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Estimation of Lunar Surface Shock Effects and Optimization of Damping Scenarios: A Case Study in Response to NASA's Request for Proposal

Abdi-Basid Ibrahim ADAN** Correspondance : abdi-basid@outlook.com

The aim of the present work is to respond to NASA's request for proposals on understanding and reducing the adverse effects of landing or take-off on the lunar surface. Two initiatives can be developed. The first is that of a natural satellite with no atmospheric layer, which suggests that any particle will fall at the same speed in the absence of any air friction effects. A rocket could land without any major impact.  The second is to take into account an atmosphere above the lunar surface. Terrestrial particles are likely to form and remain in suspension for some time. To remedy this situation, six scenarios were explored. Two alternatives have emerged from these investigations:

The first is the installation of a device (rocket accessories) to reduce the effects of the fuselage during ascent;

The second is the integration of new features into the rocket, such as vertical fuselages or a folding and unfolding locomotion slide to move the dust cloud away from the formation zone.

Keywords : NASA,Landing,Moon,Regolith,Lift-off,Artemis,StarshipVirginia,Hampton,Human Lander

1.      Introduction

In space, granular and rocky materials are subject to both gravitational and atmospheric circulation forces during a disturbance. The latter derives its ancestral force from temperature, i.e. solar radiation [1]. Without the existence of an atmospheric layer and the spherical shape, atmospheric circulation modelling would certainly have taken a wrong turn. On the lunar surface, the conditions of reasonable distance from the solar source (i.e. 150,000,000 km [2]) and sphericity can be an asset for comparison with the Earth. In the absence of a layer of air enveloping its surface, the equilibrium of a homogeneous spatial temperature distribution around a mean value cannot be justified on the lunar surface (unlike Saturn's moon Titan). For this reason, winds would not exist on the moon, nor would a sandstorm or cyclonic season. In this case, the moon's sphericity would only be useful in the vertical meridian zone, to facilitate a short-distance landing, unlike at the north and south poles.

The aim of this first work is to contribute to a philosophical understanding of how granular and rocky materials of all sizes can behave on the lunar surface after being exposed to the landing or take-off force of a rocket weighing several thousand tonnes.

Until now, rocket take-off and landing missions have been carried out in vertical motion and are assumed to have the same impact effect on surfaces, even if the weight of the re-launch is slightly different from that of the ascent, due to the variation in the weight of the on-board fuel.

The gravity field on the lunar surface is calculated at 1.62 m/s2 [3], i.e. a gravitational acceleration some six times lower than on the Earth's surface (9.81 m/s2 [4]). An Artemis rocket with crew and cargo can weigh at least 2,000 tonnes [5]. The amount of fuel and its weight are astronomically proportional to the mission's round-trip distance, engine efficiency and on-board engine technology.

For a landing mission, there is a threshold altitude at which a surface covered in dust and rock is touched by the propulsion force (e.g. 39,144 kN [5]), which keeps the weight of the craft suspended in the void and slows down gravitational attraction. In principle, the slower the ascent, the greater the impact on the surface. Contrary to what happens on Earth, the return to normal after an ascent impact on the lunar surface for a landing mission would be faster with the same time interval, whatever the characteristics of the seed and rock lifted. For rocks thrown up with kinetic force, the impact does not seem to affect the craft directly or indirectly. On the other hand, the stronger the gravitational field, the faster the rocket's ascent is expected to be, so as not to over-consume on-board fuel, while avoiding a hard landing that would disable many of the craft's functions and features. Given the Earth's gravity field, a lunar landing mission would be around six times slower and six times more fuel-efficient.

In addition, thanks to the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, recent studies [6,7] have changed our perception of the Moon, confirming the presence of a lunar atmosphere, albeit almost negligible compared with that of the Earth. The sources of this atmosphere can be multiple: meteorite bombardment, rock decomposition, solar eruptions, etc.

When examining the lunar atmospheric layer, it will be vitally important to understand the atmospheric pressure with the elements that make up the lunar atmosphere, mainly argon, helium, sodium and hydrogen. The shock effect on the lunar surface would be based essentially on the interaction potentials of these latter chemical elements.

With a view to providing some answers to NASA's project, the remainder of this article is organized as follows:

- First, we analyze an approach in which atmospheric cover is neglected.

- Secondly, we counter this approach by proposing scenarios and draft solutions.

2.      Analysis of the Artemis landing mission: case without lunar atmosphere

The riskiest incident on a lunar mission would not be the suspension of rocks and other particles in lunar space, since all rocks, whatever their size, would fall at the same speed. In addition, the spiral effect observed in the drag of turbojet aircraft would not exist on the Moon, due to the absence of air particles. What's more, the projections caused by the blast effect on landing will be projected in all directions, from the source of the ascent to extremities whose distance is proportional to the force. In this context, the risks of a mission to the Moon are much lower than on Earth. Impact with the surface does not directly or indirectly endanger the spacecraft, except in the case of nearby installations.

Prospecting the lunar surface and its stiffness composition would appear to be an indispensable asset in the study of an initial landing strip. Meteorite impact zones can represent a major hazard for rocket landings and take-offs. Projections of elements from the lunar surface can cause fallout on the rocket, due to its specific funnel shape at the point of impact with the lunar surface. The geological characteristics of the more rigid zones should be compared between the Moon's surface and that of the Earth, in order to identify an optimum zone for reducing the impact of rocket engine propulsion.

 3.      Analysis of the Artemis landing mission: case with lunar atmosphere

In this section, we analyze five scenarios whose feasibility seems to be approaching with the maturity of current technologies. This section takes into account the importance of the lunar atmosphere and proposes solutions to avoid complications with the dust cloud during ascent.

 3.1.           Scenario 1 : absorption

In the scenario shown in figure 1, at a precise and optimal altitude during ascent, the rocket detaches a circular capsule (which can be unfolded and folded), absorbing the propelled granular and rocky materials and releasing the absorbed air by filtering. This device is designed to withstand the extreme temperature of the fuselage, and to incorporate artificial intelligence to identify rocks according to their respective risks. The prototype shown in figure 1 is essentially based on the capacity and performance of rock and dust aspirators, which will be released at a given altitude before landing. The parameters of these aspirators will be designed to ensure a safe landing of Artemis on the lunar surface.

                                                                                                                                                                                                                                                                                                                                                                                                                     Figure 1. Circular vacuum cleaner for dust and granules.

 3.2.           Scenario 2 : parachuting

The scenario described in figure 2 involves parachutes being released to trap granular and rocky material rising towards the summit during ascent.  The number of parachutes used may vary to optimize landing safety. The characteristics of these parachutes must correspond to the results expected for the safety mission. In addition, each parachute must be equipped with a device that detects and predicts the area most affected by the fuselage explosion, in order to optimize deployment on the priority area. This requires the use of artificial intelligence. The feasibility of such a device seems certain to reduce rock and granule heave, as well as the formation of dust clouds.

                                                                                                                                                                                                                                                                            ��                                                                                                                                                                                                                                                                                                                                                  Figure 2. Case of a parachute trapping the effects of shock.

                                                                             3.3.           Scenario 3 : artificial vat

The scenario in figure 3 describes a prototype that deploys a device capable of sinking into the lunar soil (like a tomahawk missile) and deploying a kind of metal tank inside the soil. The latter is adapted to the overheated condition and will contain the blast, while sparing the lunar soil from being impacted by the blast.

This will prevent the formation of dust clouds and reduce the risk of dust impacting the rocket engine during landing [8].

                                                                                                                                                                                                                                                                                                                                                                             Figure 3. Case of a tank sinking to the surface of the moon.

 3.4.           Scenario 4 : surface copper

In the scenario below (figure 4), as the rocket ascends, at a precise and ideal altitude, a slide ejects from the rocket and deploys over a wide lunar surface to serve as a landing point and avoid the lifting of granules and other rocky material. Unlike the previous scenario, this is a surface deployment with automatic ground engagement. This shows just how important automatic devices and artificial intelligence are for this mission.

                                                                                                                                                                                                                                                                                                                                                                       Figure 4. Fold-out copper case as landing point.

 3.5.           Scenario 5 : fuselage horizontal

In the scenario shown in Figure 5, the rocket fuselage would have to be redesigned to incorporate a new vertical fuselage system capable of slowing down gravity. Self-deploying vertical fuselages are intended to compensate for the traditional fuselage. This approach will minimize the blast effect of the fuselage on the lunar surface.

Other modifications can also be made, including the integration of a wheel to help the rocket move away from the dust closud formation zone after landing.

                                                                                                                                                                                                                                                                                                                                                                                                                   Figure 5. Feasibility scenario of additional fuselage rotation during Artemis landing.

 3.6.           Scenario 6 : dust cover

In the final scenario of the Artemis mission back to the moon, the ship's skin should have physico-chemical properties that prevent dust from clinging to the ship. This proposal, presented in figure 6, can be based on the secret of dust adhering to materials, allowing the rocket to remain free of dust and rocks, while landing safely. In addition, it is possible to develop a device that propels small quantities of water to wet the dust and limit its effects.

                                                                                                                                                                     Figure 6. Feasibility case for a dust cover on the Artemis surface.

 4.      Relationship between distance, weight, projection effects and landing time

In this subsection, we set up an empirical program to model the impact phenomenon on a surface covered with dust and rock :

We consider the variables :

Ø  T, existence of atmospheric circulation

Ø  U, the surface area of the impact zone

Ø  V, rocket landing time.

Ø  W, shock absorption time.

Ø  X, rocket weight;

Ø  Y, local gravity field;

Ø  Z, kinetic force of the projected lunar rock fragment.

Based on this program, the following hypotheses can be formulated:

1.      The surface area of the impact zone increases with the weight of the rocket.

2.      The existence of atmospheric circulation contributes to a major risk during ascent.

3.       Landing time contributes to rocket blast impact area.

4.      Time to return to normal after landing depends on gravity and the existence of an atmosphere.

5.      The weight of the rocket is positively correlated with the level of risk of danger from surface impact effects.

To minimize the risk of clouds of dust and rocky material forming during the ascent of Artemis, this would require simulations based on mathematical formulations that describe the relationships between the variables defined above. In addition, observations of each of these variables can be used to develop a simpler model with a study of multidimensional variation.

 Conclusion

On the lunar surface, a rocket will weigh 6 times less than on Earth. Rock fragments and the formation of lunar dust clouds can be mitigated by studying the physical properties of the chemical particles that make up the lunar atmosphere. The disturbance of lunar surface materials during rocket ascent is due not only to the gravity field, but also to the atmosphere, whose density is almost negligible for the moon.

Landing with the least possible effect will require the invention of new prototypes incorporating artificial intelligence to maximize decision-making in the shortest possible time. Fuselage modifications and the integration of new rocket functionalities will also be required.

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