SAFETY | Marsmission

MISSION SAFETY

LAUNCH

From lift-off to reaching a steady orbit, many challenges arise. The process can be divided into two main parts, the first part beginning with lift-off and ending with the anticipated loss of signal to the shuttle. At this point, the rockets are at maximum energy and pose a risk of malfunctioning. The flight is monitored and assessed from the ground, where if needed due to safety concerns, the flight can be terminated. The second part is the remaining journey, flights cannot be terminated from ground control at this point. An assessment of the rockets is undertaken to identify any faults occurring from the initial launch (Poussin et al., 2017).

The DESIGN segment proposes a liquid propellant for fuel coupled with a nuclear fission reactor to power the launch. During launch a high thrust must counteract the weight pulling down whilst reaching the velocity required to escape Earth’s gravitational pull. The thrust causes the rocket to rapidly accelerate. To avoid air resistance tearing the shuttle apart, thrust must be reduced, which in turn reduces the acceleration (ESA, 2020). Having a nuclear fission reactor to power the rockets does not generate many safety concerns. Uranium emits alpha particles which cannot penetrate through skin or paper. Relatively thin shielding can protect the crew from any radiation emitted from the reactor, however, experience with fission reactors as power sources for rockets is limited (Nguyen, 2020).

Thrust and acceleration stress can have negative effects on the crew. Although G tolerance is trainable to an extent, chest compressions, neurological, cardiovascular, vision, and musculoskeletal issues can affect the crew during launch. The safety of the crew must be carefully considered in the mission design of the rockets, specifically the level of acceleration stress the rocket is subject to during launch. The cabin must be designed in such a way that in the case of an emergency, important controls are easily accessible to the crew whilst they are heavily restricted during launch (Sgobba et al., 2017). Once the shuttle is in a steady orbit and all checks are complete, the crew will begin their six month long transit to the Red Planet.

TRANSIT

Transit

The International Space Station sits just above Earth’s atmosphere and geomagnetic field where radiation is 250 times larger than below, at the Earth’s surface. Fig.1 demonstrates that travelling to Mars in open space is equivalent to 700 times the radiation at Earth’s surface which is a direct result of not being protected by Earth’s atmosphere and magnetic fields (ESA, 2019). High radiation doses can cause acute radiation syndrome, cancer, and heart problems as well as behavioural problems (Mortazavi et al., 2020). The 3 main causes for the radiation outside Earth’s protective shield are galactic cosmic rays (GCR), solar particle events (SPE), and radiation that is trapped in magnetic fields around the Earth (Clement and Sasaki, 2013).

Fig 1: Comparison of radiation doses between Earth’s surface and various higher altitude points (ESA, 2019).

GCR varies over the Sun's 11-year cycle and includes highly energetic particles (HZE) such as protons and beta particles. These particles are immensely ionising and prove difficult to protect against, however, they can be controlled by shielding techniques. As GCR varies over a cycle, risk can be reduced through monitoring the highs and lows of the Sun’s cycle (Kamsali, et.al, 2019). SPE are the product of solar flares and coronal mass ejections. They are somewhat predictable, however, they can have onset times as little as a few minutes, making them almost impossible to predict (Hassler, 2014). GCR and SPE can interact with the Earth’s atmosphere producing secondary particles like energetic protons and neutrons, which can get trapped in the magnetic fields around the Earth (Clement and Sasaki, 2013).

To ensure the crew’s safety, countermeasures must be put in place to avoid long term radiation effects. Shielding can protect against GCR however, secondary particles can be produced inside the shuttles environment as the GCR interacts with the materials in the shield (Kamsali, et.al, 2019). The shielding must be thick enough to protect the crew, however, the effectiveness of the shield drops as thickness increases. Alongside this, the weight increases with thickness, including the cost of the mission (Durante, 2014). Read more about the projected cost of a Mars mission on the FINANCE page.

LANDING

As of 2020, there have been 6 NASA missions to Mars that have successfully landed using entry, descent, and landing systems (EDL) (Grecius and Dunbar, 2019). However, these missions were unmanned, meaning they did not carry substantial loads such as a life support system (LSS), which is further detailed in the Martian Surface segment. Previous missions relied on drag force to reduce speed when entering the Martian atmosphere, due to the weight of a manned mission, these techniques may no longer be a viable option (Braun and Manning, 2007).

SpaceX is currently considering supersonic retro propulsion (SRP) as a new form of EDL systems, they were first to successfully land a rocket using SRP in 2013 (Sforzo and Braun, 2017). Due to the lack of experience with this type of system, there are several uncertainties such as the vehicle configuration, unstable drag forces, heat resistance and high variations in pressure. Currently, the vehicle configuration is quite complex and needs to be simplified to increase safety which requires more time being spent on tests and evaluations. Modelling the drag force is difficult due to high thrust causing drastic changes in pressures which creates a risk of the shuttle losing stability and control in the atmosphere (Braun, Sforzo and Campbell, 2017). Included in the EDL system is the Thermal Protection System (TPS). Thermal energy is produced through the immense drag force and air resistance the spacecraft experiences upon entry into the atmosphere. As the manned Mars mission will see the heaviest payload yet, the velocity upon entry will be large making the complexity of the TPS a cause for concern (Wright et al., 2010).

In addition to unsteady drag forces and immense heat when entering the Martian atmosphere, the conditions of the atmosphere determine the performance of the EDL system. Observations of the atmosphere are limited which makes its behaviour difficult to predict. The main concern that must be well considered in the mission design is the flight path through the atmosphere as bulk atmospheric density varies significantly over time, accounting for the largest uncertainty in the entry process (Chen et al., 2010).

Once through the atmosphere, the shuttle must begin its descent to the surface of the Red Planet. As it approaches the surface the EDL system must scan and detect any possible surface hazards so that they can be avoided accordingly. This is due to the fact that the surface is unpredictable in terms of the crater placements and large martian rocks. This may prove difficult to locate enough ground clearance to safely land (Braun and Manning, 2007). Once the crew has safely landed, they face the challenge of microgravity and dealing with a harsh environment on the Martian Surface.

MICROGRAVITY

Microgravity

Once the crew have left Earth, the gravitational force that they experience changes drastically. After the launch, the shuttle is travelling through open space and will feel almost no gravity, during this time muscles and bones will lose protein and calcium if there are no countermeasures put in place (Stein, 2012). For long time periods without gravity, such as the humans on the ISS, an exercise routine is the best way to reduce muscle and bone loss. The video below demonstrates a routine on the ISS, which is personalised for each crew member. For a Mars mission, this routine would have to be altered to accommodate for additional risks such as oxidative capacity and fatigue due to the mission duration being longer than any previous missions (Trappe et al., 2009). Once the crew have completed their transit to Mars, they will experience approximately a third of the gravity felt on Earth (table 1).

MARTIAN SURFACE

Martian Surface

As mentioned previously in the transit section, GCR and SPE must be shielded against to prevent short and long term health issues. As seen in table 1, the atmospheric shielding is minimal, therefore, the ionising radiation is 100 times more powerful on the Martian surface compared to Earth. In addition to having a thin atmosphere, the magnetic field on Mars is almost nonexistent. Due to this combination, some SPE can have particles energetic enough to reach the surface of Mars (Hassler, 2014).

Running in Space- (NASA Johnson, 2013)

Table 1: Highlights many atmospheric and surface differences between Earth and Mars. (Horneck et al., 2003)

Manned missions use a Life Support System (LSS), to regulate the environment, atmosphere, and water inside the spacecraft. The LSS is vital to the survival of the crew and must have the ability to detect malfunctions, harmful gases, and leaks inside the spacecraft. Currently, the LSS operating inside the ISS recycles approximately 93% of human waste. Ideally, an LSS suitable for a manned mission to Mars would recycle 98% of human waste, however, development into LSS efficiency is needed to reach this goal (Bettiol et al., 2018). Heat and electricity can power the LSS using radioisotope heater units (RHU) and radioisotope thermoelectric generators (RTG). They each use Americium-241 as fuel which is hazardous if released into the LSS environment. Platinum-rhodium alloy and carbon-based shielding around the RHU can prevent hazardous radioactive material from escaping into the environment (Barco et al., 2019). Unlike the ISS, a mission to the Red Planet cannot resupply on its trip. Considering the length of the mission, this is not viable, therefore the crew must grow and harvest their own food (Kiang, 2017). This includes withdrawing resources such as oxygen, water, and energy from the Martian surface and atmosphere (Haslach, Jr, 1989).

SPACESUIT

Over many years and previous missions later, the spacesuit has developed exceptionally. They have three main uses; Intra-Vehicular Activities (IVA), and Extravehicular Activities (EVA) which includes both open space, and on the surface of the Moon. A new spacesuit would have to be developed that accommodates EVA on Mars that considers the conditions on the surface (Lousada et al., 2017). The main concerns for the spacesuit include overheating, LSS failures, communication issues, technology failures, and structural failures. Flexibility and comfort are also factors as they will impact the performance of the crew, and therefore, should be considered in the design (Bettiol et al., 2018). Decompression sickness occurs when a member of the crew moves from the high-pressure spacecraft into the low-pressure spacesuit. During this transfer, bubbles can form in the bloodstream which may cause severe damage to the brain, lungs, and joints. This risk can be minimised by closing the jump between the pressure in the spacecraft and the spacesuit, however, this may come at the cost of the flexibility of the suit if it is at a higher pressure (Katuntsev, 2010 and Bettiol et al., 2018).

PSYCHOLOGICAL EFFECTS

As discussed previously, the mission to Mars is unlike any other mission. The duration is much longer and the payload is immense compared to past missions. In earlier sections the risks associated with equipment and the impacts of microgravity have been discussed, in this section, the effects of isolation and confinement on the crew are outlined.

Table 2: Comparison of ISS missions, a predicted Mars mission, and a long stay in Antarctica. The Mars mission features several high stress factors such as in the event of an emergency there is no escape and the Earth is not visible during the later transit and stay on Mars (Manzey, 2004).

Table 2 illustrates the psychological differences between ISS missions, a future Mars mission, and a 10-12 month-long stay in Antarctica. Factors in table 2 such as communication and ground-based monitoring being very restricted in addition to not being able to evacuate in the event of a mission failure may cause severe stress to some crew members (Manzey, 2004). Time spent with family and friends on Earth is replaced with isolation as part of a small crew, confined to limited living quarters which will impact the mood of the crew. This includes feeling depressed, irritable, and tensions rising between each other. Humans on Earth can be trained to cope with isolation as well as being screened for any pre-existing psychological conditions, however, this method does not guarantee crewmembers not developing behavioural conditions along the journey, therefore, support must be provided during the trip (Palinkas, 2001).

Crew members may cope better if they integrate as much as their home life into their routines as they can, personalisation of their day to day activities reduces the unfamiliar feeling of living in the space shuttle. Connections with family and friends through emails and messages is an effective countermeasure to put in place to reduce isolation. The crew should also be provided with fun activities such as reading books, and media that they can listen to and watch alone, or with other crew members (Johnson, 2010).

The research provided here was completed by Emma Coady, for more information about her professional interests and project responsibilities check the WHO WE ARE page.

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