Along a line of thought similar to that of Robert Zubrin's Mars Direct philosophy of 'living off the land', I've been thinking about the resources available on Mars and how they might be used. Many of these are well discussed areas, in the cases of potential building materials or the benefits of 'chemical factories/reactors' - producing gases for breathing or propellant etc. - but I'd like to explore one of the more current problems we face when it comes to Mars exploration; that of power.

I have always found it unfortunate that missions such as that of the current rovers, are relatively short in duration due to the power requirements and the associated realities. Unlike the radioisotope thermoelectric generators used by probes such as Cassini or Galileo, or the outright nuclear reactors used by some radar surveillance satellites and other orbital plaforms, the power systems on the rovers and landers have shorter life-spans and overall provide less power. In all other practical respects, a rover could extend it's mission considerably beyond what is the current conventional time frame.

Given the cost of heaving mass off of our planet and the associated expenditures, I have wondered how possible it would be to improve in the area of power systems - and if this could include using local resources.

Of course, electrical power derived from solar panels is produced using a local resource (or more accurately, locally taking advantage of a very distant resource, heh), but in an environment such as Mars, solar panel efficiency is reduced by panel damage - eventually to the point where it is insufficient - and it is not effective beyond a certain equatorial area.

Batteries alone, rechargable or otherwise, are not enough. I have been wondering then if it would at all be possible to actually replace the batteries...or using local resources, to 'refurbish' them.

In the first scenario, the questions are whether:

-We have sufficient expertise in delivering payloads, with the ability to 'hit' precise surface targets within an operationally useful distance range
-We can devise systems that through design and management could make use of said payloads
-Delivering said payloads and replacing the power source (batteries or perhaps even panels) for already-present scientific instrument platforms (landers/rovers etc.) is cost effective and preferable to sending new platforms

The overall idea of course is simple - why suffer the cost of sending a whole new 'vehicle', when for all practical purposes, it is the power source that is the problem, and not the scientific payload. Certainly, advances in various fields - optics, electronics and so on - would make newer hardware desirable at a specific relative frequency, but in the cost/reward equation, it may well be better to extend the lifetime of existing missions and related hardware than to fabricate, launch and deliver new ones.

Assuming the above questions are answerable in the affirmative, there are a few possible options. In terms of replacing batteries, first the rover or whatever one is dealing with, would need to be designed so that this were possible. This translates to the batteries or their 'ports' being accessible, as well as having some mechanism for their ejection/removal and replacement.

This would require sophisticated robotics - but, I believe, not something prohibitively so. It seems to me that the largest problem to be solved in a 'battery replacement scenario' is one of planning and execution. I am not an engineer however, so this would be an open question: are the technological challenges too difficultto overcome? If not, is the prospect practical enough, and profitable enough, for it to be done?

The other possible scenario is recharging the batteries on site. This could involve replacing the panels, in a similar fashion as battery replacement, or sending a 'charging station' which the existing rover would mate to for recharging. Ambitious certainly, possible non-viable from a technical standpoint, but something worth thinking about.

Another possibility, one which started my thinking about all of this, is that of using the local resources to rebuild or fabricate batteries. I had all manner of thoughts regarding sodium-sulpher batteries and some of the recent information regarding the mineral and chemical composition on Mars. It's not that simple of course, but the prospect of some of the problems with sodium-sulpher batteries - high operating temperature, albeit somewhat unstable - and some of the issues on mars, such as the need for heating of components and so on, had me wondering what was and was not possible.

So, to sum up - given the realities, might a different approach be favorable as regards robotic exploration of Mars? Perhaps in line with the strategy discussed here, establishing a re-usable power generation 'station' - exploring something that may also help to serve as a technological stepping stone towards the eventual needed systems for manned exploration? Not quite at the level of a Zubrin-style chemical reactor...but a good test, to be sure.

Any thoughts or informed opinions on feasibility?

On this particular point, I'm not familiar with sodium-sulfur batteries. When you say "high operating temperature", do you mean they generate a lot of waste heat, or they have to be warm to operate efficiently?

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A good question, my apologies for being unclear. The cells must be kept at a high temperature, it is not a question of waste heat. In the case of hot batteries such as sodium-sulphur, operating temperatures between 250 & 300 degrees C are required.

While this is not as much of a 'perfect match' as it might be were the power source having excess waste heat to use for thermal regulation, the need for this operating temperature brings with it a much higher power capacity. The (theoretical) power density of sodium-sulphur batteries is 790 Wh/kg - over 4 and a half times more than that of lead-acid batteries for example. In practice something in the range of 200-300 is acheived for sodium-sulpher, compared to 30-50 for lead acid - I feel that can be improved upon with further development, but even as it stands it is still far superior.

With an appropriate design, the heating needs for cell operation and combating the cold environment could be met by a single system - with in theory, more available (surplus) power overall, and potentially greater efficiency in terms of recharging.

The batteries require the high temperature because resistivity of solid state electrolytes is much higher than that of liquid electrolytes at lower temperatures, resulting in low power output. Resistivity of the electrolyte is decreased through heating. There is another design approach which decreases internal resistance by making the electrolytes thin - so called 'thin film' batteries. I am thinking that an approaching between the two could achieve a balance and be most efficient.

Besides the type of batteries used, I am most interested in the idea - or perhaps philosophy - of 'sending power' to the target area, as opposed to abandoning the existing rover/lander because of the lack of power, while the other systems are still capable of doing science. Yes, we would want to explore multiple areas and with newer technology, so new rovers and such would need to be sent...but it seems that we are wasting a lot of good hardware...

Well, assuming the money could be found to fund such mission extensions, if the other issues were dealt with - not a sure thing by any means.