In-Situ Propellant System for Mars Ascent Vehicles ‘Sustainable and Low Cost Transportation on the Mars’
By Ozan Kara, Technology Innovation Institute, Abu Dhabi
(SGAC Former ME Regional Coordinator 2018 – 2020)
Mars is known to have the most suitable geological features and atmospheric conditions for future human spaceflight. Based on the data from orbiters and rovers sent through deep space, Mars has the most active volcanic mountains and the highest impact craters of all the planets. Strong evidence via rover measurements moots that liquid water may have poured across the surface of Mars billions of years ago [1].
The latest dynamical models for the formation and evolution of the solar system support the water formation on the Red Planet. A recent study on Mars crater chronology focuses on the Jezero crater’s dark terrain by using radioactivity measurements [2]. Jezero is the landing site of the Mars 2020 Perseverance rover. This updated model put forward that ancient water activities can be hundreds of millions of years older than previously thought.
A recent study by Galofre [3] emphasizes that valley networks are formed by glacial erosion under the surface of Mars. They used principal-component-based analysis with several erosion-based models. They analyzed that valley formation was formed by water melting not by free-owing rivers as previously thought. There is also evidence of methane leakage between rocks. Curiosity rover detected high methane concentrations during the northern spring [4]. This may be an indication of microbial life just like on Earth. Furthermore, the location of Mars smooths the way for long-term human spaceflight.
Mars is relatively close to Earth compared to other possible planets that may be explored such as Saturn and Jupiter. Venus is a closer candidate however it has very harsh atmospheric conditions. The high temperature, high density and corrosive nature of the environment make surface of the Venus challenging to survive. Detailed features of Mars as a potential candidate for two-way human spaceflight can be found in NASA’s Mars Exploration program [5].
Although Mars is considered the best candidate for human exploration, there are some challenges during a two-way mission. Mars’s atmosphere has a density of 0.014 kg/m3 and a pressure of 610 Pa at the surface level. Low atmospheric density indicates that if Mars have had liquid water on its surface, it would have been evaporated immediately. In other words, the atmospheric pressure of Mars should be increased in order to capture water molecules in the atmosphere (above the 6.25 kPa; The Armstrong Limit). The Armstrong Limit is a crucial factor for the human body.
At 6.25 kPa, water boils at human body temperature. Breathable oxygen cannot be delivered to the body for more than a few minutes. Body fluids such as saliva, urine, tear, and alveoli in the lungs would boil away without a special pressurized body suit [6]. According to NASA [7], increasing the atmospheric pressure to 19 kPa, would allow humans to sustain themselves on the Martian surface without a pressurized suit. Astronauts would only need to wear an oxygen mask. The value of 19 kPa corresponds the 1/5th of the pressure on Earth at sea level.
Novel Propulsion System:
Human spaceflight to the Red Planet takes at least 18 months with at least six months to stay on the surface. Therefore, Martian air vehicles are needed both for surface operations and to return to the Earth. Mars has a hundred times thinner atmosphere compared to Earth. The low density and low Reynolds number of the atmosphere indicate that only air vehicles such as micro helicopters or gliders can operate in Mars’s atmosphere [8, 9]. However, these vehicles can only be used for observation purposes and are not feasible for the transportation of large payloads. An advanced propulsion system is needed to fulfil mission requirements for long-term two-way missions.
Current propulsion systems are quite expensive and technologically not feasible to fulfil two-way missions. In-situ Resources Utilization (ISRU) technologies are required for low-cost and practical propulsion systems. Both air-breathing and rocket engines can be used as an ISRU-based system. However, air-breathing engines need extremely large inlet areas due to the low atmospheric pressure of the Red Planet.
Moreover, the condensed phase combustion products make the turbojet engine impractical. All these circumstances make rocket propulsion systems more practical for Martian operations. And chemical rockets are more convenient for ISRU-based propulsion systems [10]. Chemical propulsion systems are classified into three groups due to propellant storage types; solid, liquid and hybrid propulsion [11, 12].
Hybrid propulsion offers a safe, reliable, non-hazardous and cost-effective system compared to both liquid and solid systems. Hybrids can also operate at really low temperatures that features makes hybrids quite practical for Martian operations. One of the groundwork studies related to hybrid rocket propulsion for Mars operations can be seen in Figure 1.
The conducted study from the PhD Thesis of Kara uses carbon dioxide as the oxidizer and Mg/Paraffin mixture as the fuel during the ignition. More than 300 experiments are performed to optimize the performance parameters.
Carbon dioxide has fire extinguisher features and cannot be burned in the gaseous phase. However, CO2 can only burn with metallic powders in liquid form. The high free energy level of metallic powders releases combustion with CO2. The main reason is metals have higher reactivity series compared to carbon; thus removing the C-O bonds.
Mars has 95% of CO2 in gaseous form. Gaseous form carbon dioxide can not be burned in an actual motor. Because the combustion can’t generate high chamber pressures for the launch. Thus, the system uses saturated liquid state carbon dioxide with up to 300 grams per second flow rate. There is a significant note at this point, 100% CO2 (although liquid phase) can’t be burned properly with metallic fuels. Thus, nitrous oxide (N2O) is mixed with CO2 to make the combustion more reliable. The maximum CO2 level (by weight) was tested as 80% in the oxidizer mixture. This study showed that high levels of CO2 are burned for the first time in the world in an actual rocket motor.
On the fuel side; Magnesium and aluminium powders are tested. provides easier combustion with CO2 compared to Al. Paraffin wax is also used as the binder in the fuel. Because you need to bind metallic powders to make a single solid fuel grain. Thus, 60% Mg by mass and 40% by mass paraffin Is the major fuel compound.
The reliability of the motor ignition shows that CO2 can be a prominent candidate as an In-Situ oxidizer. Paraffin/Mg/CO2/N2O propellant is the best candidate for low-cost and sustainable rocket operations. Small fractions of paraffin and nitrous oxide can be transferred from the Earth to Mars; a large fraction of the propellants can be used as in-situ resources from Mars.
The future of Mars exploration will rely on in-situ propellant manufacturing and launch vehicle systems. This study is one of the indicators that prove CO2 on Mars can burn with conventional fuels such as paraffin and metals for practical operations.
REFERENCES
- https://mars.nasa.gov/news/247/odyssey-finds-water-ice-in-abundance-under-mars-surface/
- https://arxiv.org/abs/2102.05625
- https://www.nature.com/articles/s41561-020-0618-x
- https://doi.org/10.1126/science.1261713
- https://mars.nasa.gov
- https://web.archive.org/web/20141014072430/http://imagine.gsfc.nasa.gov/docs/ask astro/answers/970603.html
- https://web.archive.org/web/20160325173807/http://www.nasa.gov/centers/dryden/research/AirSci/ER-2/pshis.html
- https://rotorcraft.arc.nasa.gov/Publications/files/Koning_Romander_Johnson_Low_Reynolds_Number_Airfoil_Evaluation_FINAL_ARC.pdf
- https://doi.org/10.13009/EUCASS2017-365
- https://doi.org/10.1016/j.actaastro.2020.05.060
- G. P. Sutton and O. Biblarz, Rocket Propulsion Elements, ser. 9th Edition. Wiley, Hoboken, NJ, 2016
- M. Chiaverini and K. Kuo, Fundamentals of Hybrid Rocket Combustion and Propulsion (Progress in Astronautics and Aeronautics), ser. 1st Edition. AIAA, March 15, 2007.
- https://www.intechopen.com/chapters/76789
INFO/NOTES OTHER:
Since the Sputnik satellite was sent to space by the Soviet Union on October 4, 1957, many spacecraft have been sent to our solar system. In 2013, NASA’s New Horizons spacecraft photographed Pluto that there are no planets and dwarf planets in the solar system that we did not discover. Therefore, we have a lot of information about the atmospheric structures and geological features of all the planets we can reach.
Based on the data from the orbital spacecraft rovers sent through deep space, Mars is known to have the most suitable geological features and atmospheric conditions for manned space flight. There are 8 rovers currently operating on the surface of Mars. In addition, it is planned to send three new rovers in 2020 by NASA and CNSA (Chinese National Space Administration). The subsurface analysis will be done by laser spectrometer used on China’s HX-1 rover. HX-1 will also examine biological activities with built-in methane sensors. In addition, the Rosalind Franklin rover will perform biological studies such as on fossils and mineral structures of potential organisms. NASA’s Mars 2020 rover will also analyze the chemical findings of organic molecules. Most importantly, Mars2020 will try to convert carbon dioxide in the atmosphere of Mars into oxygen by electrolysis.
A Mars Atlas was created from observations made with the Mars vehicles sent to date. As we can see from the Mars atlas, the northern hemisphere is flatter. Therefore, rovers were sent to these regions. According to the data obtained from spacecraft, Mars has the most active volcanic mountains of the planets in the solar system. Mars also has the largest impact craters. These impact craters hit Mars on 4 billion years ago, altering all terrestrial shapes, just like the ending dinosaurs on Earth. Methane leakages were detected among the rocks by measurements made by NASA’s Mars Express rover. Therefore, methane can be an indicator of microbial life on Mars. There is frozen carbon dioxide, which we call “dry ice”, especially in the north and south polar regions. In addition, investigations made rovers by using sensitive thermal sensors have seen frozen water channels 2.5 cm below the ground in the Arcadia Planitia region of Mars. Also, gamma-ray spectrometry and radar measurement instruments of Mars Odyssey also investigate frozen water areas.
Critical Factors of Mars Atmosphere:
The surface gravity on Mars is only about 38% of the surface gravity on Earth. The day length of Mars is 25 hours which is almost equal to the Earth. If we extract all the oceans, seas and water resources on the Earth’s surface, the area of the rest of the Earth is equal to the area of the surface of Mars. The atmosphere of Mars is composed of 96% of carbon dioxide. Although the carbon dioxide level is 96%, there is no atmospheric greenhouse effect on Earth. This is due to the low atmospheric density and the absence of water vapour in the Mars atmosphere. However, on Earth, water vapour in the atmosphere causes the greenhouse effect by holding carbon dioxide gases.
Unlike the Earth, there is no magnetic field surrounding Mars. Since there is no magnetic field protecting Mars from harmful solar rays, astronauts can be exposed to direct radiation which is a very critical issue. Of course, if we do not want to be mutated!
Another critical issue for Mars is a hundred times thinner atmospheric density. The atmospheric density on the surface of Mars is equal to the density at 35 km of the Earth’s atmosphere. Therefore, there is no dense atmosphere layer that can slow down vehicles entering Mars. In other words, during the atmospheric entry at 120 km before the surface, spacecraft have only 7 minutes to slow down from an average velocity of 21000 km/sec to 4 km/sec. This entry process has been defined as “7 minutes of terror” by NASA. It is the most dangerous moment for a whole Mars mission.
There are also two more significant effects of low atmospheric density. Due to the low atmospheric density, the sun’s rays cannot be held by the atmosphere and pass directly through the atmosphere and create thermal tides. Second, due to this thin and dry atmospheric layer, winds cannot remove dust from the surface of Mars and therefore dust particles accumulate on the surface.
