Solar Balloons for Mars Polar Exploration

I’m back. Sorry for the neglect of this blog – I can’t promise it won’t happen again.

I’m still at York University for the summer, but it’s for a good reason. I’m having the wonderful opportunity to work with a veteran of planetary exploration – Dr. John Moores – who contributed to several Mars missions (website). His chief interest is water on other planets, since it’s a chief precursor to life.

Balloon over Mars Ice

He’s mentoring me on the study of a solar-heated balloon that lands and takes off from different sites on Mars’ northern polar cap, using the ice to replenish the lifting gas it vented on the descent. That lifting gas is either water vapor or hydrogen. Dr. Moores is very interested in this concept because it has the potential to carry out scientific observations at multiple points separated from each other by many kilometers and impassable terrain. This is something not even the Mars rovers have managed to pull off. To date, the longest-lived Mars rover, Opportunity, has traveled only 39 km in 11 years.

The northern polar cap consists of many layers of ice deposited over millennia, and so for this reason it is thought to be a repository of geological and climatological data going back at least 100,000 years. The balloon gondola (called an “aerobot”) would drill through these layers and draw up the meltwater and study it to uncover more of Mars’ past.

This post is a summary of everything I’ve learned so far and the remaining work I will have to do to confirm the concept’s feasibility.

-Hydrogen is a much more potent lifting gas than water vapor, owing to its low molar mass (2 g/mol versus 18 g/mol). However, it must be electrolyzed from the purified meltwater, and the amount of water that must be mined is almost the same as if the balloon just used water vapor. I will have to investigate the amount of heating and cooling that the balloon envelope experiences, to quantify the temperatures of the water vapor. If warm enough, the amount of water vapor could be reduced to the point where the amount of mined water is the same as for hydrogen.

-The gondola will have to be a very compact vehicle to keep mass down, built similarly to the Beagle 2 lander. That probe crashed on Mars in 2003, and it is thought that the razor-thin margins in its design was a contributing factor. If minimalism is going to be a problem, the aerobot can hitch a ride on a larger lander and take off from there.

Mars Balloon Deployment

-The sun will be at a low angle during polar summer, moving from east to west without setting. This limits the solar insolation and forces the use of body-mounted solar panels on the gondola. Reflectivity of the ice may make up for this. A MATLAB program is being written to simulate the solar insolation on any point on the polar cap as a function of time.

I’ve registered for the 2014 Mars Society convention in Houston this August and will be presenting my results there – if I finish it in time. But regardless of the outcome, this has been and will be an interesting learning experience!


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