“There are many things that can go wrong,” Elon Musk warned hours before the first flight test of Starship, the largest and most powerful rocket ever created. That first attempt went to waste when there were only forty seconds left until the countdown ended. The cause, a pressurization valve that had frozen. Three days later, the gigantic rocket did manage to rise, but it exploded after four minutes. An error when the two parts that make it up had to be uncoupled caused it to deviate and activate a self-destruct system to prevent it from falling into populated areas. In fact, the Starship – the ship itself, where the crew and cargo go – exploded on nine occasions; by extension it gives its name to the entire rocket – until it was successfully landed. This, landing, is one of the most critical moments of space travel. Among many other problems, when a spacecraft descends on Mars or the Moon, the jet of the propellants causes a large amount of regolith – fragments of rock, minerals and other materials from the surface – to jump, which can create a dangerous ‘blackout effect’. ‘ limiting visibility and even causing damage to the spacecraft itself. To reduce these risks, an international team of researchers from Chungnam National University (South Korea), the University of Edinburgh and the Korea Institute of Information Science and Technology have developed a model that reproduces the moment when the ship approaches the surface. “Understanding the interaction between the thruster jet and the surface is important for the success of space missions in terms of contamination and erosion, landing precision and engineering design,” explains one of the authors of the study, which has been published in the journal Physics of Fluids. To do this, they have collected data on the propellants, the composition and topography of the place where they are going to land, as well as their atmospheric and gravitational conditions. Considering the interaction of the gas with the regolith as a system of equations, the simulation makes an estimate of the shape and size of the jet from the engines, the temperature and pressure of it and the surface, and the amount of material released or displaced. . “Our tool predicts the trajectory of the particles to avoid damage to the ship and also analyzes what the landing may be like in previously designated places,” they explain. The highlight of the data obtained is that the small regoliths reached a notable height and caused a ‘blackout effect’ during both ascent and descent, greatly reducing visibility. The complexity of a space landing The landing is a highly complex operation. Before the aforementioned regolith cloud, many other problems must be faced. In the case of a landing, for example, the first would be the approach window, that is, the moment when Earth and Mars are closest. This occurs every 26 months. Under these conditions, the trip takes approximately half a year. Entry into the planet is usually done at high speed – more than 20,000 kilometers per hour – so the angle of entry has to be calculated with millimeter precision. If the inclination is excessive, the ship could overheat and disintegrate; If it is insufficient, “it could ‘bounce’ in the atmosphere and be lost in space,” as described in an article on the matter by the European Space Agency. During the six or seven minutes that the maneuver lasts, which can be modified by atmospheric density, turbulence and wind speed, the ship has to endure extreme temperatures of up to 3,000 degrees due to friction with the Martian atmosphere. The role here of the thermal shields that cover them is essential to resist these conditions. When it is approximately ten kilometers from the surface, the device brakes suddenly up to about 1,700 km/h and deploys its supersonic parachute. The attitude measuring devices will indicate the moment at which the thrusters have to reduce speed to a minimum. Depending on the landing module you have, the retrorockets can be on until landing, turn off shortly before for a short free fall, or even incorporate air bags that inflate to protect the ship at the moment of impact. “The results obtained can be used to develop more effective and efficient landing technologies,” conclude the authors of the research. The next step will be to include more data such as chemical reactions and the collision between solid particles in the tool. All with the aim of making spacecraft landings safer.
