Experiment Description

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So what is the SCRAP Experiment really about? Well, let us try to do a reasonable summary of the experiment and the REXUS/BEXUS programme.

The title SCRAP stands for “Scattering of Radar waves on Aerosols in Plasmas”. The short description is:

“SCRAP is a student experiment, part of the REXUS programme under DLR and SNSB, and studies electron density fluctuations in dusty mesospheric plasmas.”

…but maybe that doesn’t really give you that much information.

Let’s give a longer description as well (That can also be found on our Facebook page http://www.facebook.com/SCRAPexperiment).

“The scientific objective of SCRAP is the validation of the theories on electron density fluctuations in dusty plasmas by measuring the scattering of ultra-high frequency radio waves on a cloud of metallic microparticles spread in the mesospheric plasma. These theories are often used as a basis to reconstruct the characteristics of mesospheric aerosols (mainly particle size, charge and number density) from indirect measurements, such as electron and ion density fluctuations obtained from radar and optical observations, or mass spectrometry.

These indirect methods are unavoidable, since the actual collection and preservation of mesospheric particles is subject to the technical difficulty to perform experiments in the mesosphere and a high risk of contamination. By using the ground-based incoherent scatter radar system EISCAT to observe a cloud of calibrated mesospheric dust particles, the SCRAP experiment proposes to relate theoretical predictions to a controlled object. The results would also provide a new insight on phenomena such as polar mesospheric summer echoes, anomalous radar echoes which are thought to be caused by mesospheric clouds of ice particles.”

If you feel even more confused by the explanation above, just keep reading. It should become clearer as you continue reading.

We are a team of 11 KTH students and PHD’s with academic supervisors from both KTH (Kungliga Tekniska Högskolan) and SU (Stockholm University). The idea was born by Dr. Nickolay Ivchenko of the Department of Space & Plasma Physics at the School of Electrical Engineering, KTH, in collaboration with Dr. Gunnar Tibert of the Department of Mechanics at the School of Engineering Sciences, KTH.

Trying to avoid too many of the irrelevant details you could simply say that what we want to do is to measure the radar backscatter from a cloud of well-defined (size, material etc.) aerosol particles released in the mesosphere (the part of the atmosphere at altitude around 50 to 100 km) and compare to the theoretical predictions derived from current models.

A picture representing the radar backscatter from PMSE

An example of effects of micro particles in the mesosphere are the so called “Polar Mesospheric Summer Echoes (PMSE)” that are believed to be caused by ice particles forming in the upper atmosphere which get charged by the radiation from the sun. This causes the radar backscattering (e.g. echoes, the radar waves bouncing back to the transmitter) that can be observed, especially during summer, and especially around the polar caps. That explains the name “Polar Mesospheric Summer Echoes”. The increasingly frequent PMSE’s are believed to be an indicator of the global climate change, meaning that a proper understanding of this phenomenon could be most beneficial for predictions about the global climate. Many models exist to predict how this phenomena works, but experimental data is limited. That is what the SCRAP experiment aims to change.

Approximate Event Timeline
Approximate Event Timeline
FFU ejection from the upper part of the rocket
FFU ejection from the upper part of the rocket
EISCAT Radar at Tromsø

The experiment will deploy two identical free flying units or FFU’s (essentially two discs launched in either direction from the rocket) from the rocket module. The units will release metal dust close to the apogee (highest point, roughly at around 80-90 km) of the rocket. Two alternative methods for the release of the dust are being investigated. The first method is to spray liquid suspension of the metal dust through a nozzle (like an aerosol can). The second method is to spread the metal dust using gun powder.

When the metal particles are released in the mesosphere the EISCAT radar (see http://www.eiscat.se for more info) in Tromsø, Norway will aim its mighty beam at the cloud and send a powerful signal (more than 2 MW of peak power! ) that bounces back (backscatters) from the charged particles. By measuring this backscatter, analyzing the data, comparing with theoretical models and doing other sciency stuff the team will be able to validate (or potentially falsify) the current models on mesospheric aerosols.

Measure of the radar backscatter approximately at rocket apogee
Measure of the radar backscatter approximately at rocket apogee

But in order to do all this we need a rocket to fly on, and that’s where the REXUS/BEXUS programme comes in to the picture.

The REXUS/BEXUS programme is realized under a bilateral Agency Agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB), now in collaboration with the European Space Agency (ESA). The programme gives a few different student teams from ESA member countries the opportunity to launch their rocket experiment on a REXUS sounding rocket or a BEXUS high altitude balloon from Esrange in Kiruna. If all goes as planned, the SCRAP experiment will fly with the Swedish REXUS rocket, an unguided, spin-stabilized rocket powered by an Improved Orion Motor, in the spring of 2015. For more information on the REXUS/BEXUS programme see http://www.rexusbexus.net.

The experiment is currently in a “Design & Research” phase and, as is written above, several different concepts for the dust release system are being explored. In February the team will hand in the first version of the “Student Experiment Document” and by then the preliminary design will be set.


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