Metsähovi Compact Array (MCA) is a radio telescope system, consisting of three 5.5-metre parabolic dish antennas, being built at the Aalto University Metsähovi Radio Observatory (MRO) in Kirkkonummi, Finland. After being decommissioned from their original satellite telecommunication use, the antennas were donated to MRO in 2015, where they are now being put into use as radio telescopes. In addition to operating as single-dish instruments, the three antennas in the array will be connected into a ∼100-metre size radio interferometer. Once operational, the Metsähovi Compact Array will be one of very few astronomical radio dish interferometers in Europe.

Two fundamental parameters describing a telescope’s performance are its sensitivity and angular resolution. These, in turn, are determined by the collecting area and the diameter of a parabolic antenna, respectively. An array consisting of three telescopes obviously has three times the collecting area of a single instrument. The effective resolution of an interferometer, however, does not scale with the sum of the antenna diameters, but with the maximum separation between the antennas. Therefore, by spacing the antennas out over 100 metres, the equivalent resolution of a 100-m radio telescope can be achieved. Smaller telescopes are known to be more cost-effective than larger ones when comparing science output and total costs, and with an interferometer one can achieve many benefits of a large telescope without the added expense of building and operating one. The provision of a dedicated interferometer gives interesting scientific opportunities.

However, the primary use of the whole Metsähovi Compact Array interferometer and the individual antennas is intended to be practical education, research & development, and citizen science. The project provides hands-on learning opportunities for multiple disciplines. This also extends to the build phase and offers a rare opportunity for students in astronomy, radio science, and engineering to participate in the design, construction and operation of a 100-metre scale radio interferometer.

Interferometry is a predominant technique in front-line radio astronomy, but it is difficult for students to get access to such apparatus outside of international facilities. Thus having access to an interferometer for student training gives Aalto University, and Finland generally, a key advantage for local astronomy, physics and engineering training programmes.

Building and commissioning of radio telescopes opens a variety of opportunities for hands-on training before the telescopes are even standing. For example, suitable locations for the antennas were determined during a geophysics and geoinformatics field course, and detailed mechanical drawings and measurements were carried out as part of a computer-aided design special assignment. Due to the multidisciplinary nature of the project, there is a large number of sub-projects that provide motivating and real-life problems for special assignments and thesis projects for students from various fields; signal processing, mechan-ical and electrical engineering, automation, user-interface design, data analysis, radio science and engineering, communications – and, of course, fields related to using the antennas, such as astronomy, satellite communications, etc.

Furthermore, due to the significantly steeper learning curve and technical requirements needed for commencing radio observations (compared to simply starting to use an inexpensive optical telescope), the use of radio telescopes in citizen science or amateur astronomy is very rare. There are, however, good examples of small radio telescopes being used for science communications and student & school involvement.

In this presentation we describe the Metsähovi Compact Array system in detail and describe various user cases for education, citizen science, as well as cross- and multidisciplinary projects. We also highlight non-astronomical use cases such as monitoring radio-frequency interference, satellite (downlink) communications, and development and testing of radio-frequency and interferometric instruments. Finally, we acknowledge the financial support of the Weisell foundation for the construction and instrumentation of the MCA-1 and MCA-2 radio telescopes.