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Mars atmosphere is made up mostly of carbon dioxide (more than 95% by volume), and its average ambient surface temperature of 210 K, coupled with large diurnal temperature swings can facilitate the formation of dry ice during the night. Because of its low critical temperature, frozen carbon dioxide (dry ice) can be heated at constant volume to mode...
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Context 1
... supercritical CO2 thruster unit is shown in Figure 2. Commercially-available dry ice was used to charge the pressure tank and no effort was made to remove the small amount of condensed water ice and residual air that remained in the pressure vessel, treating those molecules as surrogates for Mars atmospheric non- condensables. ...
Citations
... Using the method of characteristics for a non-ideal gas, Blass [1] and coworkers [2] designed a supersonic Mach 2 nozzle and test apparatus to measure the blowdown thrust performance of supercritical carbon dioxide as a candidate for Mars surface applications. Unfortunately, fabrication difficulties were encountered and thus far, only sonic nozzle performance has been reported [2]. ...
... Using the method of characteristics for a non-ideal gas, Blass [1] and coworkers [2] designed a supersonic Mach 2 nozzle and test apparatus to measure the blowdown thrust performance of supercritical carbon dioxide as a candidate for Mars surface applications. Unfortunately, fabrication difficulties were encountered and thus far, only sonic nozzle performance has been reported [2]. Those tests appeared to show that sonic carbon dioxide gas expansion could be sustained into a subcooled flow regime, thereby improving propulsive performance. ...
... After the pressure tank was charged with a specific mass of dry ice, the flanged end cap with O-ring seal was secured and the tank assembly was installed in the test apparatus, shown schematically in Figure 3. The basic test apparatus employed in the earlier sonic blow-down experiments [2] was utilized here. However, the specific impulse of the propellant must be calculated using the measured thrust and associated propellant mass flow rate, and the actual behavior of the supercritical fluid upstream from the nozzle was a concern. ...
We have investigated the performance of supercritical carbon dioxide as a candidate for Mars surface propulsion operations. Since Mars dry ice can be frozen out of its atmosphere and confined subsequently in a fixed volume with relative ease, the modest critical temperature and pressure of carbon dioxide can be exploited by heating the captured dry ice at constant volume. The research reported here has measured the specific impulse behavior of impure supercritical carbon dioxide produced by heating confined dry ice in a pressure vessel to temperatures up to 74 °C, followed by blow-down expansion of the resulting supercritical fluid through a supersonic Mach 2 nozzle. By varying the mass of the dry ice charge and initial temperature, it was possible to produce three types of blow-down processes. Short-duration specific impulse peaks (100 ≈ sp I sec) were observed for all three types of blow-down process, and the measured extended-duration specific impulse was 40 ≈ sp I sec. Optimal performance was produced when blow-down proceeded through the condensing, two-phase flow regime.
We have re-examined in situ resource utilization (ISRU) from the perspective of the extraordinarily successful on-going Mars Exploration Program, more than 30 years after we first alerted the science communities to the break-through advantages ISRU offered for Mars round-trip missions. Since that publication, many investigators have expanded on the original findings and have considered the applicability of this innovative systems-concept to other missions, including crewed Mars round-trips. We know a great deal more about the risks associated with sending humans beyond the Earth's magnetic shield today, but we have not yet devised systems that can sustain human missions to Mars within realistic size and budgetary constraints. This analysis is focused on the application and development of in situ resource utilization, first for remotely controlled probes, and then human missions since a crewed mission to Mars in the foreseeable future is of questionable technical, programmatic and financial feasibility. We reach the dual conclusions that: (1) Mars return missions will benefit greatly (even more than anticipated in the original paper) from the utilization of in situ resources; and (2) although other venues can also enjoy benefits, Mars is uniquely suitable for this concept, because of the high "gearing ratio" of reduced Mars surface mass and the abundance of suitable chemicals from the atmosphere and from shallow surface layers. Consequently, we have put forward an argument for moving from ISRU hardware feasibility studies to the development of deployable Mars surface systems that can be used to accelerate surface exploration. That approach can reduce the time interval between sequential surface exploration probe deployments while helping evolve a robotic surface exploration architecture that can accommodate reprogramming from a Mars surface base utilizing Earth-based exploration managers. Our proposed reprioritization of technology developments leads also to a more sustainable path toward human arrival.
