Previously on “What Challenges Humans Have To Face From Earth To Mars: PART 1 and Part 2“, we saw that Biswal and Annavarapu in their recent paper, discussed about the challenges, we have to face from Earth to Mars Exploration. They divided overall challenges into few categories like terrestrial and earthbound challenges which we have to face on the earth, interplanetary Challenges which we have to face on interplanetary space, Mars-bound and planetary surface challenges which we will have to face when we will gonna reach to Mars and during Mars exploration. I already discussed terrestrial and earthbound challenges and interplanetary challenges in the last part of this episodic series post. If you haven’t read those articles yet, kindly go through them first. In this article, we are going to discuss challenges associated with mars.. Biswal and Annavarapu divided it in two categories: Mars bound challenges and planetary surface challenges. They further elaborated these two challenges in sub-categories which I will gonna discuss below. So, let’s continue and start with.
III. Mars-Bound Challenges
A. Hazards of Exposure to Cosmic Radiation
Consequent to successful Mars Orbital Insertion, the Mars-bound challenges commence, as the crewed space vehicle need to strand in Mars orbit until further instructions from the ground for mission inception. Because the spaceship undergoes preliminary checks and validation of its components and communication relay system. So, during their stay in Mars orbit, the astronauts along with their spacecraft are exposed to high dosage of harmful galactic and extragalactic cosmic radiation as compared to low earth orbit. This radiation levels range from a minimum of 1.07 millisieverts per day to a maximum of 1.4 millisieverts per day (measured by MARIE experiment aboard 2001 Mars Odyssey) ultimately increasing the possibility of prolonged cancer and related diseases. The challenges and the consequences of radiation exposure were explicitly elucidated in last parts of this episodic posts and additional complication was explained in Hellweg’s paper. Hence, astronaut being sheltered under the Martian environment (on the surface of Mars) seems safer than stranding in low Mars orbit (LMO). Furthermore, Biswal and Annavarapu have graphically presented the comparison of radiation levels at both Earth and Mars orbit in Fig 17 and the amount of radiation assimilated by the astronauts depending on the duration of stay in LMO in Fig 18.
B. Hazards of Asteroid Impact
Astronauts aboard space vehicle in orbit or spacecraft orbiting the red planet have vulnerable to the hazard of an asteroid impact and damaging of spacecraft components. The asteroids sizes vary from micro to macro asteroids. These asteroids are ejected from the main asteroid belt due to the probabilistic collisional events occurring at a distance ranging from 2.4 to 3.4 AU from the Sun with a relative velocity of 5.4 to 8.0 km/sec. Larger asteroids can be mitigated or destroyed by directing into the Mars atmosphere, but the problem is with micrometeoroid or microasteroid that are travelling at a relative velocity of >10km/sec can cause severe damage to the spacecraft component: it includes rupture of spacecraft fuel tank through impact and penetration, affecting the spacesuit of an astronaut during extravehicular activity, and depleting the solar arrays and affecting the power production. However, this challenges cannot be completely eradicated, but proper attention required while fabricating the sensitive component of space vehicles (i.e., fuel tank, hardness of solar array, and glasses of life-support systems). Before initiating the interplanetary exploration missions sufficient thickness of walls of the fuel tank is considered during fabrication and before stepping out for extra-vehicular activity. The challenge of asteroid impact will continue to exist for future interplanetary missions beyond Mars as the main asteroid belt lies between Mars and Jupiter and spread up to hundreds of kilometers (approximately 150 million kilometers) in interplanetary space with asteroid size ranges from 50 to 150 km in diameter.
C. Communication and Solar Power Production
Communication: I have already discussed the challenges of the interplanetary communication system in last part of this episodic post. However, human exploration missions predominantly require advanced communication systems to guide and land the spacecraft modules safely on Mars. Because a small misstep during EDL phases my cost mission tragedy as two-way communication interlinks span about 20 to 45 minutes and unreachable throughout solar conjunctions. Hence enhanced and advanced communication system (i.e., laser-guided communication system that has been successfully demonstrated by NASA) either via Mars Telecommunication Orbiter (MTO) or real-time decisiveness is ideally recommended for crewed missions.
Solar Power: Power production at Mars appears to be the most strenuous task for Martian satellites since the intensity of solar irradiance evanesces from Earth to Mars shown in the Fig above. Hence for a crewed missions thousands of watts are essentially required. So larger solar arrays capable of outstretching their solar cells are preferred to meet the energy requirements to power the space vehicle and estimated power production rate is 100 watts per square meter (at a solar intensity of 588 W/m²). Further, this power option is limited during the Mars solar conjunctions when Earth and Mars are far from each other having Sun at the median point for a period of 10-15 days. Therefore, we can alternatively exploit radioisotope thermoelectric generators (RTG) to afford the basic power necessities thereby mounting the RTG at a safe distance from the crewed module with proper shielding (to avoid the effects of nuclear radiation). Data transfer rate and mean power generation capacity of some Mars spacecrafts are shown in table 4 by Biswal and Annavarapu.
D. Planetary Clearance and Mars Atmospheric Entry
Mars Entry, Descent, and Landing is the sturdy assignment for both crewed and planetary landers due to the limitation of uncertainty in predicting the natural hindrance (prevalence of the variable environmental condition and dust storms) and EDL technology. Despite this challenge, Mars entry may disrupt the communication system and can cause damage to the landing module. Therefore, this obstacle can be eluded by reporting the crews in advance (grasped in Mars orbit) about the environmental condition forecasted by Mars relay orbiters. It ensures crew about the planetary clearance and their next move. Usually, this allows the crewed landers to perform orbital entry instead of direct entry which is considered as the safest approach and recommended for crewed landing. The path for both direct and orbital entry is shown in Fig 19. Because it reduces the entry velocity for increased ballistic coefficient and faster aerocapture, the risk of crash landing due to limited EDL period, and design flexibility. Further, it enables the crews and their landing modules for an effective preparation to plunge into the Mars atmosphere.
In addition to this, the factors such as the geometry of aeroshell, diameter of parachute, entry velocity and ballistic coefficient pose a design and technical challenge for Mars landers. From the first landing attempt to the current state of technology, the geometry and mass factor of landers is limited to the diameter of the aeroshell (4.5m) and gross landing mass up to 0.9-ton. So we need to expand the diameter of aeroshell as well as parachute. Nevertheless, larger aeroshell requires larger payload fairing that seems to be more expensive than conventional launch vehicles. Alternatively, the aeroshell diameter can be enhanced with the use of hypersonic inflatable aerodynamic decelerator (HIAD) to cut down the terminal velocity and ballistic coefficient thereby increasing the drag force that will drastically reduce the terminal velocity for dynamic landing.
IV. Planetary Surface Challenges
A. Scientific Landing Site / Exploration Zone
Exploration zone with good scientific interest and resource determines the success and sustainability of the crewed mission on Mars. The scientific site should meet all necessities for the crews and should have affordable native resources for exploitation to keep alive the crew during extended surface stay mission. NASA has identified fortyseven candidate landing site for robotic and manned exploration. Of these Meridiani Planum seems to be the best site for first Crewed Mars landing and Base establishment. Because, it holds an ideal site for promising resources which includes the potential for water extraction, raw materials for infrastructure purposes, and minerals. Meridiani Planum is located at 50°N and 50°S with an elevation of below +2 km (MOLA). Additionally, it enables crews for practicing planetary cropping and plantation, food production with efficient solar power production as it lies near-equatorial latitude, and facilitates for accomplishing multidisciplinary scientific goals in terms of atmosphere, astrobiology and geosciences. Features and scientific interest of candidate landing site (Meridiani Planum) were completely reviewed by Clarke et al. in their paper.
B. Planetary Environment
Density of Mars Atmosphere: Due to the thin atmosphere of Mars, the planet is incapable of shielding its surface from being exposed to harmful cosmic radiation and pose a threat to the living astronaut on the surface. Similarly, its lean atmosphere with lower density forbids lander modules from faster aerocapture thereby limiting the EDL period. In addition to this, the composition of Mars atmosphere CO2 (95%) and O2 (0.17%) stands a challenge for the astronaut to breathe outside their spacesuit.
Low-Gravity Environment: Astronauts on Mars gets exposed to the low gravity environment affecting the periodic pattern of heartbeat, rate of blood flow, weakening the muscle and bone density, and physical movements. The human body takes time to adapt their internal organs to sustain their presence under low gravity environment. Hence, these issues can be managed by frequent practicing of physiotherapy and physical exercises or simulating artificial gravity on Mars.
Solar Irradiance and Power: The challenges of solar power do exist at every extremity beyond LEO. For a manned mission, this complication comes during the interplanetary voyage, stranded in Mars orbit, and on Mars surface. However, the intensity of solar irradiance weakens from orbit to the surface and the mean power production rate is about 20 watts per square meter (Source: InSight Mars Lander). Hence, the structure of extendable solar arrays can be employed for mass electricity production but instead, the nuclear thermoelectric generators (NTG) will be the ideal choice for power source on the surface (during the day and night). Furthermore, the intensity of solar irradiance influences the environmental temperature that poses a challenge against manned Mars exploration to stabilize the thermal stability and this challenge can be addressed with the application of Mars sub-surface habitats.
Temperature and Pressure: The frequency of temperature on Mars varies for every Martian year. Findings and observations from diverse spacecraft have shown that the temperature variance ranges from the lowest 120K near poles to the highest of 293K at the equator with an average of -210K. Hence at this range of temperature, the crew may experience complication in maintaining the thermal stability of both habitats and their body’s internal temperature to keep them warm against hypothermia. Contradictory to temperature the pressure varies from 400 Pa to 870 Pa according to the seasonal pattern. So, this challenge can be addressed by deploying Mars sub-surface habitat to balance the thermal stability during the day and night. Simulated graph of air density, solar flux, temperature, and pressure distribution on Mars shown in Fig 20.
C. Exploitation of Resources
The challenge associated with the exploitation of resources is locating a robust site for exploration as well as extraction. Because the distinct site is associated with divergent distribution and concentration of resources, the form at which they exist, and the quantity of contaminants from the aspect of planetary protection. Since transportation of resources from different sites to the base is limited due to the constraints in surface mobility and lack of long-range rovers. Further, the unavailability of the testbed to demonstrate and validate ISRU instruments under a critical and low gravity environment poses a technical challenge on the surface. Furthermore, the uncertainty in system reliability and integration remains the greatest challenge at the very beginning of the Mars Base foundation.
D. Base Construction and Surface Mobilization
For a limited crew member at the initial stage of colonization, the habitats and the other modules can be exported from the Earth. But for a larger number of the population, a Mars Base is required and construction of this massive base using labour force is not obvious due to the vulnerability of Martian Environment and exhaustion of limited survival resources. Hence robotic based construction is beneficial from the perspective of crew health and also in retaining survival resources. Similarly, system reliability and its extended operation in a critical environment remain inconsistency due to technical challenges such as unproven technologies in the appropriate testbed and solar power deficiency. In addition to this, base construction is supported by load transportation systems from various resource mining sites. This mode of transportation may prompt the systematic servicing and repairing of vehicles. Artist concept of Mars Base is shown in Fig 21.
E. Communication Interlink from Earth
The communication challenge is discussed earlier by me in the last part of this episodic post. But it is significant for the crew on Mars to stay tethered and updated about the mission plans. The communication interlink is interrupted during the superior solar conjunction for every synodic period. Hence this challenge can be addressed either by parking communication relay satellites on high non-kaplerian orbit to stride uninterrupted communication or Mars Telecommunication Orbiters (MTO) into Mars orbit prior to the mission expedition.
F. Ethical Challenge and its Implications
Astronauts either during their interplanetary transit or extended period of mission may encounter the serious effect of ethical challenge. Despite NASA’s policy, crew members aboard spacecraft may likely to experience the risk of in-space pregnancy due to their mental and extreme stressful situation throughout the mission. Besides this ethical issue can put other crew members in risk due to additional requirement of survival resources, intensive care, and attention required for the new born astronaut and mother. The complexity of space environment and microgravity may cause serious health implications to mother and child and can lead to fatal state. It is still uncertain that how far this ethical challenge can be prohibited, but the prime cause for this challenge (i.e. mental stress and psychological health) can be improved to some extent with live interaction and conversation with either family members or publics on the Earth via interplanetary internet. Further, it is recommended to select the astronauts with multidisciplinary skilled and psychologically fit in terms of social abilities. And finally…
G. Space Policy and Human Civilization
Once the progression for human civilization commences, crews from various nations may encounter the political challenge concerning the conflict of interest between nations. Because human civilization nation’s appropriation of Martian land violates the space policy of 1967 “United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including Moon and other Celestial Bodies”. According to that treaty or policy, the space and the astronomical bodies over Solar system are free for research related activities to all nations without any differentiation or discrimination. But none of the astronomical body or planetary space cannot be expropriated by any nation. Therefore, Biswal and Annavarapu recommend that having a good mutual understanding and universal conflict of interest between countries will help make the civilization towards peaceful planetary exploration and permanent base establishment. Further, if we are planning for a return or round-tip, we may encounter the hazard of back contamination from the red planet as part of Planetary Protection Policy. And this challenge can be remitted with proper screening and medical checks aboard International Space Station before landing the crews on Earth.
Reference: Malaya Kumar Biswal M and Ramesh Naidu Annavarapu, “Human Mars Exploration and Expedition Challenges”, Aerospace Research Central, 2021. https://doi.org/10.2514/6.2021-0628 https://arc.aiaa.org/doi/abs/10.2514/6.2021-0628
Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us