In recent years CubeSats have been revolutionizing research in space, enabling low-budget, small-scale, and fast-development of projects. The Rocket Experiments for University Students (REXUS) program provides students from higher education opportunities to perform their scientific and technological experiments on a sounding rocket launching to space.

A compact cosmic-ray detector, build to CubeSat specifications, has been designed to detect light produced in a scintillating material when cosmic rays pass through. At only 1 dm$^3$ in size and operating on only 1 Watt, this REXUS payload as part of the Payload for Radiation measurement and Radio-interferometry in Rockets (PR3), has measured the charged-particle rate going up in the atmosphere and into space.
Besides providing a chance for students to work on reproducing the historical discoveries of Hess, Pfotzer, Regener, Van Allen, and others in the last century, it has also been an outreach opportunity to engage the general public with astroparticle physics. But above all, it is a proof of concept for compact cosmic-ray detectors in orbit. Where the worldwide network of neutron detectors is able to monitor the cosmic-ray flux at ground level, and detectors on the ground and in space detect cosmic rays locally, global near-real-time coverage of cosmic-ray flux above the atmosphere is only feasible with an ensemble of small and cheap detectors like the one presented here.

Details on the detector design and performance, and the results from the rocket flight will be presented.