Welcome to mining industry - suite one
In space exploration, in-situ resource utilization (ISRU) is the use of resources found or manufactured on other astronomical objects as the Moon, Mars, Asteroids or others, to further the goals of a space mission.
The ability to produce propellant via In-Situ reduces Exploration Vehicle sizes, Propellant carry requirement by 50% and its tank diameter and length, as well as the number of launches for Space Travel.
Can we Mining the Atmosphere of Mars?
A study (phase 1) from NASA Innovative Advanced Concepts (NIAC) say it is really possible. This Mars Molniya Orbit Atmospheric Resource Mining report elaborate an innovative and feasible concept for a reusable Mars space transportation system that, without ever relying on propellant transported from Earth, can repeatedly launch and land on Mars. To do that, it can use propellant and electrical energy generated on orbit via plasma-harnessing, scooping, and ram-compressing the 95% CO2 Martian atmosphere, as well as the indigenous resources on the surface of Mars (CO2, H2O). Instead today's EDL technology, which limit to approximately 1-2 tons (t) of landed mass, this system can carry four crew members and cargo up to 20 metric t.
NIAC Mars Atmospheric Gas Resources Collector Vehicle (RCV) stack concept during an aerobraking CO2 collection pass in the upper atmosphere. Credit: NASA
The proposed mission architecture for the Mars Molniya Orbit Atmospheric Resource Mining concept incorporates a wide range of vehicle classes to make round-trip travel between Earth and Mars robust, affordable, and ultimately routine for cargo and crew, thereby helping to expand human civilization to Mars.
A representative decaying highly elliptic Molniya orbit around Mars.
ISRU Propellant's Selection/Application - You have to know
A Propellant need to meet many criteria to be considered as basis for transportation architecture. First, it must have thermal stability to operate in a liquid rocket engine, means the ability to cool engine throat critical heat flux, avoiding thermal decomposition and coking in engine coolant channels, as well as offers sufficiently high engine specific impulse (Isp).
From a vehicle system, it is the combined characteristic of propellant Isp and bulk density in meeting the vehicle impulsive velocity (DeltaV) mission requirement that offers either the lowest mass or lowest propellant tank volume that warrants the selection. So...
The cryogenic Liquid Hydrogen(LH2), with its Normal Boiling Point at 36.6 degree Rankin, has an excellent gravimetric heat of combustion (energy per mass) and can generates an High Engine Specific Impulse when combusted with Liquid Oxygen (LO2). Used in launch vehicles for first stage and upper stage applications, it is the fuel of choice for In-Space Propulsion Stage because that high Isp value.
Its disadvantage is that, because it has a low volumetric heat of combustion due to its low density and boiling point, it required techniques for tank insulation and Cryo-Fluid Management to reduce its boil-off. These additional complexity and low dry mass for the stage, reduce its overall usable propellant mass fraction.
Rocket Propellant (RP-1) is a high density kerosene-based fuel commonly used in launch vehicles and, it can be stored in ambient temperature, no tank insulation or tank thermal conditioning is required. Its density is closer to that of LO2, thereby offers total tank volume efficiency. But, because it freezes at -60 degree Fahrenheit (400 degree Rankin), it required thick tank insulation or heaters to avoid the fuel freezing. These latter approach are considered not practical for Space applications.
One big NASA's focus is the Methane(CH4) because it give the advantage of “green” propellant, which minimizes environmental impact with its exhausts. Also, its main advantage is the perceived ease of manufacturing via the ISRU method and provide high density which offer a lower propellant tank volume.
As part of green propellant family, Propane (C3H8) is selected because it offers a good range of low freezing point and relatively high boiling point. Like Methane's ISRU production, it can be manufactured via similar method, be subcooled and thereby, increasing its density and, by the way, reducing its tank volume.
Another Green propellant, Ethylene(C2H4)is selected because of its relative high Engine Isp and, like Methane and Ethanol, can be further subcooled to reduce tank volume.
Reference: 49th AIAA/ASME/SAE/ASEE, Joint Propulsion Conference, San Jose, California/AIAA-2013-3804.