Assessing Gale Crater as a Potential Human Mission Landing Site on Mars

Introduction: Mars is the " horizon goal " for human space flight [1]. Towards that endeavor, one must consider several factors in regards to choosing a landing site suitable for a human-rated mission including: entry, descent, and landing (EDL) characteristics, scientific diversity, and possible insitu resources [2]. Selecting any one place is a careful balance of reducing risks and increasing scientific return for the mission. " Go where you know " : There are tens of proposed landing sites for robotic missions with varying scientific interest, as well as the handful of locations currently visited by successfully landed spacecraft. For the former, sites such as Eberswalde delta, Holden crater, and Mawrth Vallis has received extensive or-bital coverage and analysis during the MSL landing site selection workshop and are well characterized. In addition, 'runner up' candidates for that mission are now on the list for evaluation for the Mars2020 rover, e.g. Jezero Crater or Nili Fossae, and contain equal (though not fully processed) orbital data for reference [3]. For legacy and current missions to Mars, three are landers, and one lander/ rover, with limited visible areal extent: Viking 1 Viking 2, Phoenix, and Path-finder/Sojourner. The remaining rover missions, MER Spirit, MER Opportunity, and MSL Curiosity offer the most ground truth over several to tens of kilometers both in and outside their nominal landing ellipses. While the HiRISE instrument provides unprecedented detail of Mars' surface to current and future missions, the insitu observations of rock density, soil mechanics, temperature fluctuations, dust opacity, radiation (via Curiosity), traversability, not to mention insitu science, are not directly measureable or resolvable by orbital assets. While we can certainly make well-educated and higher-order assessments of landing sites, revisiting anywhere we've gone before can only reduce risk by removing uncertainty or shrinking errors bars in landing site analysis. Insitu data decreases risk compared to other potential landing sites that have never been visited because of this ability to remove the unknown at the surface; albeit we've been very successful over the past two decades with landed missions. However, a human-rated mission will likely require reducing risk by an order of magnitude, thereby requiring an order of magnitude better data than we currently have; only insitu data provides this level of certainty. From a financial perspective, insitu data is 'priceless' for a human rated mission, not replicable for other sites. EDL: Like all missions, Mars' elevation limits landing sites …