To go to space, we have the classical architectural design, which is the stage design in serial with stage one and stage two, and the great advantage is that stage one creates delta-v1 and stage two creates delta-v2 and we can add the two delta-v. But the big problem is that if we go on with this architecture, let's consider, for instance, zero stage, which is the initial one, it becomes huge. Monsterous because, in fact, it's exactly the equivalent of a human pyramid. With one people, two people, three people to carry the other ones, and this becomes somewhere an exponential phenomenon. You see, like this famous monument, the exponential shape. This is very difficult and we need to improve the initial boom. The initial boost of the launch vehicle. How could we do this by combining serial and parallel architecture? Well, in serial architecture, the total delta-v is simply the sum of the partial serial delta-v, and in parallel, it's the first, which is the sum of the first in parallel and this is the base of any serial-parallel launch vehicle. Let's consider, for instance, a two-stage central rocket. Then we add here, for stage 1, we add the lateral rocket boosters, 1b and the central, and then you have two. The great advantage is that in-flight, you can launch, you can remove the boosters in-flight like this, and save so much weight during the initial phase. That is the base of any serial-parallel architecture. But to have the most important benefit from this architecture, we need technological improvement. The first one is to improve the structural ratio. The structural ratio is given by the use of composite. That's the first improvement. This gives the improvement of the structural ratio of any stage. The second one is the cooling of fuel, which improves the density of the fuel and makes the volume of the tanks lower. The third one is the optimization of the trajectory and with three improvements, in fact, we have the three steps that has been followed by SpaceX with Falcon, from Falcon 0 to Falcon 9 and from Falcon 9 to Falcon Heavy. This has required new technologies from inverse spin-off. I have to explain what this means. All these technologies comes from aerospace, terrestrial, and public systems that has been used in space. This is, in fact, a traditional way. You know that at the beginning of aviation, the first aviation manufacturer made cars, trains, bicycles like the Wright Brothers and they used these public technologies to improve the aircraft, and on these three steps, it's exactly what was implemented on the Falcon launch vehicle in order to optimize the technologies on parallel and serial architecture.