Exploration Mobility Within

Driveback ConstraintsGraham Mann

School of Information TechnologyMurdoch UniversityWestern Australia

Driving on Meridiani PlanumMars 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 CH4 or CO fuel, range 300km • cf. today’s Honda CXF (1760kg, 80kWe

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 190kWe,

carries 70 persons 200km between refills)

2019 exploration vehicles are likely to be more constrained bytime 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

0 6 12

Te (hours since dawn at equator)

0

100

200

300

400

Rs

(range in km)

Maximum safeunpressurisedrover range

Maximum safemedium rangesortie

• 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.

Opportunitylanding ellipse

haematite“island”

S1

S2 habitat

S3

Example: Desired Route for a 3-stop Sortie

Want 2 hour stops ateach of S1, S2 and S3

S3S1 S2

0

Rs

(range in km)

0 1 2 3 4 5 6 7 8 9 10 11 12

100

200

300

400

Te (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