The launch of PLD Space's Miura 1: a resounding success

Portada PLD MIURA 1

The inaugural launch of Miura 1 took place on October 7 from the El Arenosillo space center in Huelva. PLD Space has barely had time to celebrate it, immersed as they are in the process of analyzing the flight. All this analysis has served to better address the Miura 5, its real objective.

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Emblem of the inaugural Miura 1 mission. Photo: AstroAventura

The wind a powerful enemy

The biggest question that all the media came with today was why the flight plan was changed at only 48 km altitude. The terse explanation was that it was for security reasons. However, today the day has given them the opportunity to delve deeper into the causes.

The main one was the wind, which played a major role in much of the conference. It was a very unpleasant guest during the flight but also beforehand. In the previous unsuccessful attempts, especially the first one where it was the cause of the abort, the gusts were on the edge or far in excess of what was tolerated by the rocket.

This point gave rise to one of the many curious details of an inaugural launch. Due to the strong crosswind blowing between kilometers 1 and 6, much more propellant was consumed from the reaction control system (RCS).. This system, a critical part of the rocket's guidance, navigation and control, still held up and performed as expected. 

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Diapositiva que muestra el área de recogida del cohete. Foto: AstroAventura

The most awaited explanation

As always, and to no one's surprise, there was a very important economic component in the decision to launch at 80 or 48 kilometers. But the problem lay in the stark reality of insurance, which also affects space launches.

In the case of the inaugural flight of Miura 1 PLD Space had contracted civil liability insurance. This insurance covered the damages that could be caused by the rocket out of control, but only and exclusively within the perimeter area. For the following explanation it is necessary to remember that fluid dynamics is one of the branches of physics over which there is the least control.. Its best known example is weather forecasting being governed by the Navier-Stokes equations, which have no solution.

This problem is one of the reasons why aerospace engineering is so complicated. In this case, PLD Space's problem is that despite having a well-characterized weather profile around its flight zone, it violated the perimeter. Their in-flight rocket destruction models had a very wide 40% margin of error. This caused that in many cases the rocket debris fell outside its assigned area protected by air and sea exclusion zones.

Por tanto y como afirmó Raúl Torres, “aunque solo un tornillo se salga de la trayectoria y hay un barco o una persona  podríamos tener un problema muy serio”.

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Slide showing above the acceleration at each moment of the flight and below the velocity. It was explained to this media that the sharp discontinuity in acceleration around second 60 was due to shock waves from the transonic regime that altered the measurements. Photo: AstroAventura

Is the Miura 1 of any use?

Esta es una pregunta “que nos han hecho muchas veces y sigue sin quedar claro” dijo expresamente Raúl Torres.

EL Miura 5After these first analyses of the Miura 1, they have already incorporated more than a thousand improvement actions. But more than improvement actions that can be for example to know which structures have withstood worse the flight to reinforce them in the next rocket, they have validated models.

What does it mean to validate the models? Well, when a rocket is designed and built it is done almost entirely through computer simulations. These allow you to create a theoretical model of how things as complicated as the flow of comburent through the engine will behave. Or how the fuel burns inside the combustion chamber. In discussing this with the PLD team, they mentioned being at a 95% burning efficiency of 95%. However, they will need at least a 97 or 98% for the Miura 5's Teprel C's. Although the inclusion of the turbopumps will probably make that engineering work almost free. It should be noted that a 2% on a space rocket is hours of work at the highest level and generally thousands or tens of thousands of euros invested in the problem.. It is not advisable to be complacent, but in view of their regrets at having barely been able to celebrate the launch, it is not likely that they will now fall into complacency.

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The last available render of the Miura 5 was shown for the first time to those attending a press conference in Madrid. Photo: AstroAventura

The failed recovery

Another part of the conference dealt with how the rocket was lost in the recovery. Although the conclusions expressed, very consistent with the facts presented are very encouraging.

First things first, the overall performance of the rocket during reentry was excellent, even better than expected. The subsonic parachute deployed as planned and the rocket braked accordingly. It is known that the rocket reached the ocean because the telemetry shows it did, and it arrived in one piece at that point. However, when the recovery teams were sent out, the rocket did not show up. But there were no rocket fragments either, which would have explained that the rocket had been destroyed at sea.

This led the team to the conclusion that it had sunk in one piece. But how? As they explained, due to the surface wind it is likely that the rocket did not enter the sea vertically as intended.

This would have caused not the rocket, but one of the fuel tanks to rupture and allow water to enter. As it flooded, the weight of the water dragged it into the depths.

It is also explained by the fact that no rocket is designed for stresses, or to put it another way, shocks, that are not completely vertical. Even so, it is commendable that the only thing that broke was an internal part and it speaks very well of the structural engineering used.

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Image of a previous test of the Miura 1 parachute. Photo: AstroAventura

This morning there was an exciting press conference where we have seen PLD Space's senior staff explain the flight of the Miura 1. They have narrated how they have faced mother nature, especially wind and gravity. They overcame both to send a technological demonstrator further than a Spanish liquid-fueled aircraft had ever gone before. 

It remains to be seen whether the second unit of the Miura 1 will try to reach space by exceeding 100 kilometers in altitude. Something that the company has confirmed it can do.

Martin Morala Andres