Exploration Mobility Within Driveback Constraints Graham Mann School of Information Technology Murdoch University Western Australia

Driving on Meridiani Planum Mars vehicles circa 2019 Likely to be ISRU gas powered fuel cell driving four independently motorised wheels via electronic transmission Unpressurised Rover Open 4-seater resembling a tougher Apollo Lunar Rover using CH 4 or CO fuel, range 300km cf. today’s Honda CXF (1760kg, 80kW e carries 4 persons 257km between refills) Pressurised Rover Vehicle the size of a small bus or holiday camper with shirtsleeve environment, same fuel, range 1000km cf. today’s test fuel-cell buses, typically 190kW e, carries 70 persons 200km between refills) 2019 exploration vehicles are likely to be more constrained by time and safety factors than by engineering performance limitations - at least for the first crewed missions.

Constraint: Daylight Driving Only Suppose a ‘no driving at night’ policy were adopted. Range is thus limited by daylight hours – mean 12.25hrs at Meridiani Planum, all seasons At average speed ⊽ ur of 30km/hr, an unpressurised rover must stay inside a shrinking circle with a radius described by the red line of safety centered on the habitat line of safety line of feasibility (medium range class sortie) ⊽ ur = 30 kph T e (hours since dawn at equator) R s (range in km) Maximum safe unpressurised rover range Maximum safe medium range sortie But since the unpressurised rover’s earliest departure is dawn, not all points on that line can be safely reached, only those in the triangular area limited by the amber line of feasibility.

Opportunity landing ellipse haematite “island” S1 S2 habitat S3 Example: Desired Route for a 3-stop Sortie Want 2 hour stops at each of S1, S2 and S3

S3 S1 S2 0 R s (range in km) T e (hours since dawn at equator) Geometrical Safe Sortie Planning Method Planned stops are plotted as blocks beneath the 30kmh safety triangle Width of each blocks set by duration of stop, height set distance of target site, distances apart set by drive durations To be safe, this all blocks must fit entirely beneath the safety triangle In this example, a 2-hour stop at S3 is not safe. S3 may be reduced to 90 minutes to fit