Madrid in November
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Madrid in November

Text and photos by Erik Sturkell

One week in November was spent working with my impact colleague Jens Ormö in Madrid, Spain. I arrived on the evening of November 19 and took a taxi to the hotel. The hotel was conveniently located near the airport and ‘en route’ for Jens to work. It was a nice place, but the surroundings were quite boring as it’s located next to the highway (Fig. 1). This is like what you frequently see in the US with hotels, bars, and restaurants along the road and nothing else (in this case an industrial area). Nevertheless, it was convenient for us as Jens without any major detour could pick me up.

During the visit we planned how to continue the work on impact experiments using rubble pile-like projectiles (Fig. 2). To make the projectiles are a bit challenging. The projectile should be constructed in such a way that fragments stick together for as long as possible before it separates into a cluster of fragments. In the laboratory simulations, Jens uses spheroids made of polyoxymethylene of the brand ‘Delrin’. They are hard and makes fantastic projectiles. In our impact experiments, we need to construct a projectile consisting of many fragments. Instead of the 20 mm (diameter) solid spheroid, we use 300–350 one mm spheroids to get the same mass (5.5 g). The 300–350 spheroids need to be glued together, but not too solid as it must split up. Nor should it be too weak, so it falls apart too easily. A former research engineer, working for Jens, found the correct mixture of super glue and acetone (for dilution) to make the projectiles (Fig. 3). Sadly, he passed away in cancer. During this visit Jens and I had to figure out the correct mixture which spears to be about 5:1 to 10:1. We managed to do three experiments with the cluster projectile (Fig. 4). Next time we will try to make a water target. 

It’s always great to visit Jens in Spain, both from a social and professional perspective. We have several joint projects that need attention, and it’s fantastic to make impact experiments in Jens’ laboratory. We worked on projects in different stages including resurrection of certain projects. In addition, we needed to make plans for an upcoming application. The most fun part is to shoot the canon in Jens’ laboratory and figuring out how to make the projectiles (Fig. 5).

There was also time for social and cultural activities. Saturday, Jens who took me to the Christmas market at his children’s school. Maria and Jens’ daughter Anna was the Queen of Light (Lucia) and did a fantastic show (Fig. 6). Afterwards, Jens and I went downtown and visited the Spanish National Archaeological Museum. From there, we continued to Plaza de Sol, which was completely crowded with people – Christmas season has started (Puerta del Sol). We went to a bar and later a restaurant with classical Spanish food: a lot of meat. 

On Sunday we traveled one hour north in the direction of Burgos and stopped at the walled town Buitrago del Lozoya (Fig. 7). A town situated at a bend of the river Lozoya with a well-preserved town wall (Fig. 8). The site has a history that dates to pre-Roman time.

Fig. 1. The hotel at the highway.
Fig. 2. The cluster projectile in the canon.
Fig. 3. Jens mixing the glue to make the cluster projectile.
Fig. 4. Crater created by a vertical shot cluster projectile.
Fig. 5. Jens making the final adjustments before the shot in the lab.
Fig. 6. Santa Lucia.
Fig. 7. The old town of Buitrago, where the oldest parts are pre-Roman.
Fig. 8. The city wall around Buitrago.
Fig. 9. A visit to the Archeological Museum in Madrid – to be used for illustration for a Christmas calendar by ‘Geologins dag’ in Sweden.