Rockets need space, not only for flying but also for landing. For small rockets this is not a big problem as a common field is sufficient to accommodate an area large enough. However, for launching a rocket at the scale of Stratos II finding a field big enough becomes a big deal. El Arenosilio provides a predefined airspace closed off for all flights, but how do you ensure to stay in this area and where will the rocket land? The answer to these complex questions is easy; simulations. This blog post will concentrate on the efforts taken to ensure a safe flight.

The simulation tool chain used has been in-house developed by the Advanced Control Team of DARE and features full 6 degrees of freedom, staging, parachutes, accurate wind models, capability to generate monte carlo plots and more. To ensure the correctness of the output of the simulation, the programme has been validated using commercially available programmes used by space agencies to simulate the launch of rockets into an orbit and by comparing the results to real flight profiles.

Now, the actual impact zone is defined by using the extreme flight cases (extreme for wind speeds and misalignments of the rocket) of the simulation. This zone has the form of a circular section and is defined by the trajectories of the highest acceptable thrust and fin misalignment as well as the furthest ballistic flight. With the first ones defining the angles and the latter the radius of the zone. This safety zone is important as it will define the area in which no ship is allowed to enter and where the rocket needs to be picked up by a ship operated by INTA.

For recovery purposes a Monte Carlo analysis for nominal launch conditions, including fin and thrust misalignments as well as gusts, have been performed. The results of this analysis are then used to define a smaller area, the recovery area in which the rocket will most probably land. As this area is heavily dependent on wind, another set of simulations will be run on the launch day itself. This time, however, with the actual wind conditions measured by a weather balloon that is launched prior the launch. The information from the weather balloon will help to greatly narrow down the possible landing site, aiding in a fast and safe recovery of the rocket.

Estimating trajectories and defining a safety zone is another good example for the tremendous challenges that are inherently connected to launching a big rocket and can be solved by the clever application of analysis tools. For more information of analysis tools used within the Stratos II project, also read our blog posts.