Process, a method of hierarchically using paired comparison surveys to attack tough decisions, to manage the complex tradeoffs involved in selecting a system. The planners weighed ten criteria, including cost, safety, and the ability to process CO2, by asking experts to compare them against one another, and rank the alternatives by how well they satisfied each:
You can see the criteria weights for each mission below, where safety is scored as the highest priority for both, but reliability scores significantly higher for the Mars mission than the Lunar mission. Mars is much farther, so this seems intuitive:
The beauty of paired comparison surveys is that they allow everyone, like NASA mission planners, to confront the toughest tradeoffs in a straightforward and unemotional way. Everyone would agree that any system aboard a spacecraft should be reliable, but making comparisons allowed experts to place reliability in the context of all the other mission requirements and allocate resources accordingly to the winning system, the Thermally-Coupled TSAC.
I hope you have a safe and happy 4th with your family and friends. Talk soon!
JB