While I’m on the topic of keeping wires tidy on my Sawppy rover, I thought it is a good opportunity to take a little detour and look at wiring on real rovers going to Mars. Or at least, their Earthbound test counterparts which as far as I can tell got the identical treatment on wire management. After all, their job is to replicate the Mars robot explorers as closely as possible for testing here on Earth. Most of the differences are centered on electrical power supply, because these rovers can run on what is essentially an extension cord. The Spirit/Opportunity sibling “Dusty” doesn’t have working solar panels, and the Curiosity sibling “Maggie” doesn’t have a nuclear reactor. But other than that, they strive to be identical which I assume also included the wiring scheme.
Looking at the family portrait of Earthbound test vehicles, we can see that a lot of wiring out visible on the surfaces. Running alongside structural members like suspension arms and equipment bay. I found this extremely fascinating! Why are the wires outside instead of tucked inside? My first thought was that the major wires are tucked inside and those visible outside are less important auxiliary channels, but that doesn’t seem to be the case.
During discussions about the damaged wheels on Curiosity, it was mentioned that the greatest risk is not that the wheel would be unable to roll. The greatest risk are that jagged pieces of protruding wheel may cut some of these exposed wires rendering motors and sensors inoperable. This tells us those exposed cables are in fact critical to rover operation and not merely less important items left exposed. Though they are exposed, they are not wild and unruly. In fact they are exceedingly tidy. In fact, NASA and JPL have precise specifications regarding wire management, and rover wire bundle installation represents the state of the art in cable lacing.
So… why on the outside? This isn’t the kind of information that NASA JPL puts in their publicity packets, so I’m left to speculate. The first observation is that all the usual reasons to shelter wires don’t apply to Mars. Here on Earth, exposed wiring bundles are quickly degraded by exposure to the elements. In contrast, Mars has a thin atmosphere and no weather to speak of.
Second, with the wires exposed and accessible, it makes diagnosis and repair easier. This isn’t a joke about repair technicians on Mars, but referring to vehicle assembly here on Earth. As the rover is put together and their integration tested, problems would inevitably crop up. Thus there is value in accessing wires for diagnostics and repair without having to take apart components of unrelated systems. What makes things easier for a little Sawppy rover here on Earth is equally valid for a rover being prepared to go to Mars. But this is all just speculation. All we know is that the penalty of running wires externally did not outweigh whatever benefit they expected to get. Ease of access has value, as keeping track of everything in such a huge project is a major undertaking all on its own. Tracking parts for a little Sawppy rover gets confusing enough.