Reasons not to provide mechanical means to clean solar panels on Mars:
- and this is the primary reason: Wind on Mars occasionally blows the dust away. This means dust is not a major issue, but a minor one. Spirit and Opportunity functioned for years despite not having dust removal equipment.
- Mechanical operations are expensive: you've just added a series of operations that have to be designed and tested to avoid damaging the solar panels, and to avoid interference with the experiments. You've also added weight and complexity which eat into your budget.
- Dry dust is abrasive. It's all to easy to scratch the solar panels.
- Mars dust is tiny, more like cigarette smoke than the particles we recognize as dust. Any imperfections in the brush will result in dust remaining on the solar panels.
- Based on my own experiments, a fan doesn't work well: as soon as you start blowing the dust away, there'll be a cloud around the rover that will be sucked back in by the fan.
NASA is looking into technologies that can clean a solar panel. This has been identified as an enabling technology for crewed missions to Mars. Evidently, NASA does not see this as a necessity for robotic missions up to and including InSight.
These 2 options are being explored:
- Electrostatic cleaning: this leverages the static charge of dust particles. By creating an EM field, the dust can be moved to the edge of the panel.
The system takes advantage of the fact that most dust particles, particularly in dry environments, have an electric charge. A transparent electrode material such as indium tin oxide delivers an alternating current to the top surface of the panel. As it swings between being positively and negatively charged, it creates an electric field that repels positively and negatively charged particles. The electric field also helps to impart a charge to uncharged dust particles, allowing them to be quickly repelled as they come in contact with the panel. The researchers have designed the system so that the electric field works its way from one side of the solar panel to the other, gradually moving the dust along until it falls off.
...typically it only needs to be on between two and five minutes a day,
2012 paper on initial tests with a prototype panel showed promising results.
- Vibration: this removes the dust by shaking the entire panel.
Using vibrations is simpler and requires fewer modifications to the solar panel, he says. But it does not remove fine particles as well as the electrical field approach.