REXUS Payload
Auroral Polarization Experiment

APEX (Auroral Polarization EXperiment) is a payload designed for REXUS.

REXUS is a sounding rocket provided in cooperation by the European Space Agency (ESA), the Swedish National Space Agency (SNSA), and the German Aerospace Center (DLR). It can carry multiple student-build payloads up to an altitude of 80 km, and is launched in Kiruna, Sweden.
The goal of APEX is to measure the polarization of the aurora borealis, the northern lights.

Aurora Over Alaska (NASA, International Space Station, 2012-02-19)

This beautiful image of the multi-colored aurora borealis over Alaska was photographed by one of the Expedition 30 crew members aboard the International Space Station. The image also shows part of the limb and airglow over Earth.

Northern lights are caused by fast particles that are redirected by earth's magnetic field to hit earth's thin atmosphere at heights of over 100 km. (Yes, some air still exists up there.)
The exact processes present are not fully understood yet, hence measuring the polarization of the northern lights might give the science community another glimpse into this colorful phenomenon.

But what is polarization?
To understand polarization, let's delve into the nature of light. Light is an electromagnetic wave, which means it consists of oscillating electric and magnetic fields that propagate through space. These fields oscillate perpendicular to the direction of the wave's motion. The direction/angle of this oscillation gives the polarization of the light. In unpolarized light all light particles are polarized in a random direction, in fully polarized light this direction is aligned for all light particles.

To always look at the same patch of the Aurora, APEX will use a 3-axis stabilized gimbal. It will contain optical sensors to measure multiple directions of polarization at the same time. Color filters will make sure only light originating from one of the auroral spectral lines can enter the sensors.

Concept of the gimbal with 9 cameras mounted in the central "can”. The cameras are split into two pairs of 4, responsible to measure the linear polarization of one of the auroral spectral emission lines (red or green). The 9th camera will be used to capture the beauty of the aurora as a full color image.

Current Status

✅ Submission of proposal (October 2023)

✅ APEX is shortlisted for REXUS/BEXUS (October 2023)

✅ Selection Workshop at ESA ESCTEC (Noordwijk, Netherlands) with a presentation to get selected for the next launch champaign (November 2023)

❌ Get selected for the RX 33/34 Cycle

Unfortunately, we were not selected for the REXUS Cycle 33/34. ESA reasoned that our System is too complex to be fully developed in one and a half years. But we were encouraged to further improve our concept and give it another try next year.

And this is what we will do. We will restart the project with a concept phase, while in parallel developing demonstrator experiments for key technologies

✅ Concept Phase II (January-February 2024)

⬜ Internal Concept Review (February 2024)