Mars Rover Mission Context

• JPL engineers celebrated landing 900kg rover (Mini Cooper size) on Mars
• Mars rover packed with engineering innovations, focus on tire challenges
• Wheels experiencing substantial damage from rough Martian terrain
• Rover top speed: 0.15 km/h on flat hard ground
• Snail's pace still generates enough force to tear holes in aluminum wheels

Current Mars Rover Wheel Design

• All Mars rovers use solid aluminum wheels (Sojourner, Opportunity, Spirit, Curiosity)
• Curiosity rover much heavier than predecessors
• Wheel specifications:
  • 0.5m diameter, 400mm wide
  • Milled from solid aluminum block
  • 0.75mm thick over majority of circumference (credit card thickness)
  • Load-bearing threads: 6.4mm thick
• Damage expected given 0.75mm thickness supporting nearly 1-ton vehicle over sharp rocks
• NASA underestimated terrain roughness
• Load-bearing threads also damaged - wheel becomes useless if they break

Mission Economics & Priority

• Mars rover development cost: $2.5 billion
• Nuclear reactor powered
• Extending project life = top priority
• Wheel solution high on NASA's future project list

Alternative Tire Solutions Considered

Rubber Tires

• Land Rovers successfully navigate similar rough terrain on Earth
• Mars temperature challenges:
  • Temperatures drop to -130°C
  • Transforms rubber from elastic to brittle glass-like material
  • UV radiation degradation on Mars surface
• Weight concerns: rubber + steel reinforcements + rim = heavy

Steel Mesh Wheels (Lunar Rover Design)

• Flexible steel mesh with stiffer inner frame
• Thin metal strips prevent sinking into soil
• Lunar rover mass: 450kg vs Curiosity's 900kg
• Higher Mars gravity makes design unsuitable
• Wheels cannot hold vehicle weight without permanent deformation

Nitinol Spring Tire Innovation

• Goodyear developed original lunar wheel
• 2010: Goodyear + NASA received R&D 100 award for spring tire
• Properties: light, bendable, conforming, weight-capable, no permanent deformation

Nitinol Material Properties

• Nickel-titanium alloy
• Shape-memory alloy capabilities
• Bend/deform → apply heat → returns to original shape
• "Remembers" original shape

Material Science Explanation

Standard Material Behavior

• Stress below yield point: elastic deformation (returns to original shape)
• Stress beyond yield point: permanent deformation (doesn't return)
• Permanent deformation occurs when crystal lattice defects move under force
• Mars rover wheels: stress exceeds yield stress → permanent deformation → cracks → fracture

Nitinol Crystal Structure

• Below certain temperature: martensite crystal structure
• Accommodates deformation easily
• Forms twinned atom grains that align under stress
• "Detwinning" process: twin grains grow at others' expense
• Like dislocation movement in other metals - permanent without external energy

Shape Memory Process

• Heating transforms nitinol to austenite (ordered, regular crystal structure)
• Effectively resets crystal structure
• Cooling: nitinol remembers original shape
• Transformation temperature customizable by titanium content
• Increasing titanium content = higher transformation temperature

Medical Applications

• Stents designed for 37°C (body temperature) transformation
• Traditional stents: balloon inflation causes plastic deformation
• Forces on blood vessel lining → damage → scar tissue formation
• Nitinol stents: automatically expand at body temperature without excessive force

Super Elasticity for Mars Application

• No heat application needed for Mars rover
• Stress/strain induces martensite → austenite transformation
• Stress threshold triggers crystal lattice transformation to austenite
• Stress release → returns to martensite → metal recovers shape
• Allows wheels to deform to rim and still recover
• Interlocking coil design + super elasticity = unique strain tolerance
• Survives harsh Martian environment

Future Applications

• Planned for NASA's 2020 Mars rover launch designs
• Demonstrates continuous innovation potential in seemingly simple components

Design Competition Announcement

• Royal Air Force + Briggs Automotive Company partnership
• Target: young engineers
• Challenge: design numerous transport vehicle improving on previous designs
• Requirements: innovative, creative, ground-up thinking
• Consider Mars rover problems (communication, etc.)
• Top prize: 3D model development by Briggs Automotive + work experience at BAC Factory Liverpool
• BAC produces world's only road-legal single seater supercar

Distance Records

• Longest extraterrestrial journey: Opportunity Rover (45km)
• Previous record: Russian Luna cod lunar rover
• Curiosity: 20km to date