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9:55 PM (6 hours ago)
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As you know, I am fond of outside-of-the-box ideas.
Since we are embarking on the build of a new set of SIM suits, perhaps it is time to entertain such ideas for a new generation of SIM suit backpacks. The old fans - in – Tupperware systems have provided a nice but limited analog for the mechanisms that will be required by a real 'portable live support system'. I would like to propose that we consider an upgrade of SIM to include a system that is structurally and functionally a better simulation of the PLSS machinery that will be used on Mars. For a glimpse of what such a system might contain, please note the figure in the later section ofhttps://en.wikipedia.org/wiki/
We could design and build a system the included pressurized tanks, plumbing, and ducts similar to those of a real PLSS but functional, serviceable, and safe for use at MDRS. Such a system would used compressed air instead of a heavy lead acid battery. The air tank would be filled from a COTS compressor such as is probably already at use at MDRS.
Requirement:
Lets begin with a functional specification of 'provide air for a 3 hour, moderately strenuous EVA at under 10 Kg.' Translating that into gas quantities requires some assumptions about physiology. For a reference, I used several sites describing human air consumption including
Human respiration rate during sustained moderate activity such as an EVA is about 30 liters per minute. An EVA lasting 3 hours will thus require some 6000 liters of air. During that time, about 360 liters of oxygen uptake and about 300 liters of CO2 discharge will occur. This corresponds to a metabolic rate of about 640 Watts.
While there is not a strict 1:1 correlation between human respiration and the amount of air that must circulate, that is probably a good approximation.
If the consumed oxygen were all supplied (as it would be on Mars) from a pressurized cylinder, it would require a 3 liter cylinder at 1800 PSI. That appears consistent with what documentation of PLSS designs I could find on the web. We could safely simulate the mechanism of a Mars suit PLSS by using air at 100 PSI as an analog for O2 at 2000 PSI.
A 3 liter steel bottle of compressed dry air at 150 PSI holds the equivalent of about 300 liters of uncompressed air. If pressurized air from this tank is fed through a regulator and then used to
drive a needle valve aspirator where it is mixes 20:1 with ambient air it could pump 6000 liters of air through the life support system over a period of 3 hours. The aspirator venturi would include components like those used in paint spray guns.
The air pump mechanism would be little more than the minimalist shop vacuum illustrated in the following photo fromhttps://woodgears.ca/physics/
For design and parts, we may also be able to borrow from scuba and paint ball gun components.
We could also add dehumidifier and moisture recapture components that would would fill with condensed exhaled water vapor as the EVA progressed. This water (along with the water that accumulates in the pressure tank) would be drained (and used to water plants in the HAB?) as part of the post-EVA pack servicing. The air thank would also have to be refilled using an air compressor. Both of these steps would be safer and simpler than the current battery recharging procedures.
In summary, I suggest we consider a SIM pack that actually provides breathing air and that looks, feels, and works much more like and actual Mars PLSS. I'd welcome any comments on this idea.
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