Depending on which Facebook pages or Twitter feeds you follow, some of you may have caught wind that Opportunity (Mars Exploration Rover B, Figure 1) recently passed its twelfth anniversary of its landing on the red planet. Opportunity’s ongoing trek across Mars represents a fantastic accomplishment in engineering. At the time I’m writing this, the rover has been in continual operation for over 4,300 Earth days (that’s about 4,185 Sols, or Martian days). Considering its original planned mission time of 92 Earth days, Opportunity has exceeded its design lifetime by 4,700%. Imagine having a car that, instead of a lifetime of 200,000 miles with regular maintenance, drove for 1,000,000 miles with no repairs apart from downloadable software updates, and you’ll have an appreciation for the awesome engineering and design on Opportunity. Most sites covering the anniversary have focused on the rover’s scientific discoveries (if you’re interested, here’s a fascinating gallery or an extensive description of its travels). As mechanical engineers and materials scientists, however, we are equally fascinated by the engineering and design that contributed to this plucky explorer’s hearty disposition. So, in this blog and the next I’ll take a look at some of the technologies that kept Opportunity rolling for so long in such harsh conditions.
The First Leg of the Journey
Figure 2: MER-B orbital trajectory Mars Exploration Rover Launches Press Kit, June 2003, p. 29
NASA launched MER-B Opportunity atop a Delta II rocket on July 7, 2003 (one month after the launch of its twin rover, Spirit) and it spent over 200 days in space on a curving trajectory towards Mars (see Figure 2). Since Mars was 11 light-minutes away on the landing day of January 25, 2004 (meaning that light took 11 minutes to travel one way between Earth and Mars), there was a 22-minute delay between the rover sending a signal to Earth and receiving Earth’s response. Thus, Opportunity’s entry, descent and landing all had to be accomplished without any control from the controllers at the Jet Propulsion Lab (JPL). I’m sure some of you have seen the video of the Mars Exploration Rovers’ (somewhat undignified) landing sequence: after slowing it’s decent with parachutes and retrorockets, the tetrahedral landing capsule inflated a set of airbags on all four sides and simply bounced along the surface until it rolled to a stop (see Figure 3 for a step-by-step breakdown). These airbags obviously had to be incredibly strong, and the design engineers used a double layer of liquid crystal polymer called Vectran. Vectran is similar to Kevlar, but with higher resistance to extreme cold and UV radiation. This is the same fabric that NASA engineers use on astronauts’ EVA suits and Bigelow Aerospace uses on their inflatable orbital habitats.
Figure 3: MER entry, descent and landing Mars Exploration Rover Launches Press Kit, June 2003, p. 31
Martian Engineering Hazards
Once Opportunity landed, it had to face the hazards of operating on the surface of Mars. These extreme conditions pose difficult challenges to robotic equipment and the engineers and scientists designing it.
Mars is extremely cold. There’s a common misconception that outer space is incredibly cold, but in truth most equipment in space has more trouble losing heat, considering there is no atmosphere to transfer heat to. Mars, however, has an atmosphere, so it can lose heat through conduction. Moreover, that atmosphere has weather, so when the wind picks up the rover can lose heat even faster, to convection.
Martian dust is everywhere. Without water to trap dust particles or sediment them together, Martian dust is continually ground into finer and finer particles. The ultra-fine dust is abrasive and can pit solar panels and optical lenses or get past gaskets into sensitive moving joints. Dust storms on Mars can also block out a significant amount of sunlight, which can be deadly for a rover relying on solar power.
Mars lacks a magnetosphere. On Earth, this magnetic field deflects solar wind and cosmic rays, protecting us from harmful radiation. Anything on the Martian surface, however, will experience a radiation bombardment similar to conditions in outer space.
Mars is always between 4 and 24 light-minutes away. As I mentioned above, there is a delay between the rover sending information to Earth and getting a control response back. If an emergency were to occur on Mars, scientists on earth might not know for 24 minutes, and it would take another 24 to send a signal back to correct the problem.
Mars has no service stations. The mechanical engineers designing the rovers had to build components that would never expect to see any maintenance. Joints could not be cleaned out, bearings could not be re-lubricated, and components could not be replaced if they failed. Furthermore, considering the astronomical cost per pound of sending anything into orbit, the rover could not afford to carry much in terms of redundant components.
Challenging Engineering is Best Engineering
The demanding nature of the Mars mission environment is evidenced by the rover’s design lifetime of only 92 days. However, the fact that Opportunity is still rolling 4,300 days later is proof that the electrical engineers, mechanical engineers, materials scientists, and everyone else on the design teams did not underestimate the challenges they faced. In fact, solving problems like these is what engineers live for. We here at Glew Engineering salute the incredible work done by the engineers at NASA and JPL, and in the following blog I’ll take a look into some of the technology they used and the problems they solved during design and operation.
 NASA. (2003). Mars Exploration Rover Launches [Press release]. Retrieved from http://www.jpl.nasa.gov/news/press_kits/merlaunch.pdf